Analysis of the Aerosol-Cloud Interactions from Aircraft, Surface Measurements, and Cloud Parcel Model During the March 2000 IOP at the ARM SGP Site
Delene, D.J.(a), Dong, X.(a), Chen, Y.(b), Poellot, M.(a), and Penner, J.E.(b), University of North Dakota (a), University of Michigan (b)
Fourteenth Atmospheric Radiation Measurement (ARM) Science Team Meeting
One of the largest uncertainties in estimating anthropogenic forcing of climate change and in predicting future climates is the relationship between atmospheric aerosols and cloud properties. Aerosols affect cloud optical properties, cloud water content and cloud lifetime. A higher aerosol number concentration generally results in the nucleation of more smaller cloud droplets, which increases cloud albedo and results in a brighter cloud. In addition to aerosol number concentration, cloud properties are also influenced by the aerosol size distribution, aerosol composition and updraft velocity. The continuous measurements of several key cloud, aerosol and atmospheric parameters at the Department of Energy’s Atmospheric Radiation Measurement Program Southern Great Plains site make it possible to quantify to what extent different parameters affect the observed variation in cloud properties such as the cloud droplet number concentration and effective radius. The observed variations in cloud droplet number concentration and effective radius in non drizzle stratus clouds during the March 2000 IOP are investigated to understand how changes in aerosol number concentration, aerosol size distribution and updraft velocity contribute to the observed change in cloud properties. Cloud droplet number concentration and effective radius can be derived using a radiative transfer model based on microwave radiometer brightness temperature measurements and Eppley Precision Spectral Pyranometer measurements. During the March IOP, the cloud droplet number concentration and effective radius were also measured directly using the University of North Dakota’s Citation aircraft. The updraft velocity is estimated by using the maximum doppler velocity from the millimeter radar. The aerosol number concentration and aerosol size distribution are estimated by using surface-based measurements made with a condensation nuclei counter and an optical particle counter. Rawinsonde data are used to restrict the analysis to time periods when the atmosphere is well-mixed so surface based measurements are indicative of cloud based properties. Millimeter radar data are used to restrict the analysis to time periods when there is a positive updraft velocity at cloud base and when drizzle size cloud particles are not present. For this restricted data set, a cloud parcel model is run using the estimated updraft velocities and aerosol properties and the results are compared to the measured cloud properties.
Note: This is the poster abstract presented at the meeting; an extended version was not provided by the author(s).
