Characterisation and surface radiative impact of Arctic low clouds from the IAOOS field experiment

Julia Maillard,François Ravetta,Vincent Mariage,Jean-Christophe Raut,Jacques Pelon

doi:10.5194/acp-21-4079-2021

Abstract

Abstract. The Ice, Atmosphere, Arctic Ocean Observing System (IAOOS) field experiment took place from 2014 to 2019. Over this period, more than 20 instrumented buoys were deployed at the North Pole. Once locked into the ice, the buoys drifted for periods of a month to more than a year. Some of these buoys were equipped with 808 nm wavelength lidars which acquired a total of 1777 profiles over the course of the campaign. This IAOOS lidar dataset is exploited to establish a novel statistic of cloud cover and of the geometrical and optical characteristics of the lowest cloud layer. The average cloud frequency from April to December over the course of the campaign was 75 %. Cloud occurrence frequencies were above 85 % from May to October. Single layers are thickest in October/November and thinnest in the summer. Meanwhile, their optical depth is maximum in October. On the whole, the cloud base height is very low, with the great majority of first layer bases beneath 120 m. In April and October, surface temperatures are markedly warmer when the IAOOS profile contains at least one low cloud than when it does not. This temperature difference is statistically insignificant in the summer months. Indeed, summer clouds have a shortwave cooling effect which can reach −60 W m−2 and balance out their longwave warming effect.

Highlights

The Arctic is a key region of climate change: it is warming about twice as fast as the middle latitudes. This phenomenon, called “Arctic amplification”, is most commonly attributed to the ice–albedo feedback, which is due to areas of open ocean exposed by melting sea ice absorbing more solar radiation
Clouds are one of the main contributors to uncertainty in global climate models because cloud feedbacks and cloud–aerosol interactions are still poorly understood; clouds appear to be of particular importance in the Arctic (Tjernström et al, 2008), where they play a very important role in the climate system
During the Surface Heat Budget of the Arctic Ocean (SHEBA) campaign, winter cloud occurrence measured from a combined radar–lidar was 70 %

Summary

Introduction

The Arctic is a key region of climate change: it is warming about twice as fast as the middle latitudes. This phenomenon, called “Arctic amplification”, is most commonly attributed to the ice–albedo feedback, which is due to areas of open ocean exposed by melting sea ice absorbing more solar radiation. Arctic clouds are observed to influence the melting of sea ice (Kay and Gettelman, 2009) and may exert control on the ice–albedo feedback this way. These effects and processes are seasonally variable and not well represented by annual means (Kay and Gettelman, 2009)

Objectives

Methods

Findings

Conclusion