Cloud-Top Properties of Growing Cumulus prior to Conveetive Initiation as Measured by Meteosat Second Generation. Part I: Infrared Fields

摘要

Infrared (IR) data from the Meteosat Second Generation (MSG) satellite are used to understand cloud-top signatures for growing cumulus clouds prior to known conveetive initiation (CI) events, or the first occurrence of a ^35-dBZ echo from a new conveetive cloud. In the process, this study proposes how MSG 1R fields may be used to infer three physical attributes of growing cumuli, cloud depth, cloud-top glaciation, and updraft strength, with limited information redundancy. These three aspects are observed as unique signatures within MSG IR data, for which this study seeks to relate to previous research, as well as develop a new understanding on which subset of IR information best identifies these attributes. Data from 123 subjectively identified CI events observed during the 2007 Convection and Orograpically Induced Precipitation Study (COPS) field experiment conducted over southern Germany and northeastern France are processed, per conveetive cell, to meet this study's objectives. A total of 67 IR"interest fields" are initially assessed for growing cumulus clouds, with correlation and principal component analyses used to highlight the top 21 fields that are considered the best candidates for describing the three attributes. Using between 6 and 8fields per category, a method is then proposed on how growing conveetive clouds may be quantified per 3-km~2 pixel (or per cumulus cloud object) toward inferring each attribute. No independent Cl-nowcasting analysis is performed, which instead is the subject of ongoing research.