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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 127 records · Page 7
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NASA NTRS1986

A diagnostic study of baroclinic disturbances in polar air streams

Quasi-Lagrangian budgets of mass, vorticity and heat are calculated following disturbances that form within polar air streams. Observed cases are extracted from the European Centre for Medium-range Weather Forecasts analyses during the First GARP Global Experiment. Model-generated cases are extracted from the simulations of extratropical cyclogenesis by Sandgathe. These polar lows grow primarily through basic baroclinic instability processes and exhibit many features of larger maritime extratropical cyclones. Polar lows that originate on the poleward (or Cyclonic - Type C) side of the jet and have considerable midtropospheric positive vorticity advection at formation time are contrasted with lows that form on the equatorward (or Anticyclonic - Type A) side of a nearly straight upper-level jet. The midtropospheric positive vorticity advection must be present to enhance the vertical circulation when the large surface fluxes that are associated with strong outbreaks act to damp the thermal wave amplification. Although latent heat release is an important factor in both types, it is an essential energy source for the Type A low developments on the equatorward side. Although the vorticity balance is initially different for the two types of polar lows, the vorticity budgets during later stages are similar. The heat budget and the thickness tendency equation demonstrated that the self-development process that is present in larger maritime cyclones is also important for polar low intensification. The absence of favorable coupling to a jet stream is the missing factor in a model-generated Type A polar low that failed to develop. Consequently, the mid- and upper-tropospheric wind fields determine which polar lows will intensify to significant amplitudes.

Sinclair, Mark R.↗
NASA NTRS1987

Equatorial long-wave characteristics determined from satellite sea surface temperature and in situ data

SST maps and imagery derived from the NOAA 6 satellite AVHRR for June and July 1981 in the eastern tropical Pacific portray the wavelike structure of the cool water along the equator from 93 deg W to 125 deg W. Cusped waves of approximately 1000-km zonal wavelength and 25-day period propagated westward with a phase speed of 40 km/day. The observed meridional extent between the crest and trough of the waves is about 300 km. Details in the imagery show cooler water at the cusps advected north and then east with the north equatorial countercurrent (NECC), consistent with the suggestion of a series of anticyclonic eddies occupying the shear zone between the NECC and the westward flowing south equatorial current. Absolute SST estimates from the AVHRR data agree to within 0.6 C with shipboard data taken along 110 deg W between 5 deg N and 5 deg S. The wavelike structures in the SST maps are also in agreement at the surface with a vertical expendable bathythermograph temperature section made along the equator between 93 deg W and 125 deg W, which shows the phase of the waves tilting westward with increasing depth over the upper 75 m. Such a phase shift, if it extended 100-200 km meridionally in either direction from the equator, would be associated with an equatorward flux of heat. Similar phase shifts appear in temperature time series at depths of 20 and 50 m, from a mooring at 0-deg 33-min N, 110-deg 30-min W. Near-surface currents measured at this and a second mooring on the equator at 109-deg 40-min W indicate a regular pattern of northward advection when wave cusps pass them, followed by southwest flow during the passage of wave troughs, again consistent with an equatorward flux of heat, as well as with earlier theoretical and drift buoy findings.

Pullen, Patricia E.↗
NASA NTRS1986

Characteristics of precipitation regimes during the global weather experiment

Rainfall data were used in conjunction with heating rate values obtained from GLA/NASA to describe large scale heating changes and concurrent circulation fluctuations for weekly averages during the Special Observing Period I (January-March 1979) of the Global Weather Experiment. The GLA diabatic heating rates were obtained as residues of the thermodynamic energy equation during the four-dimensional data assimilation cycle (as described by Kalnay and Baker, 1984). In week one, the heating and rainfall rate profiles display a positive anomaly on the West Pacific in both fields. The anomaly appears to propagate eastward into the East Pacific and South America by the fifth week. By the week four, the negative anomaly over the Indian Ocean becomes positive. These heating patterns are reflected on positive divergent anomalies at 200 mb analyzed for the same periods. The stream-function anomalies display anticyclonic circulations over the heating anomalies.

