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Comparisons of rainrates from 3B42, IMERG Final-Run and MRMS
3B42
TMPA 3B42 files are avaliable from the NASA Goddard Earth Sciences Data and Information Services Center (GES DISC). These gridded estimates are on a 3-hour temporal resolution and a 0.25-degree by 0.25-degree spatial resolution in a global belt extending from 50S to 50N. The 3B42 estimates are produced in four stages:-
(1) the microwave precipitation estimates are calibrated and combined;
(2) infrared precipitation estimates are created using the calibrated microwave precipitation;
(3) the microwave and IR estimates are combined;
(4) rescaling to monthly data is applied. Each precipitation field is best interpreted as the precipitation rate effective at the nominal observation time.
IMERG
Integrated Multi-Satellite Retrievals for GPM (IMERG) Algorithm is intended to intercalibrate, merge, and interpolate "all" satellite microwave precipitation estimates, together with microwave-calibrated infrared (IR) satellite estimates, precipitation gauge analyses, and potentially other precipitation estimators at fine time and space scales for the TRMM and GPM eras over the entire globe. The system is run several times for each observation time, first giving a quick estimate and successively providing better estimates as more data arrive. The final step uses monthly gauge data to create research-level products. Background information and references are provided to describe the context and the relation to other similar missions. Issues involved in understanding the accuracies obtained from the calculations are discussed. Throughout, a baseline Day-1 product is described, together with options and planned improvements that might be instituted before or after launch depending on maturity and project constraints. The IMERG gridded estimates are on a 30-minute temporal resolution and a 0.1-degree by 0.1-degree spatial resolution extending from 180W to 180E and 90S to 90N for Version 6 (60S - 60N for earlier versions). For more information about IMERG, download IMERG_ATBD_V4.6.pdf Thanks to George Huffman and David T. Bolvin for providing the IMERG Final Run research product.Comparisons with MRMS
The comparisons are conducted over the CONUS (25N-50N, 125W-65W) using 3B42, IMERG and MRMS data during the commonly available periods:For V04A, Jun 2014 - Dec 2015; and Jun 2016 - Feb 2017.
For V05B, Jun 2014 - Dec 2015; and Jun 2016 - Aug 2017.
For V06A, Jun 2014 - Dec 2015; and Jun 2016 - Dec 2018.
For V06B, Jun 2014 - Dec 2015; Jun 2016 - Jul 2017; and Mar 2018 - Dec 2019.
Note: All MRMS files are missing for Jan - May 2016;
MRMS rain during Aug -Dec 2017 are abnormally lower than 3B42, GPCC and IMERG.
There are a lot of missings in Jan and Feb 2018. So the data from Aug 2017 to Feb 2018 are excluded in V06B yearly and MTD analyses.
V06A IMERG were retrated because of the bad land/ocean mask issue.
- Area-averaged daily rainfall
All data (rain and no rain) from each product at its native resolution (MRMS: 0.01o,0.5h; 3B42: 0.25o, 3h; IMERG: 0.1o, 0.5h) are accumulated to daily rainfall, and resampled to 3B42's resolution ( 0.25o, 3h), then averaged over all matched 0.25o pixels.
The daily rainfall cutoff time is 2230Z for 3B42, IMERG and MRMS. - Scatter plot for area-averaged 3-hourly rainrates (RQI=100)
- Density plot for different RQI thresholds
- PDF by 3-hourly rain occurrence and volume for different rain and RQI thresholds
- Error component plot for 3-hourly (0.25o) rainrates with different RQI thresholds
- Daily rainfall [mm] contours
Daily rainfall for each product is accumulated from its native temporal resolutions (0.5h for MRMS, 3h for 3B42, 0.5h for IMERG) at 0.25o spatial resolution. 0- and non-0 rain rates are all included.
The daily rainfall cutoff time is 2230Z. - 3-hourly rainrate [mm/h] contours
Three-hourly rainrate for each product is accumulated from its native temporal resolutions (0.5h for MRMS, 3h for 3B42, 0.5h for IMERG) at 0.25o spatial resolution. 0- and non-0 rain rates are all included.
The 3-hourly rainrate cutoff time is 0130, 0430, ..., 2230Z. - Time series of monthly ratio and correlation (V06B)
Matched data are used, conditional on raintate and RQI thresholds.
- Time series of monthly mean rain rates (V06B)
Rain/no-rain threshold is set to 0.1 mm/h.
The monthly mean rain rate is estimated by averaging all 3-hourly rainrates at 0.25-deg pixels (0s included) in the month.
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