Showing papers by "Sharon L. Vadas published in 2014"

Numerical modeling of the global changes to the thermosphere and ionosphere from the dissipation of gravity waves from deep convection

Abstract: 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.

Horizontal parameters of daytime thermospheric gravity waves and E region neutral winds over Puerto Rico

Abstract: We report on the electron density perturbation amplitudes, periods (up to 60 min), horizontal and vertical wavelengths, phase speeds, and propagation directions of daytime traveling ionospheric disturbances (TIDs) from 115 to 300 km altitude using dual-beam experiments at the Arecibo Observatory (AO), Puerto Rico. As in previous studies, we find a near continuum of waves above the AO. While the TIDs propagate in nearly all directions except purely westward, we find that most propagate southward southeastward. We find that TID amplitudes increase nearly exponentially with increasing period, although with a much smaller slope for periods >30 min. TID amplitudes peak on the bottomside of the F region. Typical vertical wavelengths increase from less than 50 km at low altitudes to ∼100–300 km. Horizontal wavelengths increase from ∼70–100 km to ∼150–500 km over the same altitude range. Median vertical wavelengths, horizontal wavelengths, and periods increase with altitude up to z∼ 100–150 m/s. We also measure the E region horizontal neutral winds and find that they peak at ∼150 m/s near z∼105 km in the middle of the day. Wave phase speeds are in general greater than these ambient winds. In addition, by tracing individual wave packets vertically in altitude, we find that a packet's vertical wavelength generally peaks near the altitude where its inferred ion velocity amplitude is maximum. The vertical wavelength generally decreases above this altitude, an observation that is consistent with gravity wave packet theory.

Atmospheric gravity waves excited by a fireball meteor: Observations and modeling

Abstract: 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∼80–100m/s, while those north of the path propagated northwestward with cH∼20–40m/s. Those south (north) of the path had horizontal wavelengths λH∼25–35km (λH∼18 km) and periods τr∼5–6 min (τr∼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 ∼25–35km, and half width half maximum of ∼2–3km.