Michigan Technological University Digital Commons @ Michigan Tech Department of Geological and Mining Department of Geological and Mining Engineering and Sciences Publications Engineering and Sciences 7-1-1997 Detection of volcanic ash clouds from Nimbus 7/total ozone mapping spectrometer C. J. Seftor Hughes STX Corporation N. C. Hsu Hughes STX Corporation J. R. Herman NASA Goddard Space Flight Center P. K. Bhartia NASA Goddard Space Flight Center O. Torres Hughes STX Corporation See next page for additional authors Follow this and additional works at: https://digitalcommons.mtu.edu/geo-fp Part of the Geology Commons, Mining Engineering Commons, and the Other Engineering Commons Recommended Citation Seftor, C. J., Hsu, N. C., Herman, J. R., Bhartia, P. K., Torres, O., Rose, W. I., Schneider, D. J., & Krotkov, N. (1997). Detection of volcanic ash clouds from Nimbus 7/total ozone mapping spectrometer. Journal of Geophysical Research, 102(D14), 16749-16579. http://dx.doi.org/10.1029/97JD00925 Retrieved from: https://digitalcommons.mtu.edu/geo-fp/79 Follow this and additional works at: https://digitalcommons.mtu.edu/geo-fp Part of the Geology Commons, Mining Engineering Commons, and the Other Engineering Commons Authors C. J. Seftor, N. C. Hsu, J. R. Herman, P. K. Bhartia, O. Torres, William I. Rose, David J. Schneider, and N. Krotkov This article is available at Digital Commons @ Michigan Tech: https://digitalcommons.mtu.edu/geo-fp/79 JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 102, NO. D14, PAGES 16,749-16,759, JULY 27, 1997 Detection of volcanic ash clouds from Nimbus 7/total ozone mapping spectrometer C. J. Seftor, • N. C. Hsu, • J. R. Herman, 2 P. K. Bhartia, 2 O. Torres, • W. I. Rose,3 D. J. Schneider,3 and N. Krotko½ Abstract. Measured radiancesfrom the Version 7 reprocessingof the Nimbus 7/total ozonemapping spectrometer (TOMS) 340- and 380-nm channelsare usedto detect absorbingparticulates injected into the atmosphereafter the E1 Chichoneruption on April 4, 1982. It is shownthat while the single-channelreflectivity determined from the 380-nm channelis able to detect cloudsand haze composedof nonabsorbingaerosols, the spectral contrastbetween the 340- and 380-nm channelsis sensitiveto absorbingparticulates such as volcanicash, desert dust, or smokefrom biomassburning. In this paper the spectral contrastbetween these two channelsis used to detect the volcanicash injection into the atmosphereand to track its evolution for severaldays. The movement of the ash cloudsis shownto be consistentwith the motionsexpected from the National Centers for EnvironmentalPrediction (NCEP)-derived balancedwind fields in the troposphereand lower stratosphere.The movementof the volcanic SO2 cloud detectedfrom TOMS data was also in agreementwith the NCEP wind at higher altitudesof up to 100-10 mbar. The verticalwind shearin the neighborhoodof the eruption site resultedin a clear separation of the ash and SO2 clouds.The location and movement of the ash cloud are consistent with informationobtained by the advancedvery high resolutionradiometer (AVHRR) instrumenton board the NOAA 7 satellite and to ground reports of ash fall. 1. Introduction On the basisof radiative transfer calculationsin a Rayleigh scatteringatmosphere, the presenceof aerosolschanges the Atmosphericradiance information from the Version 7 Nim- spectraldependence in the radiances.Depending on the char- bus 7 and Meteor 3 total ozone mapping spectrometer acteristicsof the aerosols,they can be either absorbingor (TOMS) data setshas been usedto generatea 16-yearrecord nonabsorbingin the UV spectral region [DMtmeida, 1987; of ozonechanges. Of the sixwavelength channels available on Patterson,1981; Pattersonet at., 1983; Pattersonand McMahon, these instruments, the three that are insensitive to the amount 1984]. The spectraldependence is most pronouncedfor UV- of ozonein the atmosphere(340, 360, and 380 rim) canbe used absorbingaerosols, which cause R x to increase with wave- to determine the effectivereflectivity of the lower boundary, length. While the ozone retrieval algorithm is designedto R x. R x can be determined by comparing the measured up- minimize the spectraldependence from clouds,other typesof wellingradiance to the atmosphericbackscattering from a pure nonabsorbingaerosols, under certain conditions,can causeR x Rayleighatmosphere over a Lambertian surface.If cloudsare to decreasewith wavelength. TOMS data can therefore be present, two different Lambertian surfacesare assumed,one usedto clearlydistinguish between absorbing particulates (e.g., representingthe ground and one representingclouds. The smokefrom biomassburning, desert dust, and volcanicash) calculatedreflectivity using the 380-rim channel radiance is a and nonabsorbingparticulates (e.g., water