Ice crystal number concentration estimates from lidar–radar satellite remote sensing – Part 2: Controls on the ice crystal number concentration

Edward Gryspeerdt,Philipp Kühne,Julien Delanoë,Johannes Quaas,Martina Krämer,Odran Sourdeval

doi:10.5194/acp-18-14351-2018

Abstract

Abstract. The ice crystal number concentration (Ni) is a key property of ice clouds, both radiatively and microphysically. Due to sparse in situ measurements of ice cloud properties, the controls on the Ni have remained difficult to determine. As more advanced treatments of ice clouds are included in global models, it is becoming increasingly necessary to develop strong observational constraints on the processes involved. This work uses the DARDAR-Nice Ni retrieval described in Part 1 to investigate the controls on the Ni at a global scale. The retrieved clouds are separated by type. The effects of temperature, proxies for in-cloud updraft and aerosol concentrations are investigated. Variations in the cloud top Ni (Ni(top)) consistent with both homogeneous and heterogeneous nucleation are observed along with differing relationships between aerosol and Ni(top) depending on the prevailing meteorological situation and aerosol type. Away from the cloud top, the Ni displays a different sensitivity to these controlling factors, providing a possible explanation for the low Ni sensitivity to temperature and ice nucleating particles (INP) observed in previous in situ studies. This satellite dataset provides a new way of investigating the response of cloud properties to meteorological and aerosol controls. The results presented in this work increase our confidence in the retrieved Ni and will form the basis for further study into the processes influencing ice and mixed phase clouds.

Highlights

Clouds play a central role in the Earth’s energy budget, as they are responsible for large variations in the reflected shortwave and emitted longwave radiation (Stephens et al, 2012)
A large part of this uncertainty comes from the difficulty in retrieving cirrus cloud properties at a large enough scale to separate the roles of individual factors controlling the ice crystal number concentration (Ni)
The Ni produced by heterogeneous nucleation should increase as temperatures decrease due to increasing ice nucleating particles (INP) concentrations (DeMott et al, 2010), this strong increase in Ni5(tμomp) at −40 ◦C along with a continuing Ni increase at colder temperatures is indicative of homogeneous nucleation, which is only significant at temperatures below around −35 ◦C

Summary

Introduction

Clouds play a central role in the Earth’s energy budget, as they are responsible for large variations in the reflected shortwave and emitted longwave radiation (Stephens et al, 2012). A large part of this uncertainty comes from the difficulty in retrieving cirrus cloud properties at a large enough scale to separate the roles of individual factors controlling the ice crystal number concentration (Ni). Lohmann et al, 2007; Salzmann et al, 2010) This highlights a requirement to understand the controls on the Ni in order to improve our understanding and parameterization of cloud processes. While aircraft measurements of the Ni exist, they are restricted in space and time They can be affected by shattering of ice crystals at the instrument inlet (McFarquhar et al, 2007; Jensen et al, 2009; Korolev et al, 2013) and difficulties in measuring the smallest crystals (O’Shea et al, 2016). The new DARDARNice satellite dataset described in Part 1 (Sourdeval et al, 2018a) allows the processes that control the Ni to be investigated globally

Methods

Results

Discussion

Conclusion