scholarly journals Stratospheric dryness: model simulations and satellite observations

2007 ◽  
Vol 7 (5) ◽  
pp. 1313-1332 ◽  
Author(s):  
J. Lelieveld ◽  
C. Brühl ◽  
P. Jöckel ◽  
B. Steil ◽  
P. J. Crutzen ◽  
...  
Keyword(s):  
Water Vapor ◽  
General Circulation ◽  
Large Scale ◽  
Middle Atmosphere ◽  
Circulation Model ◽  
Satellite Observations ◽  
Radiative Heating ◽  
Mixing Ratios ◽  
Tropical Tropopause ◽  
Mass Fluxes

Abstract. The mechanisms responsible for the extreme dryness of the stratosphere have been debated for decades. A key difficulty has been the lack of comprehensive models which are able to reproduce the observations. Here we examine results from the coupled lower-middle atmosphere chemistry general circulation model ECHAM5/MESSy1 together with satellite observations. Our model results match observed temperatures in the tropical lower stratosphere and realistically represent the seasonal and inter-annual variability of water vapor. The model reproduces the very low water vapor mixing ratios (below 2 ppmv) periodically observed at the tropical tropopause near 100 hPa, as well as the characteristic tape recorder signal up to about 10 hPa, providing evidence that the dehydration mechanism is well-captured. Our results confirm that the entry of tropospheric air into the tropical stratosphere is forced by large-scale wave dynamics, whereas radiative cooling regionally decelerates upwelling and can even cause downwelling. Thin cirrus forms in the cold air above cumulonimbus clouds, and the associated sedimentation of ice particles between 100 and 200 hPa reduces water mass fluxes by nearly two orders of magnitude compared to air mass fluxes. Transport into the stratosphere is supported by regional net radiative heating, to a large extent in the outer tropics. During summer very deep monsoon convection over Southeast Asia, centered over Tibet, moistens the stratosphere.

scholarly journals Stratospheric dryness

2006 ◽  
Vol 6 (6) ◽  
pp. 11247-11298 ◽  
Author(s):  
J. Lelieveld ◽  
C. Brühl ◽  
P. Jöckel ◽  
B. Steil ◽  
P. J. Crutzen ◽  
...  
Keyword(s):  
Atmospheric Chemistry ◽  
General Circulation ◽  
Large Scale ◽  
Circulation Model ◽  
Radiative Heating ◽  
Mixing Ratios ◽  
Tropical Tropopause ◽  
Dehydration Mechanism ◽  
Radiation Processes ◽  
Stratospheric Clouds

Abstract. The mechanisms responsible for the extreme dryness of the stratosphere have been debated for decades. A key difficulty has been the lack of models which are able to reproduce the observations. Here we examine results from a new atmospheric chemistry general circulation model (ECHAM5/MESSy1) together with satellite observations. Our model results match observed temperatures in the tropical lower stratosphere and realistically represent recurrent features such as the semi-annual oscillation (SAO) and the quasi-biennual oscillation (QBO), indicating that dynamical and radiation processes are simulated accurately. The model reproduces the very low water vapor mixing ratios (1–2 ppmv) periodically observed at the tropical tropopause near 100 hPa, as well as the characteristic tape recorder signal up to about 10 hPa, providing evidence that the dehydration mechanism is well-captured, albeit that the model underestimates convective overshooting and consequent moistening events. Our results show that the entry of tropospheric air into the stratosphere at low latitudes is forced by large-scale wave dynamics; however, radiative cooling can regionally limit the upwelling or even cause downwelling. In the cold air above cumulonimbus anvils thin cirrus desiccates the air through the sedimentation of ice particles, similar to polar stratospheric clouds. Transport deeper into the stratosphere occurs in regions where radiative heating becomes dominant, to a large extent in the subtropics. During summer the stratosphere is moistened by the monsoon, most strongly over Southeast Asia.

scholarly journals Observations of Temperature, Wind, Cirrus, and Trace Gases in the Tropical Tropopause Transition Layer during the MJO*

