Increasing Frequency of Midtropospheric Dry Layers in the Pacific Intertropical Convergence Zone

Abstract

Recent long-term characterization of the Pacific Intertropical Convergence Zone (ITCZ) shows that the ITCZ has narrowed, which may be due to the enhanced transport of dry air layers from the subtropics. In this study, we examine the relationship between the frequency of midtropospheric dry layers and ITCZ width. European Centre for Medium-Range Weather Forecasts Reanalysis Interim midtroposphere (400 to 600 hPa) relative humidity is used to create a 36-year (1979–2014) dry layer climatology for the Pacific ITCZ region. Analysis shows an inverse relationship between ITCZ width and dry layer frequency, with ITCZ width decreasing as the frequency of dry layers increases. Moreover, findings show that the region of greatest long-term increase in dry layer frequency occurs in the central Pacific, where the greatest narrowing of the ITCZ is also observed.