Editorial for the special edition on Global Precipitation Measurement (GPM): 5th Anniversary

The Global Precipitation Measurement (GPM) Core Observatory (CO), which is a key satellite of the Japan–U.S. joint development mission, was launched in February 2014 from Tanegashima Island (Japan) and it achieved the landmark of five years of observations in March 2019. The GPM CO spacecraft is a successor to the Tropical Rainfall Measuring Mission (TRMM), and it flies in a non-sun-synchronous orbit with an inclination angle of 65° to extend coverage into the mid–high-latitudes beyond the regions of the tropics and subtropics observed by the TRMM. It has more advanced active and passive microwave sensors than the TRMM. The Dual-frequency Precipitation Radar (DPR) onboard the GPM CO consists of two radars: a Ku-band (13.6 GHz) precipitation radar (KuPR) and a Ka-band (35.5 GHz) precipitation radar (KaPR). The DPR allows retrievals of microphysical properties of precipitation particles and latent heating profiles in the global perspective. The dual-frequency ratio (DFR), defined as the difference in effective radar reflectivity factor at the two different frequencies, can also provide new information on the existence of large ice particles such as hail and graupel. The GPM Microwave Imager (GMI) is a conically scanning microwave radiometer, operating across a wide range of frequencies (10–183 GHz), which is used to sense light rain and falling snow as well as moderate and heavy rain. Data from the GPM CO and other constellation satellites carrying microwave radiometers, e.g., the Japanese Global Change Observation Mission–Water (GCOM-W) mission, have been used to produce satellite-based precipitation datasets such as the Global Satellite Mapping of Precipitation (GSMaP) and the Integrated Multisatellite Retrievals for GPM (IMERG). The algorithms developed for the GPM are also contributing to improvement of a 17-year legacy observation dataset provided by the TRMM.

This special edition of the Journal of the Meteorological Society of Japan (JMSJ) celebrates the 5th Anniversary of the GPM, and succeeds the JMSJ special issue on Precipitation Measurements from Space (Volume 87A, March 2009, https://www.jstage.jst.go.jp/browse/jmsj/87A/0/_contents) that celebrated the 10th Anniversary of the TRMM. This special collection contains as many as 30 original articles, despite publication of GPM-related special collections by the American Meteorological Society on 3 topics: precipitation retrieval algorithms in the Journal of Atmospheric and Oceanic Technology (https://journals.ametsoc.org/collection/precip-retrieval-GPM), a ground validation field experiment in the Journal of Hydrometeorology (https://journals.ametsoc.org/collection/IFloodS2013), and science and applications in the Bulletin of the American Meteorological Society, the Journal of Hydrometeorology, the Journal of Atmospheric and Oceanic Technology, Earth Interactions, the Monthly Weather Review, and the Journal of Applied Meteorology and Climatology (https://journals.ametsoc.org/subject/GPM-science).

Nakamura (2021), an invited review article and a particular feature of this special edition, described the progress from the TRMM to the GPM, highlighting Japan's contributions to the science of these missions. This review article provides not only historical perspective but also foresight regarding new precipitation measurements from space beyond the GPM.

Articles other than the invited review article may be divided into four topics. The first is algorithm development. Seto et al. (2021) developed new precipitation rate retrieval algorithms (version 06A) for the GPM DPR. The JMSJ Editorial Committee presented the JMSJ Award in 2021 to this article. Liao et al. (2020) evaluated the performance of DFR-based snow retrieval for the GPM DPR focusing on errors associated with particle size distribution parameterizations and scattering models of individual particles. Le and Chandrasekar (2021) developed a graupel and hail identification algorithm for the GPM DPR. Meneghini et al. (2021) described the latest implementation of the surface reference technique that uses surface scattering properties to infer path attenuation through precipitation. Seiki (2021) proposed a method for detecting the three-dimensional hail distribution using GPM DPR products in combination with the atmospheric temperature from a reanalysis product. Kobayashi et al. (2021) proposed a new method that retrieves attenuation profiles using DFR profiles for the GPM DPR. Hirose et al. (2021) developed two correction methods for the incidence-angle dependency of GPM DPR using reference datasets of near-nadir measurements. Awaka et al. (2021) developed precipitation type classification algorithms for a full-scan mode of the GPM DPR, which has been in operation since May 2018. Tao et al. (2022) described the current Convective–Stratiform Heating (CSH) algorithm for the TRMM and GPM, and examined its performance using GPM combined radar–radiometer algorithm-derived surface rain rates. Yamaji et al. (2021) described and evaluated a reliability flag of the GSMaP Near-Real-Time precipitation product.

