A review of vertical coupling in the Atmosphere–Ionosphere system: Effects of waves, sudden stratospheric warmings, space weather, and of solar activity

The effect of sudden stratospheric warming (SSW) on the F2 region ionosphere has been extensively analyzed for the major event of year 2009, apart from a few reports on other major and minor events. Morphology of ionospheric responses during SSW can be better comprehended by analyzing such warming events under different solar, geomagnetic, and meteorological conditions. We investigate the features of F2 region variability following the SSW events of 2010, 2011, 2012, 2013, 2014, 2015, and 2016, using ionosonde data from the Asian region covering a broad latitudinal range from 26.6°N to 45.1°N. We find perceptible ionospheric variations in electron densities during these warming events which is accompanied by a large variation of ~117% within enhancements, as compared to a meagre variation of ~11% within depressions, during these events. We also examine 6 months data at these latitudes and longitudes and find that the maximum and minimum variations in F2 layer critical frequency are observed during each SSW period. The influence of quasi‐stationary 16 day planetary waves is seen during these SSW events. Further, a recently proposed parameter “SSW integrated strength” by Vieira et al. (2017) to characterize SSW event with respect to ionosphere is also examined. It is seen that it does not fit well for these seven SSW events at these latitudes and longitudes.

Section: Summary and Discussionmentioning

confidence: 99%

Morphology of ionospheric F₂ region variability associated with sudden stratospheric warmings

Gupta

Upadhayaya

2017

“…Studies over the last decade demonstrated that these waves can effectively propagate deep into the thermosphere despite the steeply growing molecular diffusion and thermal conduction [ Yiğit et al , ; Hickey et al , , ; Fritts and Lund , ; Gavrilov and Kshevetskii , ; Vadas and Fritts , ; Vadas et al , ; Heale et al , ] and considerably influence the state and circulation at altitudes up to the F region of the ionosphere [ Yiğit et al , ; Miyoshi et al , ]. The most recent review of these studies can be found in the works of Yiğit and Medvedev [], Yiğit et al [], and in the book by Yiğit [, Chapter 5]. In addition to the dynamical forcing, GWs contribute to heating and cooling of the thermosphere above the turbopause (∼105 km) up to F 2 layer altitudes, reaching peak values of ∼170 K d −1 [ Yiğit and Medvedev , ].…”

Section: Introductionmentioning

confidence: 99%

Influence of parameterized small‐scale gravity waves on the migrating diurnal tide in Earth's thermosphere

Yiğit

Medvedev

2017

Self Cite

Effects of subgrid‐scale gravity waves (GWs) on the diurnal migrating tides are investigated from the mesosphere to the upper thermosphere for September equinox conditions, using a general circulation model coupled with the extended spectral nonlinear GW parameterization of Yiğit et al. (). Simulations with GW effects cut off above the turbopause and included in the entire thermosphere have been conducted. GWs appreciably impact the mean circulation and cool the thermosphere down by up to 12–18%. GWs significantly affect the winds modulated by the diurnal migrating tide, in particular, in the low‐latitude mesosphere and lower thermosphere and in the high‐latitude thermosphere. These effects depend on the mutual correlation of the diurnal phases of the GW forcing and tides: GWs can either enhance or reduce the tidal amplitude. In the low‐latitude MLT, the correlation between the direction of the deposited GW momentum and the tidal phase is positive due to propagation of a broad spectrum of GW harmonics through the alternating winds. In the Northern Hemisphere high‐latitude thermosphere, GWs act against the tide due to an anticorrelation of tidal wind and GW momentum, while in the Southern high‐latitudes they weakly enhance the tidal amplitude via a combination of a partial correlation of phases and GW‐induced changes of the circulation. The variable nature of GW effects on the thermal tide can be captured in GCMs provided that a GW parameterization (1) considers a broad spectrum of harmonics, (2) properly describes their propagation, and (3) correctly accounts for the physics of wave breaking/saturation.

“…The ionosphere is a complex dynamic system whose behavior is associated not only with the Earth magnetic field changes and solar processes but also with the neutral atmosphere condition. The results of recent studies show convincingly that the sources in lower atmospheric layers (troposphere and stratosphere) