The Simulations Of The Effects Of Climate Environments On Glaciers Over The Tibetan Plateau

Using a 3-D land ice model GLIMMER, the geometries of glaciers at present day and the ice sheets at the Last Glacial Maximum (LGM) and Little Ice Age were simulated, and the changes of the glaciers in future was predicted in the Tibetan Plateau (TP). Meanwhile, the effects of climate environments on glaciers over the TP were studied. Further, utilizing the European Centre for Medium-Range Weather Forecast (ECMWF) reanalysis and the Climate Prediction Center (CPC) precipitation data, the relationship between the variability of the equilibrium line altitude (ELA) over the TP and its associated atmospheric circulation over Eastern Asia was investigated.The climate drivers of the ice model include surface air temperature, relative sea level change and ELA.For the present glaciers, the climate drivers are the present surface air temperature, relative sea level change and ELA. Two ELA were reconstructed. One is the inventoried ELA, and another is the calculated theoretical ELA (ELAt) by an empirical equation which reflects the relationship between summer air temperature and annual mean precipitation over the TP, and the calculated ELAt was compared to the observed ELA. Two climate driver schemes were formatted. Geometries of glaciers at present day were simulated by two climate driver schemes. The ice thick, ice temperature and ice velocity were also simulated by the ice model. The results show that they are similar to that observed.The effects of climate environments on glaciers were simulated. They include the effects of different localities (southeastern and southwestern slopes) on the growth and development of glaciers, the different motions of glaciers at bridge and trough of terrain and the effect of precipitation on mass balance.The results show that the ice temperature is relatively high on southeastern slope, and the greater velocity can still be produced on non-steep terrain, thus the fast flowing ice is situated at lower altitude of hill. The ice temperature is relatively low on southwestern slope, and only the ice with larger gravitational driving stress can move, thus the fast flowing ice is situated at higher altitude of hill.The motions of glaciers situated on the Himalayas and western Kunlun mountains are mainly caused by larger gravitational driving stresses. The conversions of ice temperature and ice velocity occur from bridge to trough of terrain on the eastern Nyainqentanglha Range. The ice temperature at bridge is lower. The ice at bridge starts to move due to the larger gravitational driving stress. During the course from bridge to trough of terrain, basal ice temperature rises because of the friction. While reaching the pressure melting point of ice, basal decollement occurs, and higher velocities can still be produced at trough. Thus the motion at trough is mainly caused by basal decollement.In the regions of southeastern and northwestern TP and Mount Qomolangma, the glaciers are grown on the slopes of mid-elevation or higher elevation of hill facing wind. The snow lines on the southern slopes are lower than that on the northern slopes in the regions of southeastern TP and Mount Qomolangma, and the changes of the snow lines on the western slopes and the eastern slopes are not obvious in the northwestern TP.Analyzing the relationship between the precipitation and mass balance, it is founded that rain converts to solid precipitation, and accumulation and mass balance increase at higher elevation, thus the glaciers are grown on slopes of mid-elevation or higher elevation of hill. The orographic effect and wind enhances precipitation where slope face wind. The glacier grows against wind. The larger the glacier grows on slope facing wind, the less the moisture air is advected to another side. The glaciers are hard to grow on another side. Thus, the snow line on the slopes facing wind is lower than on the opposite side.For the ice sheets at LGM, the climate drivers are the surface air temperature, relative sea level change and ELA at LGM. Two ELA were reconstructed. One is the altitudes of ancient cirques, and another is the height difference at 0oC level between July and May. Two climate driver schemes were formatted. Geometry of ice sheets at LGM were simulated to revaluate the suggestion of coalescing icesheet cover by two climate driver schemes. The results show that the ice sheets were mainly situated in the southeast and northwest TP and there were separate ice sheet centers, and no coalescing icesheet existed at the LGM.For Little Ice Age, the climate drivers are the surface air temperature, relative sea level change and ELA at Little Ice Age. The ELAt was reconstructed by the empirical equation as for the present ELAt. The ice area at Little Ice Age was simulated. It was found that the ice area was larger in 17 and 19 centuries, and was smaller in 18 century, and consistent with the variations of climate at Little Ice Age. The sensitivity tests present that glacier's area increases with the descending ELA, and the area is largest for cold ice, and the second for the ice without interior decollement, and the third for the ice without basal decollement, and the smallest for fast flowing ice. Summer air temperature affects ice area more than yearly precipitation.For the glaciers in this century, the climate drivers are the surface air temperature, relative sea level change and ELA in this century. Under SRES scenarios, the glaciers in future were predicted. The result shows that the ice area will decrease during this century, but still there are two advancements of glaciers in 2045 and 2080, respectively.The relationship between the variability of the Tibetan ELA and its associated atmospheric circulation over Eastern Asia were studied. The results show that with the decrease of ELA, the rainfall enhances over the northwestern TP and the northern region of eastern China, but reduces over the southeastern shores of China. The overlying atmospheric circulation supports the relationship. Corresponding to the decrease of ELA, an anomalous anti-cyclone appears in Ural region and an anomalous cyclone appears over Baikal lakes. The former meets with the anomalous southern wind in front of anomalous anti-cyclone in the India region, and generating anomalous convergence and ascending motion, thus resulting in enhanced rainfall over the northwestern regions of the TP. The latter reaches the northern region of eastern China, and resulting in enhanced rainfall over the region. The anomalous western flow over the south of China implies the weakened eastern flow in high-level. The western wind in low-level prevails in this region, and the vertical shear is weaken. The anomalous anti-cyclonic circulation are produced, hence the rainfall reduces over the region.