The Experts below are selected from a list of 312 Experts worldwide ranked by ideXlab platform
Andrew Gettelman - One of the best experts on this subject based on the ideXlab platform.
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multimodel assessment of the upper troposphere and lower stratosphere tropics and global trends
Journal of Geophysical Research, 2010Co-Authors: Andrew Gettelman, Thomas Birner, Slimane Bekki, Michaela I. Hegglin, Juan A. Añel, Masatomo Fujiwara, Stefanie Kremser, H Akiyoshi, John Austin, P BraesikeAbstract:The performance of 18 coupled Chemistry Climate Models (CCMs) in the Tropical Tropopause Layer (TTL) is evaluated using qualitative and quantitative diagnostics. Trends in Tropopause quantities in the tropics and the extratropical Upper Troposphere and Lower Stratosphere (UTLS) are analyzed. A quantitative grading methodology for evaluating CCMs is extended to include variability and used to develop four different grades for tropical Tropopause temperature and pressure, water vapor and ozone. Four of the 18 models and the multi‐model mean meet quantitative and qualitative standards for reproducing key processes in the TTL. Several diagnostics are performed on a subset of the models analyzing the Tropopause Inversion Layer (TIL), Lagrangian cold point and TTL transit time. Historical decreases in tropical Tropopause pressure and decreases in water vapor are simulated, lending confidence to future projections. The models simulate continued decreases in Tropopause pressure in the 21st century, along with ∼1K increases per century in cold point Tropopause temperature and 0.5–1 ppmv per century increases in water vapor above the tropical Tropopause. TTL water vapor increases below the cold point. In two models, these trends are associated with 35% increases in TTL cloud fraction. These changes indicate significant perturbations to TTL processes, specifically to deep convective heating and humidity transport. Ozone in the extratropical lowermost stratosphere has significant and hemispheric asymmetric trends. O3 is projected to increase by nearly 30% due to ozone recovery in the Southern Hemisphere (SH) and due to enhancements in the stratospheric circulation. These UTLS ozone trends may have significant effects in the TTL and the troposphere.
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the tropical Tropopause layer 1960 2100
Atmospheric Chemistry and Physics, 2009Co-Authors: Andrew Gettelman, Thomas Birner, Veronika Eyring, Slimane Bekki, Douglas E Kinnison, Martin Dameris, Hideharu Akiyoshi, Christoph Bruhl, Frank Lefevre, F. LottAbstract:The representation of the Tropical Tropopause Layer (TTL) in 13 different Chemistry Climate Models (CCMs) designed to represent the stratosphere is analyzed. Simulations for 1960–2005 and 1980–2100 are analyzed. Simulations for 1960–2005 are compared to reanalysis model output. CCMs are able to reproduce the basic structure of the TTL. There is a large (10 K) spread in annual mean tropical cold point Tropopause temperatures. CCMs are able to reproduce historical trends in Tropopause pressure obtained from reanalysis products. Simulated historical trends in cold point Tropopause temperatures are not consistent across models or reanalyses. The pressure of both the tropical Tropopause and the level of main convective outflow appear to have decreased (increased altitude) in historical runs as well as in reanalyses. Decreasing pressure trends in the tropical Tropopause and level of main convective outflow are also seen in the future. Models consistently predict decreasing Tropopause and convective outflow pressure, by several hPa/decade. Tropical cold point temperatures are projected to increase by 0.09 K/decade. Tropopause anomalies are highly correlated with tropical surface temperature anomalies and with Tropopause level ozone anomalies, less so with stratospheric temperature anomalies. Simulated stratospheric water vapor at 90 hPa increases by up to 0.5–1 ppmv by 2100. The result is consistent with the simulated increase in temperature, highlighting the correlation of Tropopause temperatures with stratospheric water vapor.
