Terry Deshler - Academia.edu (original) (raw)
Papers by Terry Deshler
Journal of Geophysical Research: Atmospheres, 1996
Validation studies of multiwavelength Cryogenic Limb Array Etalon Spectrometer (CLAES) observatio... more Validation studies of multiwavelength Cryogenic Limb Array Etalon Spectrometer (CLAES) observations of stratospheric aerosol are discussed. An error analysis of the CLAES aerosol extinction data is presented. Aerosol extinction precision values are estimated at latitudes and times at which consecutive Upper Atmosphere Research Satellite (UARS) orbits overlap. Comparisons of CLAES aerosol data with theoretical Mie calculations, based upon in situ particle size measurements at Laramie, Wyoming, are presented. CLAES aerosol data are also compared to scaled aerosol extinction measured by the Stratospheric Aerosol and Gas Experiment (SAGE II) and Atmospheric Trace Molecule Spectroscopy (ATMOS) experiments. Observed and calculated extinction spectra, from CLAES, Improved Stratospheric and Mesospheric Sounder (ISPuMS), and Halogen Occultation Experiment (HALOE) data, are compared. CLAES extinction data have precisions between 10 and 25%, instnanental biases near 30%, and accuracies between 33 and 43 %. 1. Introduction While this paper focuses upon CLAES data, several other instruments on UARS also measure stratospheric aerosol, and one This paper discusses validation studies using the first public instrument measures gaseous SO 2. Validation studies, similar to release (version 7) aerosol measurements from the Cryogenic that of CLAES, are discussed in several papers in this special Limb Array EtaIon Spectrometer (CLAES) experiment of the Journal of Geophysical Research UARS validation issue. Upper Atmosphere Research Satellite (UARS). Validation studies Discussions of UARS data, in general, are given elsewhere. of CLAES aerosol data are of interest for several reasons. It is important to understand the quantitative contribution of aerosols to the radiance profiles observed by CLAES. Mount Pinatubo erupted in June 1991, 3 months before the launch of UARS in September 1991, and as discussed below, stratospheric aerosol made an important contribution to the observed radiance profiles, at altitudes below 30 kin. It is also important to know the precision and accuracy of the CLAES aerosol data before it is used in quantitative studies. Theoretical studies which use global distributions of aerosol to test dynamical models of stratospheric circulation and theoretical studies which address issues of heterogeneous chemistry at midlatitudes and in the polar regions require estimates of precision and accuracy of the aerosol data before a meaningful comparison between theory and observation can be made.
Journal of Geophysical Research: Atmospheres, 1997
A global climatology of stratospheric aerosol surface area density has been developed using the m... more A global climatology of stratospheric aerosol surface area density has been developed using the multiwavelength aerosol extinction measurements of the Stratospheric Aerosol and Gas Experiment (SAGE) II for 1984-1994. The spatial and temporal variability of aerosol surface area density at 15.5, 20.5, and 25.5 km are presented as well as cumulative statistical distributions as a function of altitude and latitude. During this period, which encompassed the injection and dissipation of the aerosol associated with the June 1991 Mount Pinatubo eruption as well as the low loading period of 1989-1991, aerosol surface area density varied by more than a factor 30 at some altitudes. Aerosol surface area density derived from SAGE II and from the University of Wyoming optical particle counters are compared for 1991-1994 and are shown to be in generally good agreement though some differences are noted. An extension of the climatology using single-wavelength measurements by the Stratospheric Aerosol Measurement II (1978-1994) and SAGE (1979-1981) instruments is also presented. THOMASON ET AL.-GLOBAL CLIMATOLOGY OF STRATOSPHERIC AEROSOL ET AL.: GLOBAL CLIMATOLOGY OF STRATOSPHERIC AEROSOL ET AL.: GLOBAL CLIMATOLOGY OF STRATOSPHERIC AEROSOL Mount Pinatubo eruption. Cumulative median, 10-percentile, and 1-percentile distributions for the 1984-1994 period were presented as a function of altitude and latitude that can be used to parameterize aerosol-driven heterogeneous processes in global photochemical models. An empirical method was also presented for extending the climatology using aerosol extinction measurements at 1.0 •m by the Stratospheric Aerosol Measurement (SAM) II (1978-1994) and SAGE (1979-1981) instruments.