Ahrens, Glen D.↗
NASA NTRS1988

Climatology of the stratospheric polar vortex and planetary wave breaking

The distribution of Ertel's potential vorticity (PV) on the 850 K isentropic surface is used to establish a climatology for the transient evolution of the planetary scale circulation in the Northern Hemisphere winter midstratosphere. PV distributions are computed from gridded NMC daily temperature and height maps for the 10 and 30 mb levels, and show that a very good approximation for 850 K PV can be derived from 10 mb heights and temperatures alone. It is assumed that reversals of the latitudinal gradient of PV, localized in longitude and latitude may be regarded as signatures of planetary wave breaking. Wave breaking identified by such signatures tends to occur mainly in the vicinity of the Aleutian anticyclone, with a secondary maximum over Europe. The area of the polar vortex, defined as the area enclosed by PV contours greater than a certain critical value, is strongly influenced by wave breaking. Erosion of the polar vortex due to transport and mixing of PV leads to a preconditioned state, when defined in terms of vortex area, that always occurs prior to major stratospheric warmings. During winters with little PV transport or mixing, the vortex area evolves rather uniformly in response to radiative forcing. During winters with major sudden warmings, the wave breaking signature as defined here first appears at low values of PV, then rapidly moves toward higher values as the vortex area is reduced and the 'surf-zone' structure becomes well defined.

Baldwin, Mark P.↗
NASA NTRS1988

Effects of stratospheric lapse rate on thunderstorm cloud-top structure in a three-dimensional numerical simulation. I - Some basic results of comparative experiments

The effects of stratospheric temperature lapse rate on cloud top height/temperature structure for strongly sheared, mature, isolated midlatitude thunderstorms are investigated by performing three different experiments with an anelastic, three-dimensional model: (1) with an assumed stratospheric lapse rate of 0 K/km (i.e., the isothermal case), (2) with 3 K/km, and (3) with -3 K/km (i.e., the case of inversion). Kinematic storm structure is very similar in all three cases, especially in the troposphere; a strong quasi-steady updraft evolves and splits into a dominant cyclonic overshooting right-mover and a weaker, anticyclonic left-mover that does not reach the tropopause.

Schlesinger, Robert E.↗
NASA NTRS1988

The relationship of satellite-inferred stratospheric aerosol extinction to the position of the 50-mb north polar jet stream

The relationship between stratospheric aerosols and the location of the north polar night stratospheric jet stream was investigated for selected periods of four successive winters (1979-1982), using measurements from SAM II (Stratospheric Aerosol Measurement II) and SAGE I (Stratospheric Aerosol and Gas Experiment I) satellite-borne sun photometers and corresponding meteorological observations. Each period investigated included a polar stratospheric warming during which major dynamic meteorological changes are known to have perturbed the structure of the polar vortex. The analysis of variations in aerosol extinction mixing ratio patterns among winters and during major stratospheric warming events within separate winters showed a well-defined positive gradient in extinction mixing ratio and temperature across the jet stream from the cyclonic side to the anticyclonic side at altitudes between 20 and 30 km during each winter period. Estimates of extinction mixing ratio profiles measured near the center of the polar vortex suggest that a gradual subsidence took place within the polar vortex during at least three of the four winter periods.

Livingston, John M.↗
NASA NTRS1988

Synoptic and chemical evolution of the Antarctic vortex in winter and spring, 1987

The dynamical evolution of the vortex at least up to 50 mb is dominated by synoptic scales in the troposphere. In particular, there is a clear response when poleward extension of tropospheric anticyclones from latitudes of 40 and 50 S to 70 and 80 S occurs. This response is evident in isentropic potential vorticity maps, TOMS ozone fields and SAM II polar stratospheric clouds. An important feature of the high latitude Southern Hemisphere lower stratosphere is a transition at potential temperatures in the 390 to 400 K range. This transition, the vortopause, is clearly marked in aircraft profiles of O3, H2O, N2O and ClO at latitudes 68 to 72 S near the Antarctic peninsula, and also cross-sections of potential vorticity and potential temperature; above it, the isopleths are more closely spaced than below it. The aircraft measurements of H2O, O3, NO sub y, N2O, ClO, and whole air data are examined in material coordinates, theta and P sub theta, backed up by trajectory analysis. The evolution of the chemical mixing ratios is examined in these coordinates as a function of time from mid-August to late September. Conclusions are drawn about the rates of change and their causes. The meteorological and aircraft data are examined for evidence of the following kinds of motion with respect to the vortex: ingress of air aloft, subsidence, peeling off of air to lower latitudes, and folding of the vortopause. Conclusions are presented regarding the evidence for a chemical sink of ozone above and below theta = 400 K, and whether the vortex has a mass flow through it, or if the chemical sink operates on a fixed mass of air. Implications for mid-latitudes are briefly considered in the light of the conclusions.

