Siddhant Gupta - December 3

School of Meteorology Colloquium In Situ and Satellite-Based Estimates of Aerosol-Cloud Interactions Between Biomass Burning Aerosols and Marine Stratocumulus Clouds over the Southeast Atlantic Ocean Siddhant Gupta Friday, December 3rd 12:00 pm Join Google Meet: https://meet.google.com/ocw-azzw-wve Low-level, marine stratocumulus clouds provide the largest contribution of all cloud types to the

Start

December 3, 2021 - 12:00 pm

End

December 3, 2021 - 1:00 pm

School of Meteorology Colloquium

In Situ and Satellite-Based Estimates of Aerosol-Cloud Interactions Between Biomass Burning Aerosols and Marine Stratocumulus Clouds over the Southeast Atlantic Ocean

Siddhant Gupta

Friday, December 3rd

12:00 pm

Join Google Meet:

https://meet.google.com/ocw-azzw-wve

Low-level, marine stratocumulus clouds provide the largest contribution of all cloud types to the shortwave cloud radiative forcing. Small changes in marine stratocumulus due to aerosol-cloud interactions (ACIs) could partially offset the global warming due to increasing greenhouse gas concentrations in the atmosphere. In situ airborne measurements of cloud and aerosol properties from the NASA ObseRvations of Aerosols above CLouds and their intEractionS (ORACLES) field campaign are used here to quantify aerosol effects on marine stratocumulus over the southeast Atlantic Ocean and to evaluate satellite-based estimates of ACIs.

During ORACLES, 173 “contact” profiles had aerosol concentration (Na) > 500 cm-3 within 100 m above cloud tops and 156 “separated” profiles had Na < 500 cm-3 in the 100 m above cloud tops. The average droplet concentration (Nc) and cloud optical thickness (t) for contact profiles were 87 cm-3 and 1.8 higher and effective radius (Re) was 1.5 mm lower compared to separated profiles. These differences were due to higher below-cloud Na and weaker droplet evaporation near cloud top in the presence of high above-cloud Na. ACIs thus resulted in brighter clouds which would have a higher shortwave cloud radiative forcing.

Higher Nc and lower Re for contact profiles resulted in precipitation suppression with 50% lower precipitation rate (Rp) compared to separated profiles and 20% lower precipitation susceptibility to aerosols (So). Differences between So for contact and separated profiles varied with cloud thickness due to co-variability between changes in Nc and Rp due to droplet growth and increasing Na. On average, contact and separated profiles had similar surface temperature, lower tropospheric stability, and estimated inversion strength showing the differences were consistent with ACIs rather than a meteorological effect.

149 cloud profiles had a co-located retrieval from the Moderate Resolution Imaging Spectroradiometer (MODIS) onboard the Terra or Aqua satellite. On average, the MODIS Re, t, and Nc (11.4 mm, 11.7, and 150.3 cm-3) were 1.7 mm, 2.4, and less than 1 cm-3 higher than the in situ Re, t, and Nc. The low biases in MODIS retrievals were consistent for contact and separated profiles. Thus, MODIS estimates of the sign and magnitude of aerosol-induced changes in Re, t, and Nc were similar to the in situ estimates. Based on these results, studies of ACIs in marine stratocumulus over the southeast Atlantic can be extended to larger domains and directions for future work are discussed.