2014 ◽  
Vol 71 (3) ◽  
pp. 1143-1157 ◽  
Author(s):  
Katrina S. Virts ◽  
John M. Wallace
Keyword(s):  
Water Vapor ◽  
Transition Layer ◽  
Rossby Waves ◽  
Trace Gases ◽  
Satellite Observations ◽  
Radiative Heating ◽  
Mixing Ratio ◽  
Kelvin Wave ◽  
Tropical Tropopause ◽  
Water Vapor Mixing Ratio

Abstract Satellite observations of temperature, optically thin cirrus clouds, and trace gases derived from the Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC), Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO), and the Microwave Limb Sounder (MLS) are analyzed in combination with Interim European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-Interim) wind and humidity fields in the tropical tropopause transition layer (TTL), using the Madden–Julian oscillation (MJO) as a carrier signal. MJO-related deep convection induces planetary-scale Kelvin and Rossby waves in the stably stratified TTL. Regions of ascent in these waves are associated with anomalously low temperatures, high radiative heating rates, enhanced cirrus occurrence, and high carbon monoxide and low ozone concentrations. Low water vapor mixing ratio anomalies lag the low temperature anomalies by about 1–2 weeks. The anomalies in all fields propagate eastward, circumnavigating the tropical belt over a roughly 40-day interval. Equatorial cross sections reveal that the anomalies tilt eastward with height in the TTL and propagate downward from the lower stratosphere into the upper troposphere. As MJO-related convection moves into the western Pacific and dissipates, a fast-moving Kelvin wave flanked by Rossby waves propagates eastward across South America and Africa into the western Indian Ocean. The region of equatorial westerly wind anomalies behind the Kelvin wave front lengthens until it encompasses most of the tropics at the 150-hPa level, giving rise to equatorially symmetric, anomalously low zonal-mean temperature and water vapor mixing ratio and enhanced cirrus above about 100 hPa.

scholarly journals Seasonality of moisture supplies to precipitation over the Third Pole: a stable water isotopic perspective

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Xiaoxin Yang ◽  
Tandong Yao
Keyword(s):  
Water Vapor ◽  
Isotopic Composition ◽  
General Circulation ◽  
Large Scale ◽  
Circulation Model ◽  
Potential Effect ◽  
Water Vapor Transport ◽  
The Tibetan Plateau ◽  
Physical Processes ◽  
Large Scale Atmospheric Circulation

Abstract This study integrated isotopic composition in precipitation at 50 stations on and around the Tibetan Plateau (TP) and demonstrated the distinct seasonality of isotopic composition in precipitation across the study period. The potential effect of water vapor isotopes on precipitation isotopes is studied by comparing the station precipitation data with extensive isotopic patterns in atmospheric water vapor, revealing the close linkage between the two. The analysis of contemporary water vapor transport and potential helps confirm the different mechanisms behind precipitation isotopic compositions in different areas, as the southern TP is more closely related to large-scale atmospheric circulation such as local Hadley and summer monsoon circulations during other seasons than winter, while the northern TP is subject to the westerly prevalence and advective moisture supply and precipitation processes. The new data presented in this manuscript also enrich the current dataset for the study of precipitation isotopes in this region and together provide a valuable database for verification of the isotope-integrated general circulation model and explanation of related physical processes.

Diagnosis of Subtropical Humidity Dynamics Using Tracers of Last Saturation

2005 ◽  
Vol 62 (9) ◽  
pp. 3353-3367 ◽  
Author(s):  
Joseph Galewsky ◽  
Adam Sobel ◽  
Isaac Held
Keyword(s):  
Water Vapor ◽  
General Circulation ◽  
Large Scale ◽  
Transport Model ◽  
Thermal Relaxation ◽  
Circulation Model ◽  
Reanalysis Data ◽  
Tracer Transport ◽  
Dry Air ◽  
Model Match