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the impact of stratospheric ozone recovery on Tropopause height trends
Journal of Climate, 2009Co-Authors: Seokwoo Son, Thomas Birner, Andrew Gettelman, Lorenzo M. Polvani, Hideharu Akiyoshi, Darryn W Waugh, Rolando R Garcia, David A Plummer, E RozanovAbstract:The evolution of the Tropopause in the past, present, and future climate is examined by analyzing a set of long-term integrations with stratosphere-resolving chemistry climate models (CCMs). These CCMs have high vertical resolution near the Tropopause, a model top located in the mesosphere or above, and, most important, fully interactive stratospheric chemistry. Using such CCM integrations, it is found that the Tropopause pressure (height) will continue to decrease (increase) in the future, but with a trend weaker than that in the recent past. The reduction in the future Tropopause trend is shown to be directly associated with stratospheric ozone recovery. A significant ozone recovery occurs in the Southern Hemisphere lower stratosphere of the CCMs, and this leads to a relative warming there that reduces the Tropopause trend in the twenty-first century. The future Tropopause trends predicted by the CCMs are considerably smaller than those predicted by the Intergovernmental Panel on Climate Change Fourth Assessment Report (AR4) models, especially in the southern high latitudes. This difference persists even when the CCMs are compared with the subset of the AR4 model integrations for which stratospheric ozone recovery was prescribed. These results suggest that a realistic representation of the stratospheric processes might be important for a reliable estimate of Tropopause trends. The implications of these finding for the Southern Hemisphere climate change are also discussed.
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The Tropical Tropopause Layer 1960–2100
Atmospheric Chemistry and Physics, 2009Co-Authors: Andrew Gettelman, Thomas Birner, Veronika Eyring, Hideo Akiyoshi, Ch. Brühl, Franck Lefevre, Slimane Bekki, Douglas E Kinnison, Martin Dameris, F. LottAbstract:The representation of the Tropical Tropopause Layer (TTL) in 13 different Chemistry Climate Models (CCMs) designed to represent the stratosphere is analyzed. Simulations for 1960–2005 and 1980–2100 are analyzed. Simulations for 1960–2005 are compared to reanalysis model output. CCMs are able to reproduce the basic structure of the TTL. There is a large (10 K) spread in annual mean tropical cold point Tropopause temperatures. CCMs are able to reproduce historical trends in Tropopause pressure obtained from reanalysis products. Simulated historical trends in cold point Tropopause temperatures are not consistent across models or reanalyses. The pressure of both the tropical Tropopause and the level of main convective outflow appear to have decreased (increased altitude) in historical runs as well as in reanalyses. Decreasing pressure trends in the tropical Tropopause and level of main convective outflow are also seen in the future. Models consistently predict decreasing Tropopause and convective outflow pressure, by several hPa/decade. Tropical cold point temperatures are projected to increase by 0.09 K/decade. Tropopause anomalies are highly correlated with tropical surface temperature anomalies and with Tropopause level ozone anomalies, less so with stratospheric temperature anomalies. Simulated stratospheric water vapor at 90 hPa increases by up to 0.5–1 ppmv by 2100. The result is consistent with the simulated increase in temperature, highlighting the correlation of Tropopause temperatures with stratospheric water vapor.
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The Tropical Tropopause Layer 1960–2100
2008Co-Authors: Andrew Gettelman, Thomas Birner, Veronika Eyring, Hideo Akiyoshi, F. Lott, Franck Lefevre, Slimane Bekki, Martin Dameris, D. A. Plummer, Ch. BrühlAbstract:Abstract. The representation of the Tropical Tropopause Layer in 13 different Chemistry Climate Models designed to represent the stratosphere is analyzed. Simulations for 1960–present and 1980–2100 are analyzed and compared to reanalysis model output. Results indicate that the models are able to reproduce the basic structure of the TTL. There is a large spread in cold point Tropopause temperatures that may be linked to variation in TTL ozone values. The models are generally able to reproduce historical trends in Tropopause pressure obtained from reanalysis products. Simulated historical trends in cold point Tropopause temperatures and in the meridional extent of the TTL are not consistent across models. The pressure of both the tropical Tropopause and the level of main convective outflow appear to be decreasing (increasing altitude) in historical runs. Similar trends are seen in the future. Models consistently predict decreasing Tropopause and convective outflow pressure, by several hPa/decade. Tropical cold point temperatures increase by 0.2 K/decade. This indicates that tropospheric warming dominates stratospheric cooling at the tropical Tropopause. Stratospheric water vapor at 100 hPa increases by up to 0.5–1 ppmv by 2100. This is less than implied directly by the temperature and methane increases, highlighting the correlation of Tropopause temperatures with stratospheric water vapor, but also the complex nature of TTL transport.
Thomas Birner - One of the best experts on this subject based on the ideXlab platform.
