Characterization of water vapor within the planetary boundary layer based on the ARM Raman lidar observation at the SGP site

To study water vapor variation and PBL evolution, the ARM Raman lidar data obtained between March 1998 and August 2003 at the Southern Great Plains site were used. Based on the daily means and standard deviations of water vapor over 20-minute to 4-hour at five analysis periods (before- and after-sunrise, noon, sunset, and midnight), their seasonal means were calculated. Quantitatively, water vapor mixing ratio in summer is about five times larger than the one in winter. Diurnally, a clear diurnal difference is seen in summer, but it becomes less obvious in winter. The horizontal variation of water vapor over 1hr period in winter is about four times larger than the one in summer in terms percentage difference related to the mean. Also, water vapor vertical dependencies, decreasing in amount and increasing in horizontal inhomogeneity with height, is clearly observed. Although the vertical change rates vary with season, the rates are small within the PBL in general. The temporal or spatial variation of water vapor increases with calculation period length slightly depending on season and time of the day, and the standard deviation can reach about 15% of the mean within 4-hour period. Seasonal difference dominates diurnal difference in both temporal and vertical dependencies.;Additionally, the seasonal and diurnal cycles of PBL height evolution were studied. The PBL height was estimated from Raman lidar aerosol scattering ratio in 10-minute resolution. The deepest mean PBL is found in summer, particularly August (2.58 km), while the shallowest mean PBL was found in winter, particularly January (0.68 km). Although diurnal PBL height difference varies with season, the diurnal cycles are similar among seasons. As a result, the highest and the lowest PBL occur around 1600 and 400 local time, respectively. Although solar heating is an important factor controlling PBL development, the PBL evolution is lagging solar heating in both daily and seasonal scales. Comparison studies indicated that both latent heat flux and sensible heat flux, especially sensible heat flux, influence PBL evolution notably. Further analysis also suggests that temperature and water vapor impact PBL evolution.