Abstract A technique for diagnosing the mechanisms that control the humidity in a general circulation model (GCM) or observationally derived meteorological analysis dataset is presented. The technique involves defining a large number of tracers, each of which represents air that has last been saturated in a particular region of the atmosphere. The time-mean tracer fields show the typical pathways that air parcels take between one occurrence of saturation and the next. The tracers provide useful information about how different regions of the atmosphere influence the humidity elsewhere. Because saturation vapor pressure is a function only of temperature and assuming mixing ratio is conserved for unsaturated parcels, these tracer fields can also be used together with the temperature field to reconstruct the water vapor field. The technique is first applied to an idealized GCM in which the dynamics are dry and forced using the Held–Suarez thermal relaxation, but the model carries a passive waterlike tracer that is emitted at the surface and lost due to large-scale condensation with zero latent heat release and no condensate retained. The technique provides an accurate reconstruction of the simulated water vapor field. In this model, the dry air in the subtropical troposphere is produced primarily by isentropic transport and is moistened somewhat by mixing with air from lower levels, which has not been saturated since last contact with the surface. The technique is then applied to the NCEP–NCAR reanalysis data from December–February (DJF) 2001/02, using the offline tracer transport model MATCH. The results show that the dryness of the subtropical troposphere is primarily controlled by isentropic transport of very dry air by midlatitude eddies and that diabatic descent from the tropical upper troposphere plays a secondary role in controlling the dryness of the subtropics.

scholarly journals Stratospheric SO<sub>2</sub> and sulphate aerosol, model simulations and satellite observations

2013 ◽  
Vol 13 (4) ◽  
pp. 11395-11425 ◽  
Author(s):  
C. Brühl ◽  
J. Lelieveld ◽  
M. Höpfner ◽  
H. Tost
Keyword(s):  
Atmospheric Chemistry ◽  
Radiative Forcing ◽  
General Circulation ◽  
Middle Atmosphere ◽  
Lower Boundary ◽  
Circulation Model ◽  
Volcanic Eruptions ◽  
Satellite Observations ◽  
Quasi Biennial Oscillation ◽  
Tropospheric Aerosol

Abstract. A multiyear study with the atmospheric chemistry general circulation model EMAC with the aerosol module GMXe at high altitude resolution demonstrates that the sulfur gases COS and SO2, the latter from low-latitude volcanic eruptions, predominantly control the formation of stratospheric aerosol. The model consistently uses the same parameters in the troposphere and stratosphere for 7 aerosol modes applied. Lower boundary conditions for COS and other long-lived trace gases are taken from measurement networks, while estimates of volcanic SO2 emissions are based on satellite observations. We show comparisons with satellite data for aerosol extinction (e.g. SAGE) and SO2 in the middle atmosphere (MIPAS on ENVISAT). This corroborates the interannual variability induced by the Quasi-Biennial Oscillation, which is internally generated by the model. The model also realistically simulates the radiative effects of stratospheric and tropospheric aerosol including the effects on the model dynamics. The medium strength volcanic eruptions of 2005 and 2006 exerted a nonnegligible radiative forcing of up to −0.6 W m−2 in the tropics, while the large Pinatubo eruption caused a maximum though short term tropical forcing of about −10 W m−2. The study also shows that observed upper stratospheric SO2 can be simulated accurately only when a sulphur sink on meteoritic dust is included and the photolysis of gaseous H2SO4 in the near infrared is higher than assumed previously.

scholarly journals A Gray-Radiation Aquaplanet Moist GCM. Part I: Static Stability and Eddy Scale

2006 ◽  
Vol 63 (10) ◽  
pp. 2548-2566 ◽  
Author(s):  
Dargan M. W. Frierson ◽  
Isaac M. Held ◽  
Pablo Zurita-Gotor
Keyword(s):  
Water Vapor ◽  
General Circulation ◽  
Large Scale ◽  
Circulation Model ◽  
Companion Paper ◽  
Static Stability ◽  
Lapse Rate ◽  
Surface Boundary ◽  
Moist Convection ◽  
Control Value