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Residual Circulation and Tropopause Structure
Journal of the Atmospheric Sciences, 2010Co-Authors: Thomas BirnerAbstract:Abstract The effect of large-scale dynamics as represented by the residual mean meridional circulation in the transformed Eulerian sense, in particular its stratospheric part, on lower stratospheric static stability and Tropopause structure is studied using a comprehensive chemistry–climate model (CCM), reanalysis data, and simple idealized modeling. Dynamical forcing of static stability as associated with the vertical structure of the residual circulation results in a dominant dipole forcing structure with negative static stability forcing just below the Tropopause and positive static stability forcing just above the Tropopause. This dipole forcing structure effectively sharpens the Tropopause, especially during winter. Furthermore, the strong positive lowermost stratospheric static stability forcing causes a layer of strongly enhanced static stability just above the extratropical Tropopause—a Tropopause inversion layer (TIL)—especially in the winter midlatitudes. The strong positive static stability for...
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multimodel assessment of the upper troposphere and lower stratosphere tropics and global trends
Journal of Geophysical Research, 2010Co-Authors: Andrew Gettelman, Thomas Birner, Slimane Bekki, Michaela I. Hegglin, Juan A. Añel, Masatomo Fujiwara, Stefanie Kremser, H Akiyoshi, John Austin, P BraesikeAbstract:The performance of 18 coupled Chemistry Climate Models (CCMs) in the Tropical Tropopause Layer (TTL) is evaluated using qualitative and quantitative diagnostics. Trends in Tropopause quantities in the tropics and the extratropical Upper Troposphere and Lower Stratosphere (UTLS) are analyzed. A quantitative grading methodology for evaluating CCMs is extended to include variability and used to develop four different grades for tropical Tropopause temperature and pressure, water vapor and ozone. Four of the 18 models and the multi‐model mean meet quantitative and qualitative standards for reproducing key processes in the TTL. Several diagnostics are performed on a subset of the models analyzing the Tropopause Inversion Layer (TIL), Lagrangian cold point and TTL transit time. Historical decreases in tropical Tropopause pressure and decreases in water vapor are simulated, lending confidence to future projections. The models simulate continued decreases in Tropopause pressure in the 21st century, along with ∼1K increases per century in cold point Tropopause temperature and 0.5–1 ppmv per century increases in water vapor above the tropical Tropopause. TTL water vapor increases below the cold point. In two models, these trends are associated with 35% increases in TTL cloud fraction. These changes indicate significant perturbations to TTL processes, specifically to deep convective heating and humidity transport. Ozone in the extratropical lowermost stratosphere has significant and hemispheric asymmetric trends. O3 is projected to increase by nearly 30% due to ozone recovery in the Southern Hemisphere (SH) and due to enhancements in the stratospheric circulation. These UTLS ozone trends may have significant effects in the TTL and the troposphere.
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the tropical Tropopause layer 1960 2100
Atmospheric Chemistry and Physics, 2009Co-Authors: Andrew Gettelman, Thomas Birner, Veronika Eyring, Slimane Bekki, Douglas E Kinnison, Martin Dameris, Hideharu Akiyoshi, Christoph Bruhl, Frank Lefevre, F. LottAbstract:The representation of the Tropical Tropopause Layer (TTL) in 13 different Chemistry Climate Models (CCMs) designed to represent the stratosphere is analyzed. Simulations for 1960–2005 and 1980–2100 are analyzed. Simulations for 1960–2005 are compared to reanalysis model output. CCMs are able to reproduce the basic structure of the TTL. There is a large (10 K) spread in annual mean tropical cold point Tropopause temperatures. CCMs are able to reproduce historical trends in Tropopause pressure obtained from reanalysis products. Simulated historical trends in cold point Tropopause temperatures are not consistent across models or reanalyses. The pressure of both the tropical Tropopause and the level of main convective outflow appear to have decreased (increased altitude) in historical runs as well as in reanalyses. Decreasing pressure trends in the tropical Tropopause and level of main convective outflow are also seen in the future. Models consistently predict decreasing Tropopause and convective outflow pressure, by several hPa/decade. Tropical cold point temperatures are projected to increase by 0.09 K/decade. Tropopause anomalies are highly correlated with tropical surface temperature anomalies and with Tropopause level ozone anomalies, less so with stratospheric temperature anomalies. Simulated stratospheric water vapor at 90 hPa increases by up to 0.5–1 ppmv by 2100. The result is consistent with the simulated increase in temperature, highlighting the correlation of Tropopause temperatures with stratospheric water vapor.
