Abstract
This paper explores some of the mechanisms governing the accumulation of passive tracers over the tropical southern Atlantic Ocean during the northern hemisphere fall season. There has been a pioneering observation regarding ozone maxima over the South Atlantic during austral spring. The understanding of the formation of this maxima has been the prime motivation for this study. Using a global model as a frame of reference, we have carried out three kinds of experiments during the period of the Transport and Atmospheric Chemistry Near the Equator‐Atlantic (TRACE A) project of 1992. The first of these is a simple advection of total ozone (a passive tracer) in time using the Florida State University global spectral model. Integration over the period of roughly 1 week showed that the model quite closely replicates the behavior of the observed total ozone from the total ozone mapping spectrometer (TOMS). This includes many of the changes in the features of total ozone over the tropical and subtropical region of the southern Atlantic Ocean. These studies suggest a correlation of 0.8 between the observed ozone over this region and ozone modeled from “dynamics alone,” i.e., without recourse to any photochemistry. The second series of experiments invoke sustained sources of a tracer over the biomass burn region of Africa and Brazil. Furthermore, sustained sources were also introduced in the active frontal “descending air” region of the southern hemisphere and over the Asian monsoon's east‐west circulation. These experiments strongly suggest that air motions help to accumulate tracer elements over the tropical southern Atlantic Ocean. A third series of experiments address what may be required to improve the deficiencies of the vertical stratification of ozone predicted by the model over the flight region of the tropical southern Atlantic during TRACE A. Here we use the global model to optimally derive plausible accumulation of burn elements over the fire count regions of Brazil and Africa to provide passive tracer advections to closely match what was observed from reconnaissance aircraft‐based measurements of ozone over the tropical southern Atlantic Ocean.
Highlights
SouthAtlantic duringaustralspring.The understandingof the formation of this maxima hasbeen the prime motivationfor this study.Using a globalmodel as a frame of reference,we havecarriedout three kindsof experimentsduringthe period of the Transportand AtmosphericChemistryNear the Equator--Atlantic (TRACE A) projectof 1992.The first of theseis a simpleadvectionof total ozone(a passivetracer) in time usingthe Florida StateUniversityglobalspectralmodel.Integrationover the period of roughly1 week showedthat the model quite closelyreplicatesthe behaviorof the observedtotal ozonefrom the total ozonemappingspectrometer(TOMS)
We usethe globalmodel to optimallyderiveplausibleaccumulationof burn elementsover the fire countregionsof Brazil and Africa to providepassivetracer advectionsto closely match what was observed from reconnaissance aircraft-based measurements of ozone over the tropical southernAtlantic Ocean
Retrometer(TOMS) for thetotalatmosphericolumnozoneand finementsof the early satellite measurementsof total ozone stratosphericaerosoland gas experiment(SAGE) for the [Fishmanetal., 1990]wereprovidedby Thompsonetal. [1993], stratosphericcomponent.A list of acronymsis provided in who emphasizedthe correctionsfor the oceanicstratocumulus
Summary
We note the largestchanges(i.e., adjustmentin layersbetweenroughly and 1000 mbar; semi-implicittime the weightingfunction) occur between days0 and 1. This differencingscheme;centereddifferencesin the vertical for all simplysuggeststhat for the givenglobal model and the prevariablesexcept humidity,which is handled by an upstream vailing four-dimensionalmotion field an equilibratedweightdifferencingscheme(the humidityvariablesrequire a positive definite advectivescheme);fourth-orderhorizontaldiffusion [Kanamitsuet al., 1983];Kuo-typecumulusparameterization [Krishnamuftei t al., 1983];shallowconvection[Tiedke,1984]; dry convectiveadjustment;large-scalecondensation[Kanamitsu,1975];surfacefluxesvia similaritytheory[Busingeertal., 1971];verticaldistributionof fluxesutilizingdiffusiveformulaing function is realized. Harshvardanand Corsetti,1984];diurnal cycle;parameterization of low,middle,andhighcloudsbasedon thresholdrelative paredto adjacentstratocumulus-covereodcean.Our estimates of TOMS have not been corrected It would have been desirhumidityfor radiativetransfercalculationss;urfaceenergybal- able to make corrections for the albedo and the land bias. Anceiscoupledto the surfacesimilaritytheory[Krishnamuftei t al., 1991];nonlinearnormalmodeinitializationof fivevertical modes[Kitade,1981] These will be includedin future studies.The heavy arrow in Figure 5 denotesa prominentdivergentstreamlineillustrating the teleconnection between the ozone maximum and the Asian.
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