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At least 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS2012

Gravity Wave Variances and Propagation Derived from AIRS Radiances

As the first gravity wave (GW) climatology study using nadir-viewing infrared sounders, 50 Atmospheric Infrared Sounder (AIRS) radiance channels are selected to estimate GW variances at pressure levels between 2-100 hPa. The GW variance for each scan in the cross-track direction is derived from radiance perturbations in the scan, independently of adjacent scans along the orbit. Since the scanning swaths are perpendicular to the satellite orbits, which are inclined meridionally at most latitudes, the zonal component of GW propagation can be inferred by differencing the variances derived between the westmost and the eastmost viewing angles. Consistent with previous GW studies using various satellite instruments, monthly mean AIRS variance shows large enhancements over meridionally oriented mountain ranges as well as some islands at winter hemisphere high latitudes. Enhanced wave activities are also found above tropical deep convective regions. GWs prefer to propagate westward above mountain ranges, and eastward above deep convection. AIRS 90 field-of-views (FOVs), ranging from +48 deg. to −48 deg. off nadir, can detect large-amplitude GWs with a phase velocity propagating preferentially at steep angles (e.g., those from orographic and convective sources). The annual cycle dominates the GW variances and the preferred propagation directions for all latitudes. Indication of a weak two-year variation in the tropics is found, which is presumably related to the Quasi-biennial oscillation (QBO). AIRS geometry makes its out-tracks capable of detecting GWs with vertical wavelengths substantially shorter than the thickness of instrument weighting functions. The novel discovery of AIRS capability of observing shallow inertia GWs will expand the potential of satellite GW remote sensing and provide further constraints on the GW drag parameterization schemes in the general circulation models (GCMs).

AIRS↗
NASA NTRS1987

Characteristics of gravity waves generated by surface topography on Venus - Comparison with the VEGA Balloon results

Data from the 1985 VEGA Venus Balloon Mission indicate that the mountainous region known as Aphrodite influences atmospheric motions at balloon float altitudes near 54 km, an altitude located within the middle cloud region. It is shown that stationary gravity waves, generated by surface topography and Doppler-shifted by a wind blowing over the terrain, can propagate upward to the middle cloud layers. Under the right circumstances, waves are amplified considerably in excess of their amplification due to the decrease of density with altitude. The additional amplification is due to resonance that results from variations of static stability and mean zonal wind with altitude. Computed atmospheric propagation characteristics, combined with terrain slopes in Aphrodite estimated from Pioneer Venus radar altimeter data, can be sufficient to produce wind amplitudes at 54 km comparable to those observed by the VEGA-2 balloon as it overflew Aphrodite. The dominant waves have horizontal wavelengths of the order of several hundred kilometers.

Young, Richard E.↗
NASA NTRS1995

Ground-based measurements of water vapor in the middle atmosphere

We present measurements of the middle atmospheric water vapor mixing ratio profile obtained using the ground-based Naval Research Laboratory (NRL) water vapor millimeter-wave spectrometer (WVMS) instrument at the Jet Propulsion Laboratory (JPL) Table Mountain Observatory. The measurements cover a period of 262 days from January 23, 1992, to October 13, 1992. During this campaign it was possible to retrieve useful daily mixing ratio profiles for 186 days. We thus have a nearly continuous record of water vapor mixing ratios for altitudes from approximately equals 35 to 75 km. The retrievals are obtained using the optimal estimation method. Details of the error analysis are presented, and a technique is introduced that reduces baseline effects and helps to estimate the baseline error. The high-altitude (greater than or approx. equal to 65 km) data show a sharp rise prior to the expected maximum near the summer solstice and a gradual decline in the following months. The mixing ratios generally peak between 55 and 65 km, at which point the mixing ratios are 6 - 7 parts per million by volume. The highest peaks occur in January, May, and October.

