Validation for NASA�s Precipitation Measurement Missions by 33z50F



                                             Validation for NASA’s Precipitation
                                        Measurement Missions and how MPAR can Help
Precipitation Measurement Missions

                                                                         David B. Wolff
                                                                    TRMM GV Program Manager
                                                                      GPM GV Working Group
                                                                        NASA GSFC, SSAI

                                     2nd Meeting of the Working Group for the Multi-function
                                     Phased Array Radar (MPAR), March 20-21, 2007, Silver Spring, MD.

                                                                                          G O D D A R D   S P A C E F L I G H T C E N T E R
           TRMM/GPM                                                                                                                      Overview
                                     • One of the critical components of the Earth's hydrological cycle is
                                       precipitation. Rainfall is essential for providing the fresh water that
                                       sustains life. In the atmosphere, the condensation of water vapor into rain,
                                       and then rain or snow, releases vast quantities of heat, which drives the
                                       global weather and climate system.
Precipitation Measurement Missions

                                     • NASA has implemented the Precipitation Measurement Mission (PMM)
                                       program to provide reliable, long-term estimates of global precipitation in
                                       order to better understand the global water/enery cycle and its effects on the
                                       global climate.

                                     • Currently, the Tropical Rainfall Measuring Mission (TRMM) is underway.
                                         – TRMM launched in November, 1997, a planned three-year mission that has
                                           provided significant contributions to this effort, as well as support for data
                                           assimilation, hurricane tracking and forecasting, landslide forecasting et al.

                                         – The paradigm for TRMM Ground Validation was to use ground-based radars and
                                           rain gauge networks to statistically validate satellite-based estimates of
                                           precipitation. The WSR-88D radar network has been an integral part of TRMM.

                                     Courtesy GPM GV Whitepaper (Kummerow & Petersen, 2006)
                                                                                              G O D D A R D   S P A C E F L I G H T C E N T E R   2
                                       • Instrument Payload

                                           – TRMM Microwave Imager (TMI)
                                              • 10, 19, 37, 86 GHz, conical scanning
Precipitation Measurement Missions

                                           – Precipitation Radar (PR) [Japan]
                                              • 14 GHz, cross-track scanning

                                           – Visible IR Scanner (VIRS)
                                              • 5-channel, cross-track scanning

                                           – Lightning Imaging Sensor (LIS) [MSFC]
                                              • Staring optical array

                                           – Cloud & Radiant Energy System (CERES)
                                               • Radiation budget (failed after 6 mos.)

                                           Courtesy R. Adler
                                     G O D D A R D   S P A C E F L I G H T C E N T E R    3
           TRMM/GPM                                                                    TRMM GV Network

                                     Current TRMM GV
Precipitation Measurement Missions

                                     •Darwin, Australia

                                     •Houston, Texas

                                     •Kwajalein, RMI

                                     •Melbourne, FL

                                     Each site consists of
                                     radar, gauges and
                                     disdrometers (for
                                     estimating drop size

                                                             G O D D A R D   S P A C E F L I G H T C E N T E R   4
           TRMM/GPM                                               Validation of TRMM Rain Rate Estimates

                                     Sample TRMM overpass of
                                     Kwajalein, Republic of the
                                     Marshall Islands
Precipitation Measurement Missions

                                     GV Radar (2 km x 2 km)
                                     TMI (~ 50 km2)

                                     PR (4 km at nadir)
                                     Combined algorithm (4 km
                                     at nadir

                                                                       G O D D A R D   S P A C E F L I G H T C E N T E R   5
Precipitation Measurement Missions                                   Future: Global Precipitation Measurement (GPM)

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                                                                              are need ed to see this picture.

                                                                                                G O D D A R D    S P A C E F L I G H T C E N T E R   6
                                     • The next mission, currently termed the Global Precipitation Measurement
                                       (not a mission yet!) will build on the successes of TRMM.

                                       – GPM will consist of a primary “core” satellite with a dual-frequency radar and the next
Precipitation Measurement Missions

                                         generation GPM Microwave Imager (GMI)

                                       – A number (TBD) of constellation satellites, all carrying GMI instruments, which will allow
                                         for nearly global coverage (± 70°) at 3-hour sampling.

                                     • GPM GV will employ not only the current TRMM paradigm, but also expand
                                       it in order to provide physical validation of the satellite algorithms by
                                       deploying additional instrumentation, such as ground-based radiometers,
                                       disdrometers, multi-frequency and dual-polarization radars (MPAR?), and
                                       research aircraft.

                                     • The enhanced abilities of MPAR will serve this approach well given it’s
                                       ability to perform high quality, fast volume coverage, its “staring”
                                       capability, as well its proposed dual-polarization capability.

