Wednesday, 25 January 2017
Mesoscale Convective Systems (MCSs) are prolific precipitation producers over the United States, specifically in the area east of the Rocky Mountains, accounting for between 30% and 70% of the total precipitation in the warm season (April-September). In particular, the precipitation produced by the MCSs is important in crop growing areas since the precipitation can be used to facilitate the growing of the crops. This study of MCS initiation focuses on Corn Belt region of the United States where almost half of the World’s corn supply is produced. The Corn Belt region is defined as: Illinois, Indiana, Iowa, Kansas, Minnesota, Missouri, Nebraska, Ohio, North Dakota, and South Dakota. Studying the changes in MCS initiation could help lead to a better prediction of corn yields in the Corn Belt region since it could provide information to help determine if/when irrigation would be necessary. To study MCS initiation over the Corn Belt, a database was developed using North American Regional Reanalysis (NARR) data and satellite data which detailed the MCS initiations in the warm season in the years 1979 to 2013 over the United States’ Corn Belt region. This database consists of 2,158 initiations over the 35 year period. Approximately halfway through the 35 year period, there is a change in the number of initiations per year and in how MCSs initiate over the Corn Belt region. From 1979 to 1996, there is a slow increase in the number of MCS initiations. Then, from 1997 to 2013, there is a much larger increase in the number of MCSs initiating over the Corn Belt. The change in the trend of MCS initiations is not due to changes in the processing of the observations included in NARR or the inclusion of satellite data. These two time periods have different MCS initiation conditions, such as differences in: temperature at multiple levels, surface winds, Lifted Index (LI), and Geopotential Height at Cloud Base. The analysis will demonstrate that the two time periods are significantly different and will illustrate possible explanations of the cause of the difference. Possible explanations include climate change and the Pacific Decadal Oscillation (PDO). The PDO index switched signs (positive to negative) within a couple of years before the change in MCS initiation trend over the Corn Belt region. There is a possibility that the PDO influences MCS initiation over the Corn Belt.
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