211,333 research outputs found

    High Frequency Atmospheric Gravity Wave Damping in the Mesosphere

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    Correlative measurements of temperature and winds by Na lidar and brightness in OH and O2 Atmospheric band airglow have been made at Albuquerque, NM and Maui, HI for a study of high frequency (period less than 30 minutes) Atmospheric Gravity Waves. Wave studies from four nights have been made and the correlative information describes the intrinsic wave properties with altitude, their damping characteristics, and resulting accelerations to the large scale circulation in the 85-100 km altitude region. Generally, saturated to super-saturated conditions were observed below 95 km. Above this altitude, they were less saturated to freely propagating

    Seasonal and Nocturnal Variations of the Mesospheric Sodium Layer at Starfire Optical Range, New Mexico

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    The seasonal variations of the mesospheric sodium layer structure over Starfire Optical Range (SOR: 35ºN, 106.5ºW), New Mexico are characterized using 46 night data of Na wind/temperature lidar observations collected from Jan. 1998 to May 2000. The column abundance has a mean value of 5.06 x 109 cm -2 and strong annual oscillations of with a maximum in November and a minimum in June and July. The annual mean rms width of the sodium layer is 4.30 km and the mean centroid height is 91.60 km. Semiannual oscillations are evident in seasonal variations of the rms width and the centroid height. Their mean nocturnal variations show effects of tides. The photo-ionization during daytime and recombination processes of Na at night, as well as tidal dynamics, induce strong nocturnal variations in the sodium abundance with a minimum just before midnight and a maximum just before sunrise

    Vertical Dynamical Transport of Mesospheric Constituents by Dissipating Gravity Waves

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    Over 400 h of Na wind/temperature lidar observations, obtained at the Star5re Optical Range, NM, are used to study the vertical dynamical transport of Na in the mesopause region between 85 and 100 km. Dynamical transport occurs when dissipating, non-breaking gravity waves impart a net vertical displacement in atmospheric constituents as they propagate through a region. We show that the vertical constituent flux can be related in a simple way to the vertical heat flux. Breaking gravity waves also contribute to eddy transport by generating turbulence. Because eddy transport is a mixing process, it only occurs in the presence of a gradient in the concentration profile of the constituent, while dynamical transport can be sustained even in the absence of such a gradient. The dynamical Na flux is compared with the predicted eddy flux. The maximum downward dynamical flux of Na is −280 m/s cm3 at 88 km. The maximum downward eddy flux is −160 m/s cm3 at the same altitude assuming the diffusion coefficient is 200 m2/s. The observational results are consistent with theoretical predictions below 93 km and show that dynamical transport often exceeds the vertical transport associated with eddy diffusion. The theoretical models are used to predict the dynamical and eddy fluxes of atomic oxygen and show that for this constituent, dynamical transport is also a signifcant transport mechanism

    O(1S), OH, and O2(b) Airglow Layer Perturbations due to AGWs and their Implied Effects on the Atmosphere

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    The O(1S) (green line) night airglow emission in response to atmospheric gravity wave (AGW) perturbations was simulated with a linear, one-dimensional model. The results were combined with previously modeled O2(b, 0–1) atmospheric band and OH Meinel band emission response (Liu and Swenson, 2003) to derive amplitude and phase relations among multiple airglow layers in response to gravity waves with various intrinsic parameters and damping rates (β). The simulations show that the vertical profile of the standard deviation of the perturbed green line volume emission rate (VER) has a centroid altitude that is 3 km lower and a full-width-half-maximum 2.1 km smaller than the unperturbed VER profile, similar to findings for the OH and O2(b) band layers. Relative phase differences and amplitudes of vertically propagating waves can be deduced from zenith observations of the layers. Airglow weighted responses to waves are related through a cancellation factor (CF) for both layer intensity and temperature. The vertical wavelength can be deduced from relative phase information of three airglow layers separated in altitude. The vertical flux of horizontal momentum associated with gravity waves is deduced from intrinsic wave parameters. Wave damping versus altitude is used to deduce the flux divergence and local accelerations resulting from dissipative waves. The simulations are useful in calculating wave information and wave effects on the atmosphere from multiwavelength, zenith airglow observations