Tuck, A. F.↗
NASA NTRS1989

Observations of low-frequency inertia-gravity waves in the lower stratosphere over Arecibo

Results are presented of a detailed analysis of the horizontal wind data in the subtropical upper troposphere and lower stratosphere, obtained with the 430-MHz radar at Arecibo (Puerto Rico) in May 1982 and April 1983. Both sets of observations displayed a slowly varying anticyclonically rotating persistent structure in the wind field just above the tropopause, of the type that would be expected if the oscillations were associated with quasi-inertial period waves. The quasi-inertial period structure in the Arecibo observations appears to be typical of the results of a number of other studies, indicating that quasi-inertial period waves are a ubiquitous feature in the lower stratosphere, similar to what is observed in the oceans.

Cornish, C. R.↗
NASA NTRS1989

Synoptic/planetary-scale interactions and blocking over the North Atlantic Ocean

The focus was on the development of a blocking anticyclone that formed over the North Atlantic in January 1979 and a marine cyclone that deepened explosively prior to the onset of the block. The extended height tendency equation was used as the primary diagnostic tool. Focusing on the domain encompassing the migrating ridge that eventually formed the block, it was found that vorticity advection played the dominant role in the development of the ridge and the formation of the block. Also of interest was an attempt to evaluate the relative importance of synoptic-scale, planetary-scale, and synoptic/planetary-scale interactions as the block developed. To accomplish this, all data fields were partitioned into synoptic and planetary-scale components using a Barnes-type filter. Finally, the cyclone was diagnosed by examining the low level static stability fields associated with the cyclone's development.

Smith, Phillip J.↗
NASA NTRS1989

Linear properties of eddies in a Jovian troposphere forced by deep jets

A linear quasi-geostrophic beta-plane model is used to study large-scale instabilities of the Jovian upper troposphere forced from below by zonal jets. The jets are presumed to be barotropically stable in the isentropic deep interior, but barotropically unstable in the statically stable upper troposphere. The effect on this barotropic instability of weak vertical shear causing the jets to decay with height is examined. It is found that eastward jets are stabilized by weaker shear than westward jets, the most unstable eddies are strongly confined by the shear, and eddy fluxes contribute to vertical decay of the jets. The lower residual mean meridional circulation cells exhibit rising motion in regions of anticyclonic shear, but these are overlain by reverse cells.

Orsolini, Y.↗
NASA NTRS1989

Voyager 2 at Neptune - Imaging science results

Neptune's atmosphere is revealed by Voyager 2 images to contain clouds of methane ice above a lower deck of hydrogen sulfide or ammonia ices, and to be dominated by an anticyclonic storm system designated the 'Great Dark Spot'; this bears both similarities and differences to the Great Red Spot of Jupiter. Like the rings of Uranus, those of Neptune are composed of very dark, but in addition very dusty, material. Six new regular satellites have been discovered whose radii range from 25 to 200 km. Triton is noted to be a differentiated body showing evidence of early surface-melting episodes. At least two active plumes are found on Triton, which may be driven by solar heating.

Smith, B. A.↗
NASA NTRS1990

A wave dynamical interpretation of Saturn's polar hexagon

The hexagonal, pole-centered cloud feature in Saturn's northern atmosphere, as revealed in Voyager close-encounter imaging mosaics, may be interpreted as a stationary Rossby wave. The wave is embedded within a sharply peaked eastward jet (of 100 meters per second) and appears to be perturbed by at least one anticyclonic oval vortex immediately to the south. The effectively exact observational determination of the horizontal wave number and phase speed, applied to a simple model dispersion relation, suggests that the wave is vertically trapped and provides a diagnostic template for further modeling of the deep atmospheric stratification.

