# Presentation: 124572

## Aerosol Processing by Clouds: Model Evaluation and Parameterization Development

- Mikhail Ovtchinnikov
- Richard C. Easter
- Steven J. Ghan

## Motivation

- Aerosol properties are affected by clouds with implications for direct and indirect aerosol effects
- Relevant processes are numerous and interactive:
- transport (*advection, sedimentation, mixing*);
- cloud microphysics;
- aqueous chemistry.
- Many of these are poorly understood and crudely represented in models
- Accuracy and applicability of many ad hoc assumptions and approximations are not known

**Notes:**
Properties here refer to spatial distribution, size spectrum, chemical composition, radiative properties, etc. 

## Objectives

- Improve understanding of aerosol processing by clouds
- Guide collection and interpretation of measurements
- Evaluate and improve parameterizations

**Use a high-resolution cloud-scale model with interactive dynamics, microphysics, and chemistry to:**

## Background: Cloud model

**Grid size is 100****×****100×100 m****3**

**Background: Cloud model**

- (After Ovtchinnikov and Kogan, *JAS*, 2000)

- 3-D nonhydrostatic dynamics (LES)
- Nonlinear interaction of thermodynamical, microphysical, and radiative processes
- 80+ variables per grid cell: Dynamics & thermodynamics (*u, v, w, T, q, p*) and microphysics (cloud condensation nuclei ~ 12 size bins; liquid drops ~ 30 size bins; ice particles ~ 30 size bins)
- Up to 1003  1,000,000 grid cells

**Box is 7.5****×****7.5×7.5 km****3**

**Challenge:****	****to track aerosol transformations inside cloud droplets**

**Notes:**
Present treatment is unable to track most aerosol transformations inside the cloud => once cloud condensation nuclei are activated they are lost. Aerosol or CCN are re-introduced upon droplet evaporation but their properties are rather arbitrary.  

## 2D aerosol-droplet spectrum

**Single-composition aerosol (**e.g., ammonium bisulfate**)**
**30 **dry size bins** ****×**
**50 **wet size bins** ****≈**
**1,500 **total bins

**Notes:**
The dry aerosol spectrum is preserved under condensation-evaporation cycle. If coagulation and/or aqueous chemistry is included the spectrum evolves and we can track that evolution. 

## 2D spectrum evolution 

**2D spectrum evolution **

## What do we need from a field project ?

***In situ***** microphysics and chemistry observations**

**What do we need from ****a field project ?**

_**Boundary conditions and forcing**_
**Meteorology:**
**Surface properties and heat fluxes**
**Large-scale wind, T and q tendencies**
**Microphysics: **
**Aerosol sources**

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**Remote sensing and surface observations**
**Mesoscale re-analysis or output of a NWP model**
**Climatology **

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**Model**

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**Cloud and aerosol properties**

**Field campaign**

## How to evaluate the model?

- What aspects of the observed aerosol distribution and its transformation by clouds can be quantitatively reproduced in the model?
- Which of the processes or parameterizations are most important?
- What if their treatments are simplified?
- Can a comparison with observations diagnose a “better” approach?

## What will we feed backto field projects ?

- Interpretation of the results
- Assessment of sampling strategies

- Evaluation of parameterizations
- Suggested improvements

**and to other models  **

*Atmospheric chemical and microphysical transformation processes and three dimensional mixing and transport processes*
*Experiment - Understand - Model - Compare (****model evaluation****)*

## T H A N K   Y O U