The Pennsylvania State University
The Graduate School
College of Earth and Mineral Sciences
LIFECYCLES AND RADIATIVE IMPACTS OF ANVIL CIRRUS OUTFLOW DURING THE MARITIME CONTINENT THUNDERSTORM EXPERIMENT
A Thesis in Meteorology
by
Michael Philip Jensen
Abstract
The Maritime Continent Thunderstorm Experiment took place from 13 November to 10 December 1995 on the Tiwi Islands, which are located approximately 70 km north of Darwin, Australia at the edge of the tropical “boiler box” region. The basic objective of the field experiment was the study of the organization and lifecycle of the tropical island convection over the Tiwi Islands and the role of this convection in the atmospheric energy and moisture balance. To gain further insight into the properties of the cirrus outflow from these systems a suite of surface remote sensing instruments was deployed at the village of Garden Point located on the northwest corner of Melville Island (11.4S, 130.41E) and a 5.2 cm scanning radar was located at Nguiu (10.23A, 130.62E) on the southeast corner of Bathurst Island.
The radiative impact of three separate cirrus anvil systems are investigated. In order to do this, the three-dimensional structure of ice water in the cloud is parameterized from the 5.2 cm radar reflectivity measurements through a Z-IWC relationship. The Z-IWC relationship is developed by using microphysical retrievals over the Garden Point site combined with vertically pointing radar reflectivites. This relationship is then applied to the scan volume of the 5.2 cm radar. The three dimensional ice water structure is put into a two-steam radiative transfer model using an independent pixel approximation for several different stages in the lifecycle of the cloud system.
The spatial variability of ice water content within the anvil cloud is shown to have a large impact on the vertical structure of heating/cooling within the anvil. Radiative heating/cooling occurs at many different levels through the cloud area. Our analysis shows that the top layer of the cloud (in our case we consider 2 km layers) is optically thick over the entire area of the MCS, and therefore, this variability in the height of solar heating/ IR cooling is due to variability in cloud top height. There is a distinct difference between the average radiative heating profile in the presence of island-based convection compared to oceanic convection. The island-based convection results in a heating profile which concentrates cloud-top solar heating and IR cooling higher in the atmosphere and with a greater magnitude than does oceanic convection. A comparison of the large-scale radiative impact of the island-based thunderstorms upon the net radiative heating in the tropical western Pacific shows that the presence of these thunderstorms greatly changes the deposition of radiational energy in the atmospheric column. This leads to the conclusion that when considering the energy balance over the tropical western Pacific it is important to treat the maritime continent region with all of its islands separately from the oceanic regime. Especially during the transition between monsoon seasons, the island-based thunderstorms contribute a major portion of the total cloudiness over the maritime continent and therefore it is important to include their radiative impact on large scale energy budget studies in the tropical western Pacific.
Table of Contents
Chapter 1 Introduction
Chapter 2 The Maritime Continent Thunderstorm Experiment
Chapter 3 Method and Analysis
Chapter 4 Uncertainty Analysis
Chapter 5 Results
Chapter 6 Conclusions and Future Research
Acknowledgements
References
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