Convective Coupling Between the Lower Atmosphere and the Thermosphere/Ionosphere
In this talk, I discuss recent research relating the coupling of the lower and upper atmosphere via gravity waves (GWs) generated by deep convective plumes. These gravity waves are excited by the convective overshoot. Those GWs which reach the thermosphere tend to dissipate at z=120-220 km. Because of wind filtering in the lower thermosphere, they are oriented in a certain direction when they deposit their momentum in the thermosphere. This deposition of momentum accelerates the neutral fluid in the thermosphere horizontally, and is dubbed a thermospheric "body force". We discuss a case study here involving a convective plume in Brazil on 01 Oct, 2005. We find that this body force is quite large spatially, and has a large amplitude of ~ 1 m/s2. It excites large scale secondary gravity waves with horizontal waveslengths of 2000 km and horizontal phase speeds of 500 m/s. These secondary GWs propagate up to at least z=420 km, and propagate globally on the nightside to the north and south poles after 4-6 hours. These secondary GWs propagate in all directions except that perpendicular to the force direction. Additionally, large-scale LSTIDs are created which "follow" the GWs around the globe. Finally, large "mean" neutral winds and wind shear are created in the body force region, which dissipate after 4 hours. This new mechanism for the generation of large-scale GWs during geomagnetically quiet times agrees well with existing observations.
Simulation of the Tides with the Whole Atmosphere Community Climate Model
The atmospheric thermal tides are excited by absorption of solar radiation by ozone in the stratosphere and water vapor in the troposphere, and also by latent heat release in tropical convection. Tidal oscillations propagate upward and can attain very large amplitudes in the mesosphere and lower thermosphere, where they influence composition and temperature structure. We present simulations of the migrating and non- migrating tides carried out with NCAR's Whole Atmosphere Community Climate Model (WACCM), a "high-top" (ground to 140 km) comprehensive General Circulation model with coupled chemistry. We document the seasonal and inter-annual variation of the migrating tides and some of the more important non-migrating tides, and investigate their relationship to the quasi-biennial oscillation and ENSO events, both of which can be included in the latest version of WACCM.
Ionospheric disturbances induced by tsunamigenic internal gravity waves: Observation and modeling
A series of ionospheric anomalies following the Sumatra tsunami has been recently reported in the literature (Liu et al. 2006; DasGupta et al. 2006; Occhipinti et al. 2006). These anomalies show the signature in the ionosphere of tsunami-generated internal gravity waves (IGW) propagating in the neutral atmosphere overlooking the ocean. All these anomalies, observed in the total electron content (TEC) measured by GPS or altimeters, show geographical heterogeneity in the perturbed TEC amplitude and suggest a dependence of geomagnetic latitude. This latter, never treated theoretically, have been taken into account in the 3D modeling of Occhipinti et al. (2006) and used for the interpretation of the TEC Topex and Jason data. Most of the ionospheric anomalies are also deterministic and reproducible by numerical modeling (Occhipinti et al., 2006, 2008) via the ocean/neutral atmosphere/ionosphere coupling mechanism. This approach is used here to focus on the magnetic field dependence in the tsunamigenic IGW propagation in the ionosphere. The etherogenity produced in the ionosphere by a north-ward and south-ward tsunami propagation propagation in the global scale is presented here in term of TEC perturbations. [DasGupta et al., 2006] Earth Planet. Space, 35, 929-959. [Liu et al., 2006] J. Geophys. Res., 111, A05303. [Occhipinti et al., 2006] Geophys. Res. Lett., 33, L20104, 2006 [Occhipinti et al., 2008] Geophys. J. Int., 173, 3, 753-1135, 2008.
Effects of Internal Gravity Waves in the Thermosphere Above the Turbopause
We present results of the study of gravity wave (GW) effects on the circulation in the thermosphere-ionosphere (TI). A spectral GW drag scheme suitable for the thermosphere has been developed and implemented into the Coupled Middle Atmosphere-Thermosphere Model (CMAT2) extending from the lower atmosphere into the F- region. Results of the simulations demonstrate that GWs of the tropospheric origin can effectively penetrate into the upper thermosphere. Momentum deposited by these waves is not only negligible above the turbopause, but is comparable to that of ion drag, at least up to 180-200 km. Effects of the thermospheric GW drag are particularly noticeable in the winter hemisphere, where the inclusion of GW parameterization allowed to reproduce weaker westerlies and stronger high-latitude easterlies, well in agreement with the empirical Horizontal Wind Model. We shall discuss some inferences concerning the dynamic response in the F-region to the variations of the source spectrum.
All Sky Imager observations during a Sudden Stratospheric Warming: Comparisons to the Extended CMAM
An all sky imager was located at Eureka, Nunavut (80N, 86W) at the Polar Environment Atmospheric Research Laboratory in the fall of 2007. It has been operating over the past two winters and taking measurements of sodium, hydroxyl and oxygen green line airglow emissions as well as red line and N2+ emissions. During both winters, airglow observations were taken during Stratospheric Warmings. During the major warming in January 2009, significant variability in the gravity wave signatures and airglow intensity was observed. This included reversal in wave direction and variations in the form of the observed waves and changes in airglow intensity. These results are interpreted in the context of a warming which developed in a run of the extended Canadian Middle Atmosphere model during which perturbations from the stratosphere to the thermosphere occured.
Poker Flat Incoherent Scatter Radar Measurements of Winds and Waves in the D region
We discuss the use of the 450-MHz Poker Flat Incoherent Scatter Radar (PFISR) for incoherent-scatter (IS) based D-region observations, which have been undertaken since the summer of 2007. Monthly observations indicate periods of enhanced and detectable D-region IS returns, often but not always associated with energetic auroral precipitation. The nature of these active versus quiet periods are investigated. Routine observations consist of electron densities, spectral widths, and line-of-sight speeds at altitudes ranging from 60-90 km. In addition, using the pulse-to-pulse beam steering capabilities of PFISR, horizontal and vertical motions (full vector winds) are routinely resolved at high temporal (few minute) and range (0.6-1.5 km) resolution. We present evidence for gravity wave motions (medium/high frequency as well as inertial) and mean winds, from which wavelengths and intrinsic frequencies are derived.
Fabry-Perot Observations of a Secondary Peak at 20-21 Local Time in the Nocturnal Thermospheric Temperature Variation at Arequipa, Peru (16.5S, 71.5 W)
Fabry-Perot observations of the nighttime thermospheric temperature variation in the equatorial region at Arequipa, Peru (16.5 S, 71.5 W) have generally reported the detection of a midnight temperature maximum (MTM). Examination of Arequipa temperature observations for the period of 1997 to 2001 as compared with the NRL MSIS-00 empirical model also reveals the occasional appearance of a secondary temperature peak with an amplitude of 15 to 25 K in contrast to the MTM amplitude of typically 75 to 150 K. This feature is seen near 20-21 LT for perhaps 15 to 25% of the ~400 nights of winter and equinoctial observations between 1997 and 2001. There was no strong solar cycle phase dependence noted for these results. Detection was possible only when the Fabry-Perot observations in all directions were averaged to decrease the measurement error from a typical value of 40-50 K to 15-20 K. Modelling using the Whole Atmosphere Model demonstrates the detection of a similar peak near 20-21 LT in the nighttime thermal variation. The development of this peak occurs as the result of the thermal forcing by the tidal waves propagating upward from the lower thermosphere for which the multiple tidal harmonics interact with the diurnal variation of the thermospheric ion drag to produce the MTM and also sporadically, this secondary temperature peak.