Case Study Of Precipitation Clouds Over The East Asia Based On DPR And GMI Measurements

The Global Precipitation Measurement (GPM) mission is developed by JAXA of Japan and NASA of the United States to provide the next generation of global satellite precipitation products after TRMM, the GPM core observatory was launched successfully at the end of February 2014 and started its observation. Onboard the GPM core observatory is a dual-frequency precipitation radar (DPR) and the GPM Microwave Imager (GMI), the DPR consists of Ku-band (13.6 GHz) and Ka-band (35.5 GHz) channels. Two years of observations from the GPM core observatory are now available, allowing people to research the global precipitation. To data, however, the latest research devoted to the GPM mission and its newest products still lack in China. In this paper, firstly, we elaborated the GPM and its instruments, precipitation retrieval algorithm and products of the GPM mission. aiming to promote global precipitation related research and applications in China; secongly, the differences in precipitation detectability between Ku-band and Ka-band radar is studied by using individual analysis; Finally, we analysis three precipitation cases in East Asia by using DPR and GMI standard product.In this paper, we research the difference in DPR dual-bands that contains four different ways (Ka_HS、Ka_MS、Ku_NS and DPR_MS), with focus on the near surface rain, storm top height (STH), radar precipitation echo and drop-size distribution (DSD) parameters. The results obtains are as follows:(1) the difference in near surface rain between the Ku-band and Ka-band radarThe Ka_HS typically identify the near surface rain less than 10 mm/h, especially can capture light rainfall that less than 0.4 mm/h. it means that Ka high sensitivity mode is good at light rainfall (<0.4 mm/h); the Ku_MS capture rainfall between 0.4 mm/h and 10 mm/h, implying that the advantage of Ka_MS is not obvious in detecting heavy rainfall (10 mm/h) and light rainfall (0.4 mm/h); however, Ku_NS can distinguish rainfall more than 10 mm/h, implying that Ku_NS is suitable for measuring moderate to heavy rainfall, in addition, we find that DPR MS and Ku_NS is little less Than Ku NS in near surface rain, but the difference is not obvious.(2) the difference in storm top height between the Ku-band and Ka-band radarBy the comparative analysis, some noticeable features are evident in STH. The Ka_HS detect the highest STH, and Ka_MS detect lower STH than others, while the Ku_NS and DPR_MS have little systematic difference in STH.(2) the difference in radar precipitation echo between the Ku-band and Ka-bandFor the two heavy precipitation cases happened in eastern China and western pacific ocean, especially for tropical cyclone precipitation, Ka_HS still can detect precipitation echo signal with STH above 13 km, and Ka_HS can detect reflectivity of 35 dBZ near surface. By contrast, for Ku_NS, the detectable STH is below 13 km, and the reflectivity over 40 dBZ below 5 km, while above 5 km height, Ku_NS is greater than Ka_HS with the percentage of reflectivity between 15 and 20 dBZ. For the other two light precipitation cases, especially for the precipitation happened near Aleutian islands, Ka_HS hardly can not detect radar echo signal above 8 km, the strongest signal that can be measured is about 35 dBZ, while Ku_NS can detect reflectivity exceed 40dBZ with height below 3 km, meanwhile, compared with Ka_HS, Ku_NS can measure even stronger echo signal in the lower height.(3) the difference in DSD parameters between the Ku-band and Ka-band radarAanlysis of DSD distribution features show that, for heavier precipitation, the DSD parameter dBNw that obtained by DPR_MS is small compared to the other, while the other parameter Dm is bigger, meanwhile, we can find that the DSD parameters obtained by Ka_HS and DPR_MS is similar below 5 km, while above 5 km, Ku_NS is similar to DPR_MS. For the light precipitation, it is just opposite: below 3 km, dBNw obtained by DPR_MS is relatively large, and Ku_NS is similar to DPR_MS, the distribution of another parameter Dm is opposite to dBNw; above 3 km, the distribution is similar to before, but the difference between DSD parameters that obtained by different detection mode has been an increase.Based on the difference between Ku-band and Ka-band radar detecting precipitation, using the latest detection results from DPR and GMI, three typical precipitation cases are studied, the results obtained can be summarized as follows.(1) Since the typhoon Rammasun entered the South China Sea, influenced by Western Pacific subtropical high, and the sea temperature is continuous high, before Landfall Hainan Island, it rapidly intensified、structure tend to be more closely and the eye clearly visible.the Rammasun has large spiral rain bands and cloud wall, the heavy rain occurs among the cloud wall and spiral rain bands where exist many rain bands and rain clusters above 30 mm/h, they embedded in large stratiform precipitation below 10 mm/h. We can find that the precipitation in the vertical direction can be extended to 15km, but the heavy rainfall (> 15 mm/h) mailly under 6 km height. What’s more, we can find that Ku-band radar is suitable for measuring moderate to heavy rain happened in cloud wall and spiral rain bands, but Ka-band is obviously not good at it. Also, high-frequency channels can obtain clear typhoon structure early, and 183.3 GHz channel is more sensitive than 89 GHz in detecting small ice praticles.(2) DPR Dual-frequency retrieval measurements show strong convective rainfall occurred along a narrow and long cold cold front, especially when the cyclone was deepening and the cold front was enhanced after one and half hour. On the contrary, a large area of stratiform rainfalls occurred in a wide warm front region although there were several strong convective rain blocks embedding in the wide region. In addition, for strong convective rainfall the STH can reach 15 km, but for most rainfalls, the STH is near 10 km, and for large quantities of precipitatios, most happened below 5 km height. GMI measurements show that the cloud water path is rare and ice water path is large in this front cyclone rainfall.(3) Compared with the TRMM which focus on the observation of precipitation in tropical and subtropical regions, GPM can capture light rainfall and solid precipitation more accurately, both critical precipitation types for high-latitude regions. DPR Dual-frequency retrieval measurements show that DPR can capture precipitation from 0.2 mm/h to 0.5 mm/h, the Ku-band radar frequency is more sensitive to heavy and moderate rainfall, the Ka-band radar frequency is more sensitive to light rain and snow (< 2 mm/h); GMI measurements show that in this precipitation case, there are widely distributed water particles and ice particles, and the ice water content is high obviously,183.3 GHz channel is optimal for the sensing of small ice particles.