Monday, 10 February 2003: 1:45 PM
Large-scale water vapor, aerosol, and cloud distributions determined from airborne lidar (LASE) measurements during the IHOP field experiment
The Lidar Atmospheric Sensing Experiment (LASE) was flown on the NASA DC-8 aircraft to investigate large-scale variations in water vapor, aerosols, and clouds during the International H2O Project (IHOP) conducted over the Southern Great Plains during May-June 2002. The main objectives of IHOP are to better understand the influence of water vapor variability on the initiation of deep convection and to improve the quantification and prediction of precipitation associated with these storms. IHOP brought together a large array of airborne and ground-based remote sensors to investigate a set of related atmospheric processes, including convective initiation (CI), boundary layer development, boundary layer heterogeneity, nocturnal low-level jets, and morning low-level jets. All of these targeted investigations, which were the subject of individual flight missions, contribute to a better understanding of the basic atmospheric processes associated with convective initiation and precipitation quantification. LASE participated in eight DC-8 flight missions from Oklahoma City, Oklahoma, between 23 May and 14 June 2002. Four CI flights and one flight each of the other types of investigations were made with LASE during IHOP under widely varying atmospheric conditions. LASE measured nadir and zenith water vapor, aerosol, and cloud profiles along the flight track of the DC-8, which was nominally flown at an altitude of 7.3 km (24 kft). The vertical resolution of the LASE water vapor measurements is adjustable from 100 to 300 m in post-mission processing with a horizontal resolution of about 13 km (1-minute running average). The aerosol and cloud backscatter measurements were made with a vertical and horizontal resolution of 30 and 45 m, respectively.
During IHOP, the data from LASE were used on several missions to examine the spatial and temporal characteristics of the dry line and fronts and the onset of convection along them. A classic case of CI was observed on 24 May when LASE was flown on a large-scale mapping mission over the region of intensive aircraft and ground observations in the western panhandle of Oklahoma and northern panhandle of Texas. LASE observed strong gradients of water vapor across the front to the north and very dry conditions on the west side of the north-south dry line and very moist conditions on its east side. Data were taken until thunderstorms developed in the southeast region of the observation area and rapidly propagated in the northwest direction. Several more CI missions were flown under varying atmospheric conditions, and as expected, it was difficult for the forecasters to predict where and when CI would start. LASE data were obtained on each of the other investigations mentioned above, and extensive intercomparisons opportunities were available in each flight mission between the various airborne and ground-based lidar systems. The complementarity of measurements made from the different aircraft and ground sites makes this a unique data set for studying convective initiation and precipitation.
This paper discusses some of the water vapor, aerosol, and cloud data obtained by LASE during IHOP in conjunction with the different flight mission objectives. These results are related to other remote and in situ measurements made during IHOP, and they are interpreted with respect to the atmospheric processes that were being investigated.