Large Volcanic Aerosol Load in the Stratosphere Linked to Asian Monsoon Transport
Science, 2012
The Nabro stratovolcano in Eritrea, northeastern Africa, erupted on 13 June 2011, injecting appro... more The Nabro stratovolcano in Eritrea, northeastern Africa, erupted on 13 June 2011, injecting approximately 1.3 teragrams of sulfur dioxide (SO(2)) to altitudes of 9 to 14 kilometers in the upper troposphere, which resulted in a large aerosol enhancement in the stratosphere. The SO(2) was lofted into the lower stratosphere by deep convection and the circulation associated with the Asian summer monsoon while gradually converting to sulfate aerosol. This demonstrates that to affect climate, volcanic eruptions need not be strong enough to inject sulfur directly to the stratosphere.
Response to Comments on "Large Volcanic Aerosol Load in the Stratosphere Linked to Asian Monsoon Transport
Science, 2013
Fromm et al. and Vernier et al. suggest that their analyses of satellite measurements indicate th... more Fromm et al. and Vernier et al. suggest that their analyses of satellite measurements indicate that the main part of the Nabro volcanic plume from the eruption on 13 June 2011 was directly injected into the stratosphere. We address these analyses and, in addition, show that both wind trajectories and height-resolved profiles of sulfur dioxide indicate that although the eruption column may have extended higher than the Smithsonian report we highlighted, it was overwhelmingly tropospheric. Additionally, the height-resolved sulfur dioxide profiles provide further convincing evidence for convective transport of volcanic gas to the stratosphere from deep convection associated with the Asian monsoon.
Journal of the Atmospheric Sciences, 1997
The Raman lidar technique has been applied to document the evolution and dissipation of the Pinat... more The Raman lidar technique has been applied to document the evolution and dissipation of the Pinatubo aerosol between 1991 and 1995. For the first time, profiles of the particle extinction coefficient have been determined with lidar in the stratosphere after a major volcanic eruption. From the concurrent observation of particle backscatter and extinction, time series of surface-area and mass concentrations and surface-area-weighted mean (or effective) radius can be determined without having to assume critical aerosol input parameters. Based on these optical and physical parameters, the development of the perturbation of the stratospheric aerosol layer over central Europe is discussed. In terms of particle backscatter and mass the perturbation declined with an efolding decay time of 14-15 months between April 1992 and April 1994. The monthly mean particle optical depth reached 0.23 in the spring of 1992. Surface-area concentrations of the order of 10-40 mm 2 m Ϫ3 were observed below 20-km height for about 18 months. The effective radius increased from 0.1 to 0.2 m in August and September 1991 to values around 0.5 m in December 1991 and slowly decreased since then. The findings are compared with results of other lidar measurements in the Northern Hemisphere; balloon soundings at Laramie, Wyoming; high-altitude aircraft in situ and satellite observations (SAGE, AVHRR); and model calculations. A sedimentation model is used to analyze the mass removal from the stratosphere and the importance of different cleansing mechanisms. The comparison of the measured and simulated mass concentration profiles clearly indicate the strong impact of stratospheric-tropospheric exchange processes on the purging of aerosols from the stratosphere below 16 km.
Journal of Geophysical Research: Atmospheres, 1996
Validation studies of multiwavelength Cryogenic Limb Array Etalon Spectrometer (CLAES) observatio... more Validation studies of multiwavelength Cryogenic Limb Array Etalon Spectrometer (CLAES) observations of stratospheric aerosol are discussed. An error analysis of the CLAES aerosol extinction data is presented. Aerosol extinction precision values are estimated at latitudes and times at which consecutive Upper Atmosphere Research Satellite (UARS) orbits overlap. Comparisons of CLAES aerosol data with theoretical Mie calculations, based upon in situ particle size measurements at Laramie, Wyoming, are presented. CLAES aerosol data are also compared to scaled aerosol extinction measured by the Stratospheric Aerosol and Gas Experiment (SAGE II) and Atmospheric Trace Molecule Spectroscopy (ATMOS) experiments. Observed and calculated extinction spectra, from CLAES, Improved Stratospheric and Mesospheric Sounder (ISPuMS), and Halogen Occultation Experiment (HALOE) data, are compared. CLAES extinction data have precisions between 10 and 25%, instnanental biases near 30%, and accuracies between 33 and 43 %.
