HR: 0830h
AN: GC31B-0173    [PDF]
TI: The Contrast and Relation of Precipitation and Precipitable Water Over North America
AU: * Lu, E
EM: lu@atmo.arizona.edu
AF: Department of Atmospheric Sciences, The University of Arizona, 1118 E, 4th St., Tucson, AZ 85721 United States
AB: The precipitable water (W), as an important water vapor parameter, has become a conventional meteorological variable with the development in satellite observations and retrieval techniques. The dataset of W can be utilized to extract useful information on hydroclimate. For example, linkages may exist between the W and cloud, precipitation (P), storm, and other meteorological quantities. In this study, the contrast and relation of P and W are clarified at different time-scales over the United States and Mexico by using ten-year daily observational datasets. The contrast of the two variables shows that they have different spatial patterns in both the means and the perturbations of different time-scales. For the P over the land, the mean and the perturbations all have maximum centers over the three regions: South Mexico, the Northwest Coast, and the Mississippi River area. The mean of W that decreases with latitude in general is large over the eastern U.S. and small over the western U.S. and Mexico. However, the maximal perturbations of W, not appearing over the near-equator oceans where the mean gains its maximum, are "attracted" to the ocean-land adjacent areas due to the effect of small heat capacity of land. The relation of P and W possesses unique spatial patterns for different time-scales. At synoptic time-scale, P and W are well positively correlated over the entire US-Mexico although each of them has weak spatial coherence. Positive correlation is more significant over the eastern U.S., especially along the South and East Coasts. At seasonal time-scale, the W has extremely high spatial coherence over the land, all getting maximum in summer and minimum in winter, thus follows the variation pattern of surface temperature. Theoretical analysis confirms that the seasonal W is truly dominated by temperature due to its large annual range over the land, no matter how the relative humidity changes seasonally. In contrast, the seasonal P, which is influenced by atmospheric circulation and land surface process, exhibits distinct local characteristics, and can roughly be categorized into three types. Over the North American monsoon region (Mexico and the Southwest U.S.) along with the Northern Tier and Florida, the P has maximum in summer and minimum in winter. Over the Northwest Coast, maximum P appears in winter and minimum in summer. In the area around the Mississippi River, P has no distinct seasonal tendency. Therefore, the seasonal P and W are continentally controlled by different factors, although locally they could be linked through interactions between surface temperature and atmospheric circulation. At interannual time-scale, the summer averaged correlation of monthly P and W is significantly positive over the North American monsoon region and Florida. In addition to the partial contribution from the synoptic relation of P and W, other factors controlling the interannual relation need to be studied in future.
DE: 1655 Water cycles (1836)
DE: 1800 HYDROLOGY
DE: 1854 Precipitation (3354)
DE: 3309 Climatology (1620)
DE: 3322 Land/atmosphere interactions
SC: Global Climate Change [GC]
MN: 2003 Fall Meeting