Understanding midlatitude cloud responses to circulation shifts through dynamical cloud-controlling factors

Abstract:

In a changing climate, changes in midlatitude clouds as a result of shifts in general circulation patterns are widely thought to be a potential source of radiative feedbacks onto the climate system. Previous work has suggested that two general circulation shifts anticipated to occur in a warming climate (a poleward expansion of the Hadley cell and a poleward shift in the midlatitude jet) are associated with different radiative responses of midlatitude clouds, but it remains unclear as to why. In this study, we examine dynamical cloud-controlling factors to explain why the cloud-radiative response to the circulation shifts vary. In particular, we find that mid-tropospheric vertical velocity anomalies vary greatly between a shift of the midlatitude jet and a poleward expansion of the Hadley cell, with anomalous subsidence occurring much further equatorward during poleward shifts in the Hadley cell edge when compared to poleward shifts of the midlatitude jet. In contrast, shifts in the Hadley cell edge and midlatitude jet are associated with similar anomalies in lower tropospheric stability. These dynamical shifts in the cloud-controlling factors help to explain some of the differing cloud-radiative effect anomalies observed as a result of the circulation shifts.