Contributors: Rory Gray (Met Office), Christoforos Tsamalis (Met Office)
Issued by: Met Office / Rory Gray
Date: 31/08/2020
Ref: C3S_D3.6.4-v1.2_202008_PUGS_v1.0.1.docx
Official reference number service contract: 2020/C3S_312b_Lot1_DWD/SC1
History of modifications
List of datasets covered by this document
Related documents
Acronyms
Scope of the document
This document is the Product User Guide and Specification (PUGS) document, version 1.2, for the microwave upper tropospheric humidity (UTH) ICDR product. Information about the product and a technical description of the data record, including information on the file format as well as on the data access, is provided in the CM SAF Product User Manual [D1].
Executive summary
A technical description of the data record is provided. Further details on the implementation of the retrieval processing chain, and individual algorithm descriptions, are available in the CM SAF Algorithm Theoretical Basis Document [D2]. The UTH CDR product is available in NetCDF4 file format as daily averages on a 1° × 1° latitude-longitude grid, as well as the daily mean UTH for all gridboxes with valid ascending and descending observations. Instantaneous satellite observations are used to provide a spatio-temporal averaged data record with near global coverage. The temporal coverage of the ICDR data is from 1/1/2016 to 31/5/2020. Validation has been performed against equivalent UTH derived from the ERA-Interim (to July 2019) and ERA-5 (from August 2019) reanalysis fields. The achieved product performance will be described in a Product Quality Assessment Report (PQAR), due for delivery in November 2020.
For further details refer to the CM SAF Product User Manual [D1].
1. Upper Tropospheric Humidity Climate Data Record (UTH CDR)
The UTH CDR derived from satellite microwave humidity sounder observations provides near-global coverage. The instantaneous satellite observations are used to derive a spatio-temporal averaged data record, available as twice daily (one for the ascending and the other for the descending passes) averages on a regular latitude/longitude grid with a spatial resolution of 1° × 1° degrees. Additionally, the daily mean UTH is provided, which is a weighted average of ascending and descending orbits for all the gridpoints with valid ascending and descending observations. The accuracy of the daily UTH CDR was determined by validating the global product against the equivalent UTH derived from the ERA-Interim reanalysis.
This product continues the time series started from the CM SAF dataset (1999-2015). The product is described in detail in the CM SAF Product User Manual [D1], including the retrieval method, target requirements, an illustrative example, a data record accuracy summary, and presentation of general limitations.
1.1. Product description
The UTH TCDR and ICDR derived from satellite microwave humidity sounder observations provide near-global coverage. Instantaneous satellite observations from the Microwave Humidity Sounder (MHS) instrument are used to derive a spatio-temporal averaged data record. The data are available as twice daily (one for the ascending and the other for the descending passes) averages on a regular latitude/longitude grid with a spatial resolution of 1° × 1° degrees. Additionally, the daily mean UTH is provided, which is a weighted average of ascending and descending orbits for all the gridpoints with valid ascending and descending observations.
The temporal coverage of the TCDR data record ranges from January 1999 to December 2015. The temporal coverage of the ICDR data record ranges from January 2016 to May 2020.
The data are provided in a separate file for each of multiple satellites (NOAA-18, NOAA-19, MetOp-A, MetOp-B) and separated as ascending and descending passes, as well as daily means. There are three UTH fields per day per satellite available to the users.
Detailed information about the retrieval method used to generate the UTH product, which is based on the method presented in Buehler and John (2005), can be found in the CM SAF ATBD [D2].
1.2. Target requirements
A summary of the accuracy of the CM SAF UTH data record is provided by Table 1 of the CM SAF PUM [D1]. The data record accuracy has been assessed by comparing the CM SAF UTH global, 1x1 degree, daily mean fields with the equivalent UTH derived from ERA-Interim (until July 2019) and ERA-5 (from August 2019 onwards).
1.3. Data usage information
The data used is summarised in Table 3-2 of the CM SAF PUM [D1].
The UTH products are provided as Network Common Data Format (NetCDF) files (http://www.unidata.ucar.edu/software/netcdf/). The data files are created following NetCDF Climate and Forecast (CF) Metadata Convention version 1.6 (https://cfconventions.org/cf-conventions/v1.6.0/cf-conventions.html) and NetCDF Attribute Convention for Dataset Discovery version 1.3 (http://wiki.esipfed.org/index.php/Attribute_Convention_for_Data_Discovery_1-3).
For data processing and conversion to various graphical packages input format, the usage of the climate data operators (CDO) (https://code.mpimet.mpg.de/projects/cdo/) is recommended, available under GNU Public License (GPL) from the Max-Planck-Institut fuer Meteorologie (MPI-M) (http://www.mpimet.mpg.de).
The relative humidity Jacobian, which is used to define the UTH, moves vertically depending on the water vapour load in the atmosphere, and so UTH is not an averaged relative humidity in a fixed vertical layer of the troposphere. Therefore, to compare this data record with other products, potential users need to conduct radiative transfer simulations using temperature and water vapour profiles from other sources to obtain corresponding brightness temperatures, before transforming to UTH retrieval.
The UTH retrieval is generally not valid outside ±60° latitudes because of the very low water vapour loading in the upper troposphere of those regions. A global data record is provided with the appropriate masking to enable maximum exploitation of the data. Users may decide to apply further screening on the available data taking into account the number of valid retrievals per grid-box together with the total number of observations.
Further details about each data record, including limitations and shortcomings, can be found in the CM SAF ATBD [D2].
2. Data access information
The internet addresshttps://cds.climate.copernicus.eu allows direct access to the data ordering interface. On this webpage a detailed description of how to use it for product search and ordering is given. Further user service including information and documentation about the C3S and C3S products are available via the C3S home page (https://climate.copernicus.eu).
Figures and Tables
Figures and tables are provided in the CM SAF Product User Manual [D1].
References
Buehler, S.A. and V.O. John (2005), A Simple Method to Relate Microwave Radiances to Upper Tropospheric Humidity, J. Geophys. Res., 110, D02110, doi:10.1029/2004JD005111
Further references are provided in the CM SAF Product User Manual [D1].
This document has been produced in the context of the Copernicus Climate Change Service (C3S).
The activities leading to these results have been contracted by the European Centre for Medium-Range Weather Forecasts, operator of C3S on behalf of the European Union (Delegation agreement signed on 11/11/2014). All information in this document is provided "as is" and no guarantee or warranty is given that the information is fit for any particular purpose.
The users thereof use the information at their sole risk and liability. For the avoidance of all doubt , the European Commission and the European Centre for Medium - Range Weather Forecasts have no liability in respect of this document, which is merely representing the author's view.
