Cirrus cloud radiative effects are largely affected by ice microphysical properties, including ice water content (IWC), ice crystal number concentration (Ni) and mean diameter (Di). These characteristics vary significantly due to thermodynamic, dynamical and aerosol conditions. In this work, a global-scale observation dataset is used to examine regional variations of cirrus cloud microphysical properties, as well as several key controlling factors, i.e., temperature, relative humidity with respect to ice (RHi), vertical velocity (w), and aerosol number concentrations (Na). Results are compared with simulations from the National Center for Atmospheric Research (NCAR) Community Atmosphere Model version 6 (CAM6). The differences between simulations and observations are found to vary with latitude and temperature. Specifically, simulations are found to underestimate IWC by a factor of 5–30 in all regions. Simulated Ni is overestimated in most regions except Northern Hemisphere midlatitude and polar regions. Simulated Di is underestimated, especially for warmer conditions (−50 °C to −40 °C) and higher Na, possibly due to less effective ice particle growth/sedimentation and weaker aerosol indirect effects, respectively. For RHi effects, the frequency and magnitude of ice supersaturation is underestimated in simulations for clear-sky conditions, and the simulated IWC and Ni show maximum values at 80 % RHi instead of 110 % as observed. For w effects, both observations and simulations show variances of w (σw) decreasing from tropics to polar regions, but simulations show much higher σw for in-cloud condition than clear-sky condition. These findings provide an observation-based guideline for improving simulated ice microphysical properties and their relationships with key controlling factors at various geographical locations.
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Effects of thermodynamics, dynamics and aerosols on cirrus clouds based on in situ observations and NCAR CAM6
Abstract. Cirrus cloud radiative effects are largely affected byice microphysical properties, including ice water content (IWC), ice crystalnumber concentration (Ni) and mean diameter (Di). These characteristics varysignificantly due to thermodynamic, dynamical and aerosol conditions. Inthis work, a global-scale observation dataset is used to examine regionalvariations of cirrus cloud microphysical properties, as well as several keycontrolling factors, i.e., temperature, relative humidity with respect toice (RHi), vertical velocity (w) and aerosol number concentrations (Na).Results are compared with simulations from the National Center forAtmospheric Research (NCAR) Community Atmosphere Model version 6 (CAM6).Observed and simulated ice mass and number concentrations are constrained to≥62.5 µm to reduce potential uncertainty from shattered ice indata collection. The differences between simulations and observations arefound to vary with latitude and temperature. Comparing with averagedobservations at ∼100 km horizontal scale, simulations arefound to underestimate (overestimate) IWC by a factor of 3–10 in theNorthern (Southern) Hemisphere. Simulated Ni is overestimated in mostregions except the Northern Hemisphere midlatitudes. Simulated Di isunderestimated by a factor of 2, especially for warmer conditions(−50 to −40 ∘C), possibly due tomisrepresentation of ice particle growth/sedimentation. For RHi effects, thefrequency and magnitude of ice supersaturation are underestimated insimulations for clear-sky conditions. The simulated IWC and Ni show bimodaldistributions with maximum values at 100 % and 80 % RHi, differing fromthe unimodal distributions that peak at 100 % in the observations. For weffects, both observations and simulations show variances of w (σw) decreasing from the tropics to polar regions, but simulations show muchhigher σw for the in-cloud condition than the clear-sky condition.Compared with observations, simulations show weaker aerosol indirect effectswith a smaller increase of IWC and Di at higher Na. These findings provide anobservation-based guideline for improving simulated ice microphysicalproperties and their relationships with key controlling factors at variousgeographical locations.
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- NSF-PAR ID:
- 10216772
- Date Published:
- Journal Name:
- Atmospheric Chemistry and Physics
- Volume:
- 21
- Issue:
- 3
- ISSN:
- 1680-7324
- Page Range / eLocation ID:
- 1835 to 1859
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.5194/acp-21-1835-2021
