GEOPHYSICALRESEARCH LETTERS, VOL. 19, NO. 2, PAGES151-154, JANUARY 24, 1992 GLOBALTRACKING OF TItE SO2CLOUDS FROM THE JUNE,1991 MOUNT PINATUBO ERUPTIONS GreggJ.S. Bluth UniversitiesSpace Research Association, NASA/Goddard Space Flight Center Scott D. Doiron HughesSTX Corporation, NASA/Goddard Space Flight Center CharlesC. Schnetzler,Arlin J. Krueger, and Louis S. Walter EarthSciences Directorate, NASA/Goddard Space Flight Center •Ab•tract.The explosiveJune 1991 eruptionsof Mount anomalouslyhigh ozone values were noticed over Mexico. Pinatuboproduced the largestsulfur dioxide cloud detected Thesehigh values were caused by sulfurdioxide interference, bythe Total Ozone Mapping Spectrometer (TOMS) during andit thereforebecame necessary to separatethe its13 yearsof operation:approximately 20 milliontons of volcanogenicSO2 signal from the ozone data [Krueger, SO2,predominantly from the cataclysmic June 15th eruption. 1983]. Examinationof absorptioncoefficients for SO2in the TheSO2 cloud observed by the TOMS encircledthe Earthin spectralrange measured by theTOMS led to the about22 days(~21 m/s); however, during the f•t threedays developmentof analgorithm to quantifythe SO2 amounts theleading edge of the SO2cloud moved with a speedthat [Krueger,1985]. Sincethen, all eruptions(including 1978- averaged~35 m/s. Comparedto the 1982E! Chich6n 1982data) with potential for measurableamounts of erupted eruptions,Pinatubo outgassed nearly three times the amount SO2have been routinely examined. of SO2during its explosivephases. The maincloud As a monitor of volcanism,the TOMS insmmaentis best straddledthe equator within the fn'st two weeksof eruption, usedto detectand track SO2 emitted from the explosive whereasthe E! Chich6ncloud remained primarily in the phasesof eruptions.The TOMS observessulfur dioxide northernhemisphere. Our measurementsindicate that Mount primarilyin thestratosphere, and its detectionlimit of a given Pinatubohas produced a muchlarger and perhaps longer- eruptioncloud is about5 kilotons(kt) SO2. Major lastingSO2 cloud; thus, climatic responses to thePinatubo advantagesof theTOMS areits capabilityto detectexplosive eruptionmay exceed those of E1Chich6n. eruptionsvirtually anywhere on the sunlitEarth within 24 hoursand its abilityto measurethe completespatial extent of Introduction large,explosive eruptions. Previous volcanic events examinedusing the TOMS instrumentinclude the 1982 E1 Mount Pinatubois an andesiticisland arc volcano, located Chich6neruptions [Krueger, 1983], Nevado del Ruiz in 1985 onsouthern Luzon Island, Philippines. Wolfe andSelf [Kruegeret al., 1990],the 1989Redoubt activity [C. [!983] brieflydescribe the volcano, and cite the most recent Schnetzler,unpublished manuscript, 199I], andthe 1991 eruptionas occurring approximately 635 yearsearlier (from CerroHudson eruptions [Doiron et al., !991]. carbon-14dating of mudflowdeposits), but noted that Pinatubohad never been studied in greatdetail and that there Satellite Data mayhave been more recent, undocumented eruptions. In June1991 the volcano erupted in a seriesof minor The TOMS instrumentdaily observationsof the Mount explosionsleading up to a cataclysmiceruption June 14-15 Pinatuboeruptions are summarizedin Table 1 andin Figure [Lynchet al., 1991]. A largeamount of solidand gaseous la-d. Total columnamounts of SO2 are givenin unitsof materialwas ejected from the volcano, and a significant milli arm-cm.This unit represents the amountof gaswhich proportionof theash was deposited in theSouth China sea. is affectingthe reflection of ultravioletlight througha Thecombined tephra and pyroclastics were estimated at 3-5 scanningcolumn (from the satelliteto the Earth'sreflecting kin3dense rock equivalent [Scott et al., !991]. surface),given in termsof the one dimensionalthickness of The TOMS instrument on board the Nimbus-7 satellite has the puregas layer at STP. The massof SO2is calculatedby providedglobal SO2 and ozone data since 1978 by measuring integratingover the cloudarea to obtaina volume,then theultraviolet albedo, the ratio of backscatteredEarth convertingto tons. Typicalvolcanic SO2 clouds detected by radianceto incomingsolar irradiance. The satellite is in a the TOMS rangefrom 20 to severalhundred milli am-cm. polarsun-synchronous orbit and crosses the equator every 26 The error estimationfor the TOMS SO2 valueshas been degrees(2900 kin) of longitude atlocal noon, observing the describedby Kruegeret al. [!990]. The totalerror in wholeearth once a day(13.7 orbits/day). The TOMS was reportedvalues, :t: 30%, is basedon uncertaintiesin the designedwith the intention of globallymapping total ozone algorithmcalculation, absorption level measurements,and only,but after the eruption of E! Chich6nin April 1982 backgroundnoise. EruptionCloud