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NASA NTRS1984

Improved HIRS2/MSU soundings using tropopause information

In the GLAS physical retrieval scheme, all temperature profiles are expressed as an expansion about a global mean using empirical orthogonal functions derived from a sample of radiosondes. Total ozone burden, a parameter highly correlated with tropopause height, should be useful in improving sounding accuracy. The ability to estimate tropopause information from layer mean temperatures suggests incorporating the layer mean temperatures estimated from the sounding itself to give estimates of tropopause pressure and temperature. While information completely independent of sounding and first guess data is preferable, additional information is in fact added to the system by the statistical relationships between tropopause temperature and pressure and layer mean temperature profiles. This should not be confused with use of statistical relationships between temperature profiles and satellite observations, which form the basis of a statistical retrieval system but is in no way used in the physical retrieval scheme.

Susskind, J.↗

NASA NTRS1985

Applications of Fuzzy Clustering Techniques to Stratified by Tropopause MSU Temperature Retrievals

The fuzzy partitioned clustering method was applied to predict tropopause height only using microwave information with an eye towards using it on real data under cloudy conditions. In the second stage stratified by tropopause regression temperature retrievals included using only the three or four microwave channels for each 40 mb range. The first step in the experiment is the fuzzy partitioned clustering of the microwave brightness temperatures. This method is a combination of standard hard clustering and discriminant analysis. The fuzzy partitioned clustering uses all the generated probabilities of membership of each pattern vector in any of the given clusters. These probabilities are generated by discriminant analysis to locate the correct cluster. The ultimate goal of standard discriminant analysis is to provide the unique (correct) cluster to which the pattern vector belongs. It was only the maximum of all the generated probabilities. The method uses all the probabilities and weight the regressions generated within each cluster. These regression formulas predict the tropopause height from the microwave brightness temperatures. In the second step the microwave regression temperature retrievals are stratified by tropopause height every 40 mb. The control experiment is defined, the data are stratified by land/ocean, summer/winter, and latitude bands.

Munteanu, M. J.↗

NASA NTRS1984

The President's Day cyclone of 18-19 February 1979 - Influence of a tropopause fold on rapid cyclogenesis

The surface and satellite imagery data from the cyclone of February 18-19, 1979 are analyzed. Operational radiosonde data are utilized to study the tropopause fold associated with the polar jet streak. Patterns of vertical motion compatible with the tropopause fold are calculated by the diagnostic ageostrophic circulation equation of Sawyer (1956) and Eliassen (1962); the verification of the calculated patterns is described. The relationship between the stratospheric extrusion and the folded tropopause is determined by examining the potential vorticity and ozone concentrations. The influence of the stratospheric extrusion within the folded tropopause on the development of the cyclone is investigated by analyzing the potential vorticity, static stability, and absolute vorticity from the Eulerian and Lagrangian perspective.

Uccellini, L. W.↗

NASA NTRS1987

The Arctic tropopause fold

Analyses of research-aircraft observations, satellite total-columnar-ozone retrievals, and synoptic upper-air soundings are used to describe the structure of Arctic jetstreams and their associated frontal zones and tropopause folds. These analyses document the presence of major tropopause folding events within the Arctic that occur at the flanks of large-scale (about 2000 km) polar vortices. One example shows a solar vortex and its associated tropopause fold and Arctic front that migrated from the high Canadian Arctic southward into midlatitudes over central North America. Total columnar ozone measurements from the Total Ozone Mapping Spectrometer are shown to identify the location of polar vortices and the mesoscale (about 200 km) ozone gradients at the flanks of these vortices, which coincide with regions of Arctic tropopause folding and associated stratospheric-tropospheric exchange processes.

