Showing papers by "David C. Fritts published in 2002"

CASES-99: A Comprehensive Investigation of the Stable Nocturnal Boundary Layer

Abstract: The Cooperative Atmosphere-Surface Exchange Study—1999 (CASES-99) refers to a field experiment carried out in southeast Kansas during October 1999 and the subsequent program of investigation. Comprehensive data, primarily taken during the nighttime but typically including the evening and morning transition, supports data analyses, theoretical studies, and state-of-the-art numerical modeling in a concerted effort by participants to investigate four areas of scientific interest. The choice of these scientific topics is motivated by both the need to delineate physical processes that characterize the stable boundary layer, which are as yet not clearly understood, and the specific scientific goals of the investigators. Each of the scientific goals should be largely achievable with the measurements taken, as is shown with preliminary analysis within the scope of three of the four scientific goals. Underlying this effort is the fundamental motivation to eliminate deficiencies in surface layer and turbul...

An estimate of strong local body forcing and gravity wave radiation based on OH airglow and meteor radar observations

Abstract: [1] Airglow measurements of gravity wave and smaller-scale flow features, used together with other measurements of larger-scale winds, provide a unique ability to quantify gravity wave dynamics at mesopause altitudes. We consider here an event observed with an OH airglow imager and the meteor radar at the MU Observatory in Japan. This was a wave breaking event of unusually large amplitude and momentum flux. Our hypothesis is that such events are relatively common, and that the resulting local forcing of the mean flow represents a vigorous source of secondary gravity waves that penetrate well into the thermosphere. Our analysis suggests a gravity wave momentum flux of ∼900 m2s−2, far larger than estimated by other techniques, and a mean flow acceleration of ∼80 ms−1 in less than an hour. We also estimate the scales and frequencies of the secondary waves resulting from this local body forcing.

The importance of spatial variability in the generation of secondary gravity waves from local body forces

Abstract: [1] We hypothesized earlier that the zonal mean body force required to close the mesospheric jets is sporadic in time, and is composed of a large number of spatially and temporally localized body forces. To explore the effects of such localization, we randomly generate a series of localized, 3D body forces in the mesosphere which create a mean acceleration of ∼100 m s−1 day−1 over this forcing volume. Secondary waves are also generated, and because they have large vertical scales, phase speeds, and vertical group velocities, they may induce important variabilities in the lower thermosphere where they dissipate. We find that the secondary waves from spatially smoothed body forces have much smaller momentum fluxes, frequencies, and vertical group velocities. Thus, global models having coarse resolution may be missing a significant source of sporadic wave drag and its effect throughout the middle atmosphere and lower thermosphere.

Up-gully flow in the great plains region : a mechanism for perturbing the nighttime lower atmosphere?

Abstract: [1] Studies using data gathered during CASES-99 show that when the near-surface nighttime wind direction shifts through the “up-gully” direction of a significant gully near the tower, the flow produces a pronounced but localized upward surge of vertical velocity up to at least 55 m. This surge generates an outward propagating wave packet having horizontal and vertical wavelengths on the order of 100–250 m with tilted wave fronts consistent with upward phase propagation. The wave packet is observable (with significant delays) by other sensors out to 850 m. As a working hypothesis we assume that the up-gully flow is constricted and strengthened as it progresses up the narrowing gully. We theorize that, upon exiting the gully, the flow has a pronounced and tightly confined vertical component that in turn produces a packet of internal propagating gravity waves.

Sublimb CO2 4200 nm measurements of small-scale internal gravity wave (GW) sources and their propagation and effects on the OH airglow

Abstract: The Waves middle class Explorer mission (WE) is proposed to observe and quantify the effects of small-scale internal Gravity Waves (GW) in the Earth's atmosphere from source regions in the troposphere and lower stratosphere to the mesosphere, lower thermosphere, and ionosphere (MLTI) where the GW have their most dramatic effects. These are now understood to be a key element in defining large-scale circulation, thermal and constituent structures, and variability of the stratosphere and MLTI. The WE instrumentation consists of 5 nadir and limb viewing sensors of the wave perturbed emission structure due to GW throughout the source and affected regions. The WE PI is Prof. G.R. Swenson. This paper addresses the measurement strategy and implementation for two of these instruments, the Source Wave And Propagation Imager (SWAPI), and the Hydroxyl Airglow Wave Imager (HAWI). The SWAPI uses multi-spectral sublimb imaging measurements in the CO 2 (nu) 3 band near 4210 nm to identify GW sources, and their propagation through the stratosphere. Its measurement strategy is driven by data, particularly sublimb images in the CO 2 (nu) 3 band that were obtained by instrumentation deployed on the Midcourse Space Experiment (MSX) satellite, and by the WE team member's data analysis and models. Similarly team member's ground based observational experience and data analysis drives the HAWI measurement strategy.