Lunar-solar interactions in the equatorial electrojet

Gasperini, Federico; Forbes, Jeffrey M.

doi:10.1002/2014gl059294

Cited by 12 publications

(15 citation statements)

References 15 publications

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“…According to numerical simulations, that pattern could be also due to a phase shift in the solar semidiurnal tide [e.g., Pedatella and Liu , ]. The presence of M 2 during SSWs has been also reported from other ground‐based observations as well as in situ observations on‐board satellites [e.g., Stening , ; Gasperini and Forbes , ; Lühr et al , ; Park et al , ; Yamazaki et al , ; Yamazaki , , ; Yamazaki and Kosch , ; Zhang et al , ]. Lunar tides in the ionosphere have been observed at other times, but their amplitudes are much smaller than at times of SSWs, i.e., northern hemispheric winter [e.g., Bartels , ; Chapman and Lindzen , ; Matsushita , ; Stening and Fejer , ; Stening and Rastogi , ; Pedatella and Forbes , ; Aveiro and Hysell , ; Eccles et al , ].…”

Section: Introductionmentioning

confidence: 73%

Upper mesospheric lunar tides over middle and high latitudes during sudden stratospheric warming events

et al. 2015

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In recent years there have been a series of reported ground‐ and satellite‐based observations of lunar tide signatures in the equatorial and low latitude ionosphere/thermosphere around sudden stratospheric warming (SSW) events. This lower atmosphere/ionosphere coupling has been suggested to be via the E region dynamo. In this work we present the results of analyzing 6 years of hourly upper mesospheric winds from specular meteor radars over a midlatitude (54°N) station and a high latitude (69°N) station. Instead of correlating our results with typical definitions of SSWs, we use the definition of polar vortex weaking (PVW) used by Zhang and Forbes (). This definition provides a better representation of the strength in middle atmospheric dynamics that should be responsible for the waves propagating to the E region. We have performed a wave decomposition on hourly wind data in 21 day segments, shifted by 1 day. In addition to the radar wind data, the analysis has been applied to simulations from Whole Atmosphere Community Climate Model Extended version and the thermosphere‐ionosphere‐mesosphere electrodynamics general circulation model. Our results indicate that the semidiurnal lunar tide (M2) enhances in northern hemispheric winter months, over both middle and high latitudes. The time and magnitude of M2 are highly correlated with the time and associated zonal wind of PVW. At middle/high latitudes, M2 in the upper mesosphere occurs after/before the PVW. At both latitudes, the maximum amplitude of M2 is directly proportional to the strength of PVW westward wind. We have found that M2 amplitudes could be comparable to semidiurnal solar tide amplitudes, particularly around PVW and equinoxes. Besides these general results, we have also found peculiarities in some events, particularly at high latitudes. These peculiarities point to the need of considering the longitudinal features of the polar stratosphere and the upper mesosphere and lower thermosphere regions. For example, during SSW 2009, we found that M2 enhances many days before PVW which is not in agreement with most of our results.

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Section: Introductionmentioning

confidence: 73%

Upper mesospheric lunar tides over middle and high latitudes during sudden stratospheric warming events

et al. 2015

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“…It is well known that F10.7 exhibits an evident 27-day periodicity throughout the year due to the 27-day rotation of the Sun (Takahashi et al, 2010;Gasperini and Forbes, 2014). As the mesopause is the coldest region in the atmospheric temperature profile, it is impossible for the strong quasi-27-day oscillation in the MLT observed by meteor radar to be driven through direct absorption of solar radiation in the local region though the oscillation in the zonal wind near the mesopause is in phase with that in F10.7, as shown in Fig.…”

Section: Discussionmentioning

confidence: 99%

Observational evidence of quasi-27-day oscillation propagating from the lower atmosphere to the mesosphere over 20° N

et al. 2015

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Abstract. By using meteor radar, radiosonde and satellite observations over 20 • N and NCEP/NCAR reanalysis data during 81 days from 22 December 2004 to 12 March 2005, a quasi-27-day oscillation propagating from the troposphere to the mesosphere is reported. A pronounced 27-day periodicity is observed in the raw zonal wind from meteor radar. Spectral analysis shows that the oscillation also occurs in the meridional wind and temperature and propagates westward with wavenumber s = 1; thus the oscillation is of Rossby wave type. The oscillation attains a large amplitude of about 12 m s −1 in the eastward wind shear region of the troposphere. When the wind shear reverses, its amplitude rapidly decays, and the background wind gradually evolves to be westward. However, the oscillation can penetrate through the weak westward wind field due to its relatively large phase speed. After this, the oscillation restrengthens with its upward propagation and reaches about 20 m s −1 in the mesosphere. Reanalysis data show that the oscillation can propagate to the mid and high latitudes from the low latitudes and has large amplitudes over there. There is another interesting phenomenon that a quasi-46-day oscillation appears simultaneously in the troposphere, but it cannot penetrate through the westward wind field because of its smaller phase speed. In the observational interval, a quasi-27-day periodicity in outgoing long-wave radiation (OLR) and specific humidity is found in a latitudinal zone of 5-20 • N. Thus the quasi-27-day oscillation may be an atmospheric response to forcing due to the convective activity with a period of about 27 days in the tropical region.

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“…Also, the effect of the semi-monthly lunar tide (= 14.77 days) can easily alias into the 16-day spectrum, especially when the amplitude and phase of the lunar tide are changing with time, such as during stratospheric sudden warming events. Furthermore, Gasperini and Forbes (2014) showed that the combined effect of solar rotation (= 27 days) and lunar tide (= 14.77 days) can cause sideband frequencies corresponding to 9.55-and 32.61-day periods. Love and Rigler (2014) also found various spectral components within the 2-16 day range that arise from solar and lunar tides and intermodulations among them.…”

Section: Planetary Wave Effectmentioning

confidence: 99%

Sq and EEJ—A Review on the Daily Variation of the Geomagnetic Field Caused by Ionospheric Dynamo Currents

2016

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A record of the geomagnetic field on the ground sometimes shows smooth daily variations on the order of a few tens of nano teslas. These daily variations, commonly known as Sq, are caused by electric currents of several μA/m 2 flowing on the sunlit side of the Eregion ionosphere at about 90-150 km heights. We review advances in our understanding of the geomagnetic daily variation and its source ionospheric currents during the past 75 years. Observations and existing theories are first outlined as background knowledge for the nonspecialist. Data analysis methods, such as spherical harmonic analysis, are then described in detail. Various aspects of the geomagnetic daily variation are discussed and interpreted using these results. Finally, remaining issues are highlighted to provide possible directions for future work.

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Lunar-solar interactions in the equatorial electrojet

Cited by 12 publications

References 15 publications

Upper mesospheric lunar tides over middle and high latitudes during sudden stratospheric warming events

Upper mesospheric lunar tides over middle and high latitudes during sudden stratospheric warming events

Observational evidence of quasi-27-day oscillation propagating from the lower atmosphere to the mesosphere over 20° N

Sq and EEJ—A Review on the Daily Variation of the Geomagnetic Field Caused by Ionospheric Dynamo Currents

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