Variations in Precipitating Convective Feature Populations with ITCZ Width in the Pacific Ocean

Abstract

Many recent studies have aimed to better understand changes in the characteristics of the intertropical convergence zone (ITCZ), including ITCZ location, width, and precipitation intensity. However, very few studies have looked at the relationship between characteristics of convection within the ITCZ and ITCZ width. The present work uses information from an ITCZ identification database and Tropical Rainfall Measuring Mission (TRMM) precipitation feature (PF) database to quantify variations in convective characteristics across the ITCZ in the Pacific Ocean. Data are partitioned into wide and narrow ITCZ regimes to quantify differences in convection between different ITCZ regimes. Under the wide regime, convection deeper than 5 km, with areas greater than 100 km 2 , or stratiform rain fractions greater than 0.5 is, on average, 24%, 23%, and 12% more frequent, respectively. In the narrow regime, the signal is reversed, with average increases in the frequency of convection with heights below 5 km, areas less than 100 km 2 , or stratiform rain fractions less than 0.5 of 15%, 4%, and 6%, respectively. Positive and negative anomalies in columnar water vapor (CWV) and sea surface temperature (SST) across the ITCZ are observed in the wide and narrow regimes, respectively. There is also a strong positive correlation between an El Niño-Southern Oscillation (ENSO) index and ITCZ width anomalies, with wide (narrow) ITCZs occurring during warm (cold) phases of ENSO. This implies that the strengthening and weakening of the Walker circulation associated with ENSO may play a role in modulating the convective populations that contribute to the Pacific ITCZ width variations.

More Intense, Organized Deep Convection With Shrinking Tropical Ascent Regions

“…Across the Pacific Ocean, correlations tend to be positive, signifying increases in PF volumetric and average RR and stratiform area as A u decreases. Note that these findings are opposite of those of a previous study of convection in the Pacific (K. R. Wodzicki & Rapp, 2020) because that study examined the intensity of convection in the Pacific as the Pacific ITCZ and Pacific Hadley cell varied, whereas the present results show regional variability related to tropics wide changes. At the margins of the climatological ascent region (black contour) in the Pacific, namely in the SPCZ, there tends to be negative correlations, while positive correlations exist near the center of the ascent regions.…”

Examination of the Daily Cycle Wind Vector Modes of Variability from the Constellation of Microwave Scatterometers and Radiometers

“…The descending branch is dominated by a subtropical high-pressure area, which suppresses convection. The Southern Pacific Converge Zone (SPCZ) extends southeast from the tropical West Pacific warm pool toward French Polynesia, although its size and orientation vary [37], especially during strong El Niño years. For comparison, Figure 14 contrasts the February GPM IMERG precipitation total from the IMERG data during winter 2015 (strong El Niño) and winter 2017 (weak La Niña).…”

Anthropogenic Weakening of the Atmospheric Circulation During the Satellite Era

“…Changes in the atmospheric overturning circulation have important implications for the pattern of precipitation change, as well as the frequency of droughts and extreme precipitation events (Chadwick et al., 2013; Lau & Kim, 2015; Su et al., 2014, 2019; Wodzicki & Rapp, 2020). Atmospheric overturning circulation and SST pattern are closely tied to the climate feedback from tropical low cloud covers and thus has a strong impact on climate sensitivity (Andrews et al., 2022; Loeb et al., 2020; Sherwood et al., 2014).…”