Date of Award

1-1-2011

Document Type

Campus Access Thesis

Department

Geography

First Advisor

Cary J Mock

Second Advisor

Gregory J Carbone

Abstract

Increased convection in a globally warming climate should result in increased cloud cover; however effects are not clear in cloud type and geographic coverage. This thesis examines questions regarding this complex problem by focusing on a specific cloud type in a finite geographic region. It used datasets of manually taken cirrus cloud observations, average near-surface temperature, and teleconnection indices to examine cirrus cloudiness over the conterminous United States from 1971-1991.

Monthly trends in cirrus cloudiness, relationships with near-surface temperature and their relationships with teleconnection indices were assessed spatially and as global averages. Results were calculated for 158 weather stations for each month using cirrus frequency and amount-when-present (AWP) variables. A total of 37,359 monthly observations were examined for each variable. Cirrus frequency and AWP were found to be closely related to teleconnection indices and near-surface temperature respectively. Major cirrus frequency trends were confirmed over the Gulf Coast region at greater than 6%

per-decade. The relationship between cirrus AWP and near-surface temperature is related by a global average at r2=0.80. Cirrus amount-when-present tended to be high (low) when surface temperatures were low (high), likely reflect frontal based cloud genesis during cold months and local convection based genesis during warm months. Cirrus frequency showed strongest correlation patterns during winter and spring months. Pacific North American (PNA) and Multivariate ENSO Index (MEI) teleconnection indices showed strong correlations and spatial patterns.

The study found that significant trending existed in cirrus frequency over the conterminous United States from 1971-1991, and that cirrus cloudiness is at times related to teleconnection indices and near-surface temperature. Findings suggest that teleconnection indices could play a role in cirrus trending and that near-surface temperature could be affected by these changes. Manually derived cloud variables, frequency and amount-when-present, are potentially valuable for climatic analysis and are currently not utilized. Future research should examine daily data for comparison to surface frontal systems. Cirrus frequency should be closely compared with satellite cloud observations, and research should determine if cloud frequency and amount-when-present would be valuable for analysis in climate models.

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