In the past, studies of stratosphere-troposphere exchange of mass and chemical species have mainly emphasized the synoptic- and small-scale mechanisms of exchange This review, however, includes also the global-scale aspects of exchange, such as the transport across an isentropic surface (potential temperature about 380 K) that in the tropics lies just above the tropopause, near the 100-hPa pressure level Such a surface divides the stratosphere into an “overworld” and an extratropical “lowermost stratosphere” that for transport purposes need to be sharply distinguished This approach places stratosphere-troposphere exchange in the framework of the general circulation and helps to clarify the roles of the different mechanisms involved and the interplay between large and small scales The role of waves and eddies in the extratropical overworld is emphasized There, wave-induced forces drive a kind of global-scale extratropical “fluid-dynamical suction pump,” which withdraws air upward and poleward from the tropical lower stratosphere and pushes it poleward and downward into the extratropical troposphere The resulting global-scale circulation drives the stratosphere away from radiative equilibrium conditions Wave-induced forces may be considered to exert a nonlocal control, mainly downward in the extratropics but reaching laterally into the tropics, over the transport of mass across lower stratospheric isentropic surfaces This mass transport is for many purposes a useful measure of global-scale stratosphere-troposphere exchange, especially on seasonal or longer timescales Because the strongest wave-induced forces occur in the northern hemisphere winter season, the exchange rate is also a maximum at that season The global exchange rate is not determined by details of near-tropopause phenomena such as penetrative cumulus convection or small-scale mixing associated with upper level fronts and cyclones These smaller-scale processes must be considered, however, in order to understand the finer details of exchange Moist convection appears to play an important role in the tropics in accounting for the extreme dehydration of air entering the stratosphere Stratospheric air finds its way back into the troposphere through a vast variety of irreversible eddy exchange phenomena, including tropopause folding and the formation of so-called tropical upper tropospheric troughs and consequent irreversible exchange General circulation models are able to simulate the mean global-scale mass exchange and its seasonal cycle but are not able to properly resolve the tropical dehydration process Two-dimensional (height-latitude) models commonly used for assessment of human impact on the ozone layer include representation of stratosphere-troposphere exchange that is adequate to allow reasonable simulation of photochemical processes occurring in the overworld However, for assessing changes in the lowermost stratosphere, the strong longitudinal asymmetries in stratosphere-troposphere exchange render current two-dimensional models inadequate Either current transport parameterizations must be improved, or else, more likely, such changes can be adequately assessed only by three-dimensional models

Stratosphere‐troposphere exchange

Using the objectively analyzed FGGE II-b upper-air data, the large-scale circulation, heat sources and moisture sinks over the Tibetan Plateau and surrounding areas are examined for a 9-month period from December 1978 to August 1979. In addition to the FGGE data, special soundings obtained during the Chinese Qinghai-Xizang (Tibet) Plateau Meteorological Experiment (QXPMEX) from May to August 1979 are also used in the objective analyses. The evolution of the large-scale flow patterns, temperature, outgoing longwave radiation (OLR) and vertical circulation is described in order to identify the distinct seasonal changes from winter to summer that lead to the onset of the Asian summer monsoon. The Tibetan Plateau maintains a large-scale thermally driven vertical circulation which is originally separated from the planetary-scale monsoon system. The rising motion exists only on the western Plateau in winter and then spreads to the whole Plateau as the season progresses. The monsoon onset over Asia is an interaction process between the Plateau-induced circulation and the circulation associated with the principal rainbelt migrating northward. During winter the Plateau is a heat sink, but it is surrounded by regions of more intense cooling. In spring the Plateau becomes a heat source, but the cooling in the surrounding areas continues. The sensible heat flux from the surface provides the major source of heating on the Plateau. However, additional contribution from condensation heating is observed in the western Plateau during all seasons and, more significantly, in the eastern Plateau during summer. The sensible heating of the elevated Plateau surface and the radiative cooling in the environment maintain the horizontal temperature contrast that drives the thermally direct vertical circulation. The detailed examination of the warming process of the upper troposphere during two transition periods, i, e., the onset of the Southeast Asian monsoon in May and that of the Indian monsoon in June, reveals that the temperature increase over the eastern Plateau during the first onset was mainly the result of diabatic heating, whereas that over the Iran-Afghanistan-western Plateau region leading to the second onset was caused by intense subsidence. There are large diurnal variations in the boundary layer and vertical circulation over the Plateau. As a result of diurnal heating of the surface, a deep mixed layer of nearly uniform potential temperature exists over the Plateau in the evening (1200 UTC), suggesting the role of thermal convection in the upward transport of heat. However, moisture is not well mixed vertically and there is a large horizontal temperature gradient in the boundary layer. From late spring to summer the boundary layer becomes more stable for dry convection. On the other hand, the vertical distributions of equivalent potential temperature in late spring and afterwards show a conditionally unstable stratification for moist convection with the increase of moisture of surface air.