Journal of Geophysical Research, 1995
In 1994 an intensive program of balloon-borne frost point measurements was performed at McMurdo, ... more In 1994 an intensive program of balloon-borne frost point measurements was performed at McMurdo, Antarctica. During this program a total of 19 frost point soundings was obtained between February 7 and October 5, which cover a wide range of undisturbed through strongly dehydrated situations. Together with several soundings from South Pole station between 1990 and 1994, they give a comprehensive picture of the general development of the dehydration in the Antarctic stratospheric vortex. The period of dehydration typically starts around the middle of June, and a rapid formation of large particles leads to a fast dehydration of the vortex. The evaporation of falling particles leads to rehydration layers, which have significantly higher water vapor concentrations than the undisturbed stratosphere. Through the formation of these rehydration layers in the early stages of the dehydration we can estimate a particle fall speed of 1/3 km/d and thus a mean particle size of 4 gin. Ice saturation was observed over McMurdo in only two cases and only well after the onset of the dehydration. From the inspection of synoptic maps it then follows that a small cold region inside the vortex seems to be sufficient to dehydrate the entire vortex. Above 20 km the dehydration is completed by the end of July. From the descent of the upper dehydration edge we can estimate a mean descent rate in,side the vortex of 1.5 kin/month. In McMurdo we observed occasional penetration of the vortex edge in cases where the vortex edge was close to McMurdo, however, these cases seem to have little effect on the bulk of the vortex. A sounding from November 3, 1990, at South Pole shows that the dehydration may persist into November and indicates that there is no si•tmificant transport into the vortex throughout winter and early spring. 13,922 VOMEL ET AL.: DEI-1YDRA•ON OF THE ANTARCTIC STRATOSPHERIC VORTEX 3O ..
Journal of Geophysical Research, 2003
Vertical profiles of size-resolved aerosol concentrations above Laramie, Wyoming (41°N), have bee... more Vertical profiles of size-resolved aerosol concentrations above Laramie, Wyoming (41°N), have been measured for the past thirty years, 1971-2001. During this period, two somewhat different optical particle counters have been used to measure particles with radii !0.15 mm, whereas the instrument to measure condensation nuclei (CN) has not changed significantly since the late 1970s. The two optical particle counters measure aerosols !0.15, 0.25 mm and aerosols !0.15-2.0 mm in twelve size classes. These measurements have concentration (N) uncertainties / ±N À0.5 , but with a minimum of ±10%. Sizing uncertainties are about ±10%. The impact of these uncertainties on size distribution fitting parameters and aerosol moments are approximately ±30% and ±40%. The long-term record from these measurements indicates that volcanoes have controlled stratospheric aerosol abundance for 20 of the past 30 years. The present period, beginning in 1997, represents the longest volcanically quiescent period in the record. These and other measurements clearly show that stratospheric aerosol are now in a background state, a state rarely occurring in recent times, and that this background state is not significantly different than observations in 1979. Aerosol volumes and surface areas, inferred from size distributions fit to the measurements, are compared with SAGE II satellite estimates of surface area and volume. For volume the measurements are in agreement within measurement error throughout the record. For surface area there is good agreement for a volcanic aerosol laden stratosphere, but for background aerosol conditions the SAGE II estimates are about 40% less than the in situ measurements. Present aerosol surface areas are $1.0 (0.6) mm 2 cm À3 in the 15-20 (20-25) km layer based on in situ measurements. The Laramie size distribution record is now available to the community over the internet.