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the impact of stratospheric ozone recovery on Tropopause height trends
Journal of Climate, 2009Co-Authors: Seokwoo Son, Thomas Birner, Andrew Gettelman, Lorenzo M. Polvani, Hideharu Akiyoshi, Darryn W Waugh, Rolando R Garcia, David A Plummer, E RozanovAbstract:The evolution of the Tropopause in the past, present, and future climate is examined by analyzing a set of long-term integrations with stratosphere-resolving chemistry climate models (CCMs). These CCMs have high vertical resolution near the Tropopause, a model top located in the mesosphere or above, and, most important, fully interactive stratospheric chemistry. Using such CCM integrations, it is found that the Tropopause pressure (height) will continue to decrease (increase) in the future, but with a trend weaker than that in the recent past. The reduction in the future Tropopause trend is shown to be directly associated with stratospheric ozone recovery. A significant ozone recovery occurs in the Southern Hemisphere lower stratosphere of the CCMs, and this leads to a relative warming there that reduces the Tropopause trend in the twenty-first century. The future Tropopause trends predicted by the CCMs are considerably smaller than those predicted by the Intergovernmental Panel on Climate Change Fourth Assessment Report (AR4) models, especially in the southern high latitudes. This difference persists even when the CCMs are compared with the subset of the AR4 model integrations for which stratospheric ozone recovery was prescribed. These results suggest that a realistic representation of the stratospheric processes might be important for a reliable estimate of Tropopause trends. The implications of these finding for the Southern Hemisphere climate change are also discussed.
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The Tropical Tropopause Layer 1960–2100
Atmospheric Chemistry and Physics, 2009Co-Authors: Andrew Gettelman, Thomas Birner, Veronika Eyring, Hideo Akiyoshi, Ch. Brühl, Franck Lefevre, Slimane Bekki, Douglas E Kinnison, Martin Dameris, F. LottAbstract:The representation of the Tropical Tropopause Layer (TTL) in 13 different Chemistry Climate Models (CCMs) designed to represent the stratosphere is analyzed. Simulations for 1960–2005 and 1980–2100 are analyzed. Simulations for 1960–2005 are compared to reanalysis model output. CCMs are able to reproduce the basic structure of the TTL. There is a large (10 K) spread in annual mean tropical cold point Tropopause temperatures. CCMs are able to reproduce historical trends in Tropopause pressure obtained from reanalysis products. Simulated historical trends in cold point Tropopause temperatures are not consistent across models or reanalyses. The pressure of both the tropical Tropopause and the level of main convective outflow appear to have decreased (increased altitude) in historical runs as well as in reanalyses. Decreasing pressure trends in the tropical Tropopause and level of main convective outflow are also seen in the future. Models consistently predict decreasing Tropopause and convective outflow pressure, by several hPa/decade. Tropical cold point temperatures are projected to increase by 0.09 K/decade. Tropopause anomalies are highly correlated with tropical surface temperature anomalies and with Tropopause level ozone anomalies, less so with stratospheric temperature anomalies. Simulated stratospheric water vapor at 90 hPa increases by up to 0.5–1 ppmv by 2100. The result is consistent with the simulated increase in temperature, highlighting the correlation of Tropopause temperatures with stratospheric water vapor.
F. Lott - One of the best experts on this subject based on the ideXlab platform.
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the tropical Tropopause layer 1960 2100
Atmospheric Chemistry and Physics, 2009Co-Authors: Andrew Gettelman, Thomas Birner, Veronika Eyring, Slimane Bekki, Douglas E Kinnison, Martin Dameris, Hideharu Akiyoshi, Christoph Bruhl, Frank Lefevre, F. LottAbstract:The representation of the Tropical Tropopause Layer (TTL) in 13 different Chemistry Climate Models (CCMs) designed to represent the stratosphere is analyzed. Simulations for 1960–2005 and 1980–2100 are analyzed. Simulations for 1960–2005 are compared to reanalysis model output. CCMs are able to reproduce the basic structure of the TTL. There is a large (10 K) spread in annual mean tropical cold point Tropopause temperatures. CCMs are able to reproduce historical trends in Tropopause pressure obtained from reanalysis products. Simulated historical trends in cold point Tropopause temperatures are not consistent across models or reanalyses. The pressure of both the tropical Tropopause and the level of main convective outflow appear to have decreased (increased altitude) in historical runs as well as in reanalyses. Decreasing pressure trends in the tropical Tropopause and level of main convective outflow are also seen in the future. Models consistently predict decreasing Tropopause and convective outflow pressure, by several hPa/decade. Tropical cold point temperatures are projected to increase by 0.09 K/decade. Tropopause anomalies are highly correlated with tropical surface temperature anomalies and with Tropopause level ozone anomalies, less so with stratospheric temperature anomalies. Simulated stratospheric water vapor at 90 hPa increases by up to 0.5–1 ppmv by 2100. The result is consistent with the simulated increase in temperature, highlighting the correlation of Tropopause temperatures with stratospheric water vapor.
