Fast and ultrafast Kelvin wave modulations of the equatorial evening F region vertical drift and spread F development

Abstract

In this paper, we investigate the role of eastward and upward propagating fast (FK) and ultrafast Kelvin (UFK) waves in the day-to-day variability of equatorial evening prereversal vertical drift and post sunset generation of spread F/plasma bubble irregularities. Meteor wind data from Cariri and Cachoeira Paulista (Brazil) and medium frequency (MF) radar wind data from Tirunelveli (India) are analyzed together with Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics/Sounding of the Atmosphere using Broadband Emission Radiometry (TIMED/SABER) temperature in the 40-to 100-km region to characterize the zonal and vertical propagations of these waves. Also analyzed are the F region evening vertical drift and spread F (ESF) development features as diagnosed by Digisonde (Lowell Digisonde International, LLC, Lowell, MA, USA) operated at Fortaleza and Sao Luis in Brazil. The SABER temperature data permitted determination of the upward propagation characteristics of the FK (E1) waves with propagation speed in the range of 4 km/day. The radar mesosphere and lower thermosphere (MLT) winds in the widely separated longitude sectors have yielded the eastward phase velocity of both the FK and UFK waves. The vertical propagation of these waves cause strong oscillation in the F region evening prereversal vertical drift, observed for the first time at both FK and UFK periodicities. A delay of a few (approximately 10) days is observed in the F region vertical drift perturbation with respect to the corresponding FK/UFK zonal wind oscillations, or temperature oscillations in the MLT region, which has permitted a direct identification of the sunset electrodynamic coupling process as being responsible for the generation of the FK/UFK-induced vertical drift oscillation. The vertical drift oscillations are found to cause significant modulation in the spread F/plasma bubble irregularity development. The overall results highlight the role of FK/UFK waves in the day-to-day variability of the ESF in its occurrence season.

Unseasonal development of post-sunset F-region irregularities over Southeast Asia on 28 July 2014: 1. Forcing from above?

“…Recent research has shown that the vertical plasma drift in the F region above the equator can also be influenced by lower atmospheric variability in the form of tides and planetary waves (e.g., Abdu et al 2006Abdu et al , 2015Maute et al 2014); i.e., forcing from below. Atmospheric gravity waves from the troposphere are also suspected to influence the F-region vertical plasma drift (Li et al 2016) and play a role in the seeding and development of EPBs (e.g., McClure et al 1998;Tsunoda 2010a, b); atmospheric gravity waves therefore represent another form of forcing from below.…”

Electrodynamics of ionospheric weather over low latitudes

“…Planetary wave oscillations in the equatorial ionosphere are more often observed during non-SSW periods, as have been well established from numerous investigations in recent years (see for example, Forbes and Leveroni 1992;Chen 1992;Pancheva et al 2003;Takahashi et al 2009;Abdu et al 2006Abdu et al , 2015a. In their upward propagation, (waves of longer vertical wavelengths attaining higher altitude) these waves nonlinearly interact with ; b The corresponding Digisonde ionograms; c TIMED/GUVI 135.6 nm images extending in the entire longitude span showing the global distribution of the EIA brightness and the patches of brightness depletions indicating plasma bubbles symmetric on either side of the dip equator (Kil et al 2006) tidal modes whereby electric fields are generated in the dynamo region with consequent modulation of the electrodynamical coupling processes.…”

“…Achieving the desired level of predictive capability on low latitude ionospheric weather disturbances remains to be a long-term objective by the scientific community. Some guidelines can be proposed as examples of those helpful for the continuing progress: (1) Detection and characterization of upward propagating Planetary waves/Kelvin waves at stratospheric and mesospheric heights can be used to predict with a few days in advance their modifications of the EIA, the PRE and the associated ESF/bubble developments, from the knowledge of the upward propagation velocities and other-related characteristics of these waves (Abdu et al 2015a). On a similar principle, the identification of tropospheric convective activity in the equatorial region (associated with the inter-tropical convergence zone, ITCZ) and characterization of the upward propagating gravity waves therefrom will be a step toward predicting ESF/plasma bubble occurrence a few hours ahead of its post-sunset development; (2) Measurement of solar wind and interplanetary magnetic field from satellites (such as the ACE) stationed the at L1 libration point (at 1.5 million km away, and 1 h upstream of the Earth) can be used to predict, with the help of assimilative modeling, the development of equatorial bubble/ESF irregularities and the EIA around 1.5 h ahead of their occurrences.…”

“…UFK wave activity can cause also significant modulation in the equatorial evening prereversal vertical drift (PRE) and consequently in the development of post-sunset spread F (ESF) plasma bubble irregularities. Figure 7a shows a case of strong modulation of the ESF intensity as well as onset time of the ESF irregularities as observed by a Digisonde over Fortaleza during a UFK wave episode that occurred in October 2005 (Abdu et al 2015a). It may be noted that the larger PRE amplitude around the day 290 was responsible for the larger intensity and earlier onset time of the post-sunset ESF.…”

“…Three-day oscillation, centered at the equator, is clearly defined, with the upward propagation of the wave being evident from the delay in the peak intensity seen with increasing heights. Their interaction with the upward propagating tides resulted in the generation (Abdu et al 2015a). The upward propagation of these waves was at a rate of 4-5 km per day, thereby attesting to the fact that the upward propagating UFK and FK waves were responsible for the enhanced development of the PRE and ESF over Brazil.…”