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At least 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Observations and theories related to Antarctic ozone changes

In 1985, there was a report of a large, sudden, and unanticipated decrease in the abundance of springtime Antarctic ozone over the last decade. By 1987, ozone decreases of more than 50 percent in the total column, and 95 percent locally between 15 and 20 km, had been observed. The scientific community quickly rose to the challenge of explaining this remarkable discovery; theoreticians soon developed a series of chemical and dynamical hypotheses to explain the ozone loss. Three basic theories were proposed to explain the springtime ozone hole. (1) The ozone hole is caused by the increasing atmospheric loadings of manmade chemicals containing chlorine (chlorofluorocarbons (CFC's) and bromine (halons)). These chemicals efficiently destroy ozone in the lower stratosphere in the Antarctic because of the special geophysical conditions, of an isolated air mass (polar vortex) with very cold temperatures, that exist there. (2) The circulation of the atmosphere in spring has changed from being predominantly downward over Antarctica to upward. This would mean that ozone poor air from the troposphere, instead of ozone rich air from the upper stratosphere, would be transported into the lower Antarctic stratosphere. (3) The abundance of the oxides of nitrogen in the lower Antarctic stratosphere is periodically enhanced by solar activity. Nitrogen oxides are produced in the upper mesosphere and thermosphere and then transported downward into the lower stratosphere in Antarctica, resulting in the chemical destruction of ozone. The climatology and trends of ozone, temperature, and polar stratospheric clouds are discussed. Also, the transport and chemical theories for the Antarctic ozone hole are presented.

Hartmann, D.↗
NASA NTRS1994

NCAR CCM2 simulation of the modern Antarctic climate

The National Center for Atmospheric Research (NCAR) community climate model version 2 (CCM2) simulation of the circumpolar trough, surface air temperature, the polar vortex, cloudiness, winds, and atmospheric moisture and energy budgets are examined to validate the model's representation of the present-day Antarctic climate. The results show that the CCM2 can well simulate many important climate features over Antarctica, such as the location and intensity of the circumpolar trough, the coreless winter over the plateau, the intensity and horizontal distribution of the surface inversion, the speed and streamline pattern of the katabatic winds, the double jet stream feature over the southern Indian and Pacific oceans, and the arid climate over the continent. However, there are also some serious errors in the model. Some are due to old problems but some are caused by the new parameterizations in the model. The model errors over high southern latitudes can be summarized as follows: The circumpolar trough, the polar vertex, and the westerlies in midlatitudes are too strong; the semiannual cycle of the circumpolar trough is distorted compared to the observations; the low centers of the circumpolar trough and the troughs in the middle and upper troposphere are shifted eastward by 15 deg - 40 deg longitude; the surface temperatures are too cold over the plateau in summer and over the coastline in winter; the polar tropopause continues to have a cold bias; and the cloudiness is too high over the continent. These biases are induced by two major factors: (1) the cloud optical properties in tropical and middle latitudes, which cause the eastward shift of troughs and surface low centers and the error in the semiannual cycle, and (2) the cold bias of the surface air temperature, which is attributed to the oversimulation of cloudiness over the continent, especially during summer, and the uniform 2-m-thick sea ice. The constant thickness of sea ice suppresses the energy flux from the ocean to the atmosphere and hence reduces the air temperature near the coast during winter. Finally, although the simulated Antarctic climate still suffers these biases, the overall performance of the CCM2 is much better than that of the CCM1-T42. Therefore the CCM2 is good enough to be used for climate change studies, especially over Antarctica.

Tzeng, Ren-Yow↗
NASA NTRS1979

The behavior of tropical ozone during the stratospheric warming of March-April 1976

The backscatter ultraviolet spectrometer on the Atmosphere Explorer-E satellite obtained ozone data for the upper stratosphere and lower mesosphere from an equatorial orbit near the time of the March-April 1976 stratospheric warming. A simple inversion technique allows the extraction of information on the absolute ozone abundance and its longitudinal variation from the measured radiances. Between altitudes of 35 and 60 km tropical O3 in constant pressure layers exhibits increased spatial variations on length scales of 20 to 30 deg in longitude after the onset of the polar warming, indicating enhanced wave activity. One week after the polar vortex breakdown, upper stratospheric O3 begins a relaxation toward the unperturbed state, while that in the lower mesosphere continues to show maximum variations near + or 10% of the longitudinally averaged value. Although the degree of horizontal structure increases during the warming, the absolute O3 amounts averaged over longitude between 35 and 60 km in altitude remain nearly constant in time. The observed behavior is consistent with that expected from enhanced vertical transport of O3 in the tropics with accompanying adiabatic temperature changes which alter the chemical loss rate.

