WRF Model Simulations of Aqueous Chemistry

8/3/2019 WRF Model Simulations of Aqueous Chemistry

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Si-Wan Kim, Mary C. Barth, William C. Skamarock

National Center for Atmosphere Research

Boulder, Colorado, USA


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The Weather and Research Forecast (WRF)

Model is a next-generation mesoscale numerical

weather prediction system,Can be used to solves conservative(flux form),

nonhydrostatic compressible equations,

Suitable for a broad spectrum of applicationsacross scales ranging from meters to thousands of

kilometers.


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INTRODUCTION

Model studies have shown that convective injections

of peroxides and formaldehyde in the boundary layer

(BL) to the upper troposphere (UT) can produce HOxand ozone in the UT(Chatfield and Crutzen, 1984;

Prather and Jocob, 1997).

Deep convection on the BL air venting andscavenging of peroxides using aircraft observation in

the marine environment.


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These aircraft observations were not exactly

coincident with convective events in time, which puts

some limitations on the interpretation of data due to

uncertainties in chemical reactions, advection andconvection processes.

To understand this interaction, a modelling framework

that is complementary to observations needs to be

developed.


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The Weather and Research Forecast (WRF)

model coupled with aqueous chemistry and

microphysical transfer processes and examine theimportance of cloud physics and chemistry on

peroxides and formaldehyde concentrations by

simulating the 10 July 1996 STERAO stormwhich was observed in northeastern Colorado.


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The aqueous chemistry is computed for thecloud water and rain assuming a pH of 4.5.Most chemical species are initialized with

values measured in the inflow region of thestorm; other species are estimated from valuesfound in the literature or from the Julymonthly-mean mixing ratio for northeastern

Colorado calculated by the 3-dimensionalglobal transport model, MOZART.


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The simulated storm has radar reflectivity compa-rable to the observed storm

(Figure1, maximum reflectivity greater than 50 dBZ). Observed radarreflectivity obtained from the CSU CHILL radar reveals a multi-cellular system

(2 cells), as does the radar reflectivity calculated from the model results (3 cells).

The observed storm reaches lower stratosphere, while the simulated storm does

not develop to that height.

Radar reflectivity of a cross section through the storm from (a)simulation at t = 4200 s and (b) CHILL radar.


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The results of the simulations show theimportance of both cloud physics and cloudchemistry on the spatial distribution of solublespecies. Other factors, such as cloud-modifiedphotolysis frequencies, lightning-production ofNOx, and interactions between gas and icephases, could also influence the spatial

distribution of chemical species. These processeswill be implemented in the future.

WRF Model Simulations of Aqueous Chemistry

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