    Gravity Wave Characteristics in the Lower Atmosphere at South Pole

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    A 4-year (1993-1996) temperature and wind data set obtained from over 2000 high-resolution balloon soundings at South Pole is used to study gravity wave characteristics in the atmosphere and lower stratosphere. Extensive analyses of energy density, spectra, and static stability are performed to present a comprehensive view of the gravity waves are ubiquitous and often fairly strong at the South Pole, even though the generation mechanisms are not clear. Gravity wave characteristics are, in general, similar to those obtained at other high-latitude southern hemisphere stations. Potential energies vary between about 0.5 J/kg and 5 J/kg with season and altitude. Variations in kinetic energies are not well correlated with potential energy variations and range from 1 J/kg to 11 J/kg. We observe significant seasonal variations of the slope and magnitude of the vertical wavenumber spectrum of temperature fluctuations, especially in the stratosphere. In general, the gravity waves in the stratosphere are stronger (weaker) in austral spring (fall). Stability analysis shows that instabilities are more likely to occur in the troposphere than in the stratosphere. The probability of wave instability is 13.7% in the troposphere and 5.4 % in the stratosphere. This is due to the less stratification of the troposphere, where the buoyancy period averages 8.3 min compared to 4.9 min in the stratosphere. Dynamic (shear) instability is more likely to occur than convective instability (11% versus 2.6% in the troposphere and 4.7% versus 0.7% in the stratosphere), due to the prevailing strong wind shear. The instability probabilities vary seasonally with the austral winter exhibiting the probability of instabilities (dynamic and convective instabilities combined) in both the troposphere and stratosphere

    Maintenance of Circulation Anomalies during the 1988 Drought and 1993 Floods over the United States

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    The large-scale circulation anomalies associated with the 1988 drought and the 1993 floods are investigated with the National Centers for Environmental Prediction Reanalysis data and a linear stationary wave model. The transient vorticity and thermal forcings are explicitly calculated and the diabatic heating is derived as a residual in the thermodynamic energy equation. Using the April–June (AMJ) data for 1988, and June–August (JJA) data for 1993, the linear stationary wave model is able to reproduce the main features of the geopotential height anomaly for the two seasons when all forcings are included. This provides a basis for further investigation of stationary wave response to different forcing mechanisms using the linear model. Within the linear model framework, the linear model responses to different forcings are examined separately. The results indicate that the 1988 anomaly over the United States is a result of both the diabatic heating and the transient vorticity and thermal forcings. The large anticyclonic anomalies over the North Pacific and Canada are forced mainly by the diabatic heating. The 1993 anomaly, however, is dominated by the response to transient vorticity forcing. By further separating the linear model responses to regional diabatic heating anomalies in 1988, the results indicate that the western North Pacific heating is entirely responsible for the anticyclonic center over the North Pacific, which causes the northward shift and intensification of the Pacific jet stream. The eastern North Pacific heating/cooling couplet is the most important for maintaining the North American circulation anomaly. The tropical eastern Pacific cooling/heating anomalies associated with the La Nina condition have negligible influence on the North American circulation. In 1993, the strong diabatic heating over the North American continent largely compensates the effect of the cooling over the North Pacific. The dynamics of the AMJ and JJA climate is further explored by calculating its Green’s function for both diabatic heating and vorticity forcing. The results again show negligible influence from the equatorial Pacific. The most effective location for diabatic heating to generate a North American circulation anomaly is along the west coast of North America, where the zonal wind is relatively weak. There is little sensitivity in the Green’s function solution to the different basic states

    A Modeling Study of O2 and OH Airglow Perturbations Induced by Atmospheric Gravity Waves

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    A one-dimensional model is used to investigate the relations between gravity waves and O2 and OH airglows perturbations. The amplitude and phase of the airglow perturbations induced by gravity waves (with period \u3e 20 min) are calculated for different vertical wavelength (10–50 km) and damping rate. The model shows that for vertically propagating gravity waves, the amplitude of airglow perturbations observed from ground is larger for longer vertical wavelength, because of the smaller cancellation effect within each layer. The ratio of the amplitudes between O2 and OH is smaller for larger wave damping. For upward propagating (downward phase progression) waves, the intensity perturbation in O2 leads OH, and their phase difference (O2 minus OH) is larger for smaller vertical length and/or stronger damping. The rotational temperature perturbation leads intensity perturbation in both layers. Their phase difference is also larger for smaller vertical length but is smaller for stronger damping. Based on these relations, the vertical wavelength and damping rate of gravity waves can be derived from simultaneous measurements of airglow perturbations in O2 and OH layers

