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At least 469 records · Page 26
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NASA NTRS1984

Large Scale Rossby Waves During FGGE

The purpose was to explore the behavior and significance of global-scale rotational normal modes (free Rossby waves) in the atmosphere. Although these modes received a great deal of attention n the past, the lack of accurate global data severely hampered efforts at estimating the amplitudes and time dependence of these waves in the real atmosphere. With the First GARP Global Experiment, the availability of accurate data that is truly global in coverage presents an important opportunity for a better understanding of the role of Rossby waves in the atmosphere. In the results presented, emphasis is placed on the temporal evolution of the amplitude and phase of the Rossby waves, rather than on characteristics of the time spectra of these waves. The first steps of the analysis consisted of projecting the 500 mb height and wind data onto Hough functions for each synoptic time. The seasonal cycle and time mean were removed separately for each season, and all remaining eastward propagating components removed on a seasonal basis; all remaining westward propagating components were retained.

Lindzen, R. S.↗
NASA NTRS1985

The heating of the solar wind by the interstellar neutral gas

Solar wind heating by ionization and assimilation of the interstellar neutral wind is investigated using a numerical model of the interaction. The model is a time-dependent, one-dimensional, spherically symmetric, one-fluid code which includes mass, momentum, and energy sources due to the efficient incorporation of ionized interstellar hydrogen. Solar wind data at 1 AU from October 12, 1978 to February 25, 1980 were input to the inner boundary of the model and propagated out to 10 AU. Then, 52-day averages of proton temperature as functions of radius were produced for three values of the interstellar hydrogen density: 0.0, 0.03, and 0.1 per cu cm. It is concluded that, within the context of the model, the observations of solar wind proton temperatures at Voyager 1 and Pioneer 11 are consistent with heating of the solar wind by an interaction with inflowing interstellar neutral hydrogen. The density of this inflowing gas is near 0.03/cu cm.

Isenberg, P. A.↗
NASA NTRS1984

Gravity-wave spectra in the atmosphere observed by MST radar, part 4.2B

A universal spectrum of atmospheric buoyancy waves is proposed based on data from radiosonde, Doppler navigation, not-wire anemometer and Jimsphere balloon. The possible existence of such a universal spectrum clearly will have significant impact on several areas in the study of the middle atmosphere dynamics such as the parameterization of sub-grid scale gravity waves in global circulation models; the transport of trace constituents and heat in the middle atmosphere, etc. Therefore, it is important to examine more global wind data with temporal and spatial resolutions suitable for the investigation of the wave spectra. Mesosphere-stratosphere-troposphere (MST) radar observations offer an excellent opportunity for such studies. It is important to realize that radar measures the line-of-sight velocity which, in general, contains the combination of the vertical and horizontal components of the wave-associated particle velocity. Starting from a general oblique radar observation configuration, applying the dispersion relation for the gravity waves, the spectrum for the observed fluctuations in the line-of-sight gravity-wave spectrum is investigated through a filter function. The consequence of the filter function on data analysis is discussed.

Scheffler, A. O.↗
NASA NTRS1973

The diurnal wind variation in the lowest 1500 ft in central Oklahoma - June 1966-May 1967.

A one-year accumulation of wind data from a television tower in northern Oklahoma City has been analyzed on a diurnal basis. The annual mean speeds below the third level at 296 ft are lowest at night and highest during the day, and conversely the speeds up to the seventh level at 1458 ft are lowest during the day and highest at night. Generally, speed changes occur in short time periods shortly after sunrise and near sunset. Resultant wind directions veer most with height from 1700 to 1000 CST and least during midday. At all levels winds veer with time between 2100 and approximately 1100 CST and then back with time during the remaining hours.

Crawford, K. C.↗
NASA NTRS1986

Development of a variational SEASAT data analysis technique

Oceans are data-sparse areas in terms of conventional weather observations. The surface pressure field obtained solely by analyzing the conventional weather data is not expected to possess high accuracy. On the other hand, in entering asynoptic data such as satellite-derived temperature soundings into an atmospheric prediction system, an improved surface analysis is crucial for obtaining more accurate weather predictions because the mass distribution of the entire atmosphere will be better represented in the system as a result of the more accurate surface pressure field. In order to obtain improved surface pressure analyses over the oceans, a variational adjustment technique was developed to help blend the densely distributed surface wind data derived from the SEASAT-A radar observations into the sparsely distributed conventional pressure data. A simple marine boundary layer scheme employed in the adjustment technique was discussed. In addition, a few aspects of the current technique were determined by numerical experiments.

