Project Detail

Observations & Modeling of Orographic Cumulus Dev Using Data Collected During CuPIDO 2006

Develop 3D geometrical structure of a cloud from stereo camera as part of CUPIDO 2006 experiement.

Lead: Zehnder, Joseph
Collaborators: Razdan, Anshuman;Hu, Jiuxiang;McCartney, Peter H.;Nielson, Gregory;Rowe, Jeremy
RA: Koneru, Ujwal
Sponsor: National Science Foundation
Date: 06/01/2004  - 01/31/2009
Web site: http://prism.asu.edu/research/santa.php

Abstract

This project will focus on the development of orographic cumulus, and in particular, the transition from shallow to deep convection and the accompanying modification of the thermodynamic profile. The formation of orographic cumulus over in the desert southwest offers an ideal test environment to explore these issues. The convection develops over the tops of the mountains in generally clear air, so the initial location is well defined. One can sample the pre-cloud environment and characterize modifications due to the convection. The surface forcing (latent and sensible heat) is sufficiently strong so that even in marginally unstable conditions, modification of the vertical profile may result in eventual deep convection. These factors result in a wide variety of time scales associated with onset of the initial, shallow convection, transition from shallow to deep convection and recovery time between deep convective events.

This project will rely on refinement of existing image analysis techniques and data cataloguing tools developed at Arizona State University to automatically identify cloud boundaries and track volumetric changes over time. This project approaches the problem by using pixel segmentation based on hue to transform, segment, and model the cloud volume using triangular mesh, iteratively identifying and automatically morphing the underlying 3D model to represent volumetric changes over time, and using iterative feedback to refine the process. Software has been developed during this project that runs on Windows and Mac OS systems, and utilizes range-finding from image pairs to assist in the analysis. The ultimate goal of this project is to provide a tool that will aid in accurately predicting weather patterns.

Mountain (orographic) thunderstorms The major mountain ranges in central Arizona (the Mogollon Rim) and the so called "Sky Islands" (Santa Catalina, Santa Rita and Rincon mountains) near Tucson serve as the initial locations for cloud and thunderstorm formation in Arizona. The typical scenario over the sky islands involves convection beginning in clear air in the early to mid- morning. As the sun rises, it strikes the sides of the mountains more directly than the surrounding area and this provides a localized surface sensible heating. Evaporation from the previous day's rain and evapotranspiration from the plants contribute to the flux of latent heat that also destabilizes the boundary layer over the mountains. On a typical day, the clouds begin to build over the Santa Catalinas at about 9am local time.

The Wyoming Cloud Radar CR is a 95 GHz polarimetric Doppler radar installed primarily on the WKA. The WKA/WCR configuration includes four fixed antennas (see figure and table above) that allow horizontal and/or vertical scans of the clouds along the flight track. Read more...

A measure of the amount of energy present in the environment for cloud and thunderstorm formation is called Convective Available Potential Energy or CAPE. CAPE is a measure of the temperature difference between a rising air and the environment into which the air is rising (vertically integrated positive buoyancy). Soundings in southern Arizona typically have about 1500-2000 Joules/Kg of CAPE, which classifies them in the moderately unstable range. The area doesn't experience the severe, tornado producing supercell thunderstorms common in the Great Plains, but the monsoon thunderstorms can produce localized high winds and heavy rains. In spite of there being sufficient CAPE to generate thunderstorms, the clouds develop slowly and in stages. Shallow convection in the form of convective plumes or turrets build, first into cumulus congestus and then, in many cases, into deep cumulonimbus. In general, the transition from the initial stages of convection to the appearance of a thunderstorm over the Catalinas is about 3 hours. In many cases, the orographic thunderstorm dissipates or moves from the top of the mountain and a second episode of convection begins, with a transition from shallow to deep convection occurring on a similar time scale.