Frederick, J. E.↗
NASA NTRS1980

Numerical simulation of stratospheric sudden warmings with a primitive equation spectral model

A 26-level primitive equation spherical harmonic spectral model allowing for wave-wave and wave-zonal flow interactions is presented for the study of stratospheric sudden warmings. The warmings are simulated by the forcing of a single planetary wave at the tropopause. Four numerical experiments were performed. Nonlinear wave-wave interactions appear to play an important role in the evolution of the flow and temperature fields in the middle to upper stratosphere. In the case involving both wave-wave and wave-zonal flow interactions, this was manifested by the split in the initial polar vortex into a quasi-wave number 2 pattern. In the cases at 60 deg N, easterlies develop first in the upper mesosphere and descend gradually. About the same time or a little later, easterlies also develop in the mid-stratosphere. The linear cases exhibit warmings which are more shallow and more intense at 30 km than the nonlinear cases.

Lordi, N. J.↗
NASA NTRS1983

Ozone variations observed during the International Ozone Rocket Sonde Intercomparison

The International Ozone Rocket Sonde Intercomparison (IORI) conducted at Wallops Island during October 1979 provided a unique opportunity to observe ozone variations in great detail from several observing systems. The measurement period lasted 15 days during which time ozone observations were taken by ground-based, balloon, rocket, and satellite instruments. These data provided a unique opportunity for diagnosing regional stratospheric variability over a 2 week period. Examination of NMC analyses indicated that during this period the stratospheric polar vortex moved southeastward bringing air form high latitudes to Wallops Island above 10 mb. A concurrent change was observed in the upper stratosphere ozone fields observed by Nimbus-7 SBUV and in the ozone vertical distribution measured by the rocket soundings. In this study the satellite and rocket measurements are compared. The agreement is good, certainly within the errors of the measurements.

Hilsenrath, E.↗
NASA NTRS1983

Solar variability and quasi-stationary planetary wave behavior

A steady state analysis of winter winds shows that the speed of the upper atmospheric polar vortex approaches and occasionally exceeds the value required to reflect externally forced planetary wave 1 energy back towards the surface of the earth. Historical observations suggest that solar UV variability and geomagnetic disturbances are two primary forces which modulate the planetary wave trapping mechanism. Through the solar-terrestrial process described, small changes in the sun's behavior can be physically linked to both shortand long-term changes in tropospheric weather patterns.

Springer, B. D.↗
NASA NTRS1983

Transport and the seasonal variation of ozone

The transport mechanisms responsible for the seasonal behavior of total ozone are deduced from the comparison of model results to stratospheric data. The seasonal transport is dominated by a combination of the diabatic circulation and transient planetary wave activity acting on a diffusively and photochemically determined background state. The seasonal variation is not correctly modeled as a diffusive process. The buildup of total ozone at high latitudes during winter is dependent upon transient planetary wave activity of sufficient strength to cause the breakdown of the polar vortex. While midwinter warmings are responsible for enhanced ozone transport to high latitudes, the final warming marking the transition from zonal mean westerlies to zonal mean easterlies is the most important event leading to the spring maximum. The final warming is not followed by reacceleration of the mean flow; so that the ozone transport associated with this event is more pronounced than that associated with midwinter warmings.

Rood, R. B.↗
NASA NTRS1985

Characteristics of polar stratospheric clouds as observed by SAM II, SAGE, and lidar

Satellite and lidar data sets developed over several years of observations are analyzed to detail the macroscopic and microphysical characteristics of polar stratospheric clouds (PSCs). Mappings were made of the sizes, locations, probabilities of occurrence and temperature dependence of the PSCs, and indicated that PSCs are correlated with an extended stratospheric cloud bank in the cold polar vortex region. The bank is bounded by a 188 K isotherm, and the probability of occurrence drops to 50 percent at the 193 K isotherm. Values of 6.3 particles/cu cm and radii averaging 0.0725 micron/particle are calculated, along with an estimated downward velocity of 0.01 m/sec.

Mccormick, M. P.↗
NASA NTRS1985

Mean Winds of the Mesosphere (60-80 Km), as Measured by MF Radars

Winds data obtained from medium frequency (MF) radars for heights of 60 to 80 km are discussed: locations are Saskatoon (52 N, 107 W), Christchurch (44 S, 173 W), Adelside (35 S, 183 E) and Townsville (20 S, 147 E). Whereas well defined summer easterly jets centered near 70 km develop in summer, no regular buildups and decays are observed in winter at midlatitudes. Part of this variability can be associated with stratospheric warmings, which develop into breakdown of the polar vortex in the Northern Hemisphere. Amplitude and phase profiles of the annual and semiannual oscillations are also presented. The radar winds from Saskatoon are compared and combined with rocket derived winds up to 60 km from Primrose Lake (54 N, 110 W) to give consistent cross sections from 20 to 110 km. The SH radar winds are compared with a model based on rocket winds which extends up to 80 km. The latter evidence considerable smoothing, as no winter variability is evident. The other consistent difference is that heights of the summer easterly maxima for the model are 5 to 10 km lower than the radar winds at all latitudes.

Manson, A. H.↗
NASA NTRS1985

On the use of potential vorticity for the diagnosis of stratospheric synoptics

According to quasi-geostrophic approximation, regions of strong cross flow gradient of geopotential vortivity support Rossby wave propagation. Using potential vorticity as a dynamical tracer, the polar vortex can be considered as a material entity. In addition to synoptic charts of geopotential heights and temperatures, maps of potential vorticity are used to describe some distinct features of the circulation of the winter stratosphere.