Nedoluha, Gerald E.↗
NASA NTRS1989

STS-30 Post Flight Press Conference

Live footage shows the crewmembers of STS-30, Commander David M. Walker, Pilot Ronald J. Grabe, Mission Specialists Norman E. Thagard, Mary L. Cleave and Mark C. Lee, participating in the Post Flight Press Conference. The astronauts took turns narrating the footage taken from the inside of the cockpit during lift-off. The crew answer questions from the audience as well as some of the NASA Centers. Included are various stills of Magellan, and some ground shots of the Florida Peninsula, Bahamas, North West Nicaragua, California, the Himalayan Mountains, the Canary Islands, Houston, Dust Storms across the Sahara, and some waves in the South China Seas.

Source record↗
NASA NTRS2019

CoSMIR Performance During the GPM Olympex Campaign

The airborne Conical Scanning Millimeter-wave Imaging Radiometer (CoSMIR) participated in the Global Precipitation Measurement (GPM) Olympic Mountains Experiment (OLYMPEX) from November to December 2015 with great success. With similar channels as the GPM Microwave Imager (GMI) at 89-183 GHz, CoSMIR served as a proxy for GMI by flying onboard the DC-8 aircraft for a total of 17 science flights, collecting over 72 hours of observations. The high-quality, calibrated brightness temperature dataset is the result of several improvements made to CoSMIR prior to OLYMPEX to make the instrument more reliable. This paper describes these improvements and gives a detailed summary of the CoSMIR measurements obtained from OLYMPEX. CoSMIR experienced minor performance issues during the campaign, most of which were not excessive and only resulted in a loss of approximately four hours of data for the entire campaign. Performance issues are discussed and shown how they were mitigated to achieve a quality dataset. Comparisons of CoSMIR and GMI observations are presented to show that the CoSMIR measurements agree well with GMI. The CoSMIR dataset is publicly available as part of the OLYMPEX data suite and can reliably be used in GPM algorithm development and related studies.

Airborne radiometer↗
NASA NTRS1974

Radiation measurements over a snowfield at an elevated site

The components of short wave radiation were measured over a snowfield in a valley of the Rocky Mountains at a height of 2700 m above sea level. Global and reflected radiation were obtained by a set of Eppley pyranometers. In addition, the direct solar radiation and the turbidity of the atmosphere were derived from pyrheliometric data on cloud-free days. Emphasis was given to the reflectance of the snowfield in relation to the position of the sun, especially at low elevation angles. These reflectance values were measured for cloudless as well as for cloudy days and compared with already published values for arctic and antarctic conditions.

Korff, H. C.↗
NASA NTRS1988

Equatorial waves simulated by the NCAR community climate model

The equatorial planetary waves simulated by the NCAR CCM1 general circulation model were investigated in terms of space-time spectral analysis (Kao, 1968; Hayashi, 1971, 1973) and energetic analysis (Hayashi, 1980). These analyses are particularly applied to grid-point data on latitude circles. In order to test some physical factors which may affect the generation of tropical transient planetary waves, three different model simulations with the CCM1 (the control, the no-mountain, and the no-cloud experiments) were analyzed.

Cheng, Xinhua↗
NASA NTRS1990

Spectral characterization of forest damage occurring on Whiteface Mountain, NY - Studies with the Fluorescence Line Imager (FLI) and ground-based spectrometers

Ground-based spectral characteristics of fir wave damage and an analysis of calibrated FLI data acquired along the same fir wave utilized for the in situ measurements are presented. Derivative curve data were produced from both in situ and FLI reflectance measurements for the red edge spectral region for birch and for various portions of a fir wave. The results suggested that with proper atmospheric correction of airborne imaging spectrometer data sets, the derivative curve approach will provide an accurate means of assessing red edge parameters, and that such data will permit identification of specific types of forest damage on the basis of spectral fine features.

Rock, B. N.↗
NASA NTRS1988

Folded resonance and seasonal vacillation in a thermally-forced baroclinic wave model

An eight-variable dynamical system is developed, representing a generalization of most previous low-order models of planetary wave behavior. As a special case a three component model, somewhat more general than a recent model of Lorenz and representing only thermal-monsoonal forcing (i.e., no mountains), is studied and shown to be capable of exhibiting a 'folded resonance' equilibrium portrait suggestive of that which seems to be required to account for the observed bimodality of the atmospheric long-wave amplitude. When forced by seasonal thermal variations the system can exhibit vacillatory fluctuation qualitatively similar to observations.