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The Tropical Tropopause Layer 1960–2100
Atmospheric Chemistry and Physics, 2009Co-Authors: Andrew Gettelman, Thomas Birner, Veronika Eyring, Hideo Akiyoshi, Ch. Brühl, Franck Lefevre, Slimane Bekki, Douglas E Kinnison, Martin Dameris, F. LottAbstract:The representation of the Tropical Tropopause Layer (TTL) in 13 different Chemistry Climate Models (CCMs) designed to represent the stratosphere is analyzed. Simulations for 1960–2005 and 1980–2100 are analyzed. Simulations for 1960–2005 are compared to reanalysis model output. CCMs are able to reproduce the basic structure of the TTL. There is a large (10 K) spread in annual mean tropical cold point Tropopause temperatures. CCMs are able to reproduce historical trends in Tropopause pressure obtained from reanalysis products. Simulated historical trends in cold point Tropopause temperatures are not consistent across models or reanalyses. The pressure of both the tropical Tropopause and the level of main convective outflow appear to have decreased (increased altitude) in historical runs as well as in reanalyses. Decreasing pressure trends in the tropical Tropopause and level of main convective outflow are also seen in the future. Models consistently predict decreasing Tropopause and convective outflow pressure, by several hPa/decade. Tropical cold point temperatures are projected to increase by 0.09 K/decade. Tropopause anomalies are highly correlated with tropical surface temperature anomalies and with Tropopause level ozone anomalies, less so with stratospheric temperature anomalies. Simulated stratospheric water vapor at 90 hPa increases by up to 0.5–1 ppmv by 2100. The result is consistent with the simulated increase in temperature, highlighting the correlation of Tropopause temperatures with stratospheric water vapor.
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The Tropical Tropopause Layer 1960–2100
2008Co-Authors: Andrew Gettelman, Thomas Birner, Veronika Eyring, Hideo Akiyoshi, F. Lott, Franck Lefevre, Slimane Bekki, Martin Dameris, D. A. Plummer, Ch. BrühlAbstract:Abstract. The representation of the Tropical Tropopause Layer in 13 different Chemistry Climate Models designed to represent the stratosphere is analyzed. Simulations for 1960–present and 1980–2100 are analyzed and compared to reanalysis model output. Results indicate that the models are able to reproduce the basic structure of the TTL. There is a large spread in cold point Tropopause temperatures that may be linked to variation in TTL ozone values. The models are generally able to reproduce historical trends in Tropopause pressure obtained from reanalysis products. Simulated historical trends in cold point Tropopause temperatures and in the meridional extent of the TTL are not consistent across models. The pressure of both the tropical Tropopause and the level of main convective outflow appear to be decreasing (increasing altitude) in historical runs. Similar trends are seen in the future. Models consistently predict decreasing Tropopause and convective outflow pressure, by several hPa/decade. Tropical cold point temperatures increase by 0.2 K/decade. This indicates that tropospheric warming dominates stratospheric cooling at the tropical Tropopause. Stratospheric water vapor at 100 hPa increases by up to 0.5–1 ppmv by 2100. This is less than implied directly by the temperature and methane increases, highlighting the correlation of Tropopause temperatures with stratospheric water vapor, but also the complex nature of TTL transport.
William J. Randel - One of the best experts on this subject based on the ideXlab platform.
