Linking Observed Long-term Changes in ITCZ Characteristics and the Morphology of Convective Systems

Many recent modeling studies suggest that the region of heavy precipitation associated with the Intertropical Convergence Zone (ITCZ) becomes narrower while precipitation becomes more intense in enhanced greenhouse gas forcing scenarios. Although there have been many observational studies defining the climatological location of the ITCZ and the intensity of general tropical precipitation, there has been less work using observations to determine the extent of the ITCZ. To test whether we observe ITCZ changes in the current climate, satellite observations from the Tropical Rainfall Measuring Mission (TRMM), the Global Precipitation Climatology Project (GPCP), and ERA-Interim reanalysis are combined to develop an automated identification of the ITCZ and metrics describing its characteristics, including ITCZ center location, width, and precipitation intensity. Results from 1979-2015 show that the ITCZ meridional extent has decreased, with a simultaneous increase in precipitation intensity, especially in the center of the ITCZ. These results imply changes in the morphology of convection in the ITCZ associated with the large-scale changes in ITCZ extent. To better understand the relationship between ITCZ variability and the convection within it, TRMM Precipitation Radar (PR) precipitation features within the boundaries of the ITCZ are identified and the distribution of convective characteristics are examined for the top (wide) and bottom (narrow) quartiles of ITCZ width. Preliminary results show positive anomalies in the density of ITCZ convection when the ITCZ is narrow. Deeper echo top heights, higher maximum reflectivities at 6 km, and larger feature sizes are all more frequently observed for narrow ITCZs compared to wide ITCZs, which suggests a shift in the distribution of deep convection as the ITCZ narrows that is consistent with modeling studies of projected ITCZ changes.