Difference between revisions of "MERRA-2"

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'''''NOTE: Page under construction!  We will be filling in more information in the days to come...'''''
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MERRA-2 is a reanalysis data product from [http://gmao.gsfc.nasa.gov NASA/GMAO].  It is currently being produced with the GMAO/GEOS-5 Data Assimilation System Version 5.12.4.  MERRA-2 is intended to replace the [[MERRA]] reanalysis product (which was created with GEOS-5.2.0).  It has a native resolution of 0.5° lat x 0.625° lon x 72 hybrid sigma/pressure levels.  MERRA-2 data is stored on the same vertical grid as the [[GEOS-FP|GEOS-5 "forward processing" (what we call GEOS-FP)]] and [[MERRA]] met field product.
 
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MERRA2 is a reanalysis data product from [http://gmao.gsfc.nasa.gov NASA/GMAO].  It is currently being produced with the GMAO/GEOS-5 Data Assimilation System Version 5.12.4.  MERRA2 is intended to replace the [[MERRA]] reanalysis product (which was created with GEOS-5.3.0).  It has a native resolution of 0.5° lat x 0.625° lon x 72 hybrid sigma/pressure levels.  MERRA2 data is stored on the same vertical grid as the [{GEOS-FP|GEOS-5 "forward processing" (what we call GEOS-FP)]] and [[MERRA]] met field product.s
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For more information, please see:
 
For more information, please see:
  
#[[List of MERRA2 met fields|List of MERRA2 met fields for GEOS-Chem]]
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#[http://gmao.gsfc.nasa.gov/pubs/docs/Bosilovich785.pdf MERRA-2 (v1.0) file specification document (25 Sept 2015)]
#[[MERRA2 implementation details|Information about implementing MERRA2 into GEOS-Chem]]
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#[[List of MERRA-2 met fields|List of MERRA-2 met fields for GEOS-Chem]]
 +
#[[MERRA-2 implementation details|Information about implementing MERRA-2 into GEOS-Chem]]
 
#[[Overview of GMAO met data products]]
 
#[[Overview of GMAO met data products]]
 
#[http://acmg.seas.harvard.edu/geos/wiki_docs/geos5/GEOS5_Glossary_11_01_2011.pdf Glossary of variables produced by the GEOS-DAS]
 
#[http://acmg.seas.harvard.edu/geos/wiki_docs/geos5/GEOS5_Glossary_11_01_2011.pdf Glossary of variables produced by the GEOS-DAS]
#[[Version history of GMAO met data products]]
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#[https://gmao.gsfc.nasa.gov/GMAO_products/reanalysis_products.php Version history of GMAO reanalysis products]]
  
 
== Overview ==
 
== Overview ==
  
'''''NOTE: MERRA is currently being produced with the GMAO/GEOS-5 Data Assimilation system, versions 5.12.4.  This is a slightly newer version of the GEOS/DAS than what is used to produce the GEOS-5 "forward processing" data, as described below.  The description below mostly applies to MERRA-2 data, except that the native resolution of the archived MERRA2 data files is now 0.5° x 0.625°.'''''
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<span style="color:red">'''''NOTE: MERRA is currently being produced with the GMAO/GEOS-5 Data Assimilation system, version 5.12.4.  This is a slightly different version of the GEOS/DAS than what is used to produce the GEOS-5 "forward processing" data.  The description below mostly applies to MERRA-2 data, except that the native resolution of the archived MERRA-2 data files is now 0.5&deg; x 0.625&deg;.'''''</span>
  
 
From the [http://acmg.seas.harvard.edu/geos/wiki_docs/geos5/GEOS_5_FP_File_Specification_ON4v1_0.pdf GEOS5-FP file specification document, Version 1.0 (11 Jun 2013)], p. 1:
 
From the [http://acmg.seas.harvard.edu/geos/wiki_docs/geos5/GEOS_5_FP_File_Specification_ON4v1_0.pdf GEOS5-FP file specification document, Version 1.0 (11 Jun 2013)], p. 1:
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{| border=1 cellspacing=0 cellpadding=5  
 
{| border=1 cellspacing=0 cellpadding=5  
|-valign="top"
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|-valign="top" bgcolor="#CCCCCC"
!width="180px" bgcolor="#CCCCCC"|GMAO<br>version number
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!width="180px" |GMAO<br>version number
!width="180px" bgcolor="#CCCCCC"|Start date<br> (in GEOS-FP archive)
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!width="180px" |Dates produced
!width="180px" bgcolor="#CCCCCC"|End date<br>(in GEOS-FP archive)
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!width="180px" |Start date<br> (in our MERRA-2 archive)
 +
!width="180px" |End date<br>(in our MERRA-2 archive)
  
 
|-valign="top" align="center"
 
|-valign="top" align="center"
|[[#GEOS-5.7.2|GEOS-5.7.2]]
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|[https://gmao.gsfc.nasa.gov/GMAO_products/NRT_products.php GEOS-5.12.4]<br>"MERRA-2_100 Stream"
|01 Apr 2012
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|1979-1990
|10 Jun 2013
+
|TBD
 +
|TBD
  
 
|-valign="top" align="center"
 
|-valign="top" align="center"
|[[#GEOS-5.11.0|GEOS-5.11.0]]
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|[https://gmao.gsfc.nasa.gov/GMAO_products/NRT_products.php GEOS-5.12.4]<br>"MERRA-2_200 Stream"
|11 Jun 2013
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|1991-1999
|20 Aug 2014 (06:00 UTC)
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|TBD
 +
|TBD
  
 
|-valign="top" align="center"
 
|-valign="top" align="center"
|[[#GEOS-5.13.0|GEOS-5.13.0]]
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|[https://gmao.gsfc.nasa.gov/GMAO_products/NRT_products.php GEOS-5.12.4]<br>"MERRA-2_300 Stream"
|20 Aug 2014 (06:00 UTC)
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|2000-2009
|present
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|TBD
 +
|TBD
 +
 
 +
|-valign="top" align="center"
 +
|[https://gmao.gsfc.nasa.gov/GMAO_products/NRT_products.php GEOS-5.12.4]<br>"MERRA-2_400 Stream"
 +
|2010-
 +
|TBD
 +
|TBD
  
 
|}
 
|}
  
NOTE: The first day of data available in our GEOS-FP met field archive is 01 Apr 2012.  But GMAO was producing "forward processing" data for some time prior to this date.
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--[[User:Bmy|Bob Y.]] ([[User talk:Bmy|talk]]) 18:11, 20 August 2015 (UTC)
  
--[[User:Bmy|Bob Y.]] ([[User talk:Bmy|talk]]) 21:46, 14 July 2015 (UTC)
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=== Acknowledge the source of MERRA-2 data in your publications ===
  
=== Acknowledge the source of GEOS-FP data in your publications ===
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If your GEOS-Chem research depends on the MERRA-2 meteorological data producs, please consider adding an acknowledgment to your citations, such as:
  
If your GEOS-Chem research depends on the GEOS-FP meteorological data producs, please consider adding an acknowledgment to your citations, such as:
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<blockquote>The MERRA-2 data used in this study/project have been provided by the Global Modeling and Assimilation Office (GMAO) at NASA Goddard Space Flight Center.</blockquote>
  
<blockquote>The GEOS5-FP data used in this study/project have been provided by the Global Modeling and Assimilation Office (GMAO) at NASA Goddard Space Flight Center.</blockquote>
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--[[User:Bmy|Bob Y.]] ([[User talk:Bmy|talk]]) 19:25, 3 August 2015 (UTC)
 
+
--[[User:Bmy|Bob Y.]] 15:00, 16 August 2013 (EDT)
+
  
 
=== Developers ===
 
=== Developers ===
  
The following table credits the various individuals who have assisted with the development of the GEOS-FP met data product and its incorporation into GEOS-Chem:
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The following table credits the various individuals who have assisted with the development of the MERRA-2 met data product and its incorporation into GEOS-Chem:
  
