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At least 109 records · Page 6
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NASA NTRS2018

Microphysical Properties of Tropical Tropopause Layer Cirrus

Pervasive cirrus clouds in the tropical tropopause layer (TTL) play an important role in determining the composition of stratospheric air through dehydration of tropospheric air entering the stratosphere. This dehydration affects Earth's energy budget and climate, yet uncertainties remain regarding the microphysical processes that govern TTL cirrus. TTL cirrus were sampled with the NASA Global Hawk UAV for over 30 hr in the Western Pacific in 2014 during the Airborne Tropical TRopopause EXperiment. In situ measurements by a Fast Cloud Droplet Probe and Hawkeye probe (combination Fast Cloud Droplet Probe, Two‐Dimensional Stereo optical array probe, and Cloud Particle Imager) provided particle concentrations and sizing between 1‐ and 1,280‐μm diameter and high resolution images for habit identification. We present the variability in ice concentrations, size distributions, and habits as functions of temperature, altitude, and time since convective influence. Observed ice particles were predominantly small and quasi‐spheroidal in shape, with the percentage of quasi‐spheroids increasing with decreasing temperature. In comparison to the large fraction of the population consisting of quasi‐spheroids, faceted habits (columns, plates, rosettes, and budding rosettes) constituted a smaller percentage of the overall population and exhibited the opposite correlation with temperature. The trend of higher percentages of faceted crystals occurring at warmer temperatures may be due to diffusional growth or aggregation as particles descend through cloud, and/or the more rapid diffusional growth rate at warmer temperatures. Sampling was typically well away from deep convection, however, and very few aggregates were observed, so the trend of higher percentages of faceted habits is likely attributable to diffusional growth.

Woods, Sarah↗
NASA NTRS2019

How Do UTLS Jet and Tropopause Dynamics Influence Ozone Variability? Investigations Supporting the SPARC OCTAV-UTLS Activity

Understanding changes in UTLS ozone is exceptionally challenging because of large spatial and temporal variability and because of the difficulty of satellite measurements in the UTLS. It is also exceptionally important: for example, to understand climate impacts of radiatively active substances and to understand physical and biological effects of pollution transport and stratosphere-troposphere exchange (STE). Multi-decadal global observations of UTLS ozone are now available from numerous satellite platforms, as well as local and regional observations from aircraft, balloons, and lidar. The upper tropospheric (UT) jets and tropopauses are important drivers of composition variability in the UTLS, acting as transport barriers and controlling STE and long-range transport. We report here on investigations of relationships between extratropical UTLS ozone variability and dynamical diagnostics of mixing / transport barriers, Rossby Wave breaking, and stratosphere-troposphere exchange. We will view these relationships in the context of ozone mapped into dynamical coordinates with respect to the UTLS jets and / or the tropopause. This work will help provide direction for analyses within the Stratosphere-troposphere Processes And their Role in Climate (SPARC) Observed Composition Trends and Variability in the UTLS (OCTAV-UTLS) activity, which aims to use dynamical coordinate mapping to help detect and attribute observed UTLS composition trends, and to project future data needs to better quantify those trends. The work we report on here will focus on satellite ozone observations (primarily from the Aura Microwave Limb Sounder, additionally from ACE-FTS and OSIRIS) and assimilated ozone and dynamical fields (from multiple reanalyses); we will also provide some examples of comparisons with aircraft and balloon observations.

Manney, Gloria L.↗
NASA NTRS2015

Gravity Waves and Vertical Mixing in the Tropical Tropopause Layer during ATTREX

Vertical mixing in the Tropical Tropopause Layer is thought to be weak outside regionsof convective injection. Nevertheless, some studies indicate a rolefor nonconvective vertical mixing processes in maintaining tracer distributions.The TTL also has a broad spectrum of high amplitude gravity waves, which havebeen shown to play an important role in the water vapor distribution. These gravitywaves, a result of tropical convection, also havesubstantial shears associated with them (which may produce turbulent mixing). Recent aircraft experiments, specificallythe Airborne Tropical TRopopause EXperiment (ATTREX), have yielded an unprecendentedmeteorological dataset in the TTL, including not only the temperatures and horizontalwinds (which can be obtained from radiosondes), but high frequency vertical winds. These highfrequency measurements yield an opportunity to study turbulence in the nonconvectiveenvironment. The numerous vertical profiles, essentially producing curtains of high resolutionmeasurements across broad regions of the tropics, also yield an opportunity to obtain bothhorizontal and vertical information about medium scale gravity waves.This presentation examines three phases of ATTREX (fall, 2011, winter 2013, and winter 2014) inthe eastern and western Pacific. The focus will be on high amplitude wave motions, theirstructure, and turbulence.

