presented by Jorgen B. Jensen NCAR/EOL/RAF
Why should a large-scale modeler be concerned about the implementation of an ill-measured and ill-represented group of aerosol particles - the giant aerosol particles? The obvious answer is that these aerosols may impact both the radiative balance and the formation of warm rain. Whereas some large-scale models include the radiative effects of giant aerosols, almost no large-scale models include the effects of warm rain formation based on giant aerosols.
This talk focuses almost exclusively on the warm rain formation of giant seasalt aerosol particles, as they are globally the most common kind of giant aerosols and due to their high hygroscopicity.
The first part of this talk uses a cloud process model with condensation and stochastic Monte-Carlo coalescence to examine the relative impact of small and giant aerosols on warm rain formation in both stratocumulus and cumulus. The cumulus study includes a comparison with observations from the recent RICO field experiment.
The second part of the talk goes through the various steps needed for implementing a seasalt-based warm rain initiation scheme into both climate and cloud-resolving models with bulk microphysics:
- An aerosol model for calculating the generation rate of giant sea-salt aerosol particles,
- The continuity equations needed for representing the mass of seasalt in air and cloud drops and in precipitation drops, and
- A box model for the condensation and coalescence growth of drops formed on giant aerosol particles, with the final result being the calculation of autoconversion rates. The autoconversion rate depends critically on cloud age.
While many of the model calculations are based on published size distributions of seasalt particles, future calculations will include measurements obtained using an automated optical digital microscope currently being developed in the EOL. Measurements for analysis were obtained during RICO.
Seminar is from
9:30 am to 10:30 am in FL2 Room 1022
on Thursday, March 24, 2005.
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