Saltzman, Barry↗
NASA NTRS1992

Lee waves, benign and malignant

The flow of an incompressible, stratified fluid over an obstacle will produce an oscillation in which buoyancy is the restoring force, called a gravity wave. For disturbances of this scale, the atmosphere may be treated as incompressible; and even the linear approximation will explain many of the phenomena observed in the lee of mountains. However, nonlinearities arise in two ways: (1) through the large (scaled) size of the mountain, and (2) from dynamically singular levels in the fluid field. These produce a complicated array of phenomena that present hazards to aircraft and to lee surface areas. If there is no dynamic barrier, these waves can penetrate vertically into the middle atmosphere (30-100 km attitude), where recent observations show them to be of a length scale that must involve the Coriolis force in any modeling. At these altitudes, the amplitude of the waves is very large, and the waves are studied with a view to their potential impact on the projected National Aerospace Plane. This paper presents the results of analyses and state-of-the-art numerical simulations, validated where possible by observational data.

Wurtele, M. G.↗
NASA NTRS1994

Surface ozone variability at Kislovodsk Observatory

The results of the surface ozone observations at the Observatory 'Kislovodsk', situated in the North Caucasus at the altitude 2070 m a.s.l., are given. The observatory is in the background conditions and the variations of the surface ozone are determined by the natural dynamic and photochemical processes. The mean value of the concentration and its seasonal variations are very near to those obtained at the high-mountain stations in Alps. The daily variations have the features, which remain stable during all warm period of the year (April-October). These features, including the minimum of the surface ozone at noon, are formed by the mountain-valley circulation. The significant variations of the surface ozone are connected with the unstationary lee waves.

Elansky, Nikolay F.↗
NASA NTRS2003

Boundary Layer Aerosol Composition over Sierra Nevada Mountains using 9.11- and 10.59-micron CW Lidars and Modeled Backscatter from Size Distribution Data

An inversion technique has been developed to determine volume fractions of an atmospheric aerosol composed primarily of ammonium sulfate and ammonium nitrate and water combined with fixed concentration of elemental and organic carbon. It is based on measured aerosol backscatter obtained with 9.11 - and 10.59-micron wavelength continuous wave CO2 lidars and modeled backscatter from aerosol size distribution data. The technique is demonstrated during a flight of the NASA DC-8 aircraft over the Sierra Nevada Mountain Range, California on 19 September, 1995. Volume fraction of each component and effective complex refractive index of the composite particle were determined assuming an internally mixed composite aerosol model. The volume fractions were also used to re-compute aerosol backscatter, providing good agreement with the lidar-measured data. The robustness of the technique for determining volume fractions was extended with a comparison of calculated 2.1,-micron backscatter from size distribution data with the measured lidar data converted to 2.1,-micron backscatter using an earlier derived algorithm, verifying the algorithm as well as the backscatter calculations.

Cutten, D. R.↗
NASA NTRS2001

Idealized Simulations of the Effects of Amazon Convection and Baroclinic Waves on the South Atlantic Convergence Zone

The South Atlantic Convergence Zone (SACZ) is a NW-SE oriented, stationary region of enhanced convergence and convection that extends southeastward from the ITCZ convection anchored over the Amazon region. On daily satellite images each SACZ episode is seen as a progression of one or several midlatitude cold fronts that intrude into the subtropics and tropics, becoming stationary over southeastern Brazil for a few days. Previous studies have shown that while Amazon convection plays a fundamental role in the formation of the SACZ, Atlantic sea surface temperatures and the Andes Mountains play a relatively minor role in the strength and location of the SACZ. The role of interactions between Amazon convection and midlatitude baroclinic waves in establishing the origin, position, and maintenance of the SACZ is studied here using idealized dry, multilayer global model simulations that do not include the effects of topography. The model simulations produce SACZ-like regions of low-level convergence in the presence of Amazon convection embedded in a mean-flow that contains propagating baroclinic waves. The results of these simulations indicate that Amazon convection plays two fundamental roles in the formation and location of the SACZ. First, it produces a NW-SE oriented region of low-level convergence to the SE of Amazon convection. Second, it produces a storm-track region and accompanying stronger midlatitude baroclinic waves in the region of the SACZ. It is suggested that in the presence of moist effects, the 'seedling' SACZ regions produced in these simulations can be enhanced to produce the observed SACZ.