 
{| border=1 cellspacing=0 cellpadding=5  
 
{| border=1 cellspacing=0 cellpadding=5  
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|-
 
|-
 
|Bob Yantosca ([[GCST]])
 
|Bob Yantosca ([[GCST]])
|Creation of GEOS-FP data processing software
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|Creation of MERRA-2 data processing software
 
|-
 
|-
 
|[[GEOS-Chem Support Team]]
 
|[[GEOS-Chem Support Team]]
|[[GEOS-FP_implementation_details|Making GEOS-Chem compatible with GEOS-FP met data]]
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|[[MERRA-2_implementation_details|Making GEOS-Chem compatible with MERRA-2 met data]]
|-
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|Sajeev Philip ([[GCST]])<br>Junwei Xu ([[GCST]])
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|Downloading, regridding, and storing GEOS-FP met fields (all global and nested grids)
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|-
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|Junwei Xu ([[GCST]])
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|Preparing emissions etc. data for the China nested-grid simulation (0.25&deg; x 0.3125&deg;) with GEOS-FP
+
|-
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||Junwei Xu ([[GCST]])
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|Preparing emissions etc. data for the Europe nested-grid simulation (0.25&deg; x 0.3125&deg;) with GEOS-FP
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|-
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|Patrick Kim (Harvard)<br>Karen Yu (Harvard)<br>Lei Zhu (Harvard)<br>Katherine Travis (Harvard)<br>Jenny Fisher (Wollongong)
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|Developmment of the North American nested grid simulation (0.25&deg; x 0.3125&deg;) with GEOS-FP
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|-
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|Yuxuan Wang (UT-Galveston)<br>Libao Choi (Tsinghua)
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|Development of the Southeast Asia nested grid simulation (0.25&deg; x 0.3125&deg;) with GEOS-FP
+
 
|}
 
|}
  
--[[User:Bmy|Bob Y.]] 11:27, 27 February 2014 (EST)
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--[[User:Bmy|Bob Y.]] ([[User talk:Bmy|talk]]) 19:21, 3 August 2015 (UTC)
  
== GEOS-FP grid structure ==
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== MERRA-2 grid structure ==
  
 
This section describes the horizontal and vertical grids used by the GEOS-FP data products.
 
This section describes the horizontal and vertical grids used by the GEOS-FP data products.
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|Horizontal-only
 
|Horizontal-only
 
|Nx
 
|Nx
|[http://acmg.seas.harvard.edu/geos/doc/man/appendix_2.html#GMAO_025 0.25&deg; x 0.3125&deg;]
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|[[GEOS-Chem_horizontal_grids#GMAO_0.5_x_0.625_grid|0.5&deg; x 0.625&deg;]]
 
|1 level
 
|1 level
 
|Surface data fields<br>(e.g. PS, EVAP, HFLUX, etc.)
 
|Surface data fields<br>(e.g. PS, EVAP, HFLUX, etc.)
Line 173: Line 165:
 
|Model level
 
|Model level
 
|Nv
 
|Nv
|[http://acmg.seas.harvard.edu/geos/doc/man/appendix_2.html#GMAO_025 0.25&deg; x 0.3125&deg;]
+
|[[GEOS-Chem_horizontal_grids#GMAO_0.5_x_0.625_grid|0.5&deg; x 0.625&deg;]]
|[http://acmg.seas.harvard.edu/geos/doc/man/appendix_3.html#GEOS-5_native 72 hybrid levels]
+
|[[GEOS-Chem_vertical_grids#72-layer_vertical_grid|72 hybrid levels]]
 
|Most 3D data fields<br>(e.g. U, V, T, etc.)
 
|Most 3D data fields<br>(e.g. U, V, T, etc.)
|Vertical levels are identical to<br>[[GEOS-5|GEOS-5.2.0]] and [[MERRA]] data  
+
|Vertical levels are identical to<br>[[GEOS-5|GEOS-5]], [[MERRA]], and [[GEOS-FP]] data  
  
 
|-valign="top" align="center"
 
|-valign="top" align="center"
 
|Model edges
 
|Model edges
 
|Ne
 
|Ne
|[http://acmg.seas.harvard.edu/geos/doc/man/appendix_2.html#GMAO_025 0.25&deg; x 0.3125&deg;]
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|[[GEOS-Chem_horizontal_grids#GMAO_0.5_x_0.625_grid|0.5&deg; x 0.625&deg;]]
|[http://acmg.seas.harvard.edu/geos/doc/man/appendix_3.html#GEOS-5_native 73 hybrid level edges]
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|[[GEOS-Chem_vertical_grids#72-layer_vertical_grid|73 hybrid level edges]]
|Data fields defined on level edges<br>(e.g. PLE)
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|Data fields defined on level edges<br>(e.g. CMFMC, PLE, etc.)
|Vertical level edges are identical to<br>[[GEOS-5|GEOS-5.2.0]] and [[MERRA]] data
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|Vertical level edges are identical to<br>[[GEOS-5|GEOS-5.2.0]], [[MERRA]], and [[GEOS-FP]] data
  
 
|-valign="top" align="center"
 
|-valign="top" align="center"
 
| Pressure
 
| Pressure
 
| Np
 
| Np
| [http://acmg.seas.harvard.edu/geos/doc/man/appendix_2.html#GMAO_025 0.25&deg; x 0.3125&deg;]
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|[[GEOS-Chem_horizontal_grids#GMAO_0.5_x_0.625_grid|0.5&deg; x 0.625&deg;]]
 
| 42 pressure levels:<br>
 
| 42 pressure levels:<br>
 
1000, 975, 950, 925, 900, 875,<br>
 
1000, 975, 950, 925, 900, 875,<br>
Line 205: Line 197:
 
=== Output grids ===
 
=== Output grids ===
  
We download the GEOS-FP data at its native 0.25&deg; x 0.3125&deg; horizontal resolution.  For use with GEOS-Chem, we cut and/or regrid the 0.25&deg; x 0.3125&deg; data to the following grids:
+
We download the MERRA-2 data at its native 0.5&deg; x 0.625&deg; horizontal resolution.  For use with GEOS-Chem, we cut and/or regrid the 0.5&deg; x 0.625&deg; data to the following grids:
  
# GEOS-Chem 0.25&deg; x 0.3125&deg; nested grids for [http://acmg.seas.harvard.edu/geos/doc/man/appendix_2.html#GMAO_025_CH China], [http://acmg.seas.harvard.edu/geos/doc/man/appendix_2.html#GMAO_025_NA North America], [http://acmg.seas.harvard.edu/geos/doc/man/appendix_2.html#GMAO_025_EU Europe], and [http://acmg.seas.harvard.edu/geos/doc/man/appendix_2.html#GMAO_025_SE SE Asia] (introduced in [[GEOS-Chem v9-02]])
+
# GEOS-Chem 0.5&deg; x 0.625&deg; nested grids for [[GEOS-Chem_horizontal_grids#0.5_x_0.625_AS_nested_grid|Asia (China + India)]], [[GEOS-Chem_horizontal_grids#0.5_x_0.625_EU_nested_grid|Europe]], and [[GEOS-Chem_horizontal_grids#0.5_x_0.625_NA_nested_grid|North America]].
# [http://acmg.seas.harvard.edu/geos/doc/man/appendix_2.html#GMAO_2x25 GEOS-Chem 2&deg; x 2.5&deg; grid]
+
#[[GEOS-Chem_horizontal_grids#GMAO_2_x_2.5_grid|GEOS-Chem 2&deg; x 2.5&deg; grid]]
# [http://acmg.seas.harvard.edu/geos/doc/man/appendix_2.html#GMAO_4x5 GEOS-Chem 4&deg; x 5&deg; grid]
+
#[[GEOS-Chem_horizontal_grids#GMAO_4_x_5_grid|GEOS-Chem 4&deg; x 5&deg; grid]]
  
--[[User:Bmy|Bob Y.]] 15:52, 16 August 2013 (EDT)
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--[[User:Bmy|Bob Yantosca]] ([[User talk:Bmy|talk]]) 22:49, 28 November 2016 (UTC)
  
== GEOS-FP file naming convention ==
+
== MERRA-2 file naming convention ==
  
The following description of the naming convention used for GEOS-FP raw data files is paraphrased from Section 5.1 and 5.2 of the [http://acmg.seas.harvard.edu/geos/wiki_docs/geos5/GEOS_5_FP_File_Specification_ON4v1_0.pdf GEOS5-FP file specification document, Version 1.0 (11 Jun 2013)], pp 8-11:
+
The following description of the naming convention used for MERRA "raw" data files is paraphrased and adapted from Section 5.1 and 5.2 of the [http://acmg.seas.harvard.edu/geos/wiki_docs/geos5/MERRA_FileSpec_DRAFT_09_02_2008.pdf MERRA File Specification Document], pp 10ff:
  
 
=== Standard names ===
 
=== Standard names ===
 
'''''NOTE: For GEOS-Chem we only use the GEOS-FP assimilation product.  We have therefore omitted information about the GEOS-FP forecast product.'''''
 