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the extratropical Tropopause inversion layer global observations with gps data and a radiative forcing mechanism
Journal of the Atmospheric Sciences, 2007Co-Authors: William J. Randel, Piers M ForsterAbstract:Global characteristics of the extratropical Tropopause inversion layer identified in radiosonde observations by Birner are studied using high vertical resolution temperature profiles from GPS radio occultation measurements. The GPS data are organized according to the height of the thermal Tropopause in each profile, and a temperature inversion layer above the Tropopause (with an average magnitude of 3-5 K) is found to be a ubiquitous, climatological feature. The GPS data show that the inversion layer is present for all seasons in both hemispheres, spanning the subtropics to the pole, and there is not strong longitudinal structure. Dependence of the inversion layer on upper-troposphere vorticity is studied; while anticyclones exhibit a substantially stronger inversion than cyclones (as expected from balanced dynamics), the inversion is evident for all circulation types. Radiative transfer calculations indicate that strong gradients in both ozone and water vapor near the Tropopause contribute to the inversion. Significant absorption of both longwave and shortwave radiation by ozone occurs, warming the region above the Tropopause. Water vapor near and immediately above the Tropopause contributes to cooling, effectively enhancing the inversion.
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recent widening of the tropical belt evidence from Tropopause observations
Journal of Geophysical Research, 2007Co-Authors: Dian J. Seidel, William J. RandelAbstract:[1] Radiosonde measurements and reanalysis data are used to examine long-term changes in Tropopause behavior in the subtropics. Tropopause heights in the subtropics exhibit a bimodal distribution, with maxima in occurrence frequency above 15 km (characteristic of the tropical Tropopause) and below 13 km (typical of the extratropical Tropopause). Both the radiosonde and reanalysis data show that the frequency of occurrence of high Tropopause days in the subtropics of both hemispheres has systematically increased during the past few decades, so that tropical characteristics occur more frequently in recent years. This behavior is consistent with a widening of the tropical belt, and the data indicate an expansion of about 5–8° latitude during 1979–2005.
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Observational characteristics of double Tropopauses
Journal of Geophysical Research, 2007Co-Authors: William J. Randel, Dian J. Seidel, Laura L. PanAbstract:[1] Temperature profiles in the extratropics often exhibit multiple Tropopauses (as defined using the lapse rate definition). In this work we study the observational characteristics of double Tropopauses based on radiosondes, ERA40 reanalysis, and GPS radio occultation temperature profiles. Double Tropopauses are associated with a characteristic break in the thermal Tropopause near the subtropical jet, wherein the low latitude (tropical) Tropopause extends to higher latitudes, overlying the lower Tropopause; this behavior can extend to polar latitudes. Tropopause statistics derived from radiosondes and GPS data show good agreement, and GPS data allow mapping of double Tropopause characteristics over the globe. The occurrence frequency shows a strong seasonal variation over NH midlatitudes, with ∼50-70% occurrence in profiles during winter, and a small fraction (∼10%) over most of the hemisphere during summer (with the exception of a localized maximum over the poleward flank of the Asian monsoon anticyclone). SH midlatitude statistics show a smaller seasonal variation, with occurrence frequencies of ∼30-50% over the year (maximum during winter). Over the extratropics, the occurrence frequency is substantially higher for cyclonic circulation systems. Few double Tropopauses are observed in the tropics. Ozone measurements from balloons and satellites show that profiles with double Tropopauses exhibit systematically less ozone in the lower stratosphere than those with a single Tropopause. Together with the meteorological data, the ozone observations identify double Tropopauses as regions of enhanced transport from the tropics to higher latitudes above the subtropical jet cores.
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Variability and trends in the global Tropopause estimated from radiosonde data
Journal of Geophysical Research, 2006Co-Authors: Dian J. Seidel, William J. RandelAbstract:[1] This study examines global Tropopause variability on synoptic, monthly, seasonal, and multidecadal timescales using 1980–2004 radiosonde data. On synoptic and monthly timescales, Tropopause height variations are anticorrelated with stratospheric temperature variations and positively correlated with tropospheric temperature variations. Correlations are stronger in the extratropics than in the tropics, for the upper troposphere (500–300 hPa) than for the lower troposphere, and for the lower stratosphere than for the middle stratosphere. The extratropical Tropopause is more sensitive to temperature changes than the tropical Tropopause, and in both regions, monthly anomalies of Tropopause height are more sensitive to stratospheric temperature change than tropospheric, rising 2–3 km per degree cooling of the lower stratosphere. Tropopause height trends over 1980–2004 are upward at almost all of the (predominantly extratropical) stations analyzed, yielding an estimated global trend of 64 ± 21 m/decade, a corresponding Tropopause pressure trend of −1.7 ± 0.6 hPa/decade, and Tropopause temperature decrease of 0.41 ± 0.09 K/decade. These Tropopause trends are accompanied by significant stratospheric cooling and smaller tropospheric warming. However, the Tropopause trends are spatially correlated with stratospheric temperature trends and uncorrelated with tropospheric temperature trends. This association of Tropopause height and stratospheric temperature trends, together with the presence of a significant quasi-biennial oscillation signal in Tropopause height, suggests that at these lowest frequencies the Tropopause is primarily coupled with stratospheric temperatures. Therefore, as an indicator of climate change, long-term changes in the Tropopause may carry less information about changes throughout the vertical temperature profile than has been suggested by previous studies using reanalyses and global climate models.
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definitions and sharpness of the extratropical Tropopause a trace gas perspective
Journal of Geophysical Research, 2004Co-Authors: Laura L. Pan, William J. Randel, B L Gary, M J Mahoney, E J HintsaAbstract:[1] Definitions of the extratropical Tropopause are examined from the perspective of chemical composition. Fine-scale measurements of temperature, ozone, carbon monoxide, and water vapor from approximately 70 aircraft flights, with ascending and descending Tropopause crossings near 40°N and 65°N, are used in this analysis. Using the relationship of the stratospheric tracer O3 and the tropospheric tracer CO, we address the issues of Tropopause sharpness and where the transitions from troposphere to stratosphere occur in terms of the chemical composition. Tracer relationships indicate that mixing of stratospheric and tropospheric air masses occurs in the vicinity of the Tropopause to form a transition layer. Statistically, this transition layer is centered on the thermal Tropopause. Furthermore, we show that the transition is much sharper near 65°N (a region away from the subtropical jet) but spans a larger altitude range near 40°N (in the vicinity of the subtropical jet). This latter feature is consistent with enhanced stratosphere-troposphere exchange and mixing activity near the Tropopause break.
Slimane Bekki - One of the best experts on this subject based on the ideXlab platform.
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multimodel assessment of the upper troposphere and lower stratosphere tropics and global trends
Journal of Geophysical Research, 2010Co-Authors: Andrew Gettelman, Thomas Birner, Slimane Bekki, Michaela I. Hegglin, Juan A. Añel, Masatomo Fujiwara, Stefanie Kremser, H Akiyoshi, John Austin, P BraesikeAbstract:The performance of 18 coupled Chemistry Climate Models (CCMs) in the Tropical Tropopause Layer (TTL) is evaluated using qualitative and quantitative diagnostics. Trends in Tropopause quantities in the tropics and the extratropical Upper Troposphere and Lower Stratosphere (UTLS) are analyzed. A quantitative grading methodology for evaluating CCMs is extended to include variability and used to develop four different grades for tropical Tropopause temperature and pressure, water vapor and ozone. Four of the 18 models and the multi‐model mean meet quantitative and qualitative standards for reproducing key processes in the TTL. Several diagnostics are performed on a subset of the models analyzing the Tropopause Inversion Layer (TIL), Lagrangian cold point and TTL transit time. Historical decreases in tropical Tropopause pressure and decreases in water vapor are simulated, lending confidence to future projections. The models simulate continued decreases in Tropopause pressure in the 21st century, along with ∼1K increases per century in cold point Tropopause temperature and 0.5–1 ppmv per century increases in water vapor above the tropical Tropopause. TTL water vapor increases below the cold point. In two models, these trends are associated with 35% increases in TTL cloud fraction. These changes indicate significant perturbations to TTL processes, specifically to deep convective heating and humidity transport. Ozone in the extratropical lowermost stratosphere has significant and hemispheric asymmetric trends. O3 is projected to increase by nearly 30% due to ozone recovery in the Southern Hemisphere (SH) and due to enhancements in the stratospheric circulation. These UTLS ozone trends may have significant effects in the TTL and the troposphere.
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the tropical Tropopause layer 1960 2100
Atmospheric Chemistry and Physics, 2009Co-Authors: Andrew Gettelman, Thomas Birner, Veronika Eyring, Slimane Bekki, Douglas E Kinnison, Martin Dameris, Hideharu Akiyoshi, Christoph Bruhl, Frank Lefevre, F. LottAbstract:The representation of the Tropical Tropopause Layer (TTL) in 13 different Chemistry Climate Models (CCMs) designed to represent the stratosphere is analyzed. Simulations for 1960–2005 and 1980–2100 are analyzed. Simulations for 1960–2005 are compared to reanalysis model output. CCMs are able to reproduce the basic structure of the TTL. There is a large (10 K) spread in annual mean tropical cold point Tropopause temperatures. CCMs are able to reproduce historical trends in Tropopause pressure obtained from reanalysis products. Simulated historical trends in cold point Tropopause temperatures are not consistent across models or reanalyses. The pressure of both the tropical Tropopause and the level of main convective outflow appear to have decreased (increased altitude) in historical runs as well as in reanalyses. Decreasing pressure trends in the tropical Tropopause and level of main convective outflow are also seen in the future. Models consistently predict decreasing Tropopause and convective outflow pressure, by several hPa/decade. Tropical cold point temperatures are projected to increase by 0.09 K/decade. Tropopause anomalies are highly correlated with tropical surface temperature anomalies and with Tropopause level ozone anomalies, less so with stratospheric temperature anomalies. Simulated stratospheric water vapor at 90 hPa increases by up to 0.5–1 ppmv by 2100. The result is consistent with the simulated increase in temperature, highlighting the correlation of Tropopause temperatures with stratospheric water vapor.
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The Tropical Tropopause Layer 1960–2100
Atmospheric Chemistry and Physics, 2009Co-Authors: Andrew Gettelman, Thomas Birner, Veronika Eyring, Hideo Akiyoshi, Ch. Brühl, Franck Lefevre, Slimane Bekki, Douglas E Kinnison, Martin Dameris, F. LottAbstract:The representation of the Tropical Tropopause Layer (TTL) in 13 different Chemistry Climate Models (CCMs) designed to represent the stratosphere is analyzed. Simulations for 1960–2005 and 1980–2100 are analyzed. Simulations for 1960–2005 are compared to reanalysis model output. CCMs are able to reproduce the basic structure of the TTL. There is a large (10 K) spread in annual mean tropical cold point Tropopause temperatures. CCMs are able to reproduce historical trends in Tropopause pressure obtained from reanalysis products. Simulated historical trends in cold point Tropopause temperatures are not consistent across models or reanalyses. The pressure of both the tropical Tropopause and the level of main convective outflow appear to have decreased (increased altitude) in historical runs as well as in reanalyses. Decreasing pressure trends in the tropical Tropopause and level of main convective outflow are also seen in the future. Models consistently predict decreasing Tropopause and convective outflow pressure, by several hPa/decade. Tropical cold point temperatures are projected to increase by 0.09 K/decade. Tropopause anomalies are highly correlated with tropical surface temperature anomalies and with Tropopause level ozone anomalies, less so with stratospheric temperature anomalies. Simulated stratospheric water vapor at 90 hPa increases by up to 0.5–1 ppmv by 2100. The result is consistent with the simulated increase in temperature, highlighting the correlation of Tropopause temperatures with stratospheric water vapor.
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The Tropical Tropopause Layer 1960–2100
2008Co-Authors: Andrew Gettelman, Thomas Birner, Veronika Eyring, Hideo Akiyoshi, F. Lott, Franck Lefevre, Slimane Bekki, Martin Dameris, D. A. Plummer, Ch. BrühlAbstract:Abstract. The representation of the Tropical Tropopause Layer in 13 different Chemistry Climate Models designed to represent the stratosphere is analyzed. Simulations for 1960–present and 1980–2100 are analyzed and compared to reanalysis model output. Results indicate that the models are able to reproduce the basic structure of the TTL. There is a large spread in cold point Tropopause temperatures that may be linked to variation in TTL ozone values. The models are generally able to reproduce historical trends in Tropopause pressure obtained from reanalysis products. Simulated historical trends in cold point Tropopause temperatures and in the meridional extent of the TTL are not consistent across models. The pressure of both the tropical Tropopause and the level of main convective outflow appear to be decreasing (increasing altitude) in historical runs. Similar trends are seen in the future. Models consistently predict decreasing Tropopause and convective outflow pressure, by several hPa/decade. Tropical cold point temperatures increase by 0.2 K/decade. This indicates that tropospheric warming dominates stratospheric cooling at the tropical Tropopause. Stratospheric water vapor at 100 hPa increases by up to 0.5–1 ppmv by 2100. This is less than implied directly by the temperature and methane increases, highlighting the correlation of Tropopause temperatures with stratospheric water vapor, but also the complex nature of TTL transport.