Ferreira, Rosana Nieto↗
NASA NTRS1981

Quasi-linear blocks forced by orography in a hemispheric, quasi-geostrophic barotropic model

Stationary linear perturbation responses to Northern Hemisphere orography are calculated in a quasi-geostrophic barotropic model in solid-body rotation. The stationary mountain torque induced by these perturbations is then used to construct graphical solutions to the steady-state wave, mean-flow interaction problem. It is shown that multiple solutions exist in the system and are near either the forcing equilibrium of the zonal forcing or near the resonance points in the system. Some of these near-resonance solutions have block-like configurations with a confluence zone upstream from a large-amplitude structure consisting of a high at high latitudes and a low at low latitudes. These block-like configurations are shown to be near stable solutions of the system. Time-dependent calculations show that the initial state and the zonal forcing equilibrium are important in determining the long-term time evolution of the system.

Roads, J. O.↗
NASA NTRS1980

Form-drag instability, multiple equilibria and propagating planetary waves in baroclinic, orographically forced, planetary wave systems

A two-layer baroclinic model is used to study the planetary-scale motions of a thermally driven atmosphere in the presence of topography, and in doing so to extend previous results obtained with a barotropic model. Highly truncated spectral equations are used to obtain multiple wavelike stationary equilibrium states, to examine the instabilities that produce them, and to study the instabilities that feed on them and give rise to traveling planetary waves. Although the equilibria cannot exist without orography, their energy comes from the potential energy of the mean flow, not from kinetic energy transfer via the mountain torque. Low-index (blocking) equilibria as well as high-index equilibria require a large thermal driving and are associated with both orographic and baroclinic instability of the Hadley circulation. It is suggested that blocking in nature is a quasi-stable circulation arising from orographic instability with strong thermal driving; and that observed low-frequency, propagating planetary waves are due to instabilities of the quasi-stationary, topographically forced equilibria.

Charney, J. G.↗
NASA NTRS1972

Observations of the total lunar eclipse on February 10, 1971 at 3.1 mm wavelength.

Observations were made of the total lunar eclipse on February 10, 1971 at a wavelength of 3.1 mm at the Millimeter Wave Observatory of the University of Texas at Austin. Eclipse cooling curves obtained for Copernicus, Mare Serenitatis, and a mountainous region indicate maximum temperature decreases of 6.77%, 6.37%, and 7.51%, respectively. Cooling rates of about 6 K/hour were measured. The normalized solar insolation has also been calculated for each region.

Ulich, B. L.↗
NASA NTRS1985

Measurements of the surface energy budget in the southern Gobi Desert of China, and in the Rocky Mountains of Colorado

Observations of the land surface energy balance were made in the Gobi desert and at two mountain sites in northern Colorado. The Gobi study included 12 days of observations in spring (April 8 to 20, 1984) and 31 days in summer at the same site (June 17 to July 18, 1984). The Colorado study included 126 days (March 13 to July 17, 1984) at a valley site and 34 days (July 31 to September 3, 1984) at a mountain top location. The data for each study included continuous observations of upward and downward radiative fluxes in three wave bands, soil temperature and moisture at four levels, air temperature and humidity at four levels and UVW wind components at three levels. Analyses of the Gobi data include definition of the impact of variable atmospheric moisture on the surface energy balance between spring and summer. In addition, diurnal wind circulations forced by heating of the northern edge of the Tibetan Plateau were observed during both periods.

Reiter, E. R.↗