 
<blockquote>
 
The standard generic complete name for the assimilated GEOS-5 FP products will appear as follows:
 
  
 
<blockquote>
 
<blockquote>
<tt>GEOS.config.mode.collection.timestamp.file_ver.nc4</tt>
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The standard full name for the assimilated GEOS-5 MERRA-2 products will consist of five dot-delimited nodes:
 
</blockquote>
 
</blockquote>
  
A brief description of the node fields appear below:
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        runid.collection.timestamp.nc4
 
+
;GEOS: Identifies output as a data assimilation system product produced by GEOS.
+
 
+
;config: GEOS-5 runs in multiple operational configurations, targeted at different user communities. This document is specific to a single configuration, fp.
+
  
 
<blockquote>
 
<blockquote>
;fp: Operational forward-processing assimilation tailored for mission customers and other realtime users, nominally 12 hours behind real-time using a DAS version that is updated more frequently to include the latest advancements.  The current horizontal resolution is 5/16&deg; (lon) x 1/4&deg; (lat).
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The node fields, which vary from file to file, are defined as follows:<br><br>
</blockquote>
+
  
;mode: GEOS-5 runs both assimilation and forecast jobs for operational forward-processing.
+
;runid:For mainstream MERRA data, the following runid's are used:
  
<blockquote>
+
# <tt>MERRA400</tt>: Years from ?? -??
;asm: Assimilation. Uses a combination of atmospheric data analysis and model forecasting to generate a time-series of global atmospheric quantities.
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;fcst: Forecast.  After atmospheric data assimilation has completed for a given synoptic time, typically at 00z and 12z, a model forecast is used to generate a time-series of forecast products some number of days into the future.  Five or ten days is typical.
+
</blockquote>
+
  
;collection: All GEOS-5 FP data are organized into file collections that contain fields with common characteristics. These collections are used to make the data more accessible for specific purposes. Fields may appear in more than one collection. Collection names are of the form ''freq''_''dims''_''group''_''HV'', where the four attributes are:  
+
;collection: Collection names are of the form '''''freq_dims_group_HV''''', where the four attributes are:
 +
#'''''freq''''': time-independent (cnst), instantaneous (instF), or time-average (tavgF), where F indicates the frequency or averaging interval and can be any of the following:
 +
#*<tt>1</tt> = Hourly
 +
#*<tt>3</tt> = 3-Hourly
 +
#*<tt>0</tt> = Not Applicable
 +
#'''''dims''''': Can be either:
 +
#*<tt>2d</tt> for collections with only 2-dimensional fields or
 +
#*<tt>3d</tt> for collections with a mix of 2- and 3-dimensional fields.
 +
#'''''group''''': A three-letter mnemonic for the type of fields in the collection.
 +
#'''''HV''''': Horizontal and Vertical grid.
 +
#*H can be:
 +
#**<tt>N</tt>: Native (0.5&deg; x 0.625&deg;) horizontal resolution
 +
#*V can be:
 +
#**<tt>x</tt>: horizontal-only data (surface, single level, etc.) ; dims must be 2D
 +
#**<tt>p</tt>: pressure-level data (see Appendix D for levels) ; dims must be 3D
 +
#**<tt>v</tt>: model layer centers (see Appendix D ) dims must be 3D
 +
#**<tt>e</tt>: model layer edges (see Appendix D ) dims must be 3D
  
<blockquote>
+
;timestamp: This node defines the date and time associated with the data in the file. It has the form <tt>yyyymmdd</tt>  
;freq: time-independent (const), instantaneous (instF), or time-average (tavgF), where F indicates the frequency or averaging interval and can be any of the following:
+
#yyyy - year string (e.g. , <tt>2002</tt>)
<blockquote>
+
#mm - month string (e.g.., <tt>09</tt> for September)
*<tt>1</tt> = Hourly
+
#dd - day of the month string
*<tt>3</tt> = 3-Hourly
+
</blockquote>
+
  
;dims: 2d for collections with only 2-dimensional fields or 3d for collections with a mix of 2- and 3-dimensional fields.
+
;nc4: Denotes that the data is being saved in a netCDF-4 file.
  
;group:  A three-letter mnemonic for the type of fields in the collection. It is a lowercase version of the group designation used in the ESDT name, as listed in the next section.
+
<br>EXAMPLE:
 
+
;HV: Horizontal and Vertical grid.
+
 
+
<blockquote>
+
H can be:
+
*'''N''': Nominal horizontal resolution on lat/lon grid.  See config above.
+
 
+
V can be:
+
*'''x''' horizontal-only data (surface, single level, etc.) ; dims must be 2D
+
*'''p''': pressure-level data (see [[#Input grids|above for levels]]) ; dims must be 3D
+
*'''v''': model layer centers (see [[#Input grids|above for levels]]) dims must be 3D
+
*'''e''': model layer edges (see [[#Input grids|above for levels]]) dims must be 3D
+
</blockquote>
+
 
</blockquote>
 
</blockquote>
  
;timestamp: This node defines the date and time associated with the data in the file. It has the form '''yyyymmdd_hhmm''' for assimilation files.  
+
        MERRA-2_400.tavg1_2d_flx_Nx.20150101.nc4
  
 
<blockquote>
 
<blockquote>
*'''yyyy''' - year string (e.g. , <tt>2002</tt>)
+
This is an example of a MERRA-2 filename from the production segment of the original version of the fourth (most recent) assimilation streamThe data are time-averaged, two-dimensional, surface flux products, at native horizontal resolution. The file contains all data for 01 Jan 2015.
*'''mm''' - month string (e.g.., <tt>09</tt> for September)
+
*'''dd''' - day of the month string
+
*'''hh''' - hour (UTC)
+
*'''mm - minute
+
</blockquote>
+
 
+
;file_ver: This denotes the file version in the form '''V##'''. Under normal conditions ## will be 01. In the event of a processing error that requires a re-processing, this number will be incremented to identify the new version of this file.
+
 
+
;nc4: All files are in NetCDF-4 format, thus the suffix '''.nc4'''.
+
 
+
EXAMPLE:
+
 
+
  GEOS.fp.asm.tavg1_2d_slv_Nx.20131015_0430.V01.nc4
+
 
+
* fp: forward-processing
+
* asm: assimilation
+
* tavg1_2d_slv_Nx: time-averaged 1-hourly data, 2-dimensional, single-level parameters on the native resolution grid.
+
* 20131015_0430: valid time is 04:30 GMT, which represents the center point of a 1-hour time-averaging period from 04:00 GMT to 05:00 GMT.
+
 
</blockquote>
 
</blockquote>
  
--[[User:Bmy|Bob Y.]] 15:42, 16 August 2013 (EDT)
+
--[[User:Bmy|Bob Y.]] ([[User talk:Bmy|talk]]) 20:19, 31 July 2015 (UTC)
  
 
=== ESDT names ===
 
=== ESDT names ===
Line 344: Line 306:
 
--[[User:Bmy|Bob Y.]] 15:50, 16 August 2013 (EDT)
 
--[[User:Bmy|Bob Y.]] 15:50, 16 August 2013 (EDT)
  
== GEOS-FP data file collections ==
+
== MERRA-2 data file collections ==
  
The following information is taken from the [http://acmg.seas.harvard.edu/geos/wiki_docs/geos5/GEOS_5_FP_File_Specification_ON4v1_0.pdf GEOS5-FP file specification document, Version 1.0 (11 Jun 2013)], pp. 12-13. 
+
<span style="color:darkorange">'''''NOTE: the ESDT name may not be correct. We are waiting for the MERRA-2 file spec to be released, and will correct the entries in the table below at that time.'''''</span>
  
<blockquote>
+
This table shows only those MERRA-2 file collections that are required for GEOS-Chem.   
The GEOS-5 FP product is organized into the collections listed below...All data is on the model’s native horizontal grid, which is a regular latitude-longitude grid with a spacing of 1/4&deg; in latitude and 5/16&deg; in longitude. Horizontal arrays (1152,721) are ordered by longitude first, with the first point at the Dateline and the South Pole, with the inner index increasing eastward.  All 3d collections, except the inst3_3d_asm_Np, are on the model’s native, hybrid sigma-p vertical grid.   
+
</blockquote>
+
  
This table shows only those GEOS-FP file collections that are required for GEOS-Chem.  For a complete list of file collections, see the [http://acmg.seas.harvard.edu/geos/wiki_docs/geos5/GEOS_5_FP_File_Specification_ON4v1_0.pdf GEOS-FP file specification document].
+
NOTES:
 +
*All data is on the native horizontal grid (0.6125&deg; lon x 0.5deg; lat, 576 x 361 grid boxes)
 +
*Horizontal arrays have dimensions 576 (lon) x 361 (lat) x 72 (levels)
 +
**Longitudes increase eastward, starting at -180&deg;
 +
**Latitudes increase northward, starting at -90&deg;
 +
*For files containing 3D data:
 +
**Level 1 corresponds to the top of the atmosphere
 +
**Level 72 corresponts to the surface
  
  
 
{| border=1 cellspacing=0 cellpadding=5
 
{| border=1 cellspacing=0 cellpadding=5
|- bgcolor="#CCCCCC" align="center" valign="top"
+
|- bgcolor="#CCCCCC" valign="top"
!File Collection<br>Name
+
!width="150px"|File Collection<br>Name
!ESDT Name<br>(aka "Shortname")
+
!width="150px"|ESDT Name<br>(aka "Shortname")
!Description
+
!width="350px"|Description
!Times
+
!width="250px"|Times
!Approx daily<br>size (MB)
+
!width="100px"|Approx daily<br>size (MB)
  
|-align="center"
+
|-valign="top"
 
|<tt>const_2d_asm_Nx</tt>
 
|<tt>const_2d_asm_Nx</tt>
|<tt>DFPC0NXASM</tt>
+
|<tt>D??C0NXASM</tt>
 
|Constant fields
 
|Constant fields
 
|Time-invariant
 
|Time-invariant
|minimal
+
|5
  
|-align="center" valign="top"
+
|-valign="top"
 
|<tt>inst3_3d_asm_Nv</tt>
 
|<tt>inst3_3d_asm_Nv</tt>
|<tt>DFPI3NVASM</tt>
+
|<tt>D??I3NVASM</tt>
 
|Basic assimilated fields from IAU corrector
 
|Basic assimilated fields from IAU corrector
 
|Instantaneous values every 3 hours
 
|Instantaneous values every 3 hours
|6,200
+
|2,250
  
|-align="center" valign="top"
+
|-valign="top"
 
|<tt>tavg3_3d_asm_Nv</tt>
 
|<tt>tavg3_3d_asm_Nv</tt>
|<tt>DFPT3NVASM</tt>
+
|<tt>D??T3NVASM</tt>
 
|Upper-air wind tendencies by process
 
|Upper-air wind tendencies by process
 
|3-hour time-averaged values
 
|3-hour time-averaged values
|5,800
+
|2,240
  
|-align="center" valign="top"
+
|-valign="top"
 
|<tt>tavg3_3d_cld_Nv</tt>
 
|<tt>tavg3_3d_cld_Nv</tt>
|<tt>DFPT3NVCLD</tt>
+
|<tt>D??T3NVCLD</tt>
 
|Upper-air cloud related diagnostics
 
|Upper-air cloud related diagnostics
 
|3-hour time-averaged values
 
|3-hour time-averaged values
|2,200
+
|730
  
|-align="center" valign="top"
+
|-valign="top"
 
|<tt>tavg3_3d_mst_Nv</tt>
 
|<tt>tavg3_3d_mst_Nv</tt>
|<tt>DFPT3NVMST</tt>
+
|<tt>D??T3NVMST</tt>
 
|Upper-air diagnostics from moist processes at layers
 
|Upper-air diagnostics from moist processes at layers
 
|3-hour time-averaged values
 
|3-hour time-averaged values
 
|840
 
|840
  
|-align="center" valign="top"
+
|-valign="top"
 
|<tt>tavg3_3d_mst_Ne</tt>
 
|<tt>tavg3_3d_mst_Ne</tt>
|<tt>DFPT3NEMST</tt>
+
|<tt>D??T3NEMST</tt>
 
|Upper-air diagnostics from moist processes at layers
 
|Upper-air diagnostics from moist processes at layers
 
|3-hour time-averaged values
 
|3-hour time-averaged values
|760
+
|268
  
|-align="center" valign="top"
+
|-valign="top"
|<tt>tavg3_3d_rad_Nv</tt>
+
|<tt>DFPT3NVRAD</tt>
+
|Upper-air diagnostics from radiation
+
|3-hour time-averaged values
+
|2,300
+
 
+
|-align="center" valign="top"
+
 
|<tt>tavg1_2d_flx_Nx</tt>
 
|<tt>tavg1_2d_flx_Nx</tt>
|<tt>DFPT1NXFLX</tt>
+
|<tt>D??T1NXFLX</tt>
 
|Surface fluxes and related quantities
 
|Surface fluxes and related quantities
 
|1-hour time-averaged values
 
|1-hour time-averaged values
|1,100
+
|400
  
|-align="center" valign="top"
+
|-valign="top"
 
|<tt>tavg1_2d_lnd_Nx</tt>
 
|<tt>tavg1_2d_lnd_Nx</tt>
|<tt>DFPT1NXLND</tt>
+
|<tt>D??T1NXLND</tt>
 
|Land related surface quantities
 
|Land related surface quantities
 
|1-hour time-averaged values
 
|1-hour time-averaged values
|780
+
|206
  
|-align="center" valign="top"
+
|-valign="top"
 
|<tt>tavg1_2d_rad_Nx</tt>
 
|<tt>tavg1_2d_rad_Nx</tt>
|<tt>DFPT1NXRAD</tt>
+
|<tt>D??T1NXRAD</tt>
 
|Surface and TOA radiative fluxes
 
|Surface and TOA radiative fluxes
 
|1-hour time-averaged values
 
|1-hour time-averaged values
|640
+
|218
  
|-align="center" valign="top"
+
|-valign="top"
 
|<tt>tavg1_2d_slv_Nx</tt>
 
|<tt>tavg1_2d_slv_Nx</tt>
|<tt>DFPT1NXSLV</tt>
+
|<tt>D??T1NXSLV</tt>
 
|Single-level atmospheric state variables
 
|Single-level atmospheric state variables
 
|1-hour time-averaged values
 
|1-hour time-averaged values
|1,200
+
|420
  
|-align="center" valign="top"
+
|-valign="top"
 
|TOTAL
 
|TOTAL
 
|  
 
|  
 
|  
 
|  
 
|  
 
|  
|21,820
+
|7,577
  
 
|}
 
|}
  
  
[[#GEOS-FP file naming convention|As described above]], the full file name for the GEOS-FP data products takes the form:
+
[[#MERRA-2 file naming convention|As described above]], the full file name for the GEOS-FP data products takes the form:
 
                                      
 
                                      
  GEOS.fp.asm.CCCCCCCCCCCCCCC.YYYYMMDD_hhmm.V01.nc4
+
  MERRA-2_SSS.CCCCCCCCCCCCCCC.YYYYMMDD.nc4
  
 
where  
 
where  
  
 +
# <tt>SSS</tt> is the MERRA-2 stream name (currently "400")
 
# <tt>CCCCCCCCCCCCCCC</tt> is the collection name (i.e. one of the entries in the first column of the above table)
 
# <tt>CCCCCCCCCCCCCCC</tt> is the collection name (i.e. one of the entries in the first column of the above table)
# <tt>YYYYMMDD_hhmm</tt> is the UTC date (year/month/day, hour:minutes)
+
# <tt>YYYYMMDD</tt> is the UTC date (year/month/day)
  
--[[User:Bmy|Bob Y.]] 16:20, 16 August 2013 (EDT)
+
--[[User:Bmy|Bob Y.]] ([[User talk:Bmy|talk]]) 20:25, 31 July 2015 (UTC)
  