                                                                                     G O D D A R D   S P A C E F L I G H T C E N T E R   7
           TRMM/GPM                                               GPM Direct Validation Using National Radar Networks

                                     • Goal: Identify and resolve discrepancies between national
                                       networks (radars/gauges) and satellite estimates/products

                                     • Additionally:
                                        – Understand (and minimize) the errors associated with
Precipitation Measurement Missions

                                          the geometry and timing of joint satellite and ground
                                        – Quantify bias and errors contributed by ground and
                                          space-based instruments
                                        – Contribute to an error model of precipitation
                                        – Assess the first order errors of satellite rainfall
                                          retrievals over land
                                     • Prototype 20 WSSR-88D sites in the southeast US

                                     • Pre-launch
                                        – Product to validate PR/WSR-88D radar
                                          reflectivity calibration and PR attenuation

                                         – Experimental product for comparison of WSR-
                                           88D and PR estimates of rain rate

                                         – Validate scalability to full network and other

                                     • Post-launch
                                        – Pre-launch working products applied to DPR Ka /
                                          Ku bands and to GMI

                                     Courtesy: M. Schwaller, L. Liao & R. Meneghini, W. Petersen   G O D D A R D   S P A C E F L I G H T C E N T E R   8
           TRMM/GPM                                                Physical Validation of Core/Constellation Algorithms

                                     • Coordinated observations of precipitation processes and microphysics:
                                        • Dual-polarimetric and multi-frequency radar, aircraft, profiler, disdrometer and rain
                                          gauge networks.
                                     • Validation of Cloud-Resolving Model physics and improved forward RT models for
Precipitation Measurement Missions

                                       precipitation retrieval and algorithm development

                                     Observations                                                                     Models
                                                                                                         Microphysics, Radiative Transfer, Radar
                                                                                                        Ci                                 Zl1, Zl2

                                                                                               z (km)


                                                                                                          qi (kg)


                                        Rain Gauge
                                        Disdrometer                            Dual Pol.                              Retrievals
                                         X/Ka/Ku - band
                                                                   R, D0

                                     Courtesy W. Petersen                             G O D D A R D       S P A C E F L I G H T C E N T E R           9
           TRMM/GPM                                                                             Launch Forecasting and MPAR

                                     • NWS Spaceflight Meteorology Group (SMG) provides weather forecast and
                                       briefings to support space shuttle operations of NASA.
                                     • SMG forecasts range from microscale to hemispheric scale.
                                     • Currently WSR-88D play a pivotal role in shuttle weather forecasting ops.
Precipitation Measurement Missions

                                     • MPAR increased sensitivity and staring capabilities should significantly
                                       improve launch forecasting information

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                                     From Brody et al. (Weather & Forecasting,1997)         G O D D A R D     S P A C E F L I G H T C E N T E R   10
                                     •The uniqueness of the shuttle weather flight rules causes SMG to
                                      utilize the WSR-88D data differently than most other weather offices

                                       – For example, the WSR-88D 0.58 base reflectivity product occasionally detects
Precipitation Measurement Missions

                                         cloud drops and cloud streets. This assists SMG in monitoring and forecasting
                                         cloud cover amount and low cloud ceiling development in the KSC area.

                                       – Lowest level base reflectivity and velocity products are valuable for locating sea-
                                         breeze boundaries, convective outflow boundaries, and other fine lines, which help
                                         with tracking wind shifts and forecasting convective initiation and dissipation.

                                       – Higher-level base reflectivity products and layer composite reflectivity products
                                         are used to track movement and location of thunderstorm anvils.

                                     •The increased sensitivity and ‘staring’ capability of MPAR should
                                      significantly improve ‘now-casting’ operations for shuttle and other
                                      launch operations.

                                                                                 G O D D A R D   S P A C E F L I G H T C E N T E R   11
           TRMM/GPM                                                    How Would MPAR Help NASA’s PMM Goals?

                                     •MPAR would enhance PMM efforts by

                                       – Providing rapid updating via adaptive scanning and rapid volume scanning
Precipitation Measurement Missions

                                         (especially during satellite overpass periods)
                                          • Improve the process studies, e.g., cloud-resolving model (CRM) validation; and also

                                          • Making more instantaneous comparisons to DPR for direct validation

                                       – Provide a better and more frequent estimate of surface precipitation via the
                                         "ground hugging" mode
                                          • Will assist direct validation, and integrated and hydrological validation applications.

                                          • Will provide important information, now parameterized, on the vertical gradient of
                                            reflectivity and rain rate, imperative for accurate estimation of surface precipitation

                                       – Dual-polarization capability would help validate quality control, drop size
                                         distribution, hydrometeor type classification, and precipitation estimates of the
                                         GPM dual-frequency radar (DPR)

                                                                                      G O D D A R D   S P A C E F L I G H T C E N T E R   12

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