Urban Aerosol Impacts on Downwind Convective Storms

VAN DEN HEEVER,S. AND WILLIAM R. COTTON J. Appl. Meteor. Climate.,46,828-850

Speaker:陳文彬

St .Louis8 June 1999

雷達回波：contour:10dBZ

Grid1 ： 37.5kmGrid2 ： 7.5kmGrid3 ： 1.5km

Aerosol initialization concentrations

方形矩陣： downwind calculation

Time evolution of the RURAL-H - NOCITY-H temperature and water vapor mixing ratio fields

Shaded : TContours: water vapor mixing ratio

Higher background aerosol concentrationresults

RURAL-H test

Shaded: CCN個數 at 500m

Contoured at 750m:Updraft velocity

NOCITY-H test

URBAN-H test.

Time series of the total hydrometeor mass

Time series of the accumulated volumetric precipitation

Lower background aerosol concentration results

RURAL-L simulation

URBAN-L simulation

Time series of (a) the maximum updraft within the downwind region and (b) the average of themaximum updraft

Maximum downdraft within the downwind region

Time series of the (left) cloud and (right) rain mixing ratios

RURAL-L URBAN-L accumulated surface precipitation

Conclusions• When GCCN or both CCN and GCCN concentrations were enhanced, cloud

water and rain formed more rapidly. The updrafts were also stronger initially, and the downdrafts developed more quickly.

• Greater amounts of surface precipitation were also produced in these cases during the first 1.25–1.5 h. When CCN alone were enhanced, the formation of cloud water, rain, and all of the ice species was delayed, as was the development of both the updrafts and downdrafts.

• The surface precipitation was suppressed in the presence of urban-enhanced CCN concentrations.

Conclusions• GCCN and both GCCN and CCN are enhanced leads to earlier in the storm

life cycle than in the control simulation.

• Urban aerosol effects on downwind convection and precipitation could be expected to be greater in less industrialized regions of the United States, as well as in countries such as Canada and Australia, where the background aerosol concentrations are generally lower.

• The extremely complex, nonlinear relationships between the microphysics and dynamics therefore make it difficult to make absolute statements regarding the impacts of urban-enhanced CCN and GCCN on downwind convection and precipitation.