Midlatitude cloud shifts, their primary link to the Hadley cell, and their diverse radiative effects

Abstract

We investigate the interannual relationship among clouds, their radiative effects, and two key indices of the atmospheric circulation: the latitudinal positions of the Hadley cell edge and the midlatitude jet. From reanalysis data and satellite observations, we find a clear and consistent relationship between the width of the Hadley cell and the high cloud field, statistically significant in nearly all regions and seasons. In contrast, shifts of the midlatitude jet correlate significantly with high cloud shifts only in the North Atlantic region during the winter season. While in that region and season poleward high cloud shifts are associated with shortwave radiative warming, over the Southern Oceans during all seasons they are associated with shortwave radiative cooling. Finally, a trend analysis reveals that poleward high cloud shifts observed over the 1983–2009 period are more likely related to Hadley cell expansion, rather than poleward shifts of the midlatitude jets.

CMIP5 models' shortwave cloud radiative response and climate sensitivity linked to the climatological Hadley cell extent

“…We begin by examining in Figure the spatial structure of the interannual HC‐SWCRE covariability for (a) the observations and (b) the multimodel mean. In observations [ Tselioudis et al , ], the HC‐SWCRE relationship in the SH LML region is mostly negative and is dominated by SW cooling, except for a region of SW warming east of South America and a tropical SW warming intrusion in the eastern South Pacific associated with a southward and westward shift of the South Pacific Convergence Zone (SPCZ). In contrast to the observations, the multimodel mean HC‐SWCRE pattern, while showing a weak cooling in the central Pacific associated with a SPCZ shift, is dominated by a pronounced and zonally symmetric LML SW warming belt.…”

“…In models with wide climatological HCs and already strong LML subsidence, the SW warming effect is small. In the observations [ Tselioudis et al , ], there is no SW warming effect because there are more abundant and more reflective clouds, particularly at low levels, with poleward HC edge shifts. The reason for the −HC‐SWCRE models' behavior must be further explored following the analysis of Grise and Medeiros [], who highlight the strong control of the estimated boundary layer inversion strength on the low cloud field in the LML.…”

Cloud feedback mechanisms and their representation in global climate models

“…These anomalies are small in the context of global warming‐driven cloud feedback, however, so that future shifts in midlatitude circulation appear unlikely to be a major contribution to global‐mean LW cloud feedback. Given the strong seasonality of LW and SW cloud‐radiative anomalies, it remains possible that extratropical circulation shifts have non‐negligible radiative impacts on seasonal time scales . It is also possible that clouds and radiation respond more strongly to other aspects of atmospheric circulation than the midlatitude jets and storm tracks; it has been recently proposed that midlatitude cloud changes are more strongly tied to Hadley cell shifts than to the jet .…”

The Cloud Feedback Model Intercomparison Project (CFMIP) Diagnostic Codes Catalogue – metrics, diagnostics and methodologies to evaluate, understand and improve the representation of clouds and cloud feedbacks in climate models

“…Tsushima et al (2006) highlighted the importance of evaluating the ratio of ice and liquid in mixed-phase clouds in simulations of the current climate because it determines how large the phase change might be under climate change. An underestimate of the relative amount of supercooled liquid water has been found in GCMs Tan et al, 2015).…”

“…Grise and Polvani (2016) investigated the impact of these dynamical responses to climate sensitivity using CMIP5 models and found that in the Southern Hemisphere inter-model differences in the value of ECS explain ∼ 60 % of the inter-model variance in the annual-mean Hadley cell expansion but just ∼ 20 % of the variance in the annual-mean mid-latitude jet response. Tselioudis et al (2016) investigated the relationship between interannual variations of the latitudinal position of clouds and their radiative effects and those in the Hadley cell and the mid-latitude jets. They found that the interannual variations of the locations of high clouds and the Hadley cell are correlated significantly, but did not find a robust correlation between clouds and the mid-latitude jets.…”