=== Future removal of the tavg3_3d_rad_Nv collection ===
+
== MERRA-2 time archiving ==
  
In the near future, we may be able to remove relying on the '''tavg3_3d_rad_Nv''' collection. The only variable from this collection that we need for GEOS-Chem is '''CLOUD''' (the 3-D cloud fraction). This variable may be constructed from other variables in the '''tavg3_3d_cld_Nv''' collection as follows:
+
<span style="color:darkorange">'''''NOTE: MERRA-2 uses the identical time archiving as the GEOS-5 "forward processing" data product (i.e. what we refer to as [[GEOS-FP]]).'''''</span>
+
CLOUD = min( CFAN + CFLS, 1.0 )
+
  
This will allow us to save disk space by not having to download 8 files from the tavg3_3d_rad_Nv collection for each day of data that we process.
+
=== Raw data ===
  
--[[User:Bmy|Bob Y.]] 15:27, 19 August 2013 (EDT)
+
The MERRA-2 raw data are archived/averaged at the following times:
  
== GEOS-FP time archiving ==
+
{| border=1 cellspacing=0 cellpadding=5
 +
|- bgcolor="#CCCCCC" align="center" valign="top"
 +
!width="150px"|Collections
 +
!width="350px"|Description
 +
!width="500px"|Timestamps
  
=== Raw data ===
+
|-valign="top"
 +
|<tt>const_2d_asm_Nx</tt>
 +
|Time-invariant data
 +
|N/A
  
The GEOS-FP raw data are archived/averaged at the following times:
+
|-valign="top"
 +
|<tt>inst3_3d_asm_Nv</tt>
 +
|Instantaneous (snapshot) data, every 3 hours
 +
|00:00, 03:00, 06:00, 09:00, 12:00, 15:00, 18:00, 21:00 UTC
  
#'''const''': Time-invariant data
+
|-valign="top"
#'''inst3''': 3-hr instantaneous data
+
|<tt>tavg1_2d_flx_Nx<br>tavg1_2d_lnd_Nx<br>tavg1_2d_rad_Nx<br>tavg1_2d_slv_Nx</tt>
#*Times: 00:00, 03:00, 06:00, 09:00, 12:00, 15:00, 18:00, 21:00 GMT
+
|1-hour time-averaged data  
#'''tavg1''': 1-hour time-averaged data
+
|00:30, 01:30, 02:30 ... 23:30 UTC
#*Center times: 00:30, 01:30, 02:30 ... 23:30 GMT
+
*These represent the centers of each 1-hr time-averaging bin
#'''tavg3''': 3-hour time-averaged data
+
#*Center times: 01:30, 04:30, 07:30, 10:30, 13:30, 16:30, 19:30, 22:30 GMT
+
  
=== Regridded data ===
+
|-valign="top"
 +
|<tt>tavg3_3d_asm_Nv<br>tavg3_3d_cld_Nv<br>tavg3_3d_mst_Ne<br>tavg3_3d_mst_Nv<br></tt>
 +
|3-hour time-averaged data  
 +
|01:30, 04:30, 07:30, 10:30, 13:30, 16:30, 19:30, 22:30 UTC
 +
*These represent the centers of each 3-hr time-averaging bin
  
The regridded GEOS-FP data for GEOS-Chem shall keep the same temporal resolution as the GEOS-FP raw data.  To prevent file sizes from becoming larger than 2GB (i.e. the maximum netCDF-3 file size), we split the regridded GEOS-FP data among the following file types:
+
|}
  
#'''CN''' (time-invariant data)
+
--[[User:Bmy|Bob Y.]] ([[User talk:Bmy|talk]]) 20:54, 31 July 2015 (UTC)
#*Filenames <tt>GEOS572.20110101.CN.{RESOLUTION}.nc</tt>
+
#*Timestamps: For convenience we assign a file timestamp of 2011/01/01 at 00:00 GMT.
+
#'''A1''' (1-hr time-averaged data)
+
#*Filenames <tt>GEOS572.YYYYMMDD.A1.{RESOLUTION}.nc</tt>
+
#*Timestamps: see image below
+
#'''A3''' (3-hr time-averaged data)
+
#Timestamps: See image below
+
#*Filenames
+
#**<tt>GEOS572.YYYYMMDD.A3cld.{RESOLUTION}.nc</tt>
+
#**<tt>GEOS572.YYYYMMDD.A3dyn.{RESOLUTION}.nc</tt>
+
#**<tt>GEOS572.YYYYMMDD.A3mstC.{RESOLUTION}.nc</tt>
+
#**<tt>GEOS572.YYYYMMDD.A3mstE.{RESOLUTION}.nc</tt>
+
#'''I3''' (3-hr instantaneous data)
+
#* Filenames <tt>GEOS572.20110101.I3.{RESOLUTION}.nc</tt>
+
#* Timestamps: 00:00, 03:00, 06:00, 09:00, 12:00, 15:00, 18:00, 21:00 GMT.
+
  
NOTE: At present (Aug 2013), the file names still reflect the older GEOS572 nomenclature.  We will remove this at a future date.
+
=== Processed data ===
  
In the filenames abaove, the <tt>{RESOLUTION}</tt> tag indicates the horizontal resolution of the file.  Possible values are:
+
The [[List of MERRA-2 met fields|processed MERRA-2 data for GEOS-Chem]] shall keep the same temporal resolution as the MERRA-2 raw data.  To prevent file sizes from becoming larger than 2GB (i.e. the maximum netCDF-3 file size), we split the regridded MERRA-2 data among the following file types:
 +
 
 +
{| border=1 cellspacing=0 cellpadding=5
 +
|- bgcolor="#CCCCCC" align="center" valign="top"
 +
!width="275px"|Filenames
 +
!width="225px"|Description
 +
!width="500px"|Timestamps
 +
 
 +
|-valign="top"
 +
|<tt>MERRA-2.20150101.CN.{RES}.nc</tt>
 +
|Time-invariant data
 +
|For convenience we assign a file timestamp of 2015/01/01 at 00:00 GMT.
 +
 
 +
|-valign="top"
 +
|<tt>MERRA-2.YYYYMMDD.A1.{RES}.nc</tt>
 +
|1-hour time-averaged data
 +
|00:30, 01:30, 02:30 ... 23:30 UTC
 +
*These represent the centers of each 1-hr time-averaging bin
 +
 
 +
|-valign="top"
 +
|<tt>MERRA-2.YYYYMMDD.A3cld.{RES}.nc<br>MERRA-2.YYYYMMDD.A3dyn.{RES}.nc<br>MERRA-2.YYYYMMDD.A3mstC.{RES}.nc<br>MERRA-2.YYYYMMDD.A3mstE.{RES}.nc</tt>
 +
|3-hour time-averaged data
 +
|01:30, 04:30, 07:30, 10:30, 13:30, 16:30, 19:30, 22:30 UTC
 +
*These represent the centers of each 3-hr time-averaging bin
 +
 
 +
|-valign="top"
 +
|<tt>MERRA-2.YYYYMMDD.I3.{RES}.nc</tt>
 +
|3-hour time-averaged data
 +
|00:00, 03:00, 06:00, 09:00, 12:00, 15:00, 18:00, 21:00 UTC
 +
|}
 +
 
 +
 
 +
In the filenames abaove, the <tt>{RES}</tt> tag indicates the horizontal resolution of the file.  Possible values are:
 +
 
 +
{| border=1 cellspacing=0 cellpadding=5
 +
|- bgcolor="#CCCCCC" align="center" valign="top"
 +
!width="100px"|<tt>{RES}</tt>
 +
!width="400px"|Description
 +
|-valign="top"
 +
|<tt>4x5</tt>
 +
|GEOS-Chem 4&deg; x 5&deg; global grid
 +
|-valign="top"
 +
|<tt>2x25</tt>
 +
|GEOS-Chem 2&deg x 2.5&deg; global grid
 +
|-valign="top"
 +
|<tt>05x0625.CH</tt>
 +
|GEOS-Chem 0.5&deg; x 0.625&deg; China nested grid
 +
|-valign="top"
 +
|<tt>05x0625.EU</tt>
 +
|GEOS-Chem 0.5&deg; x 0.625&deg; Europe nested grid
 +
|-valign="top"
 +
|<tt>05x0625.CH</tt>
 +
|GEOS-Chem 0.5&deg; x 0.625&deg; North America nested grid
 +
|-valign="top"
 +
|<tt>05x0625.CH</tt>
 +
|GEOS-Chem 0.5&deg; x 0.625&deg; SE Asia nested grid
 +
|}
  
#<tt>4x5</tt>: GEOS_Chem 4&deg; x 5&deg; global grid
 
#<tt>2x25</tt> GEOS-Chem 2&deg x 2.5&deg; global grid
 
#<tt>025x03125.CH</tt>: GEOS-Chem 0.25&deg; x 0.3125&deg; China nested grid
 
#<tt>025x03125.NA</tt>: GEOS-Chem 0.25&deg; x 0.3125&deg; North America nested grid
 
  
 
The '''A1''' and '''A3''' files use the following bins for time-averaging.  The file timestamps in the data files indicate the center of the time-averaging bins.   
 