Abstract In this paper, a simplified moist general circulation model is developed and used to study changes in the atmospheric general circulation as the water vapor content of the atmosphere is altered. The key elements of the model physics are gray radiative transfer, in which water vapor and other constituents have no effect on radiative fluxes, a simple diffusive boundary layer with prognostic depth, and a mixed layer aquaplanet surface boundary condition. This GCM can be integrated stably without a convection parameterization, with large-scale condensation only, and this study focuses on this simplest version of the model. These simplifications provide a useful framework in which to focus on the interplay between latent heat release and large-scale dynamics. In this paper, the authors study the role of moisture in determining the tropospheric static stability and midlatitude eddy scale. In a companion paper, the effects of moisture on energy transports by baroclinic eddies are discussed. The authors vary a parameter in the Clausius–Clapeyron relation to control the amount of water in the atmosphere, and consider circulations ranging from the dry limit to 10 times a control value. The typical length scale of midlatitude eddies is found to be remarkably insensitive to the amount of moisture in the atmosphere in this model. The Rhines scale evaluated at the latitude of the maximum eddy kinetic energy fits the model results for the eddy scale well. Moist convection is important in determining the extratropical lapse rate, and the dry stability is significantly increased with increased moisture content.

scholarly journals Formation of Jets and Equatorial Superrotation on Jupiter

2009 ◽  
Vol 66 (3) ◽  
pp. 579-601 ◽  
Author(s):  
Tapio Schneider ◽  
Junjun Liu
Keyword(s):  
General Circulation ◽  
Large Scale ◽  
Thermal Structure ◽  
Circulation Model ◽  
Zonal Flow ◽  
Heat Fluxes ◽  
Radiative Heating ◽  
Control Simulation ◽  
Deep Interior ◽  
Outer Atmosphere

Abstract The zonal flow in Jupiter’s upper troposphere is organized into alternating retrograde and prograde jets, with a prograde (superrotating) jet at the equator. Existing models posit as the driver of the flow either differential radiative heating of the atmosphere or intrinsic heat fluxes emanating from the deep interior; however, they do not reproduce all large-scale features of Jupiter’s jets and thermal structure. Here it is shown that the difficulties in accounting for Jupiter’s jets and thermal structure resolve if the effects of differential radiative heating and intrinsic heat fluxes are considered together, and if upper-tropospheric dynamics are linked to a magnetohydrodynamic (MHD) drag that acts deep in the atmosphere and affects the zonal flow away from but not near the equator. Baroclinic eddies generated by differential radiative heating can account for the off-equatorial jets; meridionally propagating equatorial Rossby waves generated by intrinsic convective heat fluxes can account for the equatorial superrotation. The zonal flow extends deeply into the atmosphere, with its speed changing with depth, away from the equator up to depths at which the MHD drag acts. The theory is supported by simulations with an energetically consistent general circulation model of Jupiter’s outer atmosphere. A simulation that incorporates differential radiative heating and intrinsic heat fluxes reproduces Jupiter’s observed jets and thermal structure and makes testable predictions about as yet unobserved aspects thereof. A control simulation that incorporates only differential radiative heating but not intrinsic heat fluxes produces off-equatorial jets but no equatorial superrotation; another control simulation that incorporates only intrinsic heat fluxes but not differential radiative heating produces equatorial superrotation but no off-equatorial jets. The proposed mechanisms for the formation of jets and equatorial superrotation likely act in the atmospheres of all giant planets.

Tropical Tropospheric-Only Responses to Absorbing Aerosols

2012 ◽  
Vol 25 (7) ◽  
pp. 2471-2480 ◽  
Author(s):  
Geeta G. Persad ◽  
Yi Ming ◽  
V. Ramaswamy
Keyword(s):  
Black Carbon ◽  
General Circulation Model ◽  
General Circulation ◽  
Large Scale ◽  
Substantial Reduction ◽  
Circulation Model ◽  
Cloud Amount ◽  
Radiative Heating ◽  
Physically Based ◽  
Absorbing Aerosols

Abstract Absorbing aerosols affect the earth’s climate through direct radiative heating of the troposphere. This study analyzes the tropical tropospheric-only response to a globally uniform increase in black carbon, simulated with an atmospheric general circulation model, to gain insight into the interactions that determine the radiative flux perturbation. Over the convective regions, heating in the free troposphere hinders the vertical development of deep cumulus clouds, resulting in the detrainment of more cloudy air into the large-scale environment and stronger cloud reflection. A different mechanism operates over the subsidence regions, where heating near the boundary layer top causes a substantial reduction in low cloud amount thermodynamically by decreasing relative humidity and dynamically by lowering cloud top. These findings, which align well with previous general circulation model and large-eddy simulation calculations for black carbon, provide physically based explanations for the main characteristics of the tropical tropospheric adjustment. The implications for quantifying the climate perturbation posed by absorbing aerosols are discussed.