https://www.jstage.jst.go.jp/article/jmsj1965/70/1B/70_1B_319/_pdf

Seasonal Heating of the Tibetan Plateau and Its Effects on the Evolution of the Asian Summer Monsoon

[1] This paper provides a review of stratosphere-troposphere exchange (STE), with a focus on processes in the extratropics. It also addresses the relevance of STE for tropospheric chemistry, particularly its influence on the oxidative capacity of the troposphere. After summarizing the current state of knowledge, the objectives of the project Influence of Stratosphere-Troposphere Exchange in a Changing Climate on Atmospheric Transport and Oxidation Capacity (STACCATO), recently funded by the European Union, are outlined. Several papers in this Journal of Geophysical Research– Atmospheres special section present the results of this project, of which this paper gives an overview. STACCATO developed a new concept of STE in the extratropics, explored the capacities of different types of methods and models to diagnose STE, and identified their various strengths and shortcomings. Extensive measurements were made in central Europe, including the first monitoring over an extended period of time of beryllium-10 ( 10 Be), to provide a suitable database for case studies of stratospheric intrusions and for model validation. Photochemical models were used to examine the impact of STE on tropospheric ozone and the oxidizing capacity of the troposphere. Studies of the present interannual variability of STE and projections into the future were made using reanalysis data and climate models. INDEX TERMS: 0341 Atmospheric Composition and Structure: Middle atmosphere—constituent transport and chemistry (3334); 0368 Atmospheric Composition and Structure: Troposphere—constituent transport and chemistry; 3362 Meteorology and Atmospheric Dynamics: Stratosphere/troposphere interactions; KEYWORDS: Brewer-Dobson circulation, trajectories, Lagrangian model, reanalysis, tropopause

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2002JD002490

Stratosphere-troposphere exchange: A review, and what we have learned from STACCATO

[1] The extratropical upper troposphere and lower stratosphere (Ex-UTLS) is a transition region between the stratosphere and the troposphere. The Ex-UTLS includes the tropopause, a strong static stability gradient and dynamic barrier to transport. The barrier is reflected in tracer profiles. This region exhibits complex dynamical, radiative, and chemical characteristics that place stringent spatial and temporal requirements on observing and modeling systems. The Ex-UTLS couples the stratosphere to the troposphere through chemical constituent transport (of, e.g., ozone), by dynamically linking the stratospheric circulation with tropospheric wave patterns, and via radiative processes tied to optically thick clouds and clear-sky gradients of radiatively active gases. A comprehensive picture of the Ex-UTLS is presented that brings together different definitions of the tropopause, focusing on observed dynamical and chemical structure and their coupling. This integral view recognizes that thermal gradients and dynamic barriers are necessarily linked, that these barriers inhibit mixing and give rise to specific trace gas distributions, and that there are radiative feedbacks that help maintain this structure. The impacts of 21st century anthropogenic changes to the atmosphere due to ozone recovery and climate change will be felt in the Ex-UTLS, and recent simulations of these effects are summarized and placed in context.

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The extratropical upper troposphere and lower stratosphere

