The Experts below are selected from a list of 231 Experts worldwide ranked by ideXlab platform

Andrew J Heymsfield - One of the best experts on this subject based on the ideXlab platform.

  • ice nucleation processes in upper Tropospheric Wave clouds observed during success
    Geophysical Research Letters, 1998
    Co-Authors: E J Jensen, Owen B Toon, A Tabazadeh, G W Sachse, B E Anderson, K R Chan, C W Twohy, B W Gandrud, Steven M Aulenbach, Andrew J Heymsfield
    Abstract:

    We have compared in situ measurements near the leading-edges of Wave-clouds observed during the SUCCESS experiment with numerical simulations. Observations of high supersaturations with respect to ice (>50%) near the leading edge of a very cold Wave cloud (T <−60°C) are approximately consistent with recent theoretical and laboratory studies suggesting that large supersaturations are required to homogeneously freeze sulfate aerosols. Also, the peak ice crystal number densities observed in this cloud (about 4 cm−3) are consistent with the number densities calculated in our model. In the warmer Wave-cloud (T ≃−37°C) relatively large ice number densities were observed (20–40 cm−3). Our model calculations suggest that these large number densities are probably caused by activation of sulfate aerosols into liquid droplets followed by subsequent homogeneous freezing. If moderate numbers of effective heterogeneous freezing nuclei (0.5–1 cm−3) had been present in either of these clouds, then the number densities of ice crystals and the peak relative humidities should have been lower than the observed values.

  • Ice nucleation processes in upper Tropospheric Wave‐clouds observed during SUCCESS
    Geophysical Research Letters, 1998
    Co-Authors: E J Jensen, Owen B Toon, A Tabazadeh, G W Sachse, B E Anderson, K R Chan, C W Twohy, B W Gandrud, Steven M Aulenbach, Andrew J Heymsfield
    Abstract:

    We have compared in situ measurements near the leading-edges of Wave-clouds observed during the SUCCESS experiment with numerical simulations. Observations of high supersaturations with respect to ice (>50%) near the leading edge of a very cold Wave cloud (T

John R Albers - One of the best experts on this subject based on the ideXlab platform.

  • are sudden stratospheric warmings preceded by anomalous Tropospheric Wave activity
    Journal of Climate, 2019
    Co-Authors: Alvaro De La Camara, Thomas Birner, John R Albers
    Abstract:

    AbstractA combination of 240 years of output from a state-of-the-art chemistry–climate model and a twentieth-century reanalysis product is used to investigate to what extent sudden stratospheric wa...

  • Sensitivity of Sudden Stratospheric Warmings to Previous Stratospheric Conditions
    Journal of the Atmospheric Sciences, 2017
    Co-Authors: Alvaro De La Camara, Thomas Birner, John R Albers, Rolando R. Garcia, Peter Hitchcock, Douglas E. Kinnison, Anne K. Smith
    Abstract:

    AbstractThe Whole Atmosphere Community Climate Model, version 4 (WACCM4), is used to investigate the influence of stratospheric conditions on the development of sudden stratospheric warmings (SSWs). To this end, targeted experiments are performed on selected modeled SSW events. Specifically, the model is reinitialized three weeks before a given SSW, relaxing the surface fluxes, winds, and temperature below 10 km to the corresponding fields from the free-running simulation. Hence, the Tropospheric Wave evolution is unaltered across the targeted experiments, but the stratosphere itself can evolve freely. The stratospheric zonal-mean state is then altered 21 days prior to the selected SSWs and rerun with an ensemble of different initial conditions. It is found that a given Tropospheric evolution concomitant with the development of an SSW does not uniquely determine the occurrence of an event and that the stratospheric conditions are relevant to the subsequent evolution of the stratospheric flow toward an SSW...

R M Uller - One of the best experts on this subject based on the ideXlab platform.

  • The cold Arctic winter 1995/96 as observed by GOME and HALOE: Tropospheric Wave activity and chemical ozone loss
    Quarterly Journal of the Royal Meteorological Society, 2002
    Co-Authors: M Weber, K U Eichmann, F Wittrock, K Bramstedt, L Hild, A Richter, J P Burrows, R M Uller
    Abstract:

    The Global Ozone Monitoring Experiment aboard the European Remote Sensing Satellite ERS-2 was the only satellite instrument measuring total ozone on a near-global scale during the extremely cold Arctic winter 1995/96. Extremely low total ozone was observed within the Arctic vortex during February and March. The lowest value in this winter was 178 DU (Dobson units) over Greenland on 19 February, which was about 160 DU below the February Arctic vortex mean of total ozone. Although severe chemical ozone destruction occurred in late winter 1995/96, the extremely low values in total ozone observed after the middle of February were, in all cases, related to mini-hole events, where large horizontal divergent transport of ozone from the lower-stratospheric layer above a high tropopause rapidly reduced the total column in a localized region. The observed total-ozone minima were located near the vortex edge and in the region of minimum lower-stratospheric temperatures that were, in selected cases, sufficiently low for the formation of polar stratospheric ice clouds (PSC type II) below 188 K at the isentropic level of 475 K. Coincident ozone profile observations in early March from the Halogen Occultation Experiment on the Upper Atmosphere Research Satellite indicate that the strong chemical ozone loss was mainly confined to the polar vortex region, and that the extremely low total-ozone values below 250 DU were mainly caused by short-term reversible dynamical reductions superimposed upon chemical ozone loss occurring on longer timescales. Enhanced OClO and chlorine activation, due to strong Tropospheric Wave activity associated with an ozone mini-hole event, was only observed in early March following a stratospheric temperature drop below the ice frost point. In general, however, the observation of very low total ozone in mini-hole events does not necessarily point to significant additional chemical depletion. Copyright © 2002 Royal Meteorological Society

