青藏高原与极地气象研究进展

Progress in the Tibetan Plateau and Polar Meteorology Research

1 青藏高原气象

1 Tibetan Plateau meteorology

1.1 Precursory signals (SST and soil moisture) of summer surface temperature anomalies over the Tibetan Plateau

Understanding the variability of surface air temperature (SAT) over the Tibetan Plateau (TP) and its precursory signals is of great benefit to climate change adaptation and socioeconomic development. This study explores the precursory signals of summer SATs over the TP in oceanic and land boundary conditions. The results show that the summer eastern TP SAT is significantly correlated with three precursors in April: the high-latitude North Atlantic sea surface temperature (SST), the northern Indian Ocean SST, and the Indian soil moisture (SM). The April SST anomalies (SSTAs) in the high-latitude North Atlantic can exert a cross-season impact on the summer SAT over the TP through two processes. The SSTAs in the high-latitude North Atlantic maintain from April to summer and modulate atmospheric circulation over the eastern TP through exciting a downstream wave train during summer, and finally modulate the summer SAT over the eastern TP. In addition to the above process, the April SSTAs in the high-latitude North Atlantic may remotely regulate simultaneous SM in the Indian subcontinent through stimulating a downstream wave train pattern. Through a persistent SM-precipitation interaction, the April Indian SM anomaly can affect the local precipitation and associated condensation heating anomalies during the ensuing summer, which forces an anomalous cyclone-anticyclone pattern around the TP and accordingly affects the summer SAT over the eastern TP. Additionally, the SSTAs in the northern Indian Ocean can persist from April to summer and adjust the intensity and location of the western North Pacific subtropical high through the Kelvin-wave-induced Ekman divergence during summer, eventually affecting the summer eastern TP SAT. The three precursory signals, which synergistically contribute to the variability of the summer eastern TP SAT, can be applied in predicting the summer SAT over the eastern TP.(Wang Hui, Liu Ge, Wang Sai, He Kejun)

1.2 Retrieval of O3, NO2, BrO and OClO columns from ground-based zenith scattered light DOAS measurements in summer and autumn over the northern Tibetan Plateau

Ground-based zenith scattered light differential optical absorption spectroscopy (DOAS) measurements were performed in summer and autumn (27 May to 30 November) 2020 at Golmud (94°54′ E, 36°25′ N;2807.6 m altitude) to investigate the abundances and temporal variations of ozone (O3) and its depleting substances over the northern Tibetan Plateau (TP). The differential slant column densities (dSCDs) of O3,nitrogen dioxide (NO2), bromine monoxide (BrO), and chlorine dioxide (OClO) were simultaneously retrieved from scattered solar spectra in the zenith direction during the twilight period. The O3vertical column densities(VCDs) were derived by applying the Langley plot method, for which we investigated the sensitivities to the chosen wavelength, the a-priori O3profile and the aerosol extinction profile used in O3air mass factor (AMF)simulation as well as the selected solar zenith angle (SZA) range. The mean O3VCDs from June to November 2020 are 7.21×1018molecules m−2and 7.18×1018molecules m−2at sunrise and sunset, respectively. The derived monthly variations of the O3VCDs, ranging from a minimum of 6.9×1018molecules m−2in October to 7.5×1018molecules m−2in November, well matched the OMI satellite product, with a correlation coefficient R = 0.98.The NO2VCDs at SZA = 90°, calculated by a modified Langley plot method, were systematically larger at sunset than at sunrise as expected with a pm/am ratio of about 1.56. The maximum of the monthly NO2VCDs,averaged between sunrise and sunset, was 3.40×1015molecules m−2in July. The overall trends of the NO2VCDs were gradually decreasing with the time and similarly observed by the ground-based zenith DOAS and OMI. The average level of the BrO dSCD 90°‒80° (i.e., dSCD between 90° and 80° SZA) was 2.06×1014molecules m−2during the period of June–November 2020. The monthly BrO dSCD 90°–80° presented peaks in August and July for sunrise and sunset, respectively, and slowly increased after October. During the whole campaign period, the OClO abundance was lower than the detection limit of the instrument. This was to be expected because during that season the stratospheric temperatures were above the formation temperature of polar stratospheric clouds. Nevertheless, this finding is still of importance, because it indicates that the OClO analysis works well and is ready to be used during periods when enhanced OClO abundances can be expected. As a whole, ground-based zenith DOAS observations can serve as an effective way to measure the columns of O3and its depleting substances over the TP. The aforementioned results are helpful in investigating stratospheric O3chemistry over the third pole of the world. (Cheng Siyang, Ma Jianzhong, Zheng Xiangdong)

1.3 Monsoon clouds control the summer surface energy balance on east Rongbuk glacier (6,523 m above sea level), the northern of Mt. Qomolangma (Everest)