The second topic is validation. Wang et al. (2019) evaluated the capability of the GPM KuPR for detecting mesoscale convective systems (MCSs) over the contiguous U.S. and revealed its potential in MCS detection at the global scale. Ma et al. (2020) proposed a Bayesian correction approach to improve the GPM DPR's instantaneous rainfall rate product using ground-based dualpolarization radar observations as reference. Yu et al. (2021) demonstrated the potential of DFRbased snow retrieval by analyzing ground-based dual-wavelength radar data for a huge snowstorm event that occurred during the International Collaborative Experiment held during the Pyeongchang 2018 Olympics and Paralympic winter games (ICE-POP 2018). Kumar et al. (2021) validated the daily rainfall amount of the GSMaP rainfall product (version 7) against a dense rain gauge network over Karnataka, one of the southwestern states of India, and assimilated these dense rain gauge observations in the GSMaP rainfall product using a hybrid assimilation method to improve rainfall estimates. Komatsu et al. (2021) validated GSMaP products for a heavy rainfall event over complex terrain in Mongolia captured by the GPM CO. Nakamura et al. (2021) measured specific attenuation and equivalent radar reflectivity in a melting layer using a dual Ka-band radar system, in which the two identically designed Ka radars were arranged to face each other and observe a precipitation system in between them. Arias and Chandrasekar (2021) used the GPM spaceborne radar as a common reference for intercomparison of C-band radars during the Remote sensing of Electrification, Lightning, And Mesoscale/microscale Processes with Adaptive Ground Observations (RELAMPAGO) field campaign. Nakai et al. (2022) derived relationships between the radar reflectivity factor and liquid-equivalent snowfall rate on the basis of direct comparison of X-band radar and disdrometer observations in Niigata Prefecture, Japan.

The third topic is analysis. Radhakrishna et al. (2020) examined regional differences in raindrop size distribution across the Indian subcontinent and adjoining seas using GPM DPR products. Yamaji et al. (2020) revealed the 4-year climatology of global drop size distribution and its seasonal variability using GPM DPR products. Song et al. (2020) examined the difference between cloud top height and storm height for heavy rainfall using long-term data observed by the Precipitation Radar (PR) and Visible and InfraRed Scanner (VIRS) onboard the TRMM. Wang et al. (2020) compared convective and stratiform precipitation properties in developing and non-developing tropical disturbances over the western North Pacific using GPM DPR products. Aoki and Shige (2021) revealed large precipitation gradients along the south coast of Alaska using datasets of the GPM KuPR and the CloudSat Cloud Profiling Radar (CPR). Jian et al. (2021) investigated synoptically influenced extreme precipitation systems over the Asian–Australian monsoon region using long-term TRMM PR data. De Meyer and Roca (2021) investigated thermodynamic scaling of extreme daily precipitation over the tropical ocean using an ensemble of satellite-based precipitation products. Sawada and Ueno (2021) examined heavy winter precipitation events in Japan associated with extratropical cyclones using GPM DPR products and trajectory analysis.

The fourth topic of this special edition is application to numerical weather precipitation models. Otsuka (2019) presented an overview of a global precipitation nowcasting system using GSMaP, which has run at RIKEN in real time since January 2016 (GSMaP RIKEN Nowcast). Barreyat et al. (2021) performed several sensitivity studies on various specifications of the 1D-Bay + 3D/4D-Var method, which is being considered for the assimilation of cloudy and rainy microwave observations by Météo-France. To achieve improved assimilation of all-sky brightness temperatures observed by microwave imagers, Aonashi et al. (2021) introduced the mixed lognormal distribution and a new precipitation displacement correction method for the dual-scale neighboring ensemble-based variational assimilation scheme (EnVar) to a cloud-resolving model.

The GPM CO celebrated its 8th anniversary at the end of February 2022. When combined with the 17-year dataset of the TRMM, the period of precipitation measurements obtained by spaceborne radars will soon span a quarter of a century, contributing to satellite-based precipitation research. I hope that this special edition will come to be seen as not only a collection of recent research results but also a milestone in satellite-based precipitation research.

I thank the following guest editors who handled the papers for review process: Nobuhiro Takahashi (Nagoya University), Hirohiko Masunaga (Nagoya University), Kazumasa Aonashi (Kyoto University and Japan Aerospace Exploration Agency), Atsushi Hamada (University of Toyama), Masafumi Hirose (Meijo University), Toshio Iguchi (University of Maryland), Takuji Kubota (Japan Aerospace Exploration Agency), Kenji Nakamura (Dokkyo University), Riko Oki (Japan Aerospace Exploration Agency), Kenji Suzuki (Yamaguchi University), Yukari N. Takayabu (The University of Tokyo), and Tomoo Ushio (Osaka University). I would like to extend thanks to Masaki Satoh and Shinobu Matsukura for their support. Finally, I would like to dedicate this special edition to the memory of the late Professor Toshiaki Kozu and the late Dr. Gail Skofronick-Jackson.

References

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