Allison, M.↗
NASA NTRS1990

The China Clipper - Fast advective transport of radon-rich air from the Asian boundary layer to the upper troposphere near California

A series of upper tropospheric radon concentration measurements made over the eastern Pacific and west coast of the U.S. during the summers of 1983 and 1984 has revealed the occurrence of unexpectedly high radon concentrations for 9 of the 61 measurements. A frequency distribution plot of the set of 61 observations shows a distinct bimodal distribution, with approximately 2/5 of the observations falling close to 1 pCi/SCM, and 3/5 falling in a high concentration mode centered at about 11 pCi/SCM. Trajectory and synoptic analyses for two of the flights on which such high radon concentrations were observed indicate that this radon-rich air originated in the Asian boundary layer, ascended in cumulus updrafts, and was carried eastward in the fast moving air on the anticyclonic side of the upper tropospheric jet. The results suggest that the combination of rapid vertical transport from the surface boundary layer to the upper troposphere, followed by rapid horizontal transport eastward represents an efficient mode of long-transport for other, chemically reactive atmospheric trace constituents.

Kritz, Mark A.↗
NASA NTRS1990

Dynamics of Triton's atmosphere

It is argued here that the facts about Triton's atmosphere discovered by the recent Voyager encounter can be explained if Triton, like Mars, has a global, well-structured atmosphere in equilibrium with surface frosts. The subliming frost cap produces a polar anticyclone at low altitudes, with northeastward winds of about 5 m/s within the Ekman boundary layer. The temperature contrast between the cold frost-covered pole and the warm unforested equator produces westward winds at high altitudes.

Ingersoll, Andrew P.↗
NASA NTRS1990

North Atlantic weather regimes: A synoptic study of phase space

In the phase space of weather, low frequency variability (LFV) of the atmosphere can be captured in a large scale subspace, where a trajectory connects consecutive large scale weather maps, thus revealing flow changes and recurrences. Using this approach, Vautard applied the trajectory speed minimization method (Vautard and Legras) to atmospheric data. From 37 winters of 700 mb geopotential height anomalies over the North Atlantic and the adjacent land masses, four persistent and recurrent weather patterns, interpreted as weather regimes, were discernable: a blocking regime, a zonal regime, a Greenland anticyclone regime, and an Atlantic regime. These regimes are studied further in terms of maintenance and transitions. A regime survey unveils preferences regarding event durations and precursors for the onset or break of an event. The transition frequencies between regimes vary, and together with the transition times, suggest the existence of easier transition routes. These matters are more systematically studied using complete synoptic map sequences from a number of events.

Orrhede, Anna Karin↗
NASA NTRS1991

Synoptic/planetary-scale interactions and blocking over the North Atlantic Ocean

One segment of work in the past year focused on the diagnosis of a major blocking anticyclone and its interacting synoptic scale circulations that occurred during January 1979 over the North Atlantic Ocean. Another segment focused on the diagnosis of a second explosive cyclone development that occurred over the southeastern United States during the time of block formation. The diagnoses were accomplished using the diagnostic relationship known as the Zwack-Okossi (Z-O) development equation. Results indicate that in both cyclone cases the development occurred as a result of the favorable influence of positive vorticity advection, warm air advection, and latent heat release and ceased when one or more of these influences diminished. The advantages of the Z-O equation are described.

Smith, Phillip J.↗
NASA NTRS1990

A composite study of onset of the Australian summer monsoon

The circulation changes that accompany an onset (defined as the first occurrence of wet 850-mb westerly winds at Darwin, Australia) of the Australian summer monsoon are documented by a composite study for the years 1957-1987. Composites of atmospheric fields at stations in and about the Australian tropics are constructed relative to the onset data at Darwin. It is shown that the composite onset is dominated by a slow eastward migration of a deep-baroclinic convective circulation displaced south of the equator. This propagating anomaly exhibited many features of the so-called 40-50 day oscillation, including an upper level anticyclone that accompanies the convective anomaly.

Hendon, Harry H.↗
NASA NTRS1990

A numerical study of the outflow layer of tropical cyclones

Numerical simulations of idealized tropical cyclones with special emphasis on the outflow layer are presented. The quasi-steady state outflow layers of weak and strong cyclones are found to exhibit similar characteristics. The circulations are anticyclonic and asymmetric about the center; the outflow layer is dominated by a narrow, elongated outflow-jet contributing up to 50 percent of the angular momentum transport; the air particles in the outflow jet mostly originate from the lower level. Secondary circulations are found to influence the relative humidity and the potential vorticity at the outflow levels. In order to study the effect of upper tropospheric forcings, two variational numerical experiments using cumulus convection as the major link between the upper-level forcing and the tropical cyclone's response are conducted.

Shi, Jainn-Jong↗