Shapiro, M. A.↗

NASA NTRS1987

TOMS ozone data compared at mesoscale resolution to tropopause heights from the AVE radiosonde network and to VAS radiances over the south-central United States

Observations from 1982 are being compared between the Total Ozone Mapping Spectrometer (TOMS), the Atmospheric Variability Experiment (AVE), and the VISSR Atmospheric Sounder (VAS) across Texas and Oklahoma. TOMS data show a significant ozone maximum over northeastern Texas. AVE radiosonde analysis shows tropopause heights with the highest pressure (lowest altitudes) over central Oklahoma accompanied by a mid-level jet across northern Mexico exiting above the Texas-Gulf coast. Corresponding VAS radiances show a dry slot in the middle tropopause across central Texas accompanied by a secondary slot over Oklahoma. The maxima are separated by 100 to 500 km. The impact of TOMS data on tropopause analysis is preliminarily seen as insignificant because TOMS data is not registered with respect to AVE tropopause heights.

Chesters, Dennis↗

NASA NTRS1996

Dehydration of the Upper Troposphere and Lower Stratosphere by Subvisible Cirrus Clouds Near the Tropical Tropopause

The extreme dryness of the lower stratosphere is believed to be caused by freeze-drying of air as it enters the stratosphere through the cold tropical tropopause. Previous investigations have been focused on dehydration occurring at the tops of deep convective cloud systems, However, recent observations of a ubiquitous stratiform cirrus cloud layer near the tropical tropopause suggest the possibility of dehydration as air is slowly lifted by large-scale motions, In this study, we have evaluated this possibility using a detailed ice cloud model. Simulations of ice cloud formation in the temperature minima of gravity waves (wave periods of 1 - 2 hours) indicate that large numbers of ice crystals will likely form due to the low temperatures and rapid cooling. As a result, the crystals do not grow larger than about 10 microns, fallspeeds are no greater than a few cm/s, and little or no precipitation or dehydration occurs. However, ice cloud's formed by large-scale vertical motions (with lifetimes of a day or more) should have,fever crystals and more time for crystal sedimentation to occur, resulting in water vapor depletions as large as 1 ppmv near the tropopause. We suggest that gradual lifting near the tropical tropopause, accompanied by formation of thin cirrus, may account for the dehydration.

Jensen, Eric J.↗

NASA NTRS2001

The Colocation, or Lack Thereof, of Deep Convection and Cold Tropopause Temperatures in the Tropical Winter Western Pacific

Recent work has suggested that dehydration near the tropical tropopause during the northern hemisphere winter is separate in place and time from the actual transfer of mass from the troposphere to the stratosphere. In fact, some work suggests that dehydration takes place in an environment where the motion is downward, with such downward motion induced either by radiative cooling over cold cloud tops or turbulent heat flux divergence due to convection. Radiative heating and cooling rates at the tropical tropopause are quite small and very sensitive to the temperature profile and underlying cloudiness. Given this, the idea of downward motion in the region of coldest temperatures and dehydration implies that coldest temperatures and underlying cloudiness are colocated. This may not necessarily be the case. This paper attempts to explore, on a preliminary basis: (1) The sensitivity of radiative heating rates at the tropical tropopause to details of the temperature profile and underlying cloudiness and (2) the relative positions of high cold clouds and cold tropopause temperatures.

Pfister, Leonhard↗

NASA NTRS2002

Tropical Convection's Roles in Tropical Tropopause Cirrus

The results presented here show that tropical convection plays a role in each of the three primary processes involved in the in situ formation of tropopause cirrus. First, tropical convection transports moisture from the surface into the upper troposphere. Second, tropical convection excites Rossby waves that transport zonal momentum toward the ITCZ, thereby generating rising motion near the equator. This rising motion helps transport moisture from where it is detrained from convection to the cold-point tropopause. Finally, tropical convection excites vertically propagating tropical waves (e.g. Kelvin waves) that provide one source of large-scale cooling near the cold-point tropopause, leading to tropopause cirrus formation.

