Misako Kachi

Global Precipitation Map using Satelliteborne Microwave Radiometers by the GSMaP Project : Production and Validation

This paper documents the production and validation of retrieved rainfall data obtained from satellite-borne microwave radiometers by the Global Satellite Mapping of Precipitation (GSMaP) Project. Using various attributes of precipitation derived from Tropical Rainfall Measuring Mission (TRMM) satellite data, the GSMaP has implemented hydrometeor profiles derived from Precipitation Radar (PR), statistical rain/no-rain classification, and scattering algorithms using polarization-corrected temperatures (PCTs) at 85.5 and 37 GHz. Combined scattering-based surface rainfalls are computed depending on rainfall intensities. PCT85 is not used for stronger rainfalls, because strong depressions of PCT85 are related to tall precipitation-top heights. Therefore, for stronger rainfalls, PCT37 is used, with PCT85 used for weaker rainfalls. With the suspiciously strong rainfalls retrieved from PCT85 deleted, the combined rainfalls correspond well to the PR rain rates over land. The GSMaP algorithm for the TRMM Microwave Imager (TMI) is validated using the TRMM PR, ground radar [Kwajalein (KWAJ) radar and COBRA], and Radar Automated Meteorological Data Acquisition System (AMeDAS) precipitation analysis (RA). Monthly surface rainfalls retrieved from six microwave radiometers (GSMaP_MWR) are compared with the gauge-based dataset. Rain rates retrieved from the TMI (GSMaP_TMI) are in better agreement with the PR estimates over land everywhere except over tropical Africa in the boreal summer. Validation results of the KWAJ radar and COBRA show a good linear relationship for instantaneous rainfall rates, while validation around Japan using the RA shows a good relationship in the warm season. Poor results, connected to weak-precipitation cases, are found in the cold season around Japan.

Abrupt termination of the 1997–98 El Niño in response to a Madden–Julian oscillation

The role of the Madden–Julian oscillation—a global atmospheric wave in the tropics that is associated with convective activity and propagates eastwards with a period of about 30–60 days (refs 1, 2)—in triggering El Niño events has been discussed before. But its possible connection with a termination of El Niño has yet to be investigated, despite the difficulty in explaining the timing of El Niño terminations by the basic wind-induced oceanic-wave processes. For the extreme 1997–98 event, the mechanism of both onset and termination have been investigated, but the reason for the abruptness of the termination has yet to be resolved. Here we present global data of precipitation, sea surface temperatures and wind speeds that show a precipitation system associated with an exceptionally strong Madden–Julian oscillation travelling around the Equator in May 1998. The propagation of this atmospheric system was associated with an abrupt intensification of the easterly trade winds over the eastern equatorial Pacific Ocean. Combined with the already shallow equatorial thermocline in the central and eastern Pacific Ocean at that time, these strong winds provided the triggering mechanism for the observed accelerated ending of the 1997–98 El Niño event.

Global Change Observation Mission (GCOM) for Monitoring Carbon, Water Cycles, and Climate Change

The Japan Aerospace Exploration Agency (JAXA) is pursuing the Global Change Observation Mission (GCOM) that will inherit the Advanced Earth Observing Satellite-II (ADEOS-II) mission and develop into long-term monitoring. GCOM is not the name of a single satellite, but of a mission that consists of two series of medium-size satellites, GCOM-W (Water) and GCOM-C (Climate), and three generations of each satellite series to continue the observations for 10 to 15 years. The Advanced Microwave Scanning Radiometer-2 (AMSR2) will be the single instrument on the GCOM-W1 satellite, which is the first satellite of the GCOM series. The second satellite will be GCOM-C1, which will carry the Second-generation Global Imager (SGLI). GCOM-W will mainly contribute to the observations related to global water and energy circulation, while GCOM-C will contribute to the measurements related to the carbon cycle and radiation budget. Current target launch years are calendar year 2011 for GCOM-W1 and 2014 for C1.

