Vadas S.L.,NWRA CoRA Office |
Liu H.-L.,U.S. National Center for Atmospheric Research
Journal of Geophysical Research: Space Physics | Year: 2013
We study the response of the thermosphere and ionosphere to gravity waves (GWs) excited by 6 h of deep convection in Brazil on the evening of 01 October 2005 via the use of convective plume, ray trace, and global models. We find that primary GWs excited by convection having horizontal wavelengths of λH∼70-300 km, periods of 10-60 min, and phase speeds of cH∼50-225 m/s propagate well into the thermosphere. Their density perturbations are ρ′/ρ̄∼15- 25% at z∼150 km and are negligible at z>300 km. The dissipation of these GWs creates spatially and temporally localized body forces with amplitudes of 0.2- 1.0 m/s2at z∼120-230 km. These forces generate two counter-rotating circulation cells with horizontal velocities of 50-350 m/s. They also excite secondary GWs; those resolved by our global model have λH∼4000-5000 km and cH∼500-600 m/s. These secondary GWs propagate globally and have ρ′/ρ̄∼10- 25% and 5-15% at z=250 and 375 km, respectively. These forces also create plasma perturbations of f oF2′∼0.2-1.0 MHz, TEC′∼0.4- 1.5 TECU (total electron content unit, 1TECU =1016 elm -2), and hmF2′∼5-50 km. The large-scale traveling ionospheric disturbances (LSTIDs) induced by the secondary GWs have amplitudes of foF2′∼0.2-0.5 MHz, TEC′∼0.2- 0.6 TECU, and hmF2 ′∼5-10 km. In a companion paper, we discuss changes to the prereversal enhancement and plasma drift from these forces. Key PointsThe dissipation of GWs creates circulation cells, secondary GWs, LSTIDs ©2013. American Geophysical Union. All Rights Reserved.
Lyapustin A.,NASA |
Alexander M.J.,NWRA CoRA Office |
Ott L.,NASA |
Molod A.,The Interdisciplinary Center |
And 4 more authors.
Geophysical Research Letters | Year: 2014
Mountain lee waves have been previously observed in data from the Moderate Resolution Imaging Spectroradiometer (MODIS) "water vapor" 6.7 μm channel which has a typical peak sensitivity at 550 hPa in the free troposphere. This paper reports the first observation of mountain waves generated by the Appalachian Mountains in the MODIS total column water vapor (CWV) product derived from near-infrared (NIR) (0.94 μm) measurements, which indicate perturbations very close to the surface. The CWV waves are usually observed during spring and late fall or some summer days with low to moderate CWV (below ∼2 cm). The observed lee waves display wavelengths from 3-4 to 15 km with an amplitude of variation often comparable to ∼50-70% of the total CWV. Since the bulk of atmospheric water vapor is confined to the boundary layer, this indicates that the impact of these waves extends deep into the boundary layer, and these may be the lowest level signatures of mountain lee waves presently detected by remote sensing over the land. ©2014. American Geophysical Union. All Rights Reserved.
Vadas S.L.,NWRA CoRA Office |
Liu H.-L.,U.S. National Center for Atmospheric Research |
Lieberman R.S.,GATS, Inc.
Journal of Geophysical Research A: Space Physics | Year: 2014
During the minimum of solar cycles 23-24, the Sun was extremely quiet; however, tropospheric deep convection was strong and active. In this paper, we model the gravity waves (GWs) excited by deep convective plumes globally during 15-27 June in 2009 and in 2000 (previous solar maximum). We ray trace the GWs into the thermosphere and calculate the body force/heatings which result where they dissipate. We input these force/heatings into a global dynamical model and study the neutral and plasma changes that result. The body forces induce horizontal wind (uH') and temperature (T') perturbations, while the heatings primarily induce T'. We find that the forces create much larger T' than the heatings. uH' consists of clockwise and counterclockwise circulations and "jet"-like winds that are highly correlated with deep convection, with |uH'|∼50-200m/s. uH' and T' are much larger during 2009 than 2000. uH' decreases slightly (significantly) with altitude from z∼150 to 400 km during 2009 (2000). T' perturbations at z=350km primarily propagate westward at ∼460 m/s, consistent with migrating tides. It was found that planetary-scale diurnal and semidiurnal tides are generated in situ in the thermosphere, with amplitudes ∼10-40m/s at z=250 km. The largest-amplitude in situ tides are DW1, D0, DW2, SW2, SW3, and SW5. Smaller-amplitude in situ tides are S0, SE2, and SW3. Total electron content (TEC') perturbations of 1-2.5 (2-3.5) total electron content units (TECU, where 1 TECU = 1016 el m-2) during 2009 (2000) are created in the upper atmosphere above nearby regions of deep tropical convection. For a given local time (LT), there are 2 to 3 TEC' peaks in longitude around the Earth. ©2014. American Geophysical Union. All Rights Reserved.
Vadas S.L.,NWRA CoRA Office |
Suzuki H.,Meiji University |
Nicolls M.J.,SRI International |
Nakamura T.,Japan National Institute of Polar Research |
Harmon R.O.,Ohio Wesleyan University
Journal of Geophysical Research D: Atmospheres | Year: 2014
In a companion paper, Suzuki et al. (2013) studied an expanding circular train observed in the Na airglow for 9 min above Syowa Station, Antarctica, on 7 June 2008. This train was created by a southwestward moving fireball meteor. Here we report on "V"-shaped faint gravity waves (GWs) partially visible in many of the Na airglow images 8 to 43 min after the meteor. The GW phase lines appear to originate from the horizontal projection of the meteor path, with angles -42 to -52° south and 10 to 20° north of the path. The GWs south of the path propagated southwestward with a horizontal phase speed of cH ∼ 80-100 m/s, while those north of the path propagated northwestward with cH ∼ 20-40 m/s. Those south (north) of the path had horizontal wavelengths λH ∼ 25-35km (λH ∼ 18 km) and periods rr ∼ 5-6 min (°r ∼7-15 min). We then model the GWs excited by idealized horizontal and slanted heatings and body forces. We show that the GW phase lines form Vs when the heat/force is slanted vertically. If the central altitude of the heat/force is z0 > 92 km, the open ends of the Vs are mainly directed away from the meteor trajectory. If the heat/force is long enough, two oppositely directed Vs are created, forming an "X" at the center of the structure. We find that λH depends sensitively on the width of the heating. We obtain heating parameters which compare reasonably well with the Na observations: z0 ∼ 120 km, half-length half maximum of ∼ 25-35 km, and half width half maximum of ∼ 2-3 km. © 2014. American Geophysical Union. All Rights Reserved.