Sasaki, Y. K.↗
NASA NTRS1988

Observations and wind-forced model simulations of the mean seasonal cycle in tropical Pacific sea surface topography

This paper quantitatively evaluates simulations of the mean seasonal cycle in the tropical Pacific Ocean, using a multiple vertical-mode version of the Busalacchi and O'Brien (1980) linear model. The period studied (1979-1981) includes several coincident oceanic and surface wind data sets, as well as a fairly regular seasonal cycle leading into the 1982-1983 El Nino. Simulated mean seasonal cycles in dynamic height and sea level are compared with observed variations in expendable bathythermograph and island tide gauge data averaged over the same period. It was found that, although all simulations show characteristic features of the mean meridional ridge-trough structure in surface topography, simulated north and south equatorial ridges at 20 deg N and 20 deg S are much higher than those observed. Only weak equatorial ridges were generated near 4 N, and none of the simulations exhibited a significant equatorial trough. These discrepancies are attributed to limitations in model physics and to the wind forcing.

Mcphaden, Michael J.↗
NASA NTRS2014

A Vortical Dawn Flank Boundary Layer for Near-Radial IMF: Wind Observations on 24 October 2001

We present an example of a boundary layer tailward of the dawn terminator which is entirely populated by rolled-up flow vortices. Observations were made by Wind on 24 October 2001 as the spacecraft moved across the region at the X plane approximately equal to −13 Earth radii. Interplanetary conditions were steady with a near-radial interplanetary magnetic field (IMF). Approximately 15 vortices were observed over the 1.5 hours duration of Wind's crossing, each lasting approximately 5 min. The rolling up is inferred from the presence of a hot tenuous plasma being accelerated to speeds higher than in the adjoining magnetosheath, a circumstance which has been shown to be a reliable signature of this in single-spacecraft observations. A blob of cold dense plasma was entrained in each vortex, at whose leading edge abrupt polarity changes of field and velocity components at current sheets were regularly observed. In the frame of the average boundary layer velocity, the dense blobs were moving predominantly sunward and their scale size along the X plane was approximately 7.4 Earth radii. Inquiring into the generation mechanism of the vortices, we analyze the stability of the boundary layer to sheared flows using compressible magnetohydrodynamic Kelvin-Helmholtz theory with continuous profiles for the physical quantities. We input parameters from (i) the exact theory of magnetosheath flow under aligned solar wind field and flow vectors near the terminator and (ii) the Wind data. It is shown that the configuration is indeed Kelvin-Helmholtz (KH) unstable. This is the first reported example of KH-unstable waves at the magnetopause under a radial IMF.

Magnetosheath↗
NASA NTRS1986

Investigation of seasonal variability of the wind stress curl over the North Atlantic Ocean by means of empirical orthogonal function analysis

The seasonal variability of the wind stress curl over the North Atlantic is investigated by means of empirical orthogonal function (EOF) analysis. The curl field is calculated from 1 year of First Global GARP Experiment wind data. It was found that 44 percent of the variability is contained in four significant eigenvectors. Their spatial patterns are characterized by basin-sized oscillations with larger amplitude to the north of 40 deg N. Their associated time series coefficients have the highest amplitude during the winter and show a tendency toward a white frequency spectrum which nevertheless exhibits noticeable peaks or gaps at certain frequencies. Physically, the first EOF is seen as the seasonal fluctuations of the mean wind stress curl pattern. Five other eigenvectors are also found to be above the noise level, but they account for only a smaller percentage of variability (19 percent). They are characterized by smaller spatial scales than the basin size. Their time series coefficients show a whiter frequency spectrum.

