On-line Numerical Research On Atmospheric Aerosols And Their Interaction With Clouds And Precipitation

CUACE/Aero, the China Meteorological Administration （CMA） Unified AtmosphericChemistry Environment for aerosols, is a comprehensive numerical aerosol moduleincorporating emissions, gaseous chemistry and size-segregated multi-component aerosolalgorithm. On-line coupled into a meso-scale weather forecast model （MM5） and the CMAnew generation meteorological model-GRAPES), its performance and improvements foraerosol chemical and optical simulations have been evaluated using the observations data ofaerosols/gases from the intensive observations and from the CMA Atmosphere Watchnetwork（CAWNET）, plus aerosol optical depth （AOD） data from CMA Aerosol RemoteSensing network （CARSNET） and from Moderate Resolution Imaging Spectroradiometer（MODIS）. Targeting Beijing and North China region from July13to31,2008, when a heavyhazy weather system occurred, the model captured the general variations of PM10with mostof the data within a factor of2from the observations and a combined correlation coefficient（r） of0.38（P <0.05）. A new size distribution for the primary particle emissions wasconstructed for most of the anthropogenic aerosols such as EC, OC, sulphate, nitrate andammonium from the observed size distribution of atmospheric aerosols in Beijing. This notonly improves the correlation between the modelled and observed AOD, but also reduces theoverestimation of AOD simulated by the original model size distributions of primary aerosols.The normalised mean error has been reduced to62%with the CARSNET observations and76%with MODIS, from the original111%and143%, respectively.The interactions between aerosol-cloud-precipitation have also been developed byconnecting the aerosols from CUACE/Aero and the most complex single-moment cloudmodel REISNER2through the observed power low relationships between the numberconcentrations of aerosols and clouds in China. It showed that when CCN numberconcentration increased from500cm^-3to2000cm^-3which is the normal level in low levelatmosphere over China, the autoconversion rate from droplets to drops would decrease by anorder of2, the collection rate by snow,ice, grauple would decrease by80%,30%and20%respectively. The accretion rate by drops will decrease by11%. Sensitive tests show that the aerosol will redistribute the precipitation and made it more reasonable to the observation. Thehighest changes of72-hours accumulated rain are about10²0%of the total precipitationcompared with the control tests.For better understanding the aerosol effect on clouds and precipitation in GRAPES, theCMA new generation weather model, a two-moments cloud model WDM6has beenintroduced because of its flexibility of hydrometer mass and number concentration predictionand an introduction of CCN activation firstly. A size-segregated multi-component aerosolactivation scheme ABG has also been introduced for real time CCN activation fromCUACE/Aero into WMD6secondly. The ABG scheme has been evaluated and approved byCCN activation spectra data and aerosol mass spectra data observed in Tai Mountain inChina.Since the stratiform precipitation from WDM6shares less than10%of the totalprecipitation and the convective precipitation shares more than90%, aerosol effect onconvective precipitation should be introduced for their full and comprehensive effect on cloudand precipitation. The aerosols form CUACE/Aero and the activation scheme, ABG, havealso introduced into the Kain-Fritsch convective scheme for real time CCN activation in theupdraft flow then. The general Gamma hydrometers number distribution spectra function hasalso introduced and resolved in the convective scheme. The parameterized precipitationscheme has been improved by adding the CCN into the gamma function and the cutoff thedroplets and drops in convective cloud by25μm for relatively shallow connective flow and50for deep convective flow. Sensitive tests show that the aerosol changed the verticaldistribution of the losing and production rate of the water vapor, hydrometer mass and theheating rate from different hydrometer phase changes. More water conversed into cloud in thePBL near the high aerosol loading areas. Sensitive tests show that the correlation coefficientbetween the modeled and observed precipitation increased from0.22to0.29with thestandard deviation decreasing from3.87to2.76. More than about320mm precipitation whichmade the simulation precipitation amount increased from64%of the observation from thecontrol test to86%of the test with aerosol effects. And the over-estimates of the precipitationless than10mm have been improved too.The development of CUACE/Aero has also contributed to the Asian sand and dust stormforecasting system CUACE/Dust as well as to the establishment of the CMA Haze-fogforecasting system CUACE/Haze-fog, which is now operationally run at the NationalMeteorological Center of CMA.