The '''A1''' and '''A3''' files use the following bins for time-averaging.  The file timestamps in the data files indicate the center of the time-averaging bins.   
  
[[Image:GEOS_FP_vs_GEOS_5_timing_794x596.png]]
+
'''''<span style="color:darkorange">NOTE: MERRA-2 uses the same timing scheme as the data marked in the plot as "GEOS-FP".  (We will eventually update the image below.)</span>'''''
  
NOTE: GEOS-FP uses the same timing scheme as [[MERRA]], with the exception that MERRA has 6-hour instantaneous data but GEOS-FP has 3-hour instantaneous data.
+
[[Image:GEOS_FP_vs_GEOS_5_timing_794x596.png]]
  
Please also see our [[List of GEOS-FP met fields]] wiki page for detailed information about which fields are stored in each of these file types.
+
Please also see our [[List of MERRA-2 met fields]] wiki page for detailed information about which fields are stored in each of these file types.
  
--[[User:Bmy|Bob Y.]] 17:13, 16 August 2013 (EDT)
+
--[[User:Bmy|Bob Y.]] ([[User talk:Bmy|talk]]) 21:09, 31 July 2015 (UTC)
  
 
== Implementation into GEOS-Chem ==
 
== Implementation into GEOS-Chem ==
  
Please see our [[GEOS-FP implementation details]] wiki page for more information about how we modified GEOS-Chem for use with the GEOS-FP met field product.
+
Please see our [[MERRA-2 implementation details]] wiki page for more information about how we modified GEOS-Chem for use with the GEOS-FP met field product.
  
--[[User:Bmy|Bob Y.]] 15:18, 7 November 2013 (EST)
+
--[[User:Bmy|Bob Y.]] ([[User talk:Bmy|talk]]) 21:11, 31 July 2015 (UTC)
  
 
== References ==
 
== References ==

Latest revision as of 18:47, 28 May 2020

MERRA-2 is a reanalysis data product from NASA/GMAO. It is currently being produced with the GMAO/GEOS-5 Data Assimilation System Version 5.12.4. MERRA-2 is intended to replace the MERRA reanalysis product (which was created with GEOS-5.2.0). It has a native resolution of 0.5° lat x 0.625° lon x 72 hybrid sigma/pressure levels. MERRA-2 data is stored on the same vertical grid as the GEOS-5 "forward processing" (what we call GEOS-FP) and MERRA met field product.

For more information, please see:

  1. MERRA-2 (v1.0) file specification document (25 Sept 2015)
  2. List of MERRA-2 met fields for GEOS-Chem
  3. Information about implementing MERRA-2 into GEOS-Chem
  4. Overview of GMAO met data products
  5. Glossary of variables produced by the GEOS-DAS
  6. Version history of GMAO reanalysis products]

Overview

NOTE: MERRA is currently being produced with the GMAO/GEOS-5 Data Assimilation system, version 5.12.4. This is a slightly different version of the GEOS/DAS than what is used to produce the GEOS-5 "forward processing" data. The description below mostly applies to MERRA-2 data, except that the native resolution of the archived MERRA-2 data files is now 0.5° x 0.625°.

From the GEOS5-FP file specification document, Version 1.0 (11 Jun 2013), p. 1:

The GEOS-5 FP Atmospheric Data Assimilation System (GEOS-5 ADAS) uses an analysis developed jointly with NOAA’s National Centers for Environmental Prediction (NCEP), which allows the Global Modeling and Assimilation Office (GMAO) to take advantage of the developments at NCEP and the Joint Center for Satellite Data Assimilation (JCSDA). The GEOS-5 AGCM uses the finite-volume dynamics (Lin, 2004) integrated with various physics packages (e.g, Bacmeister et al., 2006), under the Earth System Modeling Framework (ESMF) including the Catchment Land Surface Model (CLSM) (e.g., Koster et al., 2000). The GSI analysis is a three-dimensional variational (3DVar) analysis applied in grid-point space to facilitate the implementation of anisotropic, inhomogeneous covariances (e.g., Wu et al., 2002; Derber et al., 2003). The GSI implementation for GEOS-5 FP incorporates a set of recursive filters that produce approximately Gaussian smoothing kernels and isotropic correlation functions.

The GEOS-5 ADAS is documented in Rienecker et al. (2008). More recent updates to the model are presented in Molod et al. (2011). The GEOS-5 system actively assimilates roughly 2 × 106 observations for each analysis, including about 7.5 × 105 AIRS radiance data. The input stream is roughly twice this volume, but because of the large volume, the data are thinned commensurate with the analysis grid to reduce the computational burden. Data are also rejected from the analysis through quality control procedures designed to detect, for example, the presence of cloud.

To minimize the spurious periodic perturbations of the analysis, GEOS-FP uses the Incremental Analysis Update (IAU) technique developed by Bloom et al. (1996).

The assimilation is performed at a horizontal resolution of 0.3125-degree longitude by 0.25-degree latitude and at 72 levels, extending to 0.01 hPa. All products are generated at the native resolution of the horizontal grid. The majority of data products are time-averaged, but four instantaneous products are also available. Hourly data intervals are used for two-dimensional products, while 3-hourly intervals are used for three-dimensional products. These may be on the model’s native 72-layer vertical grid or at 42 pressure surfaces extending to 0.1 hPa.

--Bob Y. 15:00, 16 August 2013 (EDT)

Version history

The following table lists the GMAO data version numbers corresponding to specific dates in our GEOS-FP met field archive for GEOS-Chem:

GMAO
version number
Dates produced Start date
(in our MERRA-2 archive)
End date
(in our MERRA-2 archive)
GEOS-5.12.4
"MERRA-2_100 Stream"
1979-1990 TBD TBD
GEOS-5.12.4
"MERRA-2_200 Stream"
1991-1999 TBD TBD
GEOS-5.12.4
"MERRA-2_300 Stream"
2000-2009 TBD TBD
GEOS-5.12.4
"MERRA-2_400 Stream"
2010- TBD TBD

--Bob Y. (talk) 18:11, 20 August 2015 (UTC)

Acknowledge the source of MERRA-2 data in your publications

If your GEOS-Chem research depends on the MERRA-2 meteorological data producs, please consider adding an acknowledgment to your citations, such as:

The MERRA-2 data used in this study/project have been provided by the Global Modeling and Assimilation Office (GMAO) at NASA Goddard Space Flight Center.

--Bob Y. (talk) 19:25, 3 August 2015 (UTC)

Developers

The following table credits the various individuals who have assisted with the development of the MERRA-2 met data product and its incorporation into GEOS-Chem:

Developers Feature
NASA/GMAO Creation of GEOS-FP assimilated meteorological data product
Bob Yantosca (GCST) Creation of MERRA-2 data processing software
GEOS-Chem Support Team Making GEOS-Chem compatible with MERRA-2 met data

--Bob Y. (talk) 19:21, 3 August 2015 (UTC)

MERRA-2 grid structure

This section describes the horizontal and vertical grids used by the GEOS-FP data products.

Input grids

From the GEOS5-FP file specification document, Version 1.0 (11 Jun 2013), p. 7:

Fields are produced on the model’s native horizontal grid, with a resolution of 5/16 degree longitude by 1/4 degree latitude.