Barnier, B.↗
NASA NTRS1992

Organization of rainfall by an unstable jet with an application to African waves

It is hypothesized that a shear instability can organize rainfall if it converges sufficient amounts of moisture. This convergence is calculated by specifying the amplitude of a downgoing wave just beneath the jet and calculating the ascent induced below as a function of the zonal wind. Data obtained question whether a jet can organize rainfall from an arbitrary large distance above the moist layer. While in the absence of shear, a wave can reach the moist layer with undiminished amplitude, the induced ascent is small - less than the estimated ascent during phase I of the GARP Atlantic Tropical Experiment (GATE) when rainfall remained unorganized. It is suggested that organization can occur only if the unstable jet is within a few kilometers of the moist and separated by large shear. A wind profile resembling the observed 600-mb African jet is considered as an example. The waves are found to be closer to the moist layer during the later summer, causing larger ascent at this time.

Miller, R. L.↗
NASA NTRS1977

A comparison of solar wind streams and coronal structure near solar minimum

Solar wind data from the MIT detectors on the IMP 7 and 8 satellites and the SOLRAD 11B satellite for the solar-minimum period September-December, 1976, were compared with X-ray images of the solar corona taken by rocket-borne telescopes on September 16 and November 17, 1976. There was no compelling evidence that a coronal hole was the source of any high speed stream. Thus it is possible that either coronal holes were not the sources of all recurrent high-speed solar wind streams during the declining phase of the solar cycle, as might be inferred from the Skylab period, or there was a change in the appearance of some magnetic field regions near the time of solar minimum.

Nolte, J. T.↗
NASA NTRS1985

Interannual variability of Martian weather

Pressure, temperature, imaging, and wind data from the Mutch Memorial Station, the Viking lander located in Mars' subtropics, are used to demonstrate the existence of two disctinct regimes of northern hemisphere winter weather on Mars. One of these regime is characterized by one or more intense global dust storms in which the optical depth reaches about 5 over most of the planet. During these events, traveling baroclinic waves of the winter hemisphere are suppressed. In the other regime, there are no global dust storms, but traveling baroclinic waves are active, and high winds associated with these storms raise large quantities of dust which remain confined to a shallow layer in the northern hemisphere. The strongest winds at the Mutch Memorial Station occur during intense storms in the latter regime.

Leovy, C. B.↗
NASA NTRS1984

Tropospheric-stratospheric exchange, part 1.1A

Much of the observational evidence of large scale tropospheric-stratospheric exchange has been obtained by radiosonde and satellite radiane data. So far mesosphere-stratosphere-troposphere (MST) radars have made mininal contributions, in part due to their recent use as a meteorological tool, intermittent operation at some facilities and sparse geographic distribution. However, as more MST facilities come on-line in more locations, the good time and height resolution data throughtout the troposphere and much of the stratosphere obtainable by MST radars will enhance the detail of stratospheric and tropospheric circulations and interactions. On smaller scales MST radars have already been used to examine convective forcing from the troposphere into the stratosphere and subsequent launching of gravity waves (LARSEN et al., 1982). Observations of persistent turbulent layers in the stratosphere over Arecibo, attributable to inertial oscillations, appear to propagate away from a source region near the tropopause (SATO and WOODMAN, 1982). MST radars offer the availability of high resolution wind data in height and time needed to observe interactions between the troposphere and stratosphere. The lack of geographic coverage (e.g., equatorial regions) and insufficient data bases at many MST facilities presently inhibit studies of large-scale interactions. At present MST radars can be used to examine smaller scale interactions.

Cornish, C. R.↗
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 NTRS1992

Southern Hemisphere Lidar Measurements of the Aerosol Clouds from Mt. Pinatubo and Mt. Hudson

On 19 Jul., 1991, during tests to determine the ability of the newly-modified CSIRO Ns:YAG lidar to measure signals from the stratosphere before the arrival of dust from the eruption of Mt. Pinatubo, a strongly scattering layer was detected at an altitude of 2 km. That evening, the spectacular sunset and twilight were typical of volcanically disturbed conditions. Lidar measurements at 532 nm were made between 1400 and 1500 EST (0400-0500 UT) on 19 Jul. through broken cloud. Approximately 3800 laser firings were averaged in 256 shot blocks. These and subsequent data have been analyzed to produce profiles of aerosol volume backscatter function and scattering ratio. Clouds again prevented a clear view of the twilights on the next two nights, although there was some evidence for an enhanced glow. The evidence suggested that the aerosol layer had disappeared. An explanation for this disappearance and the earlier than expected arrival of the layer over Melbourne was required. Nimbus 7 TOMS data for 23 Jun. showed that the SO2 from the eruption had extended at least 11000 km to the west and that the southern boundary of the cloud had reached 15 degrees S just 8 days after the climactic eruption. It can be assumed that this cloud also contained dust and sulphuric acid aerosol. It was proposed that a section had then been broken away from the main cloud and carried south by a large scale eddy between the low latitude easterlies and the strong mid-latitude westerlies which finally carried the aerosol cloud over southern Australia. Accompanying 30 mb wind data showed a counter clockwise circulation, responsible for the transport, located in the South Atlantic Ocean.