Chronology Copyright1992 by theAmerican Geophysical Union. Papernumber 91GL02792 The initial sulfurdioxide detected by the TOMS 0094-8534/92/91GL-0279.2503.00 instrumentfrom Mount Pinatubooccurred as three small SO2 151 152 Bluthet al.: TrackingSO2 Clouds from Mt. Pinatubo Table1. Summaryof TOMSData for. the 1991 Mount Pinatubo Eruption Clouds 'Image ArealExtent Measured Height Geographic Comments Date (km2) SO2(kt)* Position June 12 100 25 trop Westcoast of LuzonIsland Cloudobserved for 3 days;on June 13 measured 110 kt June 13 100 15 trop Westcoast of LuzonIsland New cloudobserved for 1 day June 14 -no new activitydetected- June 15 7500 450 trop/strat SouthChina Sea, from 10 to 15øN New, 1600km longcloud over the volcano;observed 1 day June16 3.2 x 106 15,500 strat Centered over South China Sea at New discretecloud from major minimum -15øN eruption,200 km eastof volcano June17 4.8 x 106 18,500 strat Lead cloudover tip of India; main Main cloud2000 km from origin; cloud over south Thailand at 10øN overall lengthof clouds4400 km June18 7.5 x 106 16,000 strat From Malaysia to Gulf of Aden at Main cloud3000 km from origin; -10øN latitude total cloudis 7000 km in length June19 7.4 x 106 14,000 strat Lead cloud over Sudan; main cloud Main cloud4300 km from origin; minimum over northeast Indian Ocean leadinglobe breaking apart June20 8.6 x 106 14,500 strat Lead clouds over E. Africa; main Main cloud4500 km from origin, cloudover equatorialIndian Ocean 6000 km in length June23 15.4 x 106 14,000 strat Lead cloud over Mali; main cloud Main cloud10,000 km long,main from Sumatra to central Africa SO2 massno longerdiscernable June30 54.5 x 106 12,000 strat From Indonesia to west Pacific Main cloudover 16,000km long; Ocean, 10øSto 20øN even, low level SO2 distribution * SO2calculated from near real-time TOMS '"data; actual value• Cohld'"be "larger as discussed in the text. On June 16 and June19 theTOMS instrumentexperienced problems in the areaof theSO2 cloud, where no datawere reported. cloudserupted from June 11-14. The first cloud was detected the SO2cloud was over the Gulf of Aden, correspondingto on June12th (i.e., includingany eruptionactivity from noon an 3-day averagespeed of 35 m/s. The cloud'smovement June11 to noonJune 12). This cloudmeasured 100 km 2 in wasprimarily westward, with somespreading slightly to the area,and contained -25 kt SO2. By June13th the cloudhad southtowards the equator.The SO2 estimatefor the 18th drifted 1100 km to the west, over central Vietnam, and now was 16,000 kt. measured110 kt SO2. By June 14th,the cloudcould be The June23rd imagemarked a changein thephysical barelydiscerned over the easternIndian Ocean at about configurationof theSO2 cloud (Figure lc). The cloudno 15øN, and was not seen thereafter. A secondcloud of 100 longerconsisted of a mainconcentrated mass and a leading km2area and less than 15 kt SO2was detected June 13th lobe or leadingcloud. It now extended10,000 km from over the westernedge of Luzon island,but was only observed Indonesiato centralAfrica in a fairly uniformdistribution of for one day. A third cloud was detectedon June 15th, SO2,covering an areaof about15 millionsquare kilometers. measuring7500 km 2 in areaand stretching 1600 km The leadingcloud which had sheared away from the main westward from Mount Pinatubo to southern Vietnam. T•,e cloudwas largely dispersed below the TOMS detectionlimit, SO2cloud was composed of at leastthree distinct leavingonly a tracevisible over westernAfrica. The cloud concentrationsprobably corresponding to individualeruption crossedthe equatorto asfar as 10øSlatitude. The trailing pulsesoccurring June 14th. This cloudtotaled approximately endof the cloudremained nearly fixed over Sumatra.The 450 kt SO2,but on subsequentdays it hadeither dispersed relativelylower cloudSO2/background ratios by this time belowdetection levels or was maskedby themajor eruption madequantitative measurements more difficult; the estimate cloud. of SO2 tonnagefor the June23 cloudswas -14,000 kt. The cataclysmiceruption of June15th began before noon Figure 1d showsthe SO2 cloudon June30th, two weeks andlasted until the followingmorning [Lynch et al., 1991]. after the main eruption.The cloudis spreadover 16,000km The timingof the eruptionwas suchthat it was not detected in length,straddling the equator, reaching from 10øSto 20øN. by theTOMS until the 16th. Figure la showsthat in The cloudarea extends over 50 million squarekilometers. approximately24 hoursthe centerof the SO2cloud had The leadingedges of the visiblecloud have reached the drifted 1000 km to the WSW as a discrete mass. The longitudeof California,and the trailingedge (out of the measuredamount of SO2 in this cloud is 15,500 kt but, picture)remains mired over Indonesia.This cloud measured becauseof