Rose, K.↗
NASA NTRS1985

Transport processes as manifested in satellite and lidar aerosol measurements

A large increase in stratospheric aerosol data has become available recently from the SAM II and SAGE satellite sensors and the impetus from increased volcanic perturbations. Six years of SAM II and nearly 3 years of SAGE measurements have been accumulated. The increase in large volcanic eruptions since 1979 has caused an acceleration of new data sets from worldwide lidars and airborne lidar campaigns and from various airborne in situ measurements. The SAM II and SAGE data sets show the tropical stratosphere as a source for background stratospheric aerosols, and midlatitudes as a possible sink. Analyses of SAM II data show that the aerosol within the northern wintertime polar vortex becomes isolated from the outside. Subsidence occurs within the vortex, changing the vertical aerosol distribution over the winter period. SAM II and SAGE data show that the aerosol is transported in the stratosphere from low to high latitudes in wintertime. Entry regions of tropospheric air in the Tropics are also evident in the SAGE data as shown by stratospheric cirrus clouds being formed well above the local tropopause. Nature has provided over the past 5 years a number of large volcanic eruptions which spewed tons of new aerosol into the stratosphere. These eruptions have occurred at various latitudes which allow transport differences to be studied. Satellite and lidar aerosol data will be used to describe the stratospheric motions of aerosols produced after these violet volcanic eruptions.

Mccormick, M. P.↗
NASA NTRS1987

Gravity waves

Gravity waves contributed to the establishment of the thermal structure, small scale (80 to 100 km) fluctuations in velocity (50 to 80 m/sec) and density (20 to 30%, 0 to peak). Dominant gravity wave spectrum in the middle atmosphere: x-scale, less than 100 km; z-scale, greater than 10 km; t-scale, less than 2 hr. Theorists are beginning to understand middle atmosphere motions. There are two classes: Planetary waves and equatorial motions, gravity waves and tidal motions. The former give rise to variability at large scales, which may alter apparent mean structure. Effects include density and velocity fluctuations, induced mean motions, and stratospheric warmings which lead to the breakup of the polar vortex and cooling of the mesosphere. On this scale are also equatorial quasi-biennial and semi-annual oscillations. Gravity wave and tidal motions produce large rms fluctuations in density and velocity. The magnitude of the density fluctuations compared to the mean density is of the order of the vertical wavelength, which grows with height. Relative density fluctuations are less than, or of the order of 30% below the mesopause. Such motions may cause significant and variable convection, and wind shear. There is a strong seasonal variation in gravity wave amplitude. Additional observations are needed to address and quantify mean and fluctuation statistics of both density and mean velocity, variability of the mean and fluctuations, and to identify dominant gravity wave scales and sources as well as causes of variability, both temporal and geographic.

Fritts, David↗
NASA NTRS1986

Antarctic springtime measurements of ozone, nitrogen dioxide, and aerosol extinction by SAM II, SAGE, and SAGE II

Simultaneous vertical profiles of O3, NO2, and aerosol extinction obtained with the Stratospheric Aerosol Measurement II, Stratospheric Aerosol and Gas Experiment (SAGE), and SAGE II satellite instruments across the southern polar vortex show that significant differences exist at all altitudes. Both gaseous species display lower concentrations within the vortex over measurement altitudes ranging from the tropopause to 60 km and 20 to 40 km for O3 and NO2, respectively. Aerosol extinction above 15-18 km and total aerosol stratospheric column are also lower inside the vortex than outside. Total column amounts of O3 and NO2 are found to be strongly coupled to spatial location within the vortex, with minimum total values located around the vortex center. Vertical profiles selected to emphasize the observed difference across the circumpolar vortex are presented for October 13, 1981, and October 13, 1985, near 70 and 68 deg S latitude, respectively.

Mccormick, M. P.↗
NASA NTRS1986

Characteristics of Arctic polar stratospheric clouds and as measured by airborne lidar

Airborne lidar measurements of backscattering from polar stratospheric clouds (PSCs) obtained in January 1984 are examined. The flights, principal characteristics of the lidar system, and the meteorological conditions during the flights are described. The characteristics and conditions for the formation of PSCs and the optical characteristics of the clouds are discussed. The properties of the North Polar vortex and El Chichon stratospheric aerosol are studied. Variations in the aerosol optical properties with temperature and water vapor concentrations are analyzed and modeled using a model based on volcanic aerosols and water vapor concentration. The modeled and experimental backscattering-temperature relationship are compared and good correlation is observed at pressure levels of 100 and 70 mb.

Kent, G. S.↗
NASA NTRS1987

Infrared measurements of several nitrogen species above the South Pole in December 1980 and November-December 1986

This paper reports the results of the determinations of total column amounts of HNO3 for December 1980 and November 1986, and NO and NO2 for November-December 1986, deduced from ground-based high-resolution IR solar absorption spectra recorded from the Amundsen-Scott South Pole Station. The measurements were obtained shortly after the austral spring ozone minimum and define, for the first time, the ambient levels of these nitrogen species immediately following the break up of the polar vortex.

Murcray, F. J.↗