Journal of Geophysical Research, 1996
NO mixing ratios measured from Kiruna (68øN, 20øE), Sweden, on January 22, 1992, revealed values ... more NO mixing ratios measured from Kiruna (68øN, 20øE), Sweden, on January 22, 1992, revealed values much smaller than those observed at midlatitude near equinox and had a sharper vertical gradient around 25 km. Location of the measurements was close to the terminator and near the edge of the polar vortex, which is highly distorted from concentric flow by strong planetary wave activities. These conditions necessitate accurate calculation, properly taking into account the transport and photochemical processes, in order to quantitatively explain the observed NO profile. A three-dimensional chemistry and transport model (CTM) and a trajectory model (TM) were used to interpret the profile observations within their larger spatial, temporal, and chemical context. The NOy profile calculated by the CTM is in good agreement with that observed on January 31, 1992. In addition, model NOy profiles show small variabilities depending on latitudes, and they change little between January 22 and 31. The TM uses the observed NOy values. The NO values calculated by the CTM and TM agree with observations up to 27 km. Between 20 and 27 km the NO values calculated by the trajectory model including only gas phase chemistry are much larger than those including heterogeneous chemistry, indicating that NO mixing ratios were reduced significantly by heterogeneous chemistry on sulfuric acid aerosols. Very little sunlight to generate NOx from HNO3 was available, also causing the very low NO values. The good agreement between the observed and modeled NO profiles indicates that models can reproduce the photochemical and transport processes in the region where NO values have a sharp horizontal gradient. Moreover, CTM and TM model results show that even when the NOy gradients are weak, the model NO depends upon accurate calculation of the transport and insolation for several days. 1. Toyokawa, Japan.
Geophysical Research Letters, 1990
Balloonborne aerosol measurements over the size range r=0.01 to 10 mum on 31 January 1990 are use... more Balloonborne aerosol measurements over the size range r=0.01 to 10 mum on 31 January 1990 are used to determine the HNO3 vapor mass deposited in Arctic nitric acid trihydrate (NAY) clouds in the 21-24 km region. The clouds consisted mainly of small (r~0.2 mum) particles and appeared to have been formed during recent cooling because the r>=0.15 mum aerosol concentration
Balloonborne measurements of polar stratospheric clouds and ozone at-93° C in the Arctic in February 1990
Geophysical Research Letters, 1990
Balloonborne measurements of ozone and particle size distributions at Kiruna, Sweden indicate tha... more Balloonborne measurements of ozone and particle size distributions at Kiruna, Sweden indicate that on 6 February 1990 a major cooling event occurred over northern Scandinavia, reaching temperatures as low as −93° C at 22 km. Both nitric acid trihydrate and water ice clouds formed in the 19 to 23 km region. The temperature of the appearance of the water ice clouds is consistent with about 5 ppmv of water vapor at 22 km, The particle size distributions suggest that a sizeable degree of denitrification had occurred in the 19 to 23 km region in this air mass. Although ozone levels may have been reduced by a small degree of chemical depletion, the ozone “minihole” of 165 DU observed by TOMS was probably an artifact caused by ice clouds at 22 km since two ozonesonde measurements on that day indicated total ozone values of about 285 DU.
Geophysical Research Letters, 1999
Ozone (03) measurements made with the Improved Limb Atmospheric Spectrometer (ILAS) onboard the A... more Ozone (03) measurements made with the Improved Limb Atmospheric Spectrometer (ILAS) onboard the Advanced Earth Observing Satellite (ADEOS) were validated with correlative ozonesonde measurements conducted at five stations, Andoya, Kiruna and Yakutsk in the Northern Hemisphere, and Neumayer and Syowa in the Southern Hemisphere. The ILAS Version 3.10 03 vertical profiles were compared with 79 correlative ozonesonde measurements that were made within 500 km and 3 hours in distance and time differences, respectively. The comparisons indicate that ILAS 03 typically has an accuracy within 20% between 12 and 35 km. The precision of the ILAS 03 is estimated to be +10-25% between 12 and 20 km, +5-7% between 20 and 30 km, and +5% between 30 and 40 km. regions, where there are large 03 depletions in early spring [e.g., Newman et al., 1997]. Since ADEOS was put into a sun-synchronized polar orbit, the ILAS orbital characteristics are more suitable to study ozone-related chemistry in high southern latitudes (64-88øS) and sub-polar northern latitudes (57-73øN) than are HALOE or the Stratospheric Aerosol and Gas Experiment (SAGE) II. This paper focuses on the assessment of the quality of the ILAS-retrieved Version 3.10 (V3.10) 03 mixing ratios through comparison with correlative ozonesonde measurements made at four sounding stations both in the Northern and Southern Hemispheres. A summary of comparison results and anticipated future improvements by new data processing algorithm will be given. HALOE to focus on studies of the 03 layer in high-latitude 1National Institute for Environmental Studies, Tsukuba,