Boehm, Matthew T.↗

NASA NTRS2004

Convective Generation of Cirrus Near the Tropopause

The July 2004 CRYSTAL-FACE field program, based from Key West, Florida, showed that long-lived thin tropopause cirrus (TTC) layers were common above thunderstorm anvils. This paper investigates the origins of these cloud using airborne measurements. The horizontal dimensions of the TTC were nearly identical to the convectively formed anvil beneath. However, the TTC did not appear to have originated from convective detrainment. Rather it appears to have formed in stably stratified air derived from high altitudes near the tropopause. The TTC was separated from the anvil by approx. 1 km, it lacked precipitation particles, and it was strongly depleted in HDO. Nonetheless, compared to surrounding clear air near the tropopause, the TTC was enriched in moisture and trace gases in a manner consistent with it having mixed with the same convective airmass that produced the anvil. Unlike surrounding air, the TTC had embedded a monochromatic gravity wave with a wavelength of 2 km and an amplitude of several hundred meters. Combined, this evidence, supported by a photograph from CRYSTAL-FACE, leads to the conjecture that the TTC originated as a pileus cloud layer, which formed near the tropopause ahead of vigorous convective uplift. We hypothesize that the pileus was penetrated by the convection, moistened through mixing, and once the convection subsided, it was sustained by radiative cooling due to the presence of the anvil layer beneath.

Garrett, T. J.↗

NASA NTRS2003

Evidence for Tropopause Layer Moistening by Convection During CRYSTAL-FACE

Measurements and analysis of the impact of deep convection on tropopause layer moisture are easily confounded by difficulties making precise observations with sufficient spatial coverage before and after convective events and difficulties distinguishing between changes due to local convection versus large-scale advection. The interactions between cloud microphysics and dynamics in the convective transport of moisture into the tropopause layer also result in a sufficiently complex and poorly characterized system to allow for considerable freedom in theoretical models of stratosphere-troposphere exchange. In this work we perform detailed large-eddy simulations with an explicit cloud microphysics model to study the impact of deep convection on tropopause layer moisture profiles observed over southern Florida during CRYSTALFACE. For four days during the campaign (July 11, 16, 28, and 29) we initialize a 100-km square domain with temperature and moisture profiles measured prior to convection at the PARSL ground site, and initiate convection with a warm bubble that produces an anvil at peak elevations in agreement with lidar and radar observations on that day. Comparing the moisture field after the anvils decay with the initial state, we find that convection predominantly moistens the tropopause layer (as defined by minimum temperature and minimum potential temperature lapse rate), although some drying is also predicted in localized layers. We will also present results of sensitivity tests designed to separate the roles of cloud microphysics and dynamics.

Ackerman, A.↗

NASA NTRS2008

Using Wind and Temperature Fields to Study Dehydration Mechanisms in the Tropical Tropopause Layer

The tropics are the main region for troposphere-to-stratosphere transport (TST) of air. One of the dominant mechanisms that control tropical TST of water vapor is freeze-drying by the cold tropical tropopause. This mechanism is supported by evidence from satellite observations of the "tape recorder", where seasonal changes in stratospheric water vapor are in phase with seasonal changes in tropopause temperatures in the tropics. Over the last few years, however, the concept of the tropical tropopause has evolved from a single material surface to a layer called the Tropical Tropopause Layer (TTL). A recent hypothesis on dehydration mechanisms suggests that dehydration and entry point into the stratosphere are not always co-located (Holton and Gettelman, 2001). Instead, dehydration can occur during horizontal advection through Lagrangian 'cold pools', or coldest regions along a parcel's trajectory, as air ascends within the TTL while the entry point into the stratosphere occurs at a different geographical location. In this study, we investigate the impact that these Lagrangian cold pools have on TTL moisture. For this purpose, we use in situ measurements of TTL water vapor obtained aboard NASA's WB-57 aircraft over the Eastern Tropical Pacific, and we compare these measurements to minimum saturation water vapor mixing ratios obtained from three-dimensional backward trajectory calculations. Aircraft measurements show frequent unsaturated conditions, which suggest that the entry value of stratospheric water vapor in this region was not set by local saturation conditions. Trajectory calculations, driven by both ECMWF operational analysis and reanalysis winds and temperature fields, are used to explore the impact (e.g., geographical location, timing, dehydration magnitude) of the Lagrangian cold pools intercepted by the parcels sampled by the aircraft. We find noteworthy differences in the location of the Lagrangian cold pools using the two ECMWF data sets, namely influence of the Western Tropical Pacific region when using operational analysis fields versus influence of the Eastern Tropical Pacific and South America regions when using reanalysis fields. These results have a significant impact on our scientific conclusions on dehydration mechanisms affecting the air sampled by the aircraft, given that these regions have different thermodynamic and convective properties.

