Observed Vertical Structure of Precipitation over the Southeastern Tibetan Plateau in Summer 2021

Mêdog County,with its mountains and valleys,is located in the southeastern Tibetan Plateau(TP)and at the lower reaches of the Yarlung Zangbo River.This area has the highest annual rainfall amount over the TP,and in situ measurements are very scarce due to frequent debris flows and transportation difficulties.A monitoring campaign focused on cloud and precipitation observations was established in Mêdog in 2019 as a part of the Second Tibetan Plateau Scientific Expedition and Research Program.This paper evaluates the accuracy of micro rain radar(MRR)measurements and investigates the variations in precipitation vertical structure in Mêdog using observations collected from the MRR,disdrometer,and rain gauges in summer 2021.The measurements from the three instruments show a strong consistency,with correlation coefficients exceeding 0.93.Although the profiles of integral rain parameters for different rain rate categories in Mêdog are similar to those in other regions,the vertical evolution of raindrop size distributions shows significant differences.For lightest rain,the evaporation of small raindrops and breakup of large raindrops are clear during their descent.For the rainfall rate category of 0.2–2.0 mm h−1(2.0–20.0 mm h−1),concentrations of small and medium(large)drops show almost uniform vertical structures,while the large(medium)drop number displays a positive(negative)gradient.A disturbance at height of 1.5–2.0 km above ground level(AGL)is observed in the heavy rainfall due to strong updrafts.In general,the MRR measurements in Mêdog are robust.The raindrop breakup process is more apparent in Mêdog than in other regions,resulting in high concentration of sizelimited raindrops.In addition,it is found that the interaction between steep terrain and Mêdog convective rain causes the strong updrafts between 1.5 and 2.0 km AGL.

Satellite Observations of Reflectivity Maxima above the Freezing Level Induced by Terrain

Previous studies have recognized reflectivity maxima above the freezing level(RMAF) within stratiform precipitation over mountain slopes, however, quantitative studies are limited due to the lack of adequate identification criteria. Here, we establish an identification method for RMAF precipitation and apply it to the Tropical Rainfall Measuring Mission(TRMM) Precipitation Radar(PR) observations. Using the TRMM 2A25 product from 1998 to 2013, we show that the RMAF structure in reflectivity profiles can be effectively identified. RMAF exists not only in stratiform precipitation but also in convective precipitation. RMAF frequency is positively correlated with elevation, which is thought to be caused by enhanced updrafts in the middle layers of stratiform precipitation, or in the low to middle layers of convective precipitation over mountains. The average RMAF heights in stratiform and convective precipitation were 1.35 and 2.01 km above the freezing level, respectively, which is lower than previous results. In addition, our results indicate that the RMAF structure increased the echo top height and enhanced precipitation processes above the RMAF height, but it suppressed the downward propagation of ice particles and the near-surface rain rate. Future studies of orographic precipitation should take into account the impact of the RMAF structure and its relevant dynamic triggers.

Climatological Characteristics of Summer Precipitation over East Asia Measured by TRMM PR:A Review

Precipitation is an important indicator of climate change and a critical process in the hydrological cycle, on both the global and regional scales. Methods of precipitation observation and associated analyses are of strategic importance in global climate change research. As the first space-based radar, the Tropical Rainfall Measuring Mission(TRMM)Precipitation Radar(PR) has been in operation for almost 17 years and has acquired a huge amount of cloud and precipitation data that provide a distinctive view to help expose the nature of cloud and precipitation in the tropics and subtropics. In this paper we review recent advances in summer East Asian precipitation climatology studies based on long-term TRMM PR measurements in the following three aspects:(1) the three-dimensional structure of precipitation,(2) the diurnal variation of precipitation, and(3) the recent precipitation trend. Additionally, some important prospects regarding satellite remote sensing of precipitation and its application in the near future are discussed.

Structural Characteristics of Atmospheric Temperature and Humidity inside Clouds of Convective and Stratiform Precipitation in the Rainy Season over East Asia

In this study, a merged dataset constructed from Tropical Rainfall Measuring Mission precipitation radar rain products and Integrated Global Radiosonde Archive data is used to investigate the thermal structural characteristics of convective and stratiform precipitation in the rainy season(May–August) of 1998–2012 over East Asia. The results show that the storm tops for convective precipitation are higher than those for stratiform precipitation, because of the more unstable atmospheric motions for convective precipitation. Moreover, the storm tops are higher at 1200 UTC than at 0000 UTC over land regions for both convective and stratiform precipitation, and vice versa for ocean region. Additionally, temperature anomaly patterns inside convective and stratiform precipitating clouds show a negative anomaly of about 0–2 K, which results in cooling effects in the lower troposphere. This cooling is more obvious at 1200 UTC for stratiform precipitation. The positive anomaly that appears in the middle troposphere is more than 2 K, with the strongest warming at 300 hPa. Relative humidity anomaly patterns show a positive anomaly in the middle troposphere(700–500 h Pa) prior to the occurrence of the two types of precipitation, and the increase in moisture is evident for stratiform precipitation.

Effect of solidification rate on dendrite segregation and mechanical properties of Cu-15Ni-8Sn alloy prepared by directional solidification

The microstructures and mechanical properties of the directionally solidified Cu-15Ni-8Sn alloy were investigated at solidification rates ranging from 100 to 3000μm/s.The results showed that the solidification rate significantly affects the phase distribution of the as-cast Cu-15Ni-8Sn alloy.The primary and secondary dendritic spacing reduces and eventually becomes stable as the solidification rate increases.Meanwhile,the size of the primary phase decreases,and its distribution becomes more uniform.The most severe segregation problem of this alloy has been greatly improved.Upon solidification at 100μm/s,the as-cast Cu-15Ni-8Sn alloy consists of the α-Cu matrix,γ-CuNi_(2)Sn phase,discontinuous precipitation structure,modulated structure,and DO_(22) ordered phases.However,as the solidification rate increases,the discontinuous precipitation structure,modulated structures,and DO_(22) ordered phases decrease and even disappear,reducing hardness.As the solidification rate increases,after homogenization treatment,the composition and microhardness distributions of Cu-15Ni-8Sn alloy become more uniform.The time for homogenization is also shortened.It reduces production energy usage and facilitates further mechanical processing.