Journal of Geophysical Research: Atmospheres, 1996
Validation studies of multiwavelength Cryogenic Limb Array Etalon Spectrometer (CLAES) observatio... more Validation studies of multiwavelength Cryogenic Limb Array Etalon Spectrometer (CLAES) observations of stratospheric aerosol are discussed. An error analysis of the CLAES aerosol extinction data is presented. Aerosol extinction precision values are estimated at latitudes and times at which consecutive Upper Atmosphere Research Satellite (UARS) orbits overlap. Comparisons of CLAES aerosol data with theoretical Mie calculations, based upon in situ particle size measurements at Laramie, Wyoming, are presented. CLAES aerosol data are also compared to scaled aerosol extinction measured by the Stratospheric Aerosol and Gas Experiment (SAGE II) and Atmospheric Trace Molecule Spectroscopy (ATMOS) experiments. Observed and calculated extinction spectra, from CLAES, Improved Stratospheric and Mesospheric Sounder (ISPuMS), and Halogen Occultation Experiment (HALOE) data, are compared. CLAES extinction data have precisions between 10 and 25%, instnanental biases near 30%, and accuracies between 33 and 43 %. 1. Introduction While this paper focuses upon CLAES data, several other instruments on UARS also measure stratospheric aerosol, and one This paper discusses validation studies using the first public instrument measures gaseous SO 2. Validation studies, similar to release (version 7) aerosol measurements from the Cryogenic that of CLAES, are discussed in several papers in this special Limb Array EtaIon Spectrometer (CLAES) experiment of the Journal of Geophysical Research UARS validation issue. Upper Atmosphere Research Satellite (UARS). Validation studies Discussions of UARS data, in general, are given elsewhere. of CLAES aerosol data are of interest for several reasons. It is important to understand the quantitative contribution of aerosols to the radiance profiles observed by CLAES. Mount Pinatubo erupted in June 1991, 3 months before the launch of UARS in September 1991, and as discussed below, stratospheric aerosol made an important contribution to the observed radiance profiles, at altitudes below 30 kin. It is also important to know the precision and accuracy of the CLAES aerosol data before it is used in quantitative studies. Theoretical studies which use global distributions of aerosol to test dynamical models of stratospheric circulation and theoretical studies which address issues of heterogeneous chemistry at midlatitudes and in the polar regions require estimates of precision and accuracy of the aerosol data before a meaningful comparison between theory and observation can be made.
Journal of Geophysical Research: Atmospheres, 1997
A global climatology of stratospheric aerosol surface area density has been developed using the m... more A global climatology of stratospheric aerosol surface area density has been developed using the multiwavelength aerosol extinction measurements of the Stratospheric Aerosol and Gas Experiment (SAGE) II for 1984-1994. The spatial and temporal variability of aerosol surface area density at 15.5, 20.5, and 25.5 km are presented as well as cumulative statistical distributions as a function of altitude and latitude. During this period, which encompassed the injection and dissipation of the aerosol associated with the June 1991 Mount Pinatubo eruption as well as the low loading period of 1989-1991, aerosol surface area density varied by more than a factor 30 at some altitudes. Aerosol surface area density derived from SAGE II and from the University of Wyoming optical particle counters are compared for 1991-1994 and are shown to be in generally good agreement though some differences are noted. An extension of the climatology using single-wavelength measurements by the Stratospheric Aerosol Measurement II (1978-1994) and SAGE (1979-1981) instruments is also presented. THOMASON ET AL.-GLOBAL CLIMATOLOGY OF STRATOSPHERIC AEROSOL ET AL.: GLOBAL CLIMATOLOGY OF STRATOSPHERIC AEROSOL ET AL.: GLOBAL CLIMATOLOGY OF STRATOSPHERIC AEROSOL Mount Pinatubo eruption. Cumulative median, 10-percentile, and 1-percentile distributions for the 1984-1994 period were presented as a function of altitude and latitude that can be used to parameterize aerosol-driven heterogeneous processes in global photochemical models. An empirical method was also presented for extending the climatology using aerosol extinction measurements at 1.0 •m by the Stratospheric Aerosol Measurement (SAM) II (1978-1994) and SAGE (1979-1981) instruments.
