Airborne Measurement of Cloud Perturbation Pressures Using Differential Global Positioning System (GPS)

压力梯度力是描述大气运动强迫的运动方程中的主导项。为了了解大气流动的动力学，必须了解水平压力梯度力。在过去的二十年里，机载平台已经被用来尝试识别不同尺度上水平压力场的变化，以了解中尺度到天气尺度运动场的动力学。使用基于测高的方法在不规则地形上进行飞行时遇到了严重的问题，这阻碍了PGF的广泛应用。最近的研究表明，利用差分GPS可以精确地探测中尺度到微尺度距离上的机载平台的水平压力梯度力。在这种技术中，由飞机上的双频接收器测量的GPS位置使用来自固定和精确测量的基站的GPS测量值进行校正。通过使用自动驾驶仪在等压面上飞行，可以确定等压面上的斜率，这是PGF的度量。这项技术首次成为一种通过机载平台来描述复杂地形上微尺度到中尺度大气环流强迫的手段。智力价值：本研究的主要目标是检查来自怀俄明大学空中国王（UWKA）平台的差分GPS位置测量的潜力，以确定与美国西部高平原上对流云相关的压力扰动。水平压力扰动是云动力学研究的基础，也是理解对流的关键。气压扰动是由于浮力空气团上升时伴随对流运动的大气质量调整造成的。对云压力扰动的了解将有助于了解对流运动对局部环境的强迫的空间范围和强度，并有助于验证高分辨率数值模拟实验。2008年8月将在拉勒米WY进行一次实地试验，以评估从大小到积云密集阶段的对流云造成的水平压力扰动。怀俄明大学云雷达将部署在UWKA上，以提供有关对流云内运动场的额外信息。水平压力扰动测量将沿着从云底开始的平均风的方向和垂直方向进行。后续的飞行将在云内更高的高度进行，以提供水平压力扰动垂直结构的信息。更广泛的影响：如果这些测量被证明是成功的，对云引起的水平压力扰动的GPS检测将成为机载平台上的常规测量，并成为UWKA的标准，并用于大气科学界的其他研究人员。由于水平运动的基本强迫项可以直接测量，这代表了对云物理和动力学的未来研究的重大增强。GPS技术的成功应用还将带来一系列新的测量机会，包括云夹带的研究、云运动领域的改进以及与云尺度环流相关的动力学演变。

The pressure gradient force is the dominant term in the equation of motion that describes the forcing of atmospheric motions. To understand the dynamics of atmospheric flows, it is necessary to know the horizontal pressure gradient force (PGF). For the past two decades, airborne platforms have been used in attempt to discern variations in the horizontal pressure field over a variety of scales to understand the dynamics of mesoscale to synoptic-scale motion fields. Serious problems have been encountered when conducting flight legs over irregular terrain using altimetry-based methods that have prevented the PGF application from widespread use. Recently it has been shown that accurate detection of the horizontal pressure gradient force from airborne platforms over mesoscale to microscale distances is possible by using differential GPS. In this technique, GPS position measurements by a dual-frequency receiver onboard an aircraft are corrected using GPS measurements from a fixed and precisely surveyed base station. By flying on an isobaric surface using the autopilot, the slope of the isobaric surface, which is a measure of the PGF, can be determined. This technique enables for the first time a means to depict forcing of microscale to mesoscale atmospheric circulations over complex terrain by airborne platforms. Intellectual Merit: The primary goal of this research is to examine the potential of differential GPS position measurements from the University of Wyoming King Air (UWKA) platform to determine pressure perturbations associated with convective clouds over the high western plains of the U.S. Horizontal pressure perturbations are fundamental to studies of cloud dynamics and critical to an understanding of convection. Pressure perturbations result from the atmospheric mass adjustment that accompanies convective motions as buoyant air parcels rise. Knowledge of the cloud pressure perturbations will permit an understanding of the spatial extent and magnitude of the forcing of the local environment by convective motions as well as a means to validate high resolution numerical modeling experiments. A field experiment will be conducted during August 2008 based out of Laramie WY to evaluate the horizontal pressure perturbations that result from convective clouds that range in size up to the cumulus congestus stage. The University of Wyoming Cloud Radar will be deployed on the UWKA to provide additional information regarding the motion field within convective clouds. Horizontal pressure perturbation measurements will be made in directions along and normal to the mean wind beginning at cloud base. Subsequent passes will be made at higher levels within the cloud to provide information on the vertical structure of the horizontal pressure perturbations Broader Impacts: If such measurements are shown to be successful, GPS detection of the cloud-induced horizontal pressure perturbations will become a routine measurement on airborne platforms and become standard for the UWKA and of use to other investigators within the atmospheric science community. This represents a significant enhancement for future studies of cloud physics and dynamics since the fundamental forcing term for horizontal motions can be directly measured. Successful application of this GPS technology will also enable a host of new measurement opportunities, including studies of entrainment in clouds, refinements in cloud motion field and the evolution in dynamics associated with cloud-scale circulations.