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要项。为了了解大气流动的动力学，有必要知道水平压力梯度力(PGF)。在过去的二十年里，航空平台被用来试图识别水平气压场在不同尺度上的变化，以了解中尺度到天气尺度运动场的动力学。在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，阻碍了PGF应用的广泛使用。最近的研究表明，利用差分GPS可以在中尺度到微尺度范围内精确探测来自空中平台的水平压力梯度力。在这项技术中，飞机上双频接收器的GPS位置测量是使用来自固定和精确测量的基站的GPS测量进行校正的。通过使用自动驾驶仪在等压面上飞行，可以确定等压面的斜率，这是PGF的测量。这项技术首次能够描述机载平台对复杂地形上微尺度到中尺度大气环流的强迫。智力价值：这项研究的主要目标是检验来自怀俄明大学国王航空公司(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空对流云相关的气压扰动。水平气压扰动是研究云动力学的基础，也是理解对流的关键。随着浮力气团的上升，伴随着对流运动的大气质量调整导致了气压扰动。对云压力扰动的了解将有助于了解对流运动对当地环境的强迫的空间范围和强度，以及验证高分辨率数值模拟实验的手段。2008年8月将在怀俄明州拉勒米进行一项实地试验，以评估由大小不等的对流云所引起的水平气压扰动，直至积云拥堵阶段。怀俄明大学的云雷达将部署在UWKA上，以提供关于对流云内运动场的更多信息。水平气压摄动测量将沿着云底开始的平均风的方向和垂直方向进行。随后将在云层内进行更高一层的测量，以提供关于水平压力扰动的垂直结构的信息，从而产生更广泛的影响：如果这种测量被证明是成功的，全球定位系统对云引起的水平压力扰动的探测将成为空中平台上的常规测量，并成为UWKA和大气科学界其他研究人员的标准使用。这是对未来云物理和动力学研究的重大改进，因为水平运动的基本强迫项可以直接测量。这项GPS技术的成功应用还将带来一系列新的测量机会，包括云中夹带的研究、云运动场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.