Comparison of Rainfall Products Derived from TRMM Microwave Imager and Precipitation Radar

Satellite remote sensing is an indispensable means of measuring and monitoring precipitation on a global scale. The Tropical Rainfall Measuring Mission (TRMM) is continuing to make significant progress in helping the global features of precipitation to be understood, particularly with the help of a pair of spaceborne microwave sensors, the TRMM Microwave Imager (TMI) and precipitation radar (PR). The TRMM version-5 standard products, however, are known to have a systematic inconsistency in mean monthly rainfall. To clarify the origin of this inconsistency, the authors investigate the zonal mean precipitation and the regional trends in the hydrometeor profiles in terms of the precipitation water content (PWC) and the precipitation water path (PWP) derived from the TMI profiling algorithm (2A12) and the PR profile (2A25). An excess of PR over TMI in near-surface PWC is identified in the midlatitudes (especially in winter), whereas PWP exhibits a striking excess of TMI over PR around the tropical rainfall maximum. It is shown that these inconsistencies arise from TMI underestimating the near-surface PWC in midlatitude winter and PR underestimating PWP in the Tropics. This conclusion is supported by the contoured-frequency-by-altitude diagrams as a function of PWC. Correlations between rain rate and PWC/ PWP indicate that the TMI profiling algorithm tends to provide a larger rain rate than the PR profile under a given PWC or PWP, which exaggerates the excess by TMI and cancels the excess by PR through the conversion from precipitation water to rain rate. As a consequence, the disagreement in the rainfall products between TMI and PR is a combined result of the intrinsic bias originating from the different physical principles between TMI and PR measurements and the purely algorithmic bias inherent in the conversion from precipitation water to rain rate.

Finescale Diurnal Rainfall Statistics Refined from Eight Years of TRMM PR Data

Abstract The adequacy of hourly rainfall sampling was examined in terms of the detection of diurnal variations using 8 yr (1998–2005) of data observed by the precipitation radar on the Tropical Rainfall Measuring Mission (TRMM) satellite. It was found that the monthly and hourly rain samples for each 0.2° grid point over the 8-yr period are composed of multiple precipitation systems. In this study, a “3-h-significant diurnal peak” was defined as the time of maximum rainfall with consecutive positive anomalies for more than 3 h. The fraction of the analyzed area with a 3-h-significant diurnal peak increased annually and accounted for 43% of the total global tropics at 0.2° resolution over the 8-yr period. The diurnal signature over Tibet and the Amazon showed a high degree of spatial uniformity (at >10° scale). The degree of similarity and locations of the regional diurnal characteristics are described in terms of seasonal variations and at multiple resolutions based on spatial uniformity. For example, uni...

Physical properties of maritime low clouds as retrieved by combined use of Tropical Rainfall Measuring Mission (TRMM) Microwave Imager and Visible/Infrared Scanner. 2. Climatology of warm clouds and rain

[1] In this paper, we investigate characteristics of low clouds and warm-rain production in terms of droplet growth based on the effective droplet radii retrieved by a combined use of visible, infrared, and microwave satellite remote sensing. We propose to categorize low clouds into the following groups: (1) nondrizzling, nonraining clouds; (2) nonraining clouds with drizzling near the cloud top; (3) raining clouds; and (4) clouds with no clear interpretation in terms of the effective radii derived using two different schemes. This categorization is supported by examination of the correlation between static stability and the retrieved results in the three ‘‘precipitating regions’’ (the Middle Pacific, South Pacific Convergence Zone [SPCZ], and Intertropical Convergence Zone [ITCZ] cumulus regions) and in the four ‘‘nonprecipitating regions’’ (the Californian, Peruvian, Namibian, and eastern Asian stratus regions). The rain rate derived by Precipitation Radar (PR) provides global characteristics consistent with our results. Californian and Peruvian stratus clouds are found to frequently have the drizzle mode near the cloud top, whereas Namibian strati have fewer chances to drizzle. The drizzle mode almost completely disappears in the eastern Asian region in the winter. The cloud–aerosol interaction is a promising candidate for suppressing the drizzle mode formation in nonprecipitating clouds. INDEX TERMS: 0320 Atmospheric Composition and Structure: Cloud physics and chemistry; 1610 Global Change: Atmosphere (0315, 0325); 1640 Global Change: Remote sensing; 1655 Global Change: Water cycles (1836)