Pfister, Leonhard↗
NASA NTRSDate not supplied

Comparing Tropopause-Penetrating Convection Identifications Derived from NEXRAD and GOES over the Contiguous United States

Overshooting cloud tops (OTs) are a result of powerful updrafts that rapidly transport air from the troposphere to the lower stratosphere. Aside from the well-known relationships between strong updrafts and severe weather, the boundaries of updrafts, including the OT, are turbulent, which leads to irreversible mixing of air between the stratosphere and troposphere, altering the composition of both layers. In order to better understand the impact of OTs, knowing precisely when and where they occur is vital. Within the last decade remote-sensing observations from satellites and radars have been used to identify OTs, but the results thus far have not been entirely consistent due to challenges with accurately identifying OTs with these sensor datasets. This study compares OTs identified using NEXRAD reflectivity data from the GridRad dataset with an approach that uses GOES infrared (IR) data. The GridRad method estimates the altitude of echo tops directly from the radar pointing geometry, merging a combination of radars that enables products every 5 mins, with 2 km spatial and 1 km vertical grid spacing. The GOES satellite method uses spatial patterns in tropopause-relative IR brightness temperature to derive an OT likelihood. The study region covers a large part of the contiguous United States during selected active convection dates in 2017 and includes data from GOES-13/16. A large sample of OTs observed by NEXRAD and GOES-13/16 satellites are analyzed to better understand NEXRAD and IR observations of OTs, quantify agreement between the OT detection methods, and demonstrate how the 4x increase in spatial resolution from GOES-13 to GOES-16 impacts OT algorithm detection performance. The results show that for nearly time-matched scenes, with many severe storms, GOES-13 and -16 detection accuracy is quite comparable; however, some missed detections are attributed to poorer GOES-13 image resolution. It was found that GOES-13 OT regions are ~2 K warmer than GOES-16 on average, but such differences exceed 5 K for the most intense OT regions. It is found that false GOES IR-based detections are unavoidable, given that cold cloud pixels significantly colder than the tropopause from nearby or recently decayed OTs can persist within anvils for 15 minutes or more.

John W. Cooney↗
NASA NTRSDate not supplied

Quantifying Tropopause-Overshooting Volume from Satellite and Radar Observations During the DCOTSS 2021 and 2022 Campaigns

Tropopause-overshooting cloud locations, their volume, and the percentage of anvil cloud occupied by overshooting were quantified from state-of-the-art merged NEXRAD radar and GOES-16/17 satellite products during the 2021 and 2022 Dynamics and Chemistry of the Summer Stratosphere (DCOTSS) study periods. A novel method for defining and tracking large individual storms or storm outbreak objects in space and time was presented, which enabled improved understanding of the complex feature-specific biases among GOES- and GridRad-derived overshooting metrics. GOES overshooting cloud top height was estimated using a stratospheric lapse rate approach informed by GOES visible and IR measurements of shadows from OTs and calibrated based on previously observed maximum GridRad overshooting distribution. Total overshooting volumes derived over CONUS are higher for GOES than GridRad for both years, especially during 2021. Over all storm outbreak objects with observed overshooting, GOES observed higher overshooting percentages while GridRad observed relatively higher overshooting magnitudes. The greater spatial coverage of GOES overshooting, especially noticeable during the mature and dissipation stages of outbreaks due to inherent limitations of infrared satellite data which make it difficult to differentiate cold, high-altitude outflow from true updraft cores, outweighed differences in magnitude to yield higher GOES volume. Individual events, however, revealed that the higher overshooting magnitudes observed by GridRad produce higher overshooting volumes at times. Four-dimensional trajectories of tropopause-overshooting air parcels were compared 5 days after overshooting occurred to depict the envelope of convectively impacted air in the stratosphere. The generally good agreement in parcel plume area initiated from GOES and GridRad overshooting detections suggests that geostationary satellite data can be used to estimate where and how often overshooting impacts stratospheric composition in regions without a ground-based weather radar network to estimate climate impacts of overshooting convection.

Kristopher Bedka↗
NASA NTRS1966

Tropopause detected by radar.

Tropopause detection by radar, examining detection of high altitude clear-air turbulence by radar and forward-scatter techniques

TROPOPAUSE↗
NASA NTRS2004

Tropical Tropopause Structure and Processes as Observed with GPS Radio Occultation

The vertical temperature structure of the tropical atmosphere has been explained as controlled by the combined effect of three green house gases: water vapor, carbon dioxide, and ozone. Absorption by water vapor of the light reflected off the Earth's surface would determine the temperature lapse rate in the lower troposphere up to the bottom of the Tropical Transition Layer (TTL); radiative absorption by carbon dioxide would dominate the temperature lapse rate between the bottom of the TTL and the coldest point in the upper-troposphere, the cold point tropopause (CPT), and; absorption of incoming solar radiation by ozone would control the temperature above the CPT. The TTL region can thus be very sensitive to changes in the relative abundances of these greenhouse gases. In this contribution we describe the seasonal evolution of temperature profiles in the TTL and their longitudinal structure using GPS radio occultation.