Pittman, Jasna↗

NASA NTRS2007

Effects of Convective Ice Lofting on H2O and HDO in the Tropical Tropopause Layer

We have added convective ice lofting to a Lagrangian trajectory model of near-tropopause water vapor (H2O) and its isotopologue HDO. The ice lofting simulation is based on a parameterization derived from Aura Microwave Limb Sounder (MLS) icewater content measurements. In previous papers, the Lagrangian model has accurately interannual and seasonal H2O abundances; there was no need for convection to be included in the model. We show here that this model does a poor job of simulating near-tropopause HDO, but that the addition of convective ice lofting greatly improves the HDO simulation. Convective ice lofting has a small effect on lower stratospheric H2O. H2O there is set by the minimum temperature encountered at the cold-point tropopause, so H2O added by convection below this level does not make it through this cold point and into the lower stratosphere. Thus, adding convection to the model does not degrade the model's previously demonstrated accurate simulations of H2O. We conclude that the HDO data suggest an important role for convective mass flux into the so-called tropical tropopause layer.

Dessler, A. E.↗

NASA NTRS2015

Formation of Cirrus Clouds near the Tropical Tropopause and Their Implications for Stratospheric Humidity, Radiation Budgets, and Climate

Optically-thin cirrus clouds are a nearly ubiquitous feature of the transition layer between the tropical troposphere and stratosphere (known as the Tropical Tropopause Layer). Given their high occurrence frequency, these clouds have significant impacts on the Earth's radiation budget, with a particularly strong influence on the outgoing longwave radiation. Further, ice crystal growth and sedimentation in these clouds dehydrates air in the cold TTL to very low water vapor mixing ratios. Since transport from the troposphere into the stratosphere occurs primarily through the tropical tropopause and the Brewer-Dobson circulation transports air from the TTL throughout the stratosphere, cloud processes in the TTL cold trap essentially regulate the humidity of the entire stratosphere. It has been shown that even small changes in stratospheric humidity can have significant impacts on the Earth's radiation budget and climate, with magnitudes comparable to anthropogenic changes in greenhouse gases. The humidity of air crossing the TTL cold trap depends to first order on tropical tropopause temperatures, but also on deep convection reaching the TTL, large-scale transport (in balance with TTL radiative heating), atmospheric waves, and cloud microphysical processes. Gaps in our understanding of TTL transport and cloud processes motivated the NASA Airborne Tropical TRopopause EXperiment (ATTREX). ATTREX used the long-range (16,000 km), high-altitude (20 km) Global Hawk unmanned aircraft system equipped with twelve instruments measuring clouds, water vapor, meteorological conditions, chemical tracers, chemical radicals, and radiation. I will discuss the physics of TTL cirrus formation and the impact of these clouds on water vapor and radiation budgets, including new results emerging from the ATTREX measurements.

Jensen, Eric↗

NASA NTRS2004

Where is Tropopause?

