Zhi-Yong Yin

Temporal trends and variability of daily maximum and minimum, extreme temperature events, and growing season length over the eastern and central Tibetan Plateau during 1961–2003

[1] Daily and monthly maximum and minimum surface air temperatures at 66 weather stations over the eastern and central Tibetan Plateau with elevations above 2000 m were analyzed for temporal trends and spatial variation patterns during the period 1961 - 2003. Statistically significant warming trends were identified in various measures of the temperature regime, such as temperatures of extreme events and diurnal temperature range. The warming trends in winter nighttime temperatures were among the highest when compared with other regions. We also confirmed the asymmetric pattern of greater warming trends in minimum or nighttime temperatures as compared to the daytime temperatures. The warming in regional climate caused the number of frost days to decrease significantly and the number of warm days to increase. The length of the growing season increased by approximately 17 days during the 43-year study period. Most of the record-setting months for cold events were found in the earlier part of the study period, while that of the warm events occurred mostly in the later half, especially since the 1990s. The changes in the temperature regime in this region may have brought regional-specific impacts on the ecosystems. It was found that grain production in Qinghai Province, located in the area of prominent warming trends, exhibited strong correlations with the temperatures, although such relationships were obscured by the influence of precipitation in this arid/semiarid environment in juniper tree ring records. In western Sichuan Province under a more humid environment, the tree growth ( spruces) was more closely related to the changing temperatures.

Spatial and temporal variation patterns of reference evapotranspiration across the Qinghai‐Tibetan Plateau during 1971–2004

Reference evapotranspiration (RET), an indicator of atmospheric evaporating capability over a hypothetical reference surface, was calculated using the Penman-Monteith method for 75 stations across the Qinghai-Tibetan Plateau between 1971 and 2004. Generally, both annual and seasonal RET decreased for most part of the plateau during the study period. Multivariate linear models were used to determine the contributions of climate factors to RET change, including air temperature, air humidity, solar radiation, and wind speed. Spatial differences in the causes of RET change were detected by K-means clustering analysis. It indicates that wind speed predominated the changes of RET almost throughout the year, especially in the north of the study region, whereas radiation was the leading factor in the southeast, especially during the summertime. Although the recent warming trend over the plateau would have increased RET, the combined effect of the reduced wind speed and shortened sunshine duration negated the effect of rising temperature and caused RET to decrease in general. The significant decrease in surface wind speed corresponded to the decreasing trends of upper-air zonal wind and the decline of pressure gradient, possibly as a result of the recent warming.

An Assessment of the Biases of Satellite Rainfall Estimates over the Tibetan Plateau and Correction Methods Based on Topographic Analysis

Abstract The hydrological processes over the Tibetan Plateau have significant implications on regional macroscale atmospheric circulation patterns and the Asian monsoon system. Because of its remote setting and lack of ground observations, it is difficult to study the spatial and temporal patterns of precipitation over the plateau, and satellite remote sensing technology can be used to fill in the gaps where station data are not available. In this study the authors examine monthly 1° × 1° rainfall estimates obtained from the Special Sensor Microwave Imager (SSM/I) [National Environmental Satellite, Data, and Information Service (NESDIS) algorithm] and Tropical Rainfall Measuring Mission (TRMM) 3B42 version 5 (V5) products for the months of April–October 1998–2002 over the Tibetan Plateau. By comparing the satellite estimates with ground observations at 94 weather stations in the study region, the authors derived regression models that produced significant improvements to satellite estimates based on vario...

Study of the Impact of Summer Monsoon Circulation on Spatial Distribution of Aerosols in East Asia Based on Numerical Simulations

AbstractThe regional coupled climate–chemistry/aerosol model (RegCM3) is used to investigate the difference in the spatial distribution of aerosol optical depth (AOD) between a strong summer monsoon year (SSMY; July 2003) and a weak summer monsoon year (WSMY; July 2002) under the actual- and same-emission scenarios. It is shown that the intensity of the Asian summer monsoon is primarily responsible for the AOD spatial distribution anomaly in midsummer over East Asia. Specifically, the AOD over southern China, upwind of the Asian summer monsoon, is greater in WSMY than in SSMY, but the opposite is observed for the AOD downwind over northern China and the Korean Peninsula. The AOD spatial distribution patterns simulated on the basis of the actual emission inventories for the SSMY and WSMY do not substantially differ from their counterparts that are based on the same emission inventory, confirming that the monsoon circulation, rather than local emissions or dry and wet deposition processes, is the predominan...

