127 research outputs found
Tropospheric gravity waves observed by three closely spaced ST radars
Clear-air radar experiments were carried out on the southern coast of France during the (ALPEX) Alpine experiment program vertically directed stratosphere-troposphere-radars were set up with spacings of about 5 to 6 km. The temporal and spectral characteristics of the vertical velocity fluctuations were examined. The horizontal and vertical properties of gravity waves in the lower atmosphere were analyzed. The techniques used and the first results from this wave study are described
Excerpts from the paper: Research Status and Recommendation from the Alaska Workshop on Gravity Waves and Turbulence in the Middle Atmosphere, part 1.3A
Internal gravity waves are disturbances whose intrinsic frequencies k(c - u) are smaller than the Brunt-Vaisala frequency (N). Their importance arises because: they are the major components of the total flow and temperature variability fields of the mesosphere (i.e., shears and lapse rates) and hence constitute the likely sources of turbulence; and they are associated with fluxes of momentum that communicate stresses over large distances. For example, gravity waves exert a drag on the flow in the upper mesosphere. However, in order for gravity waves to exert a net drag on the atmosphere, they must be attenuated. There are two general types of processes that seek to attenuate gravity waves: dissipation and saturation. Dissipation is any process that is effective independent of the wave amplitude, while saturation occurs when certain wave amplitude conditions are met. Radiative damping is an example of dissipation, while convective overturning is an example of saturation. The two processes are not mutually exclusive
Magnetosphere-Ionosphere Coupling Through E-region Turbulence 1: Energy Budget
During periods of intense geomagnetic activity, strong electric fields and
currents penetrate from the magnetosphere into high-latitude ionosphere where
they dissipate energy, form electrojets, and excite plasma instabilities in the
E-region ionosphere. These instabilities give rise to plasma turbulence which
induces non-linear currents and strong anomalous electron heating (AEH) as
observed by radars. These two effects can increase the global ionospheric
conductances. This paper analyzes the energy budget in the electrojet, while
the companion paper applies this analysis to develop a model of anomalous
conductivity and frictional heating useful in large-scale simulations and
models of the geospace environment. Employing first principles, this paper
proves for the general case an earlier conjecture that the source of energy for
plasma turbulence and anomalous heating equals the work by external field on
the non-linear current. Using a two-fluid model of an arbitrarily magnetized
plasma and the quasilinear approximation, this paper describes the energy
conversion process, calculates the partial sources of anomalous heating, and
reconciles the apparent contradiction between the inherently 2-D non-linear
current and the 3-D nature of AEH.Comment: 13 pages, 1 figure; 1st of two companion paper
VBP15, a glucocorticoid analogue, is effective at reducing allergic lung inflammation in mice
Asthma is a chronic inflammatory condition of the lower respiratory tract associated with airway hyperreactivity and mucus obstruction in which a majority of cases are due to an allergic response to environmental allergens. Glucocorticoids such as prednisone have been standard treatment for many inflammatory diseases for the past 60 years. However, despite their effectiveness, long-term treatment is often limited by adverse side effects believed to be caused by glucocorticoid receptor-mediated gene transcription. This has led to the pursuit of compounds that retain the anti-inflammatory properties yet lack the adverse side effects associated with traditional glucocorticoids. We have developed a novel series of steroidal analogues (VBP compounds) that have been previously shown to maintain anti-inflammatory properties such as NFκB-inhibition without inducing glucocorticoid receptor-mediated gene transcription. This study was undertaken to determine the effectiveness of the lead compound, VBP15, in a mouse model of allergic lung inflammation. We show that VBP15 is as effective as the traditional glucocorticoid, prednisolone, at reducing three major hallmarks of lung inflammation--NFκB activity, leukocyte degranulation, and pro-inflammatory cytokine release from human bronchial epithelial cells obtained from patients with asthma. Moreover, we found that VBP15 is capable of reducing inflammation of the lung in vivo to an extent similar to that of prednisone. We found that prednisolone--but not VBP15 shortens the tibia in mice upon a 5 week treatment regimen suggesting effective dissociation of side effects from efficacy. These findings suggest that VBP15 may represent a potent and safer alternative to traditional glucocorticoids in the treatment of asthma and other inflammatory diseases.Supported in part by grants from the NIH (1R41HL104939-01B; 1K26RR032082; 1P50AR060836-01; 1U54HD071601; 2R24HD050846-06, R01 HL033152-
25), DOD grants (W81XWH-11-1-0330; W81XWH-11-1-0782; W81XWH-10-1-0659; W81XWH-11-1-0809; W81XWH-09-1-0599) a translational research grant from
MDA, pilot grant from Parent Project Muscular Dystrophy (PPMD), and a contribution from the Clark Family Foundation
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The Very Stable Boundary Layer on Nights with Weak Low-Level Jets
The light-wind, clear-sky, very stable boundary layer (vSBL) is characterized by large values of bulk
Richardson number. The light winds produce weak shear, turbulence, and mixing, and resulting strong
temperature gradients near the surface. Here five nights with weak-wind, very stable boundary layers during
the Cooperative Atmosphere–Surface Exchange Study (CASES-99) are investigated. Although the winds
were light and variable near the surface, Doppler lidar profiles of wind speed often indicated persistent
profile shapes and magnitudes for periods of an hour or more, sometimes exhibiting jetlike maxima. The
near-surface structure of the boundary layer (BL) on the five nights all showed characteristics typical of the
vSBL. These characteristics included a shallow traditional BL only 10–30 m deep with weak intermittent
turbulence within the strong surface-based radiation inversion. Above this shallow BL sat a layer of very
weak turbulence and negligible turbulent mixing. The focus of this paper is on the effects of this quiescent
layer just above the shallow BL, and the impacts of this quiescent layer on turbulent transport and numerical
modeling. High-frequency time series of temperature T on a 60-m tower showed that 1) the
amplitudes of the T fluctuations were dramatically suppressed at levels above 30 m in contrast to the
relatively larger intermittent T fluctuations in the shallow BL below, and 2) the temperature at 40- to 60-m
height was nearly constant for several hours, indicating that the very cold air near the surface was not being
mixed upward to those levels. The presence of this quiescent layer indicates that the atmosphere above the
shallow BL was isolated and detached both from the surface and from the shallow BL.
Although some of the nights studied had modestly stronger winds and traveling disturbances (density
currents, gravity waves, shear instabilities), these disturbances seemed to pass through the region without
having much effect on either the SBL structure or on the atmosphere–surface decoupling. The decoupling
suggests that under very stable conditions, the surface-layer lower boundary condition for numerical
weather prediction models should act to decouple and isolate the surface from the atmosphere, for example,
as a free-slip, thermally insulated layer.
A multiday time series of ozone from an air quality campaign in Tennessee, which exhibited nocturnal
behavior typical of polluted air, showed the disappearance of ozone on weak low-level jets (LLJ) nights.
This behavior is consistent with the two-stratum structure of the vSBL, and with the nearly complete
isolation of the surface and the shallow BL from the rest of the atmosphere above, in contrast to cases with
stronger LLJs, where such coupling was stronger
Spectral characteristics of scintillations producing ionospheric irregularities in the Indian region
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