global positioning system (GPS)↗
NASA NTRS1980

Sulfate and nitrate collected by filter sampling near the tropopause

Filter samples collected near the tropopause with an F-106 aircraft and two Boeing 747 aircraft were analyzed for sulfate and nitrate ion content. Within the range of routine commercial flight altitudes (at or below 12.5 km), stratospheric mass mixing ratios for the winter-spring group averaged 0.26 ppbm for sulfate and 0.35 ppbm for nitrate. For the summer-fall group, stratosphere mixing ratios averaged 0.13 ppbm and 0.25 ppbm for sulfate and nitrate, respectively. Winter-spring group tropospheric mass mixing ratios averaged 0.08 ppbm for sulfate and 0.10 ppbm for nitrate, while summer-fall group tropospheric mixing ratios averaged 0.05 ppbm for sulfate and 0.08 ppbm for nitrate. Correlations of the filter data with available ozone data suggest that the sulfate and nitrate are transported from the stratosphere to the troposphere.

Humenik, F. M.↗
NASA NTRS1987

Three-dimensional analysis of potential vorticity associated with tropopause folds and observed variations of ozone and carbon monoxide

The usability and reliability of potential vorticity as a meteorological stratospheric tracer are evaluated. The concept of potential vorticity conservation during transport in which stratospheric and tropospheric air are mixing is tested. Aircraft data collected on April 20, 1984 in the western and southwestern U.S. are analyzed in order to derive potential vorticity data; vertical cross sections of constant-pressure data and temperature and wind speed gradients are examined. The tropopause fold observed during the April 20, 1984 aircraft flights is described. The potential vorticity, ozone mixing ratio, and carbon monoxide mixing ratio are compared; a positive correlation between potential vorticity and the ozone mixing ratio and a negative correlation between the potential vorticity and the carbon monoxide mixing ratio are detected. The data support the concepts of the conservation of potential vorticity, the entrainment and mixing of tropospheric air across the boundaries of the fold, and the applicability of potential vorticity as a stratospheric tracer.

Danielsen, Edwin F.↗
NASA NTRS1988

Relations between water vapor imagery, vertical motion, and tropopause folds

The atmospheric processes associated with the movement and development of a pronounced dry feature in a series of 6.7-micron images from March, 1982 are examined. It is found that the dark, warm image bands are due to subsidence. The advective band is produced by descent associated with the entrance region of a polar jet streak. The evolution of the development image component is coincident with a tropopause fold and associated intrusion of dry stratospheric air into the middle troposphere. The increasing brightness temperatures are simulated by altering upwind soundings based on trajectory-determined vertical motion and using both the original and altered profiles as input to a radiative transfer model.

Moore, Steven R.↗
NASA NTRS1988

NO and NO2 in the troposphere - Technique and measurements in regions of a folded tropopause

Measurements of NO, NO2, O3, and CO were obtained for tropopause fold events encountered during two flights of the NASA global tropospheric experiment aircraft in 1984. The results suggest that NO(x) may not always be a good tracer of air of recent stratospheric origin. It is suggested that the stratospheric source of NO(x) acts to introduce NO(x) over a short period and through a large vertical region of the troposphere.

Ridley, Brian A.↗
NASA NTRS1991

Air mass origins and troposphere-to-stratosphere exchange associated with mid-latitude cyclogenesis and tropopause folding inferred from Be-7 measurements

The 1984 extratropical mission of NASA's Stratosphere-Troposphere Exchange Project (STEP) studied cross-jet transport in regions of cyclogenesis and tropopause folding. Correlations of Be-7, ozone, water vapor, and potential vorticity measured on a NASA U-2 research aircraft flying in high shear regions above the jet core are indicative of mixing between the cyclonic and the anticyclonic sides of the jet and are consistent with the hypothesis that small-scale entrainments of upper tropospheric air into the lower stratosphere during cyclogenesis are important in maintaining the vertical gradients of Be-7, ozone, water vapor and other trace constituents in the lower few kilometers of the midlatitude stratosphere. Correlations between Be-7, and ozone suggest a lower tropical stratospheric origin for the ozone-poor lamina observed above the jet core.

Kritz, Mark A.↗
NASA NTRS1993

The tropopause cold trap in the Australian Monsoon during STEP/AMEX 1987

The relationship between deep convection and tropopause cold trap conditions is examined for the tropical northern Australia region during the 1986-87 summer monsoon season, emphasizing the Australia Monsoon Experiment (AMEX) period when the NASA Stratosphere-Troposphere Exchange Project (STEP) was being conducted. The factors related to the spatial and temporal variability of the cold point potential temperature (CPPT) are investigated. A framework is developed for describing the relationships among surface average equivalent potential temperature in the surface layer (AEPTSL) the height of deep convection, and stratosphere-troposphere exchange. The time-mean pattern of convection, large-scale circulation, and surface AEPTSL in the Australian monsoon and the evolution of the convective environment during the monsoon period and the extended transition season which preceded it are described. The time-mean fields of cold point level variables are examined and the statistical relationships between mean CPPT, surface AEPTSL, and deep convection are described. Day-to-day variations of CPPT are examined in terms of these time mean relationships.

Selkirk, Henry B.↗