Influence of Indian Summer Monsoon on Aerosol Loading in East Asia

Abstract The spatial and temporal variations of aerosol loading over eastern Asia specified in terms of the aerosol optical depth (AOD) at the 550-nm wavelength during July are examined in conjunction with the intensity of the Indian summer monsoon. AOD derived from Moderate Resolution Imaging Spectroradiometer (MODIS) observations, gridded reanalyses, and ground-based measurements are used in the analysis. Two contrasting years, 2002 and 2003, which represent weak and active Indian summer monsoon events, respectively, are selected for the study, with a focus on an eastern Asian southern subregion (SR; 23°–32°N, 105°–120°E) and an eastern Asian northern subregion (NR; 35°–44°N, 115°–130°E). It is shown that the interannual variation of July mean wind intensity is a major factor in regulating the midsummer spatial pattern of aerosols over eastern Asia when the Indian monsoon index is anomalously large. The AOD anomalies in the NR and SR are positive and negative, respectively, during an active monsoon year...

Using a geographic information system to improve Special Sensor Microwave Imager precipitation estimates over the Tibetan Plateau

[1] This study examines the potential of spatial modeling using geographic information systems (GIS) to improve the precipitation estimates based on Special Sensor Microwave/ Imager (SSM/I) over the Tibetan Plateau. The monthly SSM/I precipitation estimates are based on the algorithm developed at the National Environmental Satellite, Data and Information Service (NESDIS) of the National Oceanic and Atmospheric Administration (NOAA). When using SSM/I estimates to predict station precipitation directly, the R-2 values ranged from 0.005 to 0.624, with a mean of 0.334 for all months. When terrain and location variables obtained from the GIS were added to the models, the R-2 values improved to range from 0.217 to 0.739 with a mean of 0.590 for all months. These variables represent effects of orographic forcing of topography, rain barrier/rain shadow, direction of moisture-bearing winds, and distance to the sources of moisture over the Tibetan Plateau. Results from this study suggest that region-specific algorithms are necessary for the SSM/I precipitation estimates over the Tibetan Plateau and that topographic analysis based on GIS can contribute significantly in improving the performance of SSM/I estimates.

Tree ring-dated fluctuation history of Midui glacier since the little ice age in the southeastern Tibetan plateau

Fluctuation history of Midui glacier in the southeastern Tibet since the Little Ice Age (LIA) was reconstructed by the dating of lateral and terminal moraines using tree rings. Four conversions of glacier advance/stabilization to retreat were identified at around 1767, 1875, 1924 and 1964. The glacier reached its LIA maximum position at 1767. The fluctuations are consistent with those of other glaciers from the Tibetan Plateau, the Rockies and the Alps, suggesting high spatial coherency of glacier fluctuations in the Northern Hemisphere. Comparison with the summer temperature reconstruction in the southeastern Tibetan Plateau indicated that the Midui glacier fluctuation may be related to temperature variation on the centennial timescale. On the decadal scale, the fluctuation could correspond to cold/warm variation with an 8-year lag on average.

Continental drift and plateau uplift control origination and evolution of Asian and Australian monsoons

Evolutions of Asian and Australian monsoons have important significance for understanding the past global change but are still a controversial subject. Here, we explore systematically the effects of plate movement and plateau uplift on the formation and evolution of the Asian and Australian monsoons by numerical simulations based on land-sea distributions and topographic conditions for five typical geological periods during the Cenozoic. Our results suggest that the timings and causes of formation of the monsoons in South Asia, East Asia and northern Australia are different. The Indian Subcontinent, which was located in the tropical Southern Hemisphere in the Paleocene, was influenced by the austral monsoon system simulated at that time. Once it moved to the tropical Northern Hemisphere in the Eocene, the South Asian monsoon established and remained persistently thereafter. However, the monsoons of East Asia and northern Australia did not appear until the Miocene. The establishment of the simulated low-latitude South Asian (northern Australian) monsoon appeared to have strongly depended on the location of mainland India (Australia), associated with northward plate motion, without much relation to the plateau uplift. On the contrary, the establishment of the mid-latitude East Asian monsoon was mainly controlled by the uplift of Tibetan plateau.