Improvement of High-Resolution Satellite Rainfall Product for Typhoon Morakot (2009) over Taiwan

The authors improve the high-resolution Global Satellite Mapping of Precipitation (GSMaP) product for Typhoon Morakot (2009) over Taiwan by using an orographic/nonorographic rainfall classification scheme. For the estimation of the orographically forced upward motion used in the orographic/nonorographic rainfall classification scheme, the optimal horizontal length scale for averaging the elevation data is examined and found to be about 50km. It is inferred that as the air ascends en masse on the horizontal scale, it becomes unstableandconvectiondevelops.Theorographic/nonorographic rainfallclassification schemeis extendedto the GSMaP algorithm for all passive microwave radiometers in orbit, including not just microwave imagers butalsomicrowavesounders. Theretrievedrainfallrates,togetherwithinfraredimages,areusedforthehighresolution rainfall products, which leads to much better agreement with rain gauge observations.

Gauge adjusted global satellite mapping of precipitation (GSMaP_Gauge)

Precipitation is one of the most important resources for human activity, and global distribution of precipitation amount and its change are essential data for modeling the water cycle and global energy cycle. Space-borne Passive Microwave Radiometers (PMRs) are working on many satellites. PMR observes emission and scattering from precipitation and provide uniform global data. The Global Satellite Mapping of Precipitation Moving Vector with Kalman-filter (GSMaP_MVK) estimates hourly and 0.1 degree gridded precipitation map from PMRs. Because land is radiometrically warm region, estimation of precipitation over land is difficult. Global precipitation over land, however, is most important for human activity, such as management of water and flood warning. We are developing a gauge adjusted algorithm for GSMaP (GSMaP_Gauge). In this paper, we show performance of the algorithm and some initial evaluation tests. We introduce the GSMaP_Gauge algorithm and show the validation of the algorithm.

Status of AMSR2 instrument on GCOM-W1

The Global Change Observation Mission (GCOM) consists of two polar orbiting satellite observing systems, GCOM-W (Water) and GCOM-C (Climate), and three generations to achieve global and long-term monitoring of the Earth. GCOM-W1, the first satellite of the GCOM-W series, was successfully launched on May 18, 2012 (Japan Standard Time). The Advanced Microwave Scanning Radiometer-2 (AMSR2), which is a successor of AMSR on the Advanced Earth Observing Satellite-II (ADEOS-II) and AMSR for EOS (AMSR-E) on NASA’s Aqua satellite, is a single mission instrument on GCOM-W1. Basic characteristics of AMSR2 is similar to that of AMSR-E to continue the AMSR-E observations, with several enhancements including larger main reflector (2.0 m), additional channels at the C-band frequency band, and improved calibration system. AMSR-E halted its observation on October 4, 2011 due to the increase of antenna rotation torque, which is considered as the typical aging effect. Although all the efforts are being made to resume the AMSR-E observation, early initiation of the AMSR2 observation has been highly desired. After the completion of the orbit injection into the A-Train constellation, AMSR2 started rotating and initiated global observation. During the initial calibration and validation phase, brightness temperatures will be evaluated and characterized through methodologies such as the inter-calibration among similar microwave radiometers including the TRMM Microwave Imager (TMI) and WindSat on Coriolis mission.

Kalman Filtering Applications for Global Satellite Mapping of Precipitation (GSMaP)

GSMaP (Global Satellite Mapping of Precipitation) is a project aiming (1) to produce high-precision and high-resolution global precipitation maps using satellite-borne microwave radiometer data, (2) to develop reliable microwave radiometer algorithms, and (3) to establish precipitation map techniques using multi-satellite data for the coming GPM era. The GSMaP_MVK system uses a Kalman filter model to estimate precipitation rate at each 0.1° with 1-h resolution on a global basis. The input data sets are precipitation rates retrieved from the microwave radiometers and infrared images to compute the moving vector fields. Based on the moving vector fields calculated from successive IR images, precipitation fields are propagated and refined on the Kalman filter model, which uses the relationship between infrared brightness temperature and surface precipitation rate. This Kalman filter – based method shows better performance than the moving vector – only method, and the GSMaP_MVK system shows a comparable score compared with other high-resolution precipitation systems.