To identify the atmospheric controls of the summertime glacier surface energy balance in the Himalayas,in situ meteorological data collected at 6,523 m above sea level during May–July 2005 were obtained and analyzed. Our results showed that net shortwave radiation (103 W m−2) and turbulent sensible heat flux(12 W m−2) acted as energy sources, and net longwave radiation (−62 W m−2) and turbulent latent heat flux(−20 W m−2) represented heat sinks. Cloud cover controlled the summer surface energy balance. During the active period of the South Asian summer monsoon, the frequent cloud coverage increased the incoming longwave radiation more than it decreased the incident solar radiation. Intensification (weakening) of the South Asian summer monsoon strengthened (suppressed) surface melting. The melt energy measured during the nonmonsoon period was small due to the energy consumption associated with glacier volume warming,energy loss from sublimation, and large heat loss through net longwave radiation due to the low amount of incoming longwave radiation caused by the low cloudiness. The comparison of glacier surface energy balances on the Tibetan Plateau shows that on continental glaciers, net radiation is lower and accounts for a smaller contribution to energy sources, and the dominant energy sinks are sublimation and evaporation, rather than melting, which is the primary energy sink for maritime/subcontinental glaciers. This implies an important spatial variability in glacial sensitivity to different climatic conditions on the Tibetan Plateau. (Liu Weigang,Zhang Dongqi, Ding Minghu)

1.4 Links between the thermal condition of the Tibetan Plateau in summer and atmospheric circulation and climate anomalies over the Eurasian continent

We examine the links between the thermal condition of the troposphere over the Tibetan Plateau with the atmospheric circulation and climate over the Eurasian continent. The temperature of the troposphere over the Tibetan Plateau is higher than the temperature in other regions at the same latitude and is consistent with the temperature of the Eurasian troposphere on an interannual timescale. The higher temperature of the troposphere over the Tibetan Plateau leads to anomalous south–north temperature gradients from mid-latitudes over the Eurasian continent to its two flanks, accompanied by anomalous easterly and westerly winds in the upper troposphere in the subtropics and at higher latitudes. Anomalous anticyclonic circulations and subsidence motions appear between the anomalous easterly and westerly winds and contribute to the high surface air temperature over West Asia, Central Asia and East Asia via anomalous vertical temperature advection in the troposphere and change in the amount of solar radiation incident on the surface. The enhanced East Asian summer monsoon associated with the high temperature of the troposphere over the Tibetan Plateau also partly contributes to the high surface air temperature over East Asia via horizontal temperature advection. The westerly wind anomalies in the north of the mid-latitudes over the Eurasian continent indicate the enhancement and northward shift of the mid-latitude westerly jet. This is related to anomalous upward motion and higher precipitation in Northeast China and North China. Sensitivity experiments based on an atmospheric model verify the impact of anomalous tropospheric heating over the Tibetan Plateau in summer on the atmospheric circulation over the Eurasian continent. (Nan Sulan, Zhao Ping, Chen Junming, Liu Ge)

1.5 台站建设

2021年4月，于西藏自治区墨脱县新建方舱式风廓线雷达（型号CFL-03，北京无线电测量研究所）观测站，位于墨脱县气象局观测场旁，海拔1305 m，地理环境为郊外山腰，可实现0～6 km风廓线的探测。2021年7月，于云南贡山新建微波辐射计（型号MP-3000A，Radiometer）观测站，位于贡山县气象局楼顶，海拔1590 m，地理环境为郊外山腰，测量从地面至天空10 km高度垂直剖面上的温度、湿度廓线，液态水含量，云参数及有无降水等大气信息。2021年8月，于西藏自治区嘉黎县新建边界层梯度通量观测系统，位于嘉黎县气象局观测场旁，海拔4489 m，地理环境为河谷，观测要素包含5层空气温湿、5层土壤温湿、5层风速、风向、光合有效辐射、净辐射、土壤热通量、地表温度、雨量、雪深、CO2/H2O汽通量。

1.6 青藏高原大气环境立体综合观测试验

根据中国气象科学研究和西藏自治区双边协议，联合推进青藏高原野外科学试验。双方在拉萨站开展了多轴差分吸收光谱（MAX-DOAS）和大气水汽—气溶胶激光雷达地基主被动遥感观测，提升了提升青藏高原地区大气环境多组分垂直廓线观测能力，为开展青藏高原气候变化研究、青藏高原立体生态环境研究、青藏高原臭氧低谷研究等重大前沿科学问题奠定了数据基础。首次在青藏高原北部（西宁—达日—玉树线）和南部（拉萨—林芝—波密线）同时协作开展基于车载平台的青藏高原大气环境多组分三维结构动态遥感探测试验，有望对三江源地区和藏东南水汽通道上的大气环境有新认识。……