clouds,haze, and measureof the presenceof clouds,haze, or a reflectiveground volcanicH2SO 4 aerosols). surface such as snow or ice. The recalibration of Nimbus In practice, the spectral contrast is measured and tracked 7/TOMS in the Version 7 data set permits the wavelength through a quantity known as the aerosol index: dependenceof the effectivereflectivities to be calculatedwith an accuracyof about 0.1% and the absolutereflectivities to be calculatedto better than 1%. Details of the algorithmused to A= -100log10 I3807 ....q- 100 log10 I38ø/] calc' generatethe Version 7 data setsare given by McPeterset at. where (I34o/I38o).... is the measuredspectral contrast be- [1996]. Details of the Version 7 calibration of the Nimbus-7 tweenthe 340- and 380-nmradiances and (1340/1380)calcis the TOMS instrumentare givenby Wettemeyeret at. [1996] and of spectralcontrast between the 340- and 380-nm radiancescal- the Meteor 3 TOMS instrument are given by Seftor et at. culatedusing a Rayleigh scatteringatmosphere and reflectivity [1997]. determined from the 380-nm channel. Since the effective reflectivity is determined by requiring 1HughesSTX Corporation,Greenbelt, Maryland. 2NASAGoddard Space Flight Center, Greenbelt, Maryland. (138o).... : (138o)calc, 3Departmentof GeologicalEngineering and Sciences,Michigan A = - 100 log10[ (I340).... /(I340)calc]' (2) TechnologicalUniversity, Houghton. Copyright1997 by the American GeophysicalUnion. Without additional information about the absorbingparticu- Paper number 97JD00925. latesobserved in the TOMS data (e.g.,the refractiveindex and 0148-0227/97/97 JD-00925 $09.00 particle size distribution),the aerosol index can be used to 16,749 16,750 SEFTOR ET AL.: DETECTION OF VOLCANIC ASH CLOUDS FROM TOMS determinetheir locationand the relative amountof particulate a scanninginstrument, and the size of the footprint and cor- matter [Hermanet al., 1997]. respondingsize of the rectangleincrease with the scanangle. This paper is one of a seriesof papers reporting on the Figures la-ld show the derived SO2 cloud for four days, ability of TOMS instrumentsto detect troposphericaerosols. April 4, 5, 6, and 8 (data were missingon April 7) as TOMS Previouspapers have describedusing TOMS data to detect passedoverhead at localnoon (1800 UT). Figurela showsthat biomassburning [Hsu et al., 1996] and map the global distri- the initial SO2 cloud coveredan area extendingeast past the bution of UV-absorbingaerosols [Herman et al., 1997].Subse- Yucatan Peninsula and west to the Atlantic Ocean. Winds quent paperswill detail the theoreticalradiative transfer as- derived from NCEP data indicate predominantly westerly pectsof detectingtropospheric and volcanic aerosols at TOMS winds in the troposphereand easterlywinds in the strato- wavelengths. sphere.The zonal spreadingof the cloudindicates shearing of In this paper the detectionof volcanicash is demonstrated thevertical column of SO2 by these winds. On April 5 and6 the by looking at the April 4, 1982, eruptionsof E1 Chichon.The displacementof the SO2cloud was mainly toward the westand developmentof the ash cloud is mappedand its motion is northwest,following the winds at roughly 10-30 mbar. These followed. Since the TOMS wavelengthchannels can also be motionsare comparableto those seen in other observations usedto derive the total column amount and geographicaldis- [Barthet al., 1983]and in previousversions of the TOMS data tribution of SO2 in the atmosphere[Krueger et al., 1995],com- [Krueger,1983]. Krueger alsoindicated that the amountof SO2 parisonsare madebetween the motion of the ashcloud and the releasedinto the atmospherereached values higher than 700 SO2cloud. The ashcloud motions are confirmedfrom infrared DU; the upper limit of 200 placed on the SO1 precludesa satelliteobservations obtained by the NOAA 7 advancedvery comparisonwith values obtained from the Version 7 algo- rithm. high resolutionradiometer (AVHRR). Finally, in order to demonstratethe abilityto determineoptical depths from such data, a samplecalculation is performedfor April 6, 1982,from 3. The Ash Cloud a radiative transfermodel usingaerosol parameters consistent with volcanic ash. Ash from the eruption of E1 Chichonwas seen to circum- navigatethe globe [Robockand Matson, 1983] and was ob- servedto spreadvertically between 15 and 35 km over Mauna 2. The El Chichon Eruption and Resulting Loa [De Luisi, 1982].TOMS was able to track the formation SO2 Cloud and dispersionof the ash for the first few days after each Two of the E1 Chichoneruptions occurred on April 4, 1982, eruption.The distributionof the TOMS detectedash cloud at 0135 and 1122 UT, respectively[Sigurdsson et al., 1984]. afterthe April 4 eruptions,as represented by positivevalues of the aerosolindex, is shownin Figures 2a-2d. In these figures,