Large Volcanic Aerosol Load in the Stratosphere Linked to Asian Monsoon Transport
Science, 2012
The Nabro stratovolcano in Eritrea, northeastern Africa, erupted on 13 June 2011, injecting appro... more The Nabro stratovolcano in Eritrea, northeastern Africa, erupted on 13 June 2011, injecting approximately 1.3 teragrams of sulfur dioxide (SO(2)) to altitudes of 9 to 14 kilometers in the upper troposphere, which resulted in a large aerosol enhancement in the stratosphere. The SO(2) was lofted into the lower stratosphere by deep convection and the circulation associated with the Asian summer monsoon while gradually converting to sulfate aerosol. This demonstrates that to affect climate, volcanic eruptions need not be strong enough to inject sulfur directly to the stratosphere.
Response to Comments on "Large Volcanic Aerosol Load in the Stratosphere Linked to Asian Monsoon Transport
Science, 2013
Fromm et al. and Vernier et al. suggest that their analyses of satellite measurements indicate th... more Fromm et al. and Vernier et al. suggest that their analyses of satellite measurements indicate that the main part of the Nabro volcanic plume from the eruption on 13 June 2011 was directly injected into the stratosphere. We address these analyses and, in addition, show that both wind trajectories and height-resolved profiles of sulfur dioxide indicate that although the eruption column may have extended higher than the Smithsonian report we highlighted, it was overwhelmingly tropospheric. Additionally, the height-resolved sulfur dioxide profiles provide further convincing evidence for convective transport of volcanic gas to the stratosphere from deep convection associated with the Asian monsoon.
Journal of the Atmospheric Sciences, 1997
The Raman lidar technique has been applied to document the evolution and dissipation of the Pinat... more The Raman lidar technique has been applied to document the evolution and dissipation of the Pinatubo aerosol between 1991 and 1995. For the first time, profiles of the particle extinction coefficient have been determined with lidar in the stratosphere after a major volcanic eruption. From the concurrent observation of particle backscatter and extinction, time series of surface-area and mass concentrations and surface-area-weighted mean (or effective) radius can be determined without having to assume critical aerosol input parameters. Based on these optical and physical parameters, the development of the perturbation of the stratospheric aerosol layer over central Europe is discussed. In terms of particle backscatter and mass the perturbation declined with an efolding decay time of 14-15 months between April 1992 and April 1994. The monthly mean particle optical depth reached 0.23 in the spring of 1992. Surface-area concentrations of the order of 10-40 mm 2 m Ϫ3 were observed below 20-km height for about 18 months. The effective radius increased from 0.1 to 0.2 m in August and September 1991 to values around 0.5 m in December 1991 and slowly decreased since then. The findings are compared with results of other lidar measurements in the Northern Hemisphere; balloon soundings at Laramie, Wyoming; high-altitude aircraft in situ and satellite observations (SAGE, AVHRR); and model calculations. A sedimentation model is used to analyze the mass removal from the stratosphere and the importance of different cleansing mechanisms. The comparison of the measured and simulated mass concentration profiles clearly indicate the strong impact of stratospheric-tropospheric exchange processes on the purging of aerosols from the stratosphere below 16 km.
Journal of Geophysical Research: Atmospheres, 1996
Validation studies of multiwavelength Cryogenic Limb Array Etalon Spectrometer (CLAES) observatio... more Validation studies of multiwavelength Cryogenic Limb Array Etalon Spectrometer (CLAES) observations of stratospheric aerosol are discussed. An error analysis of the CLAES aerosol extinction data is presented. Aerosol extinction precision values are estimated at latitudes and times at which consecutive Upper Atmosphere Research Satellite (UARS) orbits overlap. Comparisons of CLAES aerosol data with theoretical Mie calculations, based upon in situ particle size measurements at Laramie, Wyoming, are presented. CLAES aerosol data are also compared to scaled aerosol extinction measured by the Stratospheric Aerosol and Gas Experiment (SAGE II) and Atmospheric Trace Molecule Spectroscopy (ATMOS) experiments. Observed and calculated extinction spectra, from CLAES, Improved Stratospheric and Mesospheric Sounder (ISPuMS), and Halogen Occultation Experiment (HALOE) data, are compared. CLAES extinction data have precisions between 10 and 25%, instnanental biases near 30%, and accuracies between 33 and 43 %.