    Production, Outflow, Velocity, and Radial Distribution of H2O and OH in the Coma of Comet C/1995 O1 (Hale-Bopp) from Wide-field Imaging of OH

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    Observations of OH are a useful proxy of the water production rate (Q H2O) and outflow velocity (VH2O) in comets. From wide-field images taken on 1997 March 28 and April 8 that capture the entire scale length of the OH coma of comet C/1995 O1 (Hale-Bopp), we obtain Q OH from the model-independent method of aperture summation and Q H2O from the OH photochemical branching ratio, BROH. Using an adaptive ring summation algorithm, we extract the radial brightness distribution of OH 0-0 band emission out to cometocentric distances of up to 10 to the sixth power km, both as azimuthal averages and in quadrants covering different position angles relative to the comet-Sun line. These profiles are fitted using both fixed and variable velocity two-component spherical expansion models to estimate VOH with increasing distance from the nucleus. The OH coma of Hale-Bopp was more spatially extended than those of previous comets, and this extension is best matched by a variable acceleration of H 2O and OH that acted across the entire coma, but was strongest within 1-2 × 104 km from the nucleus. Our models indicate that VOH at the edge of our detectable field of view (10 to the sixth power km) was ∼2-3 times greater in Hale-Bopp than for 1P/Halley class comet at 1 AU, which is consistent with the results of more sophisticated gas-kinetic models, extrapolation from previous observations of OH in comets with QH2O \u3e 10 to the twenty-ninth power s superscript -1, and direct radio measurements of the outer coma Hale-Bopp OH velocity. The likely source of this acceleration is thermalization of the excess energy of dissociation of H2O and OH over an extended collisional coma. When the coma is broken down by quadrants in position angle, we find an azimuthal asymmetry in the radial distribution that is characterized by an increase in the spatial extent of OH in the region between the orbit-trailing and anti-Sunward directions. Model fits specific to this area and comparison with radio OH measurements suggest greater acceleration here, with VOH ∼ 1.5 times greater at a 10 to the sixth power km cometocentric distance than elsewhere in the coma. We discuss several mechanisms that may have acted within the coma to produce the observed effect

    Atmospheric Stability and Gravity Wave Dissipation in the Mesopause Region

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    High-resolution temperature profile data collected at the Urbana Atmospheric Observatory (40ºN, 88ºW) and Starfire Optical Range, NM (35ºN, 106.5ºW) with a Na lidar are used to assess the stability of the mesopause region between 80 and 105 km. The mean diurnal and annual temperature profiles demonstrate that in the absence of gravity wave and tidal perturbations, the background atmosphere is statically stable throughout the day and year. Thin layers of instability can be generated only when the combined perturbations associated with tides and gravity waves induce large vertical shears in the horizontal wind and temperature profiles. There is a region of reduced stability below the mesopause between 80 and 90 km where the temperature lapse rate is large and the buoyancy parameter N2 is low. The vertical heat flux is maximum in this region which suggests that this is also a region of significant wave dissipation. There is also a region of enhanced stability above 95 km in the lower thermosphere where N2 is large. There appears to be little wave dissipation above 95 km because the temperature variance increases rapidly with increasing altitude in this region and the vertical heat flux is zero

    Meteor Trail Advection Observed During the 1998 Leonid Shower

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    Sodium resonance lidar observations of meteor trails are reported from the 1998 Leonid shower experimental at the Starfire Optical Range Kirtland Air Force Base, NM (35.0º N, 106.5º W ). The lidar was operating in a spatially scanning mode that allowed tracking for up to one half-hour. Three trails are presented here whose motion allowed inference of radial as well as vector wind components and apparent diffusivities. The winds are derived independently using the narrow linewidth sodium (Na) resonance Doppler lidar technique and are compared with the tracking results
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