This paper presents a 1-year “climatology” of airstreams, based on a large number of three-dimensional air parcel trajectories started daily from points on a grid covering the Northern Hemisphere troposphere and lowermost stratosphere. Different types of airstreams (warm conveyor belts, dry intrusions, stratosphere-to-troposphere flows, and troposphere-to-stratosphere flows) are identified, and their geographical distribution and associated mass fluxes are examined. Warm conveyor belt air parcels, which are deposited in the uppermost troposphere and even the lowermost stratosphere, originate most frequently in the boundary layer over the warm water pools at the eastern seaboards of North America and Asia, close to the worldwide highest anthropogenic emissions. Therefore their chemical characteristics likely range from very clean to highly polluted. Because warm conveyor belts rarely start over Europe, European trace gas emissions have fewer chances of reaching the upper troposphere and lowermost stratosphere with warm conveyor belts than emissions from other densely populated regions. On the other hand, the upper troposphere over Europe frequently receives outflow from warm conveyor belts originating over the North American seaboard. Dry intrusion activity is highest in winter and lowest in summer and shows maxima over western North America and eastern Asia. Deep intrusions from the stratosphere into the lower troposphere are almost nonexistent during the summer. Mass fluxes associated with each of the airstream types are reported and are an alternative to Eulerian mass flux estimates. All types of airstreams with strong vertical motions are highly incoherent. Rather than depositing compact air parcels, they stir air masses into a new environment and create filamentary tracer structures.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2000JD900570

A 1-year Lagrangian ``climatology'' of airstreams in the Northern Hemisphere troposphere and lowermost stratosphere

Using a dynamical definition of the tropopause, a diagnostic model of stratosphere–troposphere exchange is presented. The net transport across the tropopause is independent of the vertical coordinate. When the transport is partitioned into contributions from individual transport mechanisms, the isentropic coordinate system provides the most straightforward physical interpretation. The physical mechanisms responsible for the exchange of mass and trace constituents between the stratosphere and troposphere include diabatic processes, temporal movement of the tropopause, and transport along isentropic surfaces which intersect the tropopause. The mechanism of the isentropic transport operates in several meteorological settings of different spatial scales; the best-documented examples include tropopause folding near extratropical and subtropical jet streams and cutoff lows, as well as transverse circulations around quasi-steady jet streams. The relative importance of various mechanisms in the stratosph...

A New Formulation of the Exchange of Mass and Trace Constituents between the Stratosphere and Troposphere

The time-averaged structure of global monsoonal circulations and planetary scale transport processes are determined from the FGGE Level IIIa operational data set generated by the US National Meteorological Center. Through isentropic diagnostics, rotational and irrotational components of the horizontal mass transport and the distribution of heating for the planetary scale are analyzed for the months of January. April, July and October of 1979. The global monsoonal circulations coupled with the planetary scale of differential heating occur in the form of large scale Hadley-type and Walker-type circulations. Net heating within a given region and net cooling in another region in association with latent heat release and differences in boundary flux of energy through the earth's surface and the top of the atmosphere result in forcing of isentropic mass circulations that link energy source with energy sink regions, a result basic to thermally forced circulations. The primary planetary source of energy in the region of Indonesia-Philippines-Southeast Asia is linked through isentropic mass transport with sinks of energy in the regions of the two circumpolar vortices, the Sahara and subtropical anticyclonic circulations. This primary center of the source of energy in the Indonesia-Southeast Asia area moves seasonally from one hemisphere to the other. Other source regions of energy occur over Brazil in January and Central America and Africa in July. Through horizontal transport of mass and energy, the winter Asiatic monsoonal circulation links radiative cooling over Asia to sensible and latent heat release within mid-latitude baroclinic waves and also to latent heat release in the Indonesia, Philippine and New Guinea regions. The role of mid-latitude baroclinic waves in providing for mass and energy exchange between polar and subtropical regions within the time-averaged isentropic structure is briefly discussed. DOI: 10.1111/j.1600-0870.1985.tb00274.x

The thermally coupled response of the planetary scale circulation to the global distribution of heat sources and sinks

