Date of Award

Winter 1998

Project Type

Dissertation

Program or Major

Earth Sciences

Degree Name

Doctor of Philosophy

Abstract

The physical climate of the Himalaya is governed by monsoon circulation, a primary source of moisture to the region. To date, little research has focused on the physical and chemical climate in the Himalaya, while not much is known about the chemical climate there. This dissertation is a first attempt to investigate both the physical and chemical aspects of climate in the Nepal Himalaya with the objective of documenting current conditions and past trends as well as laying the foundation for investigations of their inter-relationship in the future.

Temperature and precipitation records from a network of meteorological station in Nepal were analyzed over the period 1971--1994. Temperature records show significant warming trends after the mid-1970's. The temperature trend in Nepal is in broad agreement with global temperature trends, while it differs from temperature trends in the neighboring Indian plains. Within Nepal, the warming trend is greater in the high elevation regions, suggesting that the mountains are more sensitive to climate change. Precipitation records from Nepal show significant variability at annual and decadal time scales, whereas long-term trends are lacking. The precipitation record from Nepal shows significant correlation with several large scale climatological parameters such as Southern Oscillation Index, sunspot numbers, temperature over Tibetan Plateau, and temperature over the Indian Ocean and southern India, while it differs considerably from the all-India precipitation record. Among others factors, El Nino events have a dominant influence on the precipitation variations in the Himalaya.

Aerosol and precipitation chemistry of the eastern Himalaya are characterized by marked seasonal fluctuations. The concentrations of water soluble major ions are low and comparable to remote tropospheric concentrations during late monsoon and post-monsoon, while concentrations during pre-monsoon and early monsoon are considerably higher, comparable to concentrations at urban sites in Europe and North America. The seasonal changes in concentrations are clearly related to changes in atmospheric circulation. Regional-scale thermally-driven valley wind systems are responsible for transporting pollutants to the Himalaya during the pre-monsoon season, whereas monsoon circulation transports pollutants during the early period of the summer monsoon. Onset of the active monsoon (mid-June) coincides with a dramatic drop in major ion concentrations and the low concentrations are maintained over the post-monsoon.

The variations in the aerosol concentrations at time scales greater than a week are well reflected in precipitation chemistry, whereas small scale variations are not. Since glaciochemical records, are generally interpreted on a seasonal or longer temporal resolution, the relationship between aerosol and precipitation chemistry supports the potentials of using glaciochemical data to document change in chemical composition of the Himalayan atmosphere in the past. (Abstract shortened by UMI.).

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