Modeling Water Vapor and Clouds as Passive Tracers in an Idealized GCM

2018 ◽  
Vol 31 (2) ◽  
pp. 775-786 ◽  
Author(s):  
Yi Ming ◽  
Isaac M. Held
Keyword(s):  
Water Vapor ◽  
General Circulation ◽  
Large Scale ◽  
Probability Distributions ◽  
Water Vapor Pressure ◽  
Substantial Reduction ◽  
Lower Troposphere ◽  
Circulation Model ◽  
Cloud Microphysics ◽  
Cloud Fraction

This paper introduces an idealized general circulation model (GCM) in which water vapor and clouds are tracked as tracers, but are not allowed to affect circulation through either latent heat release or cloud radiative effects. The cloud scheme includes an explicit treatment of cloud microphysics and diagnoses cloud fraction from a prescribed subgrid distribution of total water. The model is capable of qualitatively capturing many large-scale features of water vapor and cloud distributions outside of the boundary layer and deep tropics. The subtropical dry zones, midlatitude storm tracks, and upper-tropospheric cirrus are simulated reasonably well. The inclusion of cloud microphysics (namely rain re-evaporation) has a modest but significant effect of moistening the lower troposphere in this model. When being subjected to a uniform fractional increase of saturated water vapor pressure, the model produces little change in cloud fraction. A more realistic perturbation, which considers the nonlinearity of the Clausius–Clapeyron relation and spatial structure of CO2-induced warming, results in a substantial reduction in the free-tropospheric cloud fraction. This is reconciled with an increase of relative humidity by analyzing the probability distributions of both quantities, and may help explain partly similar decreases in cloud fraction in full GCMs. The model provides a means to isolate individual processes or model components for studying their influences on cloud simulation in the extratropical free troposphere.

scholarly journals To what extent could water isotopic measurements help us understand model biases in the water cycle over Western Siberia

2014 ◽  
Vol 14 (18) ◽  
pp. 9807-9830 ◽  
Author(s):  
V. Gryazin ◽  
C. Risi ◽  
J. Jouzel ◽  
N. Kurita ◽  
J. Worden ◽  
...  
Keyword(s):  
Water Vapor ◽  
General Circulation ◽  
Large Scale ◽  
Western Siberia ◽  
Water Cycle ◽  
Circulation Model ◽  
Added Value ◽  
Global Network ◽  
Isotopic Measurements ◽  
Dry Bias

Abstract. We evaluate the isotopic composition of water vapor and precipitation simulated by the LMDZ (Laboratoire de Météorologie Dynamique-Zoom) GCM (General Circulation Model) over Siberia using several data sets: TES (Tropospheric Emission Spectrometer) and GOSAT (Greenhouse gases Observing SATellite) satellite observations of tropospheric water vapor, GNIP (Global Network for Isotopes in Precipitation) and SNIP (Siberian Network for Isotopes in Precipitation) precipitation networks, and daily, in situ measurements of water vapor and precipitation at the Kourovka site in Western Siberia. LMDZ captures the spatial, seasonal and daily variations reasonably well, but it underestimates humidity (q) in summer and overestimates δD in the vapor and precipitation in all seasons. The performance of LMDZ is put in the context of other isotopic models from the SWING2 (Stable Water Intercomparison Group phase 2) models. There is significant spread among models in the simulation of δD, and of the δD-q relationship. This confirms that δD brings additional information compared to q only. We specifically investigate the added value of water isotopic measurements to interpret the warm and dry bias featured by most GCMs over mid and high latitude continents in summer. The analysis of the slopes in δD-q diagrams and of processes controlling δD and q variations suggests that the cause of the dry bias could be either a problem in the large-scale advection transporting too much dry and warm air from the south, or too strong boundary-layer mixing. However, δD-q diagrams using the available data do not tell the full story. Additional measurements would be needed, or a more sophisticated theoretical framework would need to be developed.

Sign in / Sign up

Export Citation Format

Share Document