Young, Stuart A.↗
NASA NTRS1986

The relationship between proton temperature and momentum flux density in the solar wind

The relationship between proton temperature and momentum flux density/unit mass at 1 AU is examined using Helios 1 solar wind data from 1974 to 1980. In high-speed plasma (V greater than 500 km/s) T(p) increases with increasing n(0) V-squared, where n(0) and T(p) are the density and proton temperature at 1 AU and V is the flow speed. In lowspeed plasma (V less than 500 km/s), T(p) does not increase with increasing n(0) V-squared, and perhaps tends to decrease slightly. These basic relationships between T(p) and n(0) V-squared are not significantly affected by stream interactions. A qualitative explanation of these results is offered in the context of a solar wind model that includes deposition of momentum and energy extending well outward into the interplanetary medium.

Lopez, R. E.↗
NASA NTRS1980

Atmospheric variability and air-sea interaction

The topics studied include: (1) processing of Northern Hemispheric precipitation data, in order to fill in the transition seasons to provide a continuous 40 year data base on the variability of continental precipitation; (2) comparison of seasonally averaged fields of sea surface temperature obtained from ship observations in the North Atlantic and North Pacific in 1970 with the corresponding fields inferred from satellite observations; (3) estimation of seasonal average of total precipitable water at those admittedly few oceanic stations where repeated vertical soundings were made in 1970 and comparison with corresponding values inferred from satellite measurements; (4) comparison of seasonally averaged evaporation fields determined from ground based observations in 1970 with the field of divergence of the seasonal total horizontal water vapor flux inferred from satellite total water measurements and NMC wind data for the lower troposphere; (5) examination of meaning of convection-inversion index.

Middleton, J. W.↗
NASA NTRS1981

Coronal streamers in the solar wind at 1 AU

Virtually all solar wind observing groups have reported substantial variations in the solar wind helium-hydrogen abundance ratio (A(He)). A study of Los Alamos Imp solar wind data has revealed an association between low A(He) and high proton density that occurs at low flow speeds and that is correlated with polarity reversals of the interplanetary magnetic field. The current investigation has the objective to present further examples of the low A(He), high proton density, low speed, magnetic field polarity association, and to document the common occurrence of multiple events lasting approximately 3-7 days. The results are presented of attempts to relate these events directly to maps or isophotes of solar coronal brightness at 1.5 solar radii. The results of the investigation suggest that a substantial fraction of the low-speed solar wind originates in coronal streamers, particularly near solar minimum.

Gosling, J. T.↗
NASA NTRS2011

Coronal Plumes in the Fast Solar Wind

The expansion of a coronal hole filled with a discrete number of higher density coronal plumes is simulated using a time-dependent two-dimensional code. A solar wind model including an exponential coronal heating function and a flux of Alfven waves propagating both inside and outside the structures is taken as a basic state. Different plasma plume profiles are obtained by using different scale heights for the heating rates. Remote sensing and solar wind in situ observations are used to constrain the parameter range of the study. Time dependence due to plume ignition and disappearance is also discussed. Velocity differences of the order of approximately 50 km/s, such as those found in microstreams in the high-speed solar wind, may be easily explained by slightly different heat deposition profiles in different plumes. Statistical pressure balance in the fast wind data may be masked by the large variety of body and surface waves which the higher density filaments may carry, so the absence of pressure balance in the microstreams should not rule out their interpretation as the extension of coronal plumes into interplanetary space. Mixing of plume-interplume material via the Kelvin-Helmholtz instability seems to be possible within the parameter ranges of the models defined here, only at large di stances from the Sun, beyond 0.2-0.3 AU. Plasma and composition measurements in the inner heliosphere, such as those which will become available with Solar Orbiter and Solar Probe Plus, should therefore definitely be able to identify plume remnants in the solar wind.

Velli, Marco↗