Varied midlatitude shortwave cloud radiative responses to Southern Hemisphere circulation shifts

Abstract

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, poleward shifts in the midlatitude jet streams and a poleward expansion of the Hadley circulation, are associated with differing effects on midlatitude clouds. This study examines two dynamical cloud‐controlling factors, mid‐tropospheric vertical velocity, and the estimated inversion strength (EIS) of the marine boundary layer temperature inversion, to explain why poleward shifts in the Southern Hemisphere midlatitude jet and Hadley cell edge have varying shortwave cloud‐radiative responses at midlatitudes. Changes in vertical velocity and EIS occur further equatorward for poleward shifts in the Hadley cell edge than they do for poleward shifts of the midlatitude jet. Because the sensitivity of shortwave cloud radiative effects (SWCRE) to variations in vertical velocity and EIS is a function of latitude, the SWCRE anomalies associated with jet and Hadley cell shifts differ. The dynamical changes associated with a poleward jet shift occur further poleward in a regime where the sensitivities of SWCRE to changes in vertical velocity and EIS balance, leading to a near‐net zero change in SWCRE in midlatitudes with a poleward jet shift. Conversely, the dynamical changes associated with Hadley cell expansion occur further equatorward at a latitude where the sensitivity of SWCRE is more strongly associated with changes in mid‐tropospheric vertical velocity, leading to a net shortwave cloud radiative warming effect in midlatitudes.

Extratropical Shortwave Cloud Feedbacks in the Context of the Global Circulation and Hydrological Cycle

“…Moistening is not uniform across the 40°–85°S region (Figure S1 in Supporting Information ). LWP is reduced in the 40°–50°S region consistent with Hadley cell expansion and drying (Grise & Medeiros, 2016; Kay et al., 2014; Kelleher & Grise, 2021; Lu et al., 2007; Sousa et al., 2018; Tselioudis et al., 2016; Figure S1 in Supporting Information ) and SW FB tends to be positive in this region (Figure 4a). In the 50–85° S region there is consistent moistening (Figure S1 in Supporting Information ), LWP increases (Figure S2 in Supporting Information ), and SW FB tends to be negative (Figure 4a).…”

“…The prediction of SW FB averaged 40°–85°S is the area‐weighted sum of these effects. Clearly, influence on the region of moistening by Hadley cell expansion modulates extratropical SW FB (Kelleher & Grise, 2021).…”

Detailing cloud property feedbacks with a regime-based decomposition

“…To the extent that internal climate variability and long-term greenhouse warming lead to distinct changes in large-scale circulation, whereas the response of cloud properties to warming within meteorological regimes is timescaleinvariant, future work should investigate whether across-timescale correspondence of cloud feedback improves if considering only the within-regime compo-nent. If so, this could provide an effective strategy for constraining a portion of cloud feedback, especially in regions where changes in large-scale meteorology or model biases in control-climate meteorology (Kelleher and Grise, 2022) may obscure the otherwise close relationship between temperature-mediated changes in cloud properties of a given morphology across time scales.…”

Climate drivers of Southern Ocean phytoplankton community composition and potential impacts on higher trophic levels

“…Changes in the westerly wind field, which result from ozone depletion and CO 2 -driven tropospheric warming, have been documented in observational and modeling studies (e.g., Grise et al, 2013;Kajtar et al, 2021). These changes are associated with increasingly positive phases of the Southern Annular Mode (SAM) and may impact cloudiness, with implications for insolation at the ocean surface (Grise et al, 2013;Kelleher and Grise, 2021). Moreover, changes in wind and buoyancy forcing of the surface ocean play an important role in mediating the supply of iron to the euphotic zone (Henley et al, 2020).…”