Abstract:Rain gauge station data from 1987 to 1996 were used to investigate spatial and temporal variability in monthly precipitation and annual and seasonal precipitation patterns over Nepal. Maximum annual precipitation increased with altitude for elevations below 2000 m but decreased for elevations of 2000-3500 m. The data revealed a negative relationship between annual precipitation and elevation only in western Nepal. Annual precipitation averaged on a 0.25°grid exceeded 3000 mm/yr in central Nepal but was less than 1000 mm/yr over Nepal's northwestern mountains. Only winter precipitation over western Nepal was heavier than precipitation over central and eastern Nepal. A time series of standardized precipitation anomalies averaged over Nepal revealed no significant long-term trends. Further, almost no stations exhibited significant long-term trends by Kendall's rank correlation analysis. A correlation analysis between summer monsoon precipitation and the All Indian Rainfall (AIR) index revealed positive and negative correlations in western and eastern Nepal, respectively. This analysis also revealed a positive correlation, but no negative correlation, between summer monsoon precipitation and the Southern Oscillation Index (SOI) in western and eastern Nepal. Composite differences in temperature, 850-hPa winds, outgoing longwave radiation (OLR), and precipitation rates between low and high AIR phases revealed that moist air from the Arabian Sea supported precipitation over western Nepal, whereas cold dry air from the Tibetan Plateau suppressed precipitation over eastern Nepal. However, composite differences in precipitation between low and high SOI phases revealed no anomalies for Nepal.

Lidar and sky radiometer systems at Sapporo, Toyama, and Nagasaki, Japan, observed the vertical distributions and optical properties of (nonspherical) dust and spherical aerosol particles from March to May 2005 as part of the Atmospheric Brown Clouds–East Asia Regional Experiment 2005 (ABC‐EAREX2005). Sky radiometer observations suggest that single scattering albedo at Nagasaki was smaller than that at Toyama and Sapporo. Relationships between the single scattering albedo and Ångstrom exponent suggest that aerosol particles observed at Toyama in March differed from those observed in April and May. In contrast, at Nagasaki, there was no obvious difference in aerosol particles among the 3 months. Aerosol optical thicknesses observed by the sky radiometer resemble the aerosol optical thicknesses observed by lidar and simulated by the Chemical Weather Forecasting System (CFORS) model. A new parameter that describes the aerosol vertical distribution, Hm, is the modified scale height of the extinction coefficient. Hm can be used as an index of the vertical aerosol extent even if the detailed structure of the vertical profile cannot be shown. Hm observed by lidar was consistent with Hm simulated by the CFORS. Relationships between the aerosol optical thickness and Hm obtained by lidar measurements and CFORS simulations suggest that dust aerosol particles are generally transported over Japan at higher altitudes than are spherical aerosol particles.

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