The three-dimensional global distributions of time-averaged atmospheric heating for January, April, July and October 1979 are estimated from the ECMWF GWE Level IIIb data set. Heating rates are calculated through a vertical integration of the isentropic equation of mass continuity. Estimates of the vertical variation of heating are presented in isobaric coordinates through interpolation of the vertical profiles of heating from isentropic to isobaric coordinates. The horizontal distributions of heating and vertical profiles from various climatological regimes of the planetary circulation provide insight into the four-dimensional structure of the thermal forcing of the atmosphere. The large-scale structure of the heating distributions appears spatially and temporally consistent with known features of the global circulation and the seasonal evolution. Major features of the global distributions include the heating in regions of deep moist convection over South America, equatorial Africa, the ITCZ, the Asian monsoon circulation and the oceanic cyclone tracks of the Northern Hemisphere. The primary centres of heating migrate meridionally and zonally with changing seasons. The meridional migration is linked directly with the annual variation of the latitude of maximum incoming solar radiation. The zonal migration is linked with the planetary scale distribution of continents and oceans and the land-sea surface temperature distribution as determined by the surface energy balance and energy transport within the atmosphere itself. Throughout the tropical-subtropical regions, the strongest heating occurs above 600 mb in association with deep convection. Within the primary centres of heating associated with the Asian monsoon circulation, the maximum heating in the vertical profile is near 400 mb. Over the oceanic storm tracks of the Northern Hemisphere, heating occurs through most of the troposphere. The lower tropospheric heating is maximized in January and in that month is significantly stronger than the heating in the middle troposphere. In July there is negligible heating in the lower troposphere. Profiles from the high latitude continental regions such as central Asia and Canada are in close agreement showing cooling through most of the troposphere in winter and modest heating in summer. Profiles from desert regions over the Sahara and western Australia are also in close agreement showing a transition from low level heating to middle and upper level cooling. Cooling occurs throughout the free troposphere in regions of subtropical anticyclonic circulations over the eastern North and South Pacific Oceans. DOI: 10.1034/j.1600-0870.1990.t01-1-00001.x

The three-dimensional distribution of atmospheric heating during the GWE

Based on surface pressure and terrain height analyses from the National Meteorological Center, mountain torques are calculated for January, April, July and October 1979 during the First GARP Global Experiment. The zonally integrated mountain torques are generally in good agreement with previous studies. For all four months, positive torque exists in the tropical latitudes as well as in the polar and subtropical latitudes of the Northern Hemisphere; negative torque exists in northern middle latitudes and most of the Southern Hemisphere. An exception occurs in July when the mountain torque is negative between 5 and 25°N and positive in the Southern Hemisphere subtropics. Over latitudes where large terrain variation exists such as near 20°S due to the Andes, the estimate obtained in this study is larger in magnitude than that from previous work. The difference is due to the differences in both grid resolution and the particular atmospheric data and topography selected. The meridional profiles of ind...

Seasonal distributions of mountain torques during FGGE

Three ground-based radars in the Pearl River Delta successfully observed Typhoon Higos (2020), which traveled over the offshore area in the South China Sea. During the observation period, the stratiform region of the outer rainband of HIGOS became active while swirling inward, merging into an unclosed eyewall and spreading outward, but its structure was asymmetric between upwind and downwind. To understand the dynamic mechanism of the asymmetry of the stratiform region in detail, the refined wind speed distributions in the inner core of Higos was retrieved by using the radar observation data and a three-dimensional, variational, direct, data assimilation, Dual-Doppler analysis (DDA). In addition, an Observing System Simulation Experiment (OSSE) was conducted with the numerical simulations by the Weather Research and Forecasting (WRF) model and numerical emulations by Cloud Resolving Model Radar SIMulator (CR-SIM) software to validate the retrieved data. From the OSSE, the emulated retrieved data were comparable with the WRF-out data. The analysis shows that the dynamic mechanisms are different between upwind and downwind in the stratiform rainband. In the former, the inflow sinks in the middle troposphere. In addition, there is an inflow in the lower troposphere, with an outflow aloft the inflow. In the latter, however, the stratiform rainband is primarily influenced by outflow from inside the rainband and inflow from outside the monsoon-related southwesterly winds. The vertical velocity characteristics in the stratiform rainband downwind also differ from those upwind. The upwind updraft was distinct in the middle troposphere, whereas the downwind updraft was caused by the convergence of the outflow from inside the stratiform rainband and the monsoon-related southwesterly inflow in the lower troposphere.

/pdf/dynamic-field-retrieval-and-analysis-of-structural-evolution-3mm3v2xh.pdf

Ming-Ying Wei

Papers

A New Formulation of the Exchange of Mass and Trace Constituents between the Stratosphere and Troposphere

The thermally coupled response of the planetary scale circulation to the global distribution of heat sources and sinks

The three-dimensional distribution of atmospheric heating during the GWE

Seasonal distributions of mountain torques during FGGE

Dynamic Field Retrieval and Analysis of Structural Evolution in Offshore Core Area of Typhoon Higos Based on Ground-Based Radar Observation