Dissertation/Thesis Abstract

A Revised Technique for Measuring Vertical Velocity Using Dropsondes
by Nelson, Timothy Connor, Ph.D., State University of New York at Albany, 2019, 297; 22587160
Abstract (Summary)

The earliest iterations of dropsondes in the 1960's obtained vertical velocity by measuring the geometric fall speed of the dropsonde and the true airspeed (TAS) of the dropsonde from a pitot-static. The vertical velocity errors from this methodology were claimed to be ±1 m s−1. Subsequent dropsonde iterations used various forms of the drag force equation to obtain vertical velocity. The accuracy of these drag force-based measurements, however, are also quite large at ±1–2 m s−1. In this dissertation, an attempt is made to improve vertical velocity errors by revisiting and revising the pitot-static-derived TAS methodology on the eXpendable Digital Dropsondes (XDDs). The primary goals were to decrease errors to ±0.1 m s−1 and introduce a prototype for a highly accurate vertical velocity dropsonde for use in tropical cyclone (TC) research.

Three variations of the traditional pitot-static (the modified pitot-static, pitot-venturi, and venturi-static) were presented and evaluated. Computational fluid dynamics (CFD) model runs suggested that the pitot-venturi would be the most optimal configuration, and it would produce the smallest vertical velocity errors. A mean pitot-venturi calibration coefficient was found from a subset of eight XDDs using a large rotating arm device. Three fully calibrated pitot-venturi vertical velocity XDDs were launched operationally from a DC-8 aircraft off of the coast of the Baja California Peninsula. The results indicate that vertical velocity errors of 0.2–0.4 m s−1 are achievable using a pitot-venturi on the XDDs.

The vertical velocities using a modified version of the drag force method were also analyzed from the 2015 Tropical Cyclone Intensity (TCI) experiment. TCI sampled Erika, Marty, Joaquin, and Patricia with, an unprecedented, 784 XDDs. The results indicate that: 1) high-spatial resolution vertical velocity measurements can be used to examine and document important convective features of TCs; 2) by improving the vertical velocity errors, it is possible to slightly improve dropsonde-derived horizontal wind speeds in the upper-levels of TCs; and, 3) the spatial resolution of XDDs should be less than 3 km in order to adequately “resolve” TC convection within transects of soundings.

Indexing (document details)
Advisor: Harrison, Lee
Commitee: Corbosiero, Kristen, Tang, Bryan, Torn, Ryan
School: State University of New York at Albany
Department: Atmospheric and Environmental Sciences
School Location: United States -- New York
Source: DAI-B 81/2(E), Dissertation Abstracts International
Subjects: Atmospheric sciences, Meteorology
Keywords: Convection, Dropsondes, Instrumentation, Pitot-static, Tropical cyclones, Vertical velocity
Publication Number: 22587160
ISBN: 9781085731010
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