This study will investigate the determinant factors behind cirrus cloud formation and evolution based on in-situ observations at various geographical locations. In addition, the global radiative forcing of observation-constrained aerosol impacts on cirrus microphysical properties will be quantified by using a climate model. The project will focus on three critical scientific issues: (1) Hemispheric differences in cirrus cloud macroscopic and microphysical properties under similar dynamical conditions; (2) Multi-scale dynamical forcings driving ice nucleation and their impacts on cirrus simulations in a climate model; and (3) Impacts of anthropogenic aerosol emissions on cirrus microphysical properties and the subsequent influences on global radiation.
To address these scientific issues, The research team will: (1) extract cirrus cloud samples from a composite in-situ dataset covering various geographical locations, and compare the formation and evolution of cirrus clouds between two hemispheres; (2) examine the micro- to mesoscale (~0.1-10 km) variabilities of water vapor and temperature, and improve the NCAR Community Atmosphere Model version 5 (CAM5) by including these observed variabilities; (3) compare the in-situ measured cirrus microphysical properties between polluted and pristine regions, and use CAM5 to quantify the consequent perturbations on global radiation balance.
Intellectual Merit: Cirrus clouds are one of the main modulators of Earth's climate system. However, due to their large spatial heterogeneity and temporal variability, cirrus clouds remain one of the poorly-represented components in current general circulation models (GCMs). This project will improve our understanding of cirrus microphysical properties in relation to dynamical conditions and aerosol backgrounds, by analyzing in-situ aircraft data obtained from both the Northern and Southern Hemispheres, polluted and pristine regions. Furthermore, the research team will use the observed characteristics to evaluate the simulations of relative humidity and cirrus clouds in CAM5 in terms of their occurrence, spatial coverage and microphysical properties. In addition, a "best-observation-matched" ice microphysics configuration will be implemented into CAM5. Overall, using micro- to mesoscale observations of cirrus formation and evolution, the research will improve cirrus cloud simulations in CAM5 and provide a new estimation on cirrus clouds' adjustments due to anthropogenic aerosol emissions (i.e., aerosol indirect forcing through perturbations of cirrus microphysical properties).
Broader Impacts: Both the observational dataset and the new model parameterization will be released to the community, including a synthesized in-situ observation dataset (a total of 8 campaigns from NSF, NASA and European Union), and a sub-grid scale parameterization of relative humidity variability for GCMs. The improved estimation of anthropogenic aerosol impact on cirrus cloud radiative forcing can contribute to uncertainty reduction in the next IPCC report. The project will greatly benefit teaching and mentoring of undergraduate and graduate students at University of Wyoming and San Jose State University. The project will also recruit and train undergraduate students for presenting their research at the local K-12 schools via San Jose State University's undergraduate Ambassador Program.
