Physical Sciences and Mathematics Commons^™

Gravity Wave Ducting In The Upper Mesosphere And Lower Thermosphere Duct System, R. L. Walterscheid, Michael P. Hickey Ph.D.

Publications

We report on a numerical study of gravity wave propagation in a pair of ducts located in a region where dramatic changes in the airglow most likely associated with ducted wave trains are observed. We examine ducting in an upper mesosphere inversion (INV) and an always present lower thermosphere stable layer (LTD) for a range of phase speeds and horizontal wavelengths characteristic of ducting events. We analyze the propagation and modal structure of ducted waves for backgrounds with increasing realism, starting with a climatological temperature profile where only the LTD is present. In succession, we add the INV based on …

Analysis And Modeling Of Ducted And Evanescent Gravity Waves Observed In The Hawaiian Airglow, D. B. Simkhada, J. B. Snively, M. J. Taylor, S. J. Franke

Publications

Short-period gravity waves of especially-small horizontal scale have been observed in the Maui, Hawaii airglow. Typical small-scale gravity wave events have been investigated, and intrinsic wave propagation characteristics have been calculated from simultaneous meteor radar wind measurements. Here we report specific cases where wave structure is significantly determined by the local wind structure, and where wave characteristics are consistent with ducted or evanescent waves throughout the mesopause region. Two of the documented events, exhibiting similar airglow signatures but dramatically different propagation conditions, are selected for simple numerical modeling case studies. First, a Doppler-ducted wave trapped within relatively weak wind flow …

Propagation Of Tsunami-Driven Gravity Waves Into The Thermosphere And Ionosphere, Michael P. Hickey, G. Schubert, R. L. Walterscheid

Publications

Recent observations have revealed large F-region electron density perturbations (~100%) and total electron content (TEC) perturbations (~30%) that appear to be correlated with tsunamis. The characteristic speed and horizontal wavelength of the disturbances are ~200 m/s and ~400 km. We describe numerical simulations using our spectral full-wave model (SFWM) of the upward propagation of a spectrum of gravity waves forced by a tsunami, and the interaction of these waves with the F-region ionosphere. The SFWM describes the propagation of linear, steady-state acoustic-gravity waves in a nonisothermal atmosphere with the inclusion of eddy and molecular diffusion of heat and momentum, ion …

Synoptic-Scale Characteristics And Precursors Of Cool-Season Precipitation Events At St. John's, Newfoundland, 1979-2005, Shawn M. Milrad, Eyad H. Atallah, John R. Gyakum

Publications

The issue of quantitative precipitation forecasting continues to be a significant challenge in operational forecasting, particularly in regions susceptible to frequent and extreme precipitation events. St. John’s, Newfoundland, Canada, is one location affected frequently by such events, particularly in the cool season (October–April). These events can include flooding rains, paralyzing snowfall, and damaging winds.

A precipitation climatology is developed at St. John’s for 1979–2005, based on discrete precipitation events occurring over a time period of up to 48 h. Threshold amounts for three categories of precipitation events (extreme, moderate, and light) are statistically derived and utilized to categorize such events. …

The Spread-F Experiment (Spreadfex): Program Overview And First Results, David C. Fritts, M. A. Abdu, B. R. Batista, I. S. Batista, P. P. Batista, R. Buriti, B. R. Clemesha, T. Dautermann, E. De Paula, B. J. Fechine, Bela Fejer, D. Gobbi, J. Haase, F. Kamalabadi, B. Laughman, L. M. Lima, H. L. Liu, A. Medeiros, Pierre-Dominique Pautet, D. M. Riggin, F. São Sabbas, J. H. A. Sobral, P. Stamus, H. Takahashi, Michael J. Taylor, Sharon L. Vadas, C. M. Wrasse

Publications

We performed an extensive experimental campaign (the spread F Experiment, or SpreadFEx) from September to November 2005 to attempt to define the role of neutral atmosphere dynamics, specifically wave motions propagating upward from the lower atmosphere, in seeding equatorial spread F and plasma bubbles extending to higher altitudes. Campaign measurements focused on the Brazilian sector and included ground-based optical, radar, digisonde, and GPS measurements at a number of fixed and temporary sites. Related data on convection and plasma bubble structures were also collected by GOES 12 and the GUVI instrument aboard the TIMED satellite. Initial results of our analyses of …

The Noctilucent Cloud (Nlc) Display During The Ecoma/Mass Sounding Rocket Flights On 3 August 2007: Morphology On Global To Local Scales, G. Baumgarten, J. Fiedler, K. H. Fricke, M. Gerding, M. Hervig, P. Hoffmann, N. Müller, Pierre-Dominique Pautet, M. Rapp, C. Robert, D. Rusch, C. Von Savigny, W. Singer

Publications

During the ECOMA/MASS rocket campaign large scale NLC/PMC was observed by satellite, lidar and camera from polar to mid latitudes. We examine the observations from different instruments to investigate the morphology of the cloud. Satellite observations show a planetary wave 2 structure. Lidar observations from Kühlungsborn (54° N), Esrange (68° N) and ALOMAR (69° N) show a highly dynamic NLC layer. Under favorable solar illumination the cloud is also observable by ground-based cameras. The cloud was detected by cameras from Trondheim (63° N), Juliusruh (55° N) and Kühlungsborn. We investigate planetary scale morphology and local scale gravity wave structures, important …

Dynamical And Precipitation Structures Of Poleward-Moving Tropical Cyclones In Eastern Canada, 1979-2005, Shawn M. Milrad, Eyad H. Atallah, John R. Gyakum

Publications

Tropical cyclones in the western North Atlantic basin are a persistent threat to human interests along the east coast of North America. Occurring mainly during the late summer and early autumn, these storms often cause strong winds and extreme rainfall and can have a large impact on the weather of eastern Canada. From 1979 to 2005, 40 named (by the National Hurricane Center) tropical cyclones tracked over eastern Canada. Based on the time tendency of the low-level (850–700 hPa) vorticity, the storms are partitioned into two groups: ‘‘intensifying’’ and ‘‘decaying.’’ The 16 intensifying and 12 decaying cases are then analyzed …

Convection: The Likely Source Of The Medium-Scale Gravity Waves Observed In The Oh Airglow Layer Near Brasilia, Brazil, During The Spreadfex Campaign, Sharon L. Vadas, Michael J. Taylor, Pierre-Dominique Pautet, P. A. Stamus, David C. Fritts, H. L. Liu, F. T. São Sabbos, V. T. Batista, H. Takahashi, V. T. Rampinelli

Publications

Six medium-scale gravity waves (GWs) with horizontal wavelengths of λH=60–160 km were detected on four nights by Taylor et al. (2009) in the OH airglow layer near Brasilia, at 15° S, 47° W, during the Spread F Experiment (SpreadFEx) in Brazil in 2005. We reverse and forward ray trace these GWs to the tropopause and into the thermosphere using a ray trace model which includes thermospheric dissipation. We identify the convective plumes, convective clusters, and convective regions which may have generated these GWs. We find that deep convection is the highly likely source of four of these GWs. We pinpoint …