Much of the earth science that is being proposed for the Stratospheric Observatory for Infrared Astronomy (SOFIA) Upper-Deck Research Facility (SURF) deals with issues related to the tropopause, which will be near SOFIA'S flight level at mid-latitudes. Interpreting in situ or remote aerosol, hydrometeor, and trace gas measurements will require accurate knowledge of the tropopause location. Examples of such measurements are presented, and a brief discussion is given on the Microwave Temperature Profiler (MTP), which the earth science community has used in the past to determine the tropopause height.

in situ↗

NASA NTRS2015

Overview of the Airborne Tropical TRopopause EXperiment (ATTREX)

The NASA Airborne Tropical TRopopause EXperiment (ATTREX) is a series of airborne campaigns focused on understanding physical processes in the Tropical Tropopause Layer (TTL) and their role in atmospheric chemistry and climate. ATTREX is using the high-altitude, long-duration NASA Global Hawk Unmanned Air System to make in situ and remote-sensing measurements spanning the Pacific. A particular ATTREX emphasis is to better understand the dehydration of air as it passes through the cold tropical tropopause region. The ATTREX payload contains 12 in situ and remote sensing instruments that measure water vapor, clouds, multiple gaseous tracers (CO, CO2, CH4, NMHC, SF6, CFCs, N2O), reactive chemical compounds (O3, BrO, NO2), meteorological parameters, and radiative fluxes. ATTREX flight series have been conducted in the fall of 2011 from Armstrong Flight Research Center (AFRC) in California, in the winter of 2013 from AFRC, and in the winter/spring of 2014 from Guam. The first two flight series provided extensive sampling of the central and eastern Pacific, whereas the last flight series permitted sampling in the western Pacific. The sampling strategy has primarily involved repeated ascents and descents through the depth of the TTL (about 13-19 km). Over 100 TTL profiles were obtained on each flight series. The ATTREX dataset includes TTL water vapor measurements with unprecedented accuracy, ice crystal size distributions and habits. The cloud and water measurements provide unique information about TTL cloud formation, the persistence of super-saturation with respect to ice, and dehydration. The plethora of tracers measured on the Global Hawk flights are providing unique information about TTL transport pathways and time scales. The meteorological measurements are revealing dynamical phenomena controlling the TTL thermal structure, and the radiation measurements are providing information about heating rates associated with TTL clouds and water vapor. This presentation will provide an overview of the ATTREX flights, examples of measurements from the flights, and plans for modeling/analysis of the ATTREX dataset.

ATTREX↗

NASA NTRS2014

Airborne Tropical TRopopause EXperiment (ATTREX) 2014 Western Pacific Campaign

Airborne↗

NASA NTRS1975

Stellar refraction - A tool to monitor the height of the tropopause from space

Calculations of stellar refraction for a setting or rising star as viewed from a spacecraft show that the tropopause is a discernible feature in a plot of refraction vs time. The height of the tropopause is easily obtained from such a plot. Since the refraction suffered by the starlight appears to be measurable with some precision from orbital altitudes, this technique is suggested as a method for remotely monitoring the height of the tropopause. Although limited to nighttime measurements, the method is independent of supporting data or model fitting and easily lends itself to on-line data reduction.

Schuerman, D. W.↗

NASA NTRS1977

Variability and transport of ozone at the tropopause from the first year of GASP data

The relationships of ozone near the tropopause with potential vorticity temperature, and distance from the tropopause are examined. Data are also used to estimate the vertical and horizontal fluxes of ozone near the tropopause. The present estimates of the total flux of ozone into the troposphere verify the model results. Although the distribution of flux between mean motions and diffusion is different and thus suggests that models with coarse horizontal resolution must continue to parameterize much vertical transport by diffusion coefficients. Monthly estimates of the horizontal transient eddy flux of ozone are generally smaller than seasonal or yearly results based on ozonesonde data. This is perhaps because the present estimates are made over monthly periods to reduce the influence of correlation between the annual variations in ozone and meridional wind. The available data support the hypothesis that transient eddy fluxes of ozone have large longitudinal variations.

Nastrom, G. D.↗