The GEOS5-FP global horizontal grid consists of IMn=1152 points in the longitudinal direction and JMn=721 points in the latitudinal direction. The horizontal native grid origin, associated with variables indexed (i=1, j=1) represents a grid point located at (180°W, 90°S). Latitude and longitude of grid points as a function of their indices (i, j) can be determined by:

     Lon(I) = -180° + [ ΔLon * ( I - 1 ) ],  I = 1, IMN
     Lat(I) =  -90° + [ ΔLat * ( J - 1 ) ],  J = 1, JMN

Where ΔLon = 5/16° = 0.3125° and ΔLat = 1/4° = 0.25°. For example, (i = 577, j = 361) corresponds to a grid point at ( 0, 0).

and also on p. 7:

Gridded products use four different vertical configurations: horizontal-only (can be vertical averages, single level, or surface values), pressure-level, model-level, or model-edge. Horizontal-only data for a given variable appear as 3-dimensional fields (x, y, time), while pressure-level, model-level, or model-edge data appear as 4-dimensional fields (x, y, z, time). In all cases the time dimension spans multiple files, as each file (granule) contains only one time. Pressure-level data is output on the LMp=42 pressure levels shown in Appendix B. The model layers used for GEOS-5 FP products are on a terrain-following hybrid sigma-p coordinate. Model-level data is output on the LM=72 layers shown in the second table of Appendix B. The model-edge products contain fields with LMe = LM + 1 levels representing the layer edges. The pressure at the model top is a fixed constant, PTOP=0.01 hPa. Pressures at model edges should be computed by summing the DELP(I,J,L) starting at PTOP. A representative pressure for the layer can then be obtained from these. In the GEOS-4 eta files, one could compute the pressure on the edges by using the “ak” and “bk” values and the surface pressure. In GEOS-5, the full 3-dimensional pressure variables are explicitly provided through (DELP(I,J,L)) and PTOP. Even though the model-level fields are on a hybrid sigma-p coordinate and their vertical location could be obtained from the “ak-bk” relationship, this may change in future GMAO systems. We thus recommend that users rely on the reported 3D pressure distribution, and not use ones computed from the “ak” and “bk”.

Note that the indexing for the GEOS-5 FP vertical coordinate system is top to bottom, i.e., layer 1 is the top layer of the atmosphere, while layer LM is adjacent to the earth’s surface. The same is true for edge variables, with level 1 being the top of the model’s atmosphere (PTOP), and level LM+1 being the surface.

The table below lists the combination of the horizontal and vertical grids onto which the GEOS-FP "raw" data products are placed:

Grid Name Horizontal
Resolution
Vertical
Resolution
Used for Notes
Horizontal-only Nx 0.5° x 0.625° 1 level Surface data fields
(e.g. PS, EVAP, HFLUX, etc.)
Model level Nv 0.5° x 0.625° 72 hybrid levels Most 3D data fields
(e.g. U, V, T, etc.)
Vertical levels are identical to
GEOS-5, MERRA, and GEOS-FP data
Model edges Ne 0.5° x 0.625° 73 hybrid level edges Data fields defined on level edges
(e.g. CMFMC, PLE, etc.)
Vertical level edges are identical to
GEOS-5.2.0, MERRA, and GEOS-FP data
Pressure Np 0.5° x 0.625° 42 pressure levels:

1000, 975, 950, 925, 900, 875,
850, 825, 800, 775, 750, 725,
700, 650, 600, 550, 500, 450,
400, 350, 300, 250, 200, 150,
100, 70, 50, 40, 30, 20,
10, 7, 5, 4, 3, 2, 1
0.7, 0.5, 0.4, 0.3, 0.1 hPa

Various 3D data fields We do not use of the pressure-level for GEOS-Chem.
We only use data on the Nx, Nv, Ne grids.

Output grids

We download the MERRA-2 data at its native 0.5° x 0.625° horizontal resolution. For use with GEOS-Chem, we cut and/or regrid the 0.5° x 0.625° data to the following grids:

  1. GEOS-Chem 0.5° x 0.625° nested grids for Asia (China + India), Europe, and North America.
  2. GEOS-Chem 2° x 2.5° grid
  3. GEOS-Chem 4° x 5° grid

--Bob Yantosca (talk) 22:49, 28 November 2016 (UTC)

MERRA-2 file naming convention

The following description of the naming convention used for MERRA "raw" data files is paraphrased and adapted from Section 5.1 and 5.2 of the MERRA File Specification Document, pp 10ff:

Standard names

The standard full name for the assimilated GEOS-5 MERRA-2 products will consist of five dot-delimited nodes:

       runid.collection.timestamp.nc4

The node fields, which vary from file to file, are defined as follows:

runid
For mainstream MERRA data, the following runid's are used:
  1. MERRA400: Years from ?? -??
collection
Collection names are of the form freq_dims_group_HV, where the four attributes are:
  1. freq: time-independent (cnst), instantaneous (instF), or time-average (tavgF), where F indicates the frequency or averaging interval and can be any of the following:
    • 1 = Hourly
    • 3 = 3-Hourly
    • 0 = Not Applicable
  2. dims: Can be either:
    • 2d for collections with only 2-dimensional fields or
    • 3d for collections with a mix of 2- and 3-dimensional fields.
  3. group: A three-letter mnemonic for the type of fields in the collection.
  4. HV: Horizontal and Vertical grid.
    • H can be:
      • N: Native (0.5° x 0.625°) horizontal resolution
    • V can be:
      • x: horizontal-only data (surface, single level, etc.) ; dims must be 2D
      • p: pressure-level data (see Appendix D for levels) ; dims must be 3D
      • v: model layer centers (see Appendix D ) dims must be 3D
      • e: model layer edges (see Appendix D ) dims must be 3D
timestamp
This node defines the date and time associated with the data in the file. It has the form yyyymmdd
  1. yyyy - year string (e.g. , 2002)
  2. mm - month string (e.g.., 09 for September)
  3. dd - day of the month string
nc4
Denotes that the data is being saved in a netCDF-4 file.


EXAMPLE:

       MERRA-2_400.tavg1_2d_flx_Nx.20150101.nc4

This is an example of a MERRA-2 filename from the production segment of the original version of the fourth (most recent) assimilation stream. The data are time-averaged, two-dimensional, surface flux products, at native horizontal resolution. The file contains all data for 01 Jan 2015.

--Bob Y. (talk) 20:19, 31 July 2015 (UTC)

ESDT names

As required by the EOSDIS system, all GEOS-5 FP products are identified by a relatively short ESDT name. While GEOS-5 FP products are not currently distributed from the GES DISC, we have retained the ESDT designations for assimilation products. This name, also known as the ShortName, is a short handle for users to access and order data products. It takes the form: DFPTFHVGGG, where: where

  1. T: Time Description:
    • I = Instantaneous
    • T = Time-averaged
    • C = Time-independent
  2. F: Frequency
    • 0 = Time-independent
    • 1 = Hourly
    • 3 = 3-Hourly
  3. H: Horizontal Resolution
    • N = Native
  4. V: Vertical Location
    • X = Two-dimensional
    • P = Pressure
    • V = model layer center
    • E = model layer edge
  5. GGG: Group
    • ASM = assimilated state variables (from the IAU corrector, see Appendix A)
    • TDT = tendencies of temperature
    • UDT = tendencies of eastward and northward wind components
    • QDT = tendencies of specific humidity
    • ODT = tendencies of ozone
    • LND = land surface variables
    • FLX = surface turbulent fluxes and related quantities
    • MST = moist processes
    • CLD = cloud-related quantities
    • RAD = radiation
    • TRB = turbulence
    • SLV = single level
    • INT = vertical integrals
    • CHM = chemistry forcing
    • AER = aerosol diagnostics
    • ADG = aerosol diagnostics (extended)
    • LSF = large-scale flux
    • OCN = ocean
    • LFO = land-surface forcing
    • NAV = navigation

--Bob Y. 15:50, 16 August 2013 (EDT)

MERRA-2 data file collections

NOTE: the ESDT name may not be correct. We are waiting for the MERRA-2 file spec to be released, and will correct the entries in the table below at that time.

This table shows only those MERRA-2 file collections that are required for GEOS-Chem.