Journal of Geophysical Research, 1995
In 1994 an intensive program of balloon-borne frost point measurements was performed at McMurdo, ... more In 1994 an intensive program of balloon-borne frost point measurements was performed at McMurdo, Antarctica. During this program a total of 19 frost point soundings was obtained between February 7 and October 5, which cover a wide range of undisturbed through strongly dehydrated situations. Together with several soundings from South Pole station between 1990 and 1994, they give a comprehensive picture of the general development of the dehydration in the Antarctic stratospheric vortex. The period of dehydration typically starts around the middle of June, and a rapid formation of large particles leads to a fast dehydration of the vortex. The evaporation of falling particles leads to rehydration layers, which have significantly higher water vapor concentrations than the undisturbed stratosphere. Through the formation of these rehydration layers in the early stages of the dehydration we can estimate a particle fall speed of 1/3 km/d and thus a mean particle size of 4 gin. Ice saturation was observed over McMurdo in only two cases and only well after the onset of the dehydration. From the inspection of synoptic maps it then follows that a small cold region inside the vortex seems to be sufficient to dehydrate the entire vortex. Above 20 km the dehydration is completed by the end of July. From the descent of the upper dehydration edge we can estimate a mean descent rate in,side the vortex of 1.5 kin/month. In McMurdo we observed occasional penetration of the vortex edge in cases where the vortex edge was close to McMurdo, however, these cases seem to have little effect on the bulk of the vortex. A sounding from November 3, 1990, at South Pole shows that the dehydration may persist into November and indicates that there is no si•tmificant transport into the vortex throughout winter and early spring. 13,922 VOMEL ET AL.: DEI-1YDRA•ON OF THE ANTARCTIC STRATOSPHERIC VORTEX 3O ..
Journal of Geophysical Research, 2003
Vertical profiles of size-resolved aerosol concentrations above Laramie, Wyoming (41°N), have bee... more Vertical profiles of size-resolved aerosol concentrations above Laramie, Wyoming (41°N), have been measured for the past thirty years, 1971-2001. During this period, two somewhat different optical particle counters have been used to measure particles with radii !0.15 mm, whereas the instrument to measure condensation nuclei (CN) has not changed significantly since the late 1970s. The two optical particle counters measure aerosols !0.15, 0.25 mm and aerosols !0.15-2.0 mm in twelve size classes. These measurements have concentration (N) uncertainties / ±N À0.5 , but with a minimum of ±10%. Sizing uncertainties are about ±10%. The impact of these uncertainties on size distribution fitting parameters and aerosol moments are approximately ±30% and ±40%. The long-term record from these measurements indicates that volcanoes have controlled stratospheric aerosol abundance for 20 of the past 30 years. The present period, beginning in 1997, represents the longest volcanically quiescent period in the record. These and other measurements clearly show that stratospheric aerosol are now in a background state, a state rarely occurring in recent times, and that this background state is not significantly different than observations in 1979. Aerosol volumes and surface areas, inferred from size distributions fit to the measurements, are compared with SAGE II satellite estimates of surface area and volume. For volume the measurements are in agreement within measurement error throughout the record. For surface area there is good agreement for a volcanic aerosol laden stratosphere, but for background aerosol conditions the SAGE II estimates are about 40% less than the in situ measurements. Present aerosol surface areas are $1.0 (0.6) mm 2 cm À3 in the 15-20 (20-25) km layer based on in situ measurements. The Laramie size distribution record is now available to the community over the internet.
Journal of Geophysical Research, 1996
NO mixing ratios measured from Kiruna (68øN, 20øE), Sweden, on January 22, 1992, revealed values ... more NO mixing ratios measured from Kiruna (68øN, 20øE), Sweden, on January 22, 1992, revealed values much smaller than those observed at midlatitude near equinox and had a sharper vertical gradient around 25 km. Location of the measurements was close to the terminator and near the edge of the polar vortex, which is highly distorted from concentric flow by strong planetary wave activities. These conditions necessitate accurate calculation, properly taking into account the transport and photochemical processes, in order to quantitatively explain the observed NO profile. A three-dimensional chemistry and transport model (CTM) and a trajectory model (TM) were used to interpret the profile observations within their larger spatial, temporal, and chemical context. The NOy profile calculated by the CTM is in good agreement with that observed on January 31, 1992. In addition, model NOy profiles show small variabilities depending on latitudes, and they change little between January 22 and 31. The TM uses the observed NOy values. The NO values calculated by the CTM and TM agree with observations up to 27 km. Between 20 and 27 km the NO values calculated by the trajectory model including only gas phase chemistry are much larger than those including heterogeneous chemistry, indicating that NO mixing ratios were reduced significantly by heterogeneous chemistry on sulfuric acid aerosols. Very little sunlight to generate NOx from HNO3 was available, also causing the very low NO values. The good agreement between the observed and modeled NO profiles indicates that models can reproduce the photochemical and transport processes in the region where NO values have a sharp horizontal gradient. Moreover, CTM and TM model results show that even when the NOy gradients are weak, the model NO depends upon accurate calculation of the transport and insolation for several days. 1. Toyokawa, Japan.
Geophysical Research Letters, 1990
Balloonborne aerosol measurements over the size range r=0.01 to 10 mum on 31 January 1990 are use... more Balloonborne aerosol measurements over the size range r=0.01 to 10 mum on 31 January 1990 are used to determine the HNO3 vapor mass deposited in Arctic nitric acid trihydrate (NAY) clouds in the 21-24 km region. The clouds consisted mainly of small (r~0.2 mum) particles and appeared to have been formed during recent cooling because the r>=0.15 mum aerosol concentration
Balloonborne measurements of polar stratospheric clouds and ozone at-93° C in the Arctic in February 1990
Geophysical Research Letters, 1990
Balloonborne measurements of ozone and particle size distributions at Kiruna, Sweden indicate tha... more Balloonborne measurements of ozone and particle size distributions at Kiruna, Sweden indicate that on 6 February 1990 a major cooling event occurred over northern Scandinavia, reaching temperatures as low as −93° C at 22 km. Both nitric acid trihydrate and water ice clouds formed in the 19 to 23 km region. The temperature of the appearance of the water ice clouds is consistent with about 5 ppmv of water vapor at 22 km, The particle size distributions suggest that a sizeable degree of denitrification had occurred in the 19 to 23 km region in this air mass. Although ozone levels may have been reduced by a small degree of chemical depletion, the ozone “minihole” of 165 DU observed by TOMS was probably an artifact caused by ice clouds at 22 km since two ozonesonde measurements on that day indicated total ozone values of about 285 DU.
Geophysical Research Letters, 1999
Ozone (03) measurements made with the Improved Limb Atmospheric Spectrometer (ILAS) onboard the A... more Ozone (03) measurements made with the Improved Limb Atmospheric Spectrometer (ILAS) onboard the Advanced Earth Observing Satellite (ADEOS) were validated with correlative ozonesonde measurements conducted at five stations, Andoya, Kiruna and Yakutsk in the Northern Hemisphere, and Neumayer and Syowa in the Southern Hemisphere. The ILAS Version 3.10 03 vertical profiles were compared with 79 correlative ozonesonde measurements that were made within 500 km and 3 hours in distance and time differences, respectively. The comparisons indicate that ILAS 03 typically has an accuracy within 20% between 12 and 35 km. The precision of the ILAS 03 is estimated to be +10-25% between 12 and 20 km, +5-7% between 20 and 30 km, and +5% between 30 and 40 km. regions, where there are large 03 depletions in early spring [e.g., Newman et al., 1997]. Since ADEOS was put into a sun-synchronized polar orbit, the ILAS orbital characteristics are more suitable to study ozone-related chemistry in high southern latitudes (64-88øS) and sub-polar northern latitudes (57-73øN) than are HALOE or the Stratospheric Aerosol and Gas Experiment (SAGE) II. This paper focuses on the assessment of the quality of the ILAS-retrieved Version 3.10 (V3.10) 03 mixing ratios through comparison with correlative ozonesonde measurements made at four sounding stations both in the Northern and Southern Hemispheres. A summary of comparison results and anticipated future improvements by new data processing algorithm will be given. HALOE to focus on studies of the 03 layer in high-latitude 1National Institute for Environmental Studies, Tsukuba,