Observations of atmospheric rivers with CloudSat CPR and Aqua AMSR-E

Abstract

"Atmospheric rivers" are filamentary water vapor structures, occurring primarily over oceans, thousands of kilometers long that form along the leading edge of cold fronts. These "rivers" are an important link between weather and climate by transporting large amounts of moisture (on the order of 108kgs-1) through the middle latitude regions and causing heavy precipitation events along coastal regions. The CloudSat satellite, launched 28 April 2006, is designed to measure vertical cloud structure and fill a long-existing gap in satellite observations. CloudSat and Aqua observed 22 river events (with multiple overpasses for each river) over a period from November 2006 to April 2007. In this project, CloudSat CPR observations of cloud location and cloud type are used along with moisture observations from Aqua AMSR-E to create a preliminary average profile of vertical cloud structure within atmospheric rivers. The CloudSat observations (using Aqua moisture and precipitation measurements as references) are first presented for case studies of four river events out of the total 22 events. The observations show deep convective (vertical extent more than 7km) and nimbostratus cloud (vertical extent more than 4km) bands more than 100km in horizontal width occurring in three of the four cases, and shallow convection (vertical extent less than 4km) occurring in the fourth case. Deep layer clouds occur most frequently during the river's early and middle stages, and these deep clouds usually erode into low and (sometimes) high cloud bands in the river's later life. The CloudSat measurements are then combined into composite frequency plots to show the typical cloud locations within and near the river with respect to the river's water vapor structure. Frequency plots are presented for all 92 overpasses along with categories of overpasses based on time of occurrence within the rivers' life spans to give a preliminary time evolution of cloud structure. Then, scatter plots comparing moisture structure properties with cloud structure properties are displayed to show any possible relationship between moisture and clouds. Finally, some statistics about the frequency of occurrence of different cloud types within the rivers are presented.