NOTES:

  • All data is on the native horizontal grid (0.6125° lon x 0.5deg; lat, 576 x 361 grid boxes)
  • Horizontal arrays have dimensions 576 (lon) x 361 (lat) x 72 (levels)
    • Longitudes increase eastward, starting at -180°
    • Latitudes increase northward, starting at -90°
  • For files containing 3D data:
    • Level 1 corresponds to the top of the atmosphere
    • Level 72 corresponts to the surface


File Collection
Name
ESDT Name
(aka "Shortname")
Description Times Approx daily
size (MB)
const_2d_asm_Nx D??C0NXASM Constant fields Time-invariant 5
inst3_3d_asm_Nv D??I3NVASM Basic assimilated fields from IAU corrector Instantaneous values every 3 hours 2,250
tavg3_3d_asm_Nv D??T3NVASM Upper-air wind tendencies by process 3-hour time-averaged values 2,240
tavg3_3d_cld_Nv D??T3NVCLD Upper-air cloud related diagnostics 3-hour time-averaged values 730
tavg3_3d_mst_Nv D??T3NVMST Upper-air diagnostics from moist processes at layers 3-hour time-averaged values 840
tavg3_3d_mst_Ne D??T3NEMST Upper-air diagnostics from moist processes at layers 3-hour time-averaged values 268
tavg1_2d_flx_Nx D??T1NXFLX Surface fluxes and related quantities 1-hour time-averaged values 400
tavg1_2d_lnd_Nx D??T1NXLND Land related surface quantities 1-hour time-averaged values 206
tavg1_2d_rad_Nx D??T1NXRAD Surface and TOA radiative fluxes 1-hour time-averaged values 218
tavg1_2d_slv_Nx D??T1NXSLV Single-level atmospheric state variables 1-hour time-averaged values 420
TOTAL 7,577


As described above, the full file name for the GEOS-FP data products takes the form:

MERRA-2_SSS.CCCCCCCCCCCCCCC.YYYYMMDD.nc4

where

  1. SSS is the MERRA-2 stream name (currently "400")
  2. CCCCCCCCCCCCCCC is the collection name (i.e. one of the entries in the first column of the above table)
  3. YYYYMMDD is the UTC date (year/month/day)

--Bob Y. (talk) 20:25, 31 July 2015 (UTC)

MERRA-2 time archiving

NOTE: MERRA-2 uses the identical time archiving as the GEOS-5 "forward processing" data product (i.e. what we refer to as GEOS-FP).

Raw data

The MERRA-2 raw data are archived/averaged at the following times:

Collections Description Timestamps
const_2d_asm_Nx Time-invariant data N/A
inst3_3d_asm_Nv Instantaneous (snapshot) data, every 3 hours 00:00, 03:00, 06:00, 09:00, 12:00, 15:00, 18:00, 21:00 UTC
tavg1_2d_flx_Nx
tavg1_2d_lnd_Nx
tavg1_2d_rad_Nx
tavg1_2d_slv_Nx
1-hour time-averaged data 00:30, 01:30, 02:30 ... 23:30 UTC
  • These represent the centers of each 1-hr time-averaging bin
tavg3_3d_asm_Nv
tavg3_3d_cld_Nv
tavg3_3d_mst_Ne
tavg3_3d_mst_Nv
3-hour time-averaged data 01:30, 04:30, 07:30, 10:30, 13:30, 16:30, 19:30, 22:30 UTC
  • These represent the centers of each 3-hr time-averaging bin

--Bob Y. (talk) 20:54, 31 July 2015 (UTC)

Processed data

The processed MERRA-2 data for GEOS-Chem shall keep the same temporal resolution as the MERRA-2 raw data. To prevent file sizes from becoming larger than 2GB (i.e. the maximum netCDF-3 file size), we split the regridded MERRA-2 data among the following file types:

Filenames Description Timestamps
MERRA-2.20150101.CN.{RES}.nc Time-invariant data For convenience we assign a file timestamp of 2015/01/01 at 00:00 GMT.
MERRA-2.YYYYMMDD.A1.{RES}.nc 1-hour time-averaged data 00:30, 01:30, 02:30 ... 23:30 UTC
  • These represent the centers of each 1-hr time-averaging bin
MERRA-2.YYYYMMDD.A3cld.{RES}.nc
MERRA-2.YYYYMMDD.A3dyn.{RES}.nc
MERRA-2.YYYYMMDD.A3mstC.{RES}.nc
MERRA-2.YYYYMMDD.A3mstE.{RES}.nc
3-hour time-averaged data 01:30, 04:30, 07:30, 10:30, 13:30, 16:30, 19:30, 22:30 UTC
  • These represent the centers of each 3-hr time-averaging bin
MERRA-2.YYYYMMDD.I3.{RES}.nc 3-hour time-averaged data 00:00, 03:00, 06:00, 09:00, 12:00, 15:00, 18:00, 21:00 UTC


In the filenames abaove, the {RES} tag indicates the horizontal resolution of the file. Possible values are:

{RES} Description
4x5 GEOS-Chem 4° x 5° global grid
2x25 GEOS-Chem 2&deg x 2.5° global grid
05x0625.CH GEOS-Chem 0.5° x 0.625° China nested grid
05x0625.EU GEOS-Chem 0.5° x 0.625° Europe nested grid
05x0625.CH GEOS-Chem 0.5° x 0.625° North America nested grid
05x0625.CH GEOS-Chem 0.5° x 0.625° SE Asia nested grid


The A1 and A3 files use the following bins for time-averaging. The file timestamps in the data files indicate the center of the time-averaging bins.

NOTE: MERRA-2 uses the same timing scheme as the data marked in the plot as "GEOS-FP". (We will eventually update the image below.)

GEOS FP vs GEOS 5 timing 794x596.png

Please also see our List of MERRA-2 met fields wiki page for detailed information about which fields are stored in each of these file types.

--Bob Y. (talk) 21:09, 31 July 2015 (UTC)

Implementation into GEOS-Chem

Please see our MERRA-2 implementation details wiki page for more information about how we modified GEOS-Chem for use with the GEOS-FP met field product.

--Bob Y. (talk) 21:11, 31 July 2015 (UTC)

References

  1. GEOS5-FP file specification document, Version 1.0 (11 Jun 2013)
  2. Bacmeister, J. T., M. J. Suarez, and F. R. Robertson, 2006. Rain Re-evaporation, Boundary Layer Convection Interactions, and Pacific Rainfall Patterns in an AGCM. J. Atmos. Sci., 63, 3383-3403.
  3. Bloom, S., L. Takacs, A. DaSilva, and D. Ledvina, 1996: Data assimilation using incremental analysis updates. Mon. Wea. Rev., 124, 1256-1271.
  4. Derber, J. C., R. J. Purser, W.-S. Wu, R. Treadon, M. Pondeca, D. Parrish, and D. Kleist, 2003: Flow-dependent Jb in a global grid-point 3D-Var. Proc. ECMWF annual seminar on recent developments in data assimilation for atmosphere and ocean. Reading, UK, 8-12 Sept. 2003.
  5. Koster, R. D., M. J. Suárez, A. Ducharne, M. Stieglitz, and P. Kumar, 2000: A catchment-based approach to modeling land surface processes in a GCM, Part 1, Model Structure. J. Geophys. Res., 105, 24809-24822.
  6. Molod, A., L. Takacs, M. Suarez, J. Bacmeister, I. Song, and A. Eichmann, The GEOS-5 Atmospheric General Circulation Model: Mean Climate and Development from MERRA to Fortuna, Technical Report Series on Global Modeling and Data Assimilation, 28, Ed: Max J. Suarez, NASA GMAO, Goddard Space Flight Center, Greenbelt, MD, April 2012. (PDF)
  7. Rienecker, M.M., M.J. Suarez, R. Todling, J. Bacmeister, L. Takacs, H.-C. Liu, W. Gu, M. Sienkiewicz, R.D. Koster, R. Gelaro, I. Stajner, and E. Nielsen, 2008: The GEOS-5 Data Assimilation System - Documentation of Versions 5.0.1, 5.1.0, and 5.2.0. Technical Report Series on Global Modeling and Data Assimilation 104606, v27.
  8. Wu, W.-S., R.J. Purser and D.F. Parrish, 2002: Three-dimensional variational analysis with spatially inhomogeneous covariances. Mon. Wea. Rev., 130, 2905-2916.

--Bob Y. (talk) 21:03, 14 July 2015 (UTC)