  • the cold arctic winter 1995 96 as observed by gome and haloe Tropospheric Wave activity and chemical ozone loss
    Quarterly Journal of the Royal Meteorological Society, 2002
    Co-Authors: M Weber, K U Eichmann, F Wittrock, K Bramstedt, L Hild, A Richter, J P Burrows, R M Uller
    Abstract:

    The Global Ozone Monitoring Experiment aboard the European Remote Sensing Satellite ERS-2 was the only satellite instrument measuring total ozone on a near-global scale during the extremely cold Arctic winter 1995/96. Extremely low total ozone was observed within the Arctic vortex during February and March. The lowest value in this winter was 178 DU (Dobson units) over Greenland on 19 February, which was about 160 DU below the February Arctic vortex mean of total ozone. Although severe chemical ozone destruction occurred in late winter 1995/96, the extremely low values in total ozone observed after the middle of February were, in all cases, related to mini-hole events, where large horizontal divergent transport of ozone from the lower-stratospheric layer above a high tropopause rapidly reduced the total column in a localized region. The observed total-ozone minima were located near the vortex edge and in the region of minimum lower-stratospheric temperatures that were, in selected cases, sufficiently low for the formation of polar stratospheric ice clouds (PSC type II) below 188 K at the isentropic level of 475 K. Coincident ozone profile observations in early March from the Halogen Occultation Experiment on the Upper Atmosphere Research Satellite indicate that the strong chemical ozone loss was mainly confined to the polar vortex region, and that the extremely low total-ozone values below 250 DU were mainly caused by short-term reversible dynamical reductions superimposed upon chemical ozone loss occurring on longer timescales. Enhanced OClO and chlorine activation, due to strong Tropospheric Wave activity associated with an ozone mini-hole event, was only observed in early March following a stratospheric temperature drop below the ice frost point. In general, however, the observation of very low total ozone in mini-hole events does not necessarily point to significant additional chemical depletion. Copyright © 2002 Royal Meteorological Society

Alvaro De La Camara - One of the best experts on this subject based on the ideXlab platform.

  • are sudden stratospheric warmings preceded by anomalous Tropospheric Wave activity
    Journal of Climate, 2019
    Co-Authors: Alvaro De La Camara, Thomas Birner, John R Albers
    Abstract:

    AbstractA combination of 240 years of output from a state-of-the-art chemistry–climate model and a twentieth-century reanalysis product is used to investigate to what extent sudden stratospheric wa...

  • Sensitivity of Sudden Stratospheric Warmings to Previous Stratospheric Conditions
    Journal of the Atmospheric Sciences, 2017
    Co-Authors: Alvaro De La Camara, Thomas Birner, John R Albers, Rolando R. Garcia, Peter Hitchcock, Douglas E. Kinnison, Anne K. Smith
    Abstract:

    AbstractThe Whole Atmosphere Community Climate Model, version 4 (WACCM4), is used to investigate the influence of stratospheric conditions on the development of sudden stratospheric warmings (SSWs). To this end, targeted experiments are performed on selected modeled SSW events. Specifically, the model is reinitialized three weeks before a given SSW, relaxing the surface fluxes, winds, and temperature below 10 km to the corresponding fields from the free-running simulation. Hence, the Tropospheric Wave evolution is unaltered across the targeted experiments, but the stratosphere itself can evolve freely. The stratospheric zonal-mean state is then altered 21 days prior to the selected SSWs and rerun with an ensemble of different initial conditions. It is found that a given Tropospheric evolution concomitant with the development of an SSW does not uniquely determine the occurrence of an event and that the stratospheric conditions are relevant to the subsequent evolution of the stratospheric flow toward an SSW...

E J Jensen - One of the best experts on this subject based on the ideXlab platform.

  • ice nucleation processes in upper Tropospheric Wave clouds observed during success
    Geophysical Research Letters, 1998
    Co-Authors: E J Jensen, Owen B Toon, A Tabazadeh, G W Sachse, B E Anderson, K R Chan, C W Twohy, B W Gandrud, Steven M Aulenbach, Andrew J Heymsfield
    Abstract:

    We have compared in situ measurements near the leading-edges of Wave-clouds observed during the SUCCESS experiment with numerical simulations. Observations of high supersaturations with respect to ice (>50%) near the leading edge of a very cold Wave cloud (T <−60°C) are approximately consistent with recent theoretical and laboratory studies suggesting that large supersaturations are required to homogeneously freeze sulfate aerosols. Also, the peak ice crystal number densities observed in this cloud (about 4 cm−3) are consistent with the number densities calculated in our model. In the warmer Wave-cloud (T ≃−37°C) relatively large ice number densities were observed (20–40 cm−3). Our model calculations suggest that these large number densities are probably caused by activation of sulfate aerosols into liquid droplets followed by subsequent homogeneous freezing. If moderate numbers of effective heterogeneous freezing nuclei (0.5–1 cm−3) had been present in either of these clouds, then the number densities of ice crystals and the peak relative humidities should have been lower than the observed values.

  • Ice nucleation processes in upper Tropospheric Wave‐clouds observed during SUCCESS
    Geophysical Research Letters, 1998
    Co-Authors: E J Jensen, Owen B Toon, A Tabazadeh, G W Sachse, B E Anderson, K R Chan, C W Twohy, B W Gandrud, Steven M Aulenbach, Andrew J Heymsfield
    Abstract:

    We have compared in situ measurements near the leading-edges of Wave-clouds observed during the SUCCESS experiment with numerical simulations. Observations of high supersaturations with respect to ice (>50%) near the leading edge of a very cold Wave cloud (T