Ice crystal number concentration estimates from lidar–radar satellite remote sensing – Part 1: Method and evaluation
Author(s)
Type
Journal Article
Abstract
The number concentration of cloud particles is a key quantity for understanding aerosol–cloud interactions and describing clouds in climate and numerical weather prediction models. In contrast with recent advances for liquid clouds, few observational constraints exist regarding the ice crystal number concentration (Ni). This study investigates how combined lidar–radar measurements can be used to provide satellite estimates of Ni, using a methodology that constrains moments of a parameterized particle size distribution (PSD). The operational liDAR–raDAR (DARDAR) product serves as an existing base for this method, which focuses on ice clouds with temperatures Tc<−30
∘C.
Theoretical considerations demonstrate the capability for accurate retrievals of Ni, apart from a possible bias in the concentration in small crystals when Tc≳−50 ∘C, due to the assumption of a monomodal PSD shape in the current method. This is verified via a comparison of satellite estimates to coincident in situ measurements, which additionally demonstrates the sufficient sensitivity of lidar–radar observations to Ni. Following these results, satellite estimates of Ni are evaluated in the context of a case study and a preliminary climatological analysis based on 10 years of global data. Despite a lack of other large-scale references, this evaluation shows a reasonable physical consistency in Ni spatial distribution patterns. Notably, increases in Ni are found towards cold temperatures and, more significantly, in the presence of strong updrafts, such as those related to convective or orographic uplifts. Further evaluation and improvement of this method are necessary, although these results already constitute a first encouraging step towards large-scale observational constraints for Ni. Part 2 of this series uses this new dataset to examine the controls on Ni.
∘C.
Theoretical considerations demonstrate the capability for accurate retrievals of Ni, apart from a possible bias in the concentration in small crystals when Tc≳−50 ∘C, due to the assumption of a monomodal PSD shape in the current method. This is verified via a comparison of satellite estimates to coincident in situ measurements, which additionally demonstrates the sufficient sensitivity of lidar–radar observations to Ni. Following these results, satellite estimates of Ni are evaluated in the context of a case study and a preliminary climatological analysis based on 10 years of global data. Despite a lack of other large-scale references, this evaluation shows a reasonable physical consistency in Ni spatial distribution patterns. Notably, increases in Ni are found towards cold temperatures and, more significantly, in the presence of strong updrafts, such as those related to convective or orographic uplifts. Further evaluation and improvement of this method are necessary, although these results already constitute a first encouraging step towards large-scale observational constraints for Ni. Part 2 of this series uses this new dataset to examine the controls on Ni.
Date Issued
2018-10-09
Date Acceptance
2018-08-20
Citation
Atmospheric Chemistry and Physics, 2018, 18 (19), pp.14327-14350
ISSN
1680-7316
Publisher
Copernicus Publications
Start Page
14327
End Page
14350
Journal / Book Title
Atmospheric Chemistry and Physics
Volume
18
Issue
19
Copyright Statement
© Author(s) 2018. This work is distributed under the Creative Commons Attribution 4.0 License (https://creativecommons.org/licenses/by/4.0/)
Subjects
Science & Technology
Life Sciences & Biomedicine
Physical Sciences
Environmental Sciences
Meteorology & Atmospheric Sciences
Environmental Sciences & Ecology
CIRRUS CLOUD FORMATION
VISIBLE OPTICAL DEPTH
IN-SITU MEASUREMENTS
WATER-CONTENT
A-TRAIN
MICROPHYSICAL PROPERTIES
SEMITRANSPARENT CIRRUS
RADIATIVE PROPERTIES
SPARTICUS CAMPAIGN
MIDLATITUDE CIRRUS
0401 Atmospheric Sciences
0201 Astronomical and Space Sciences
Meteorology & Atmospheric Sciences
Publication Status
Published
Date Publish Online
2018-10-09