Abstract
AbstractTo better understand and quantify the impact of clouds on the Greenland Ice Sheet surface mass balance (SMB), we study the spatiotemporal variability of the cloud radiative effect (CRE). The total CRE is separated in short‐term and long‐term impacts by performing multiple simulations with the SNOWPACK model for 2001‐+2010. The annual total CRE is 16.8 ± 4.5 W m−2, reducing the SMB with −157 ± 3.8 Gt yr−1. Summer cloud radiative cooling is −6.4 ± 5.7 W m−2 in the ablation area, increasing the SMB with 121 ± 2.2 Gt yr−1. The annual integrated impact is cloud‐reduced SMB of −36 Gt yr−1. The short‐term effect dominates the opposing long‐term effects through the albedo‐melt feedback. A long‐term warming effect decreases the albedo and so preconditions the surface for enhanced (summer) melt. The impact of the CRE, determined by spatial, temporal and initial conditions, explains existing conflicted views on the role of cloud radiation and emphasizes the need for accurate cloud and albedo representations in future studies.
Highlights
The Greenland ice sheet (GrIS) has been losing mass since the late 1990s primarily through a rise in surface meltwater runoff (Fettweis, Franco, et al, 2013; van den Broeke et al, 2016)
To better understand and quantify the impact of clouds on the Greenland Ice Sheet surface mass balance (SMB), we study the spatiotemporal variability of the cloud radiative effect (CRE)
For winter (December, January, February, DJF), spring (March, April, May, MAM), and fall (September, October, November, SON), the CRE is positive on the entirety of the GrIS, inducing a net warming effect at the surface
Summary
The Greenland ice sheet (GrIS) has been losing mass since the late 1990s primarily through a rise in surface meltwater runoff (Fettweis, Franco, et al, 2013; van den Broeke et al, 2016). Clouds regulate the amount of radiation received by the surface, which determines surface melt, and can trigger feedback mechanisms that induce albedo changes (Bintanja & Van Den Broeke, 1996). This is the cloud radiative effect (CRE). A warming CRE affects the conditions of the GrIS surface snow/firn, reducing meltwater refreezing and thereby accelerating bare-ice exposure (decreasing the albedo) and enhancing meltwater runoff, as discussed by Van Tricht et al (2016). Wang et al (2018) argue that clouds limit the albedo feedback and decelerate surface melt, referring to a net cooling CRE observed by automatic weather stations. The deceleration of accelerated GrIS melting since 2013 is linked by Ruan et al (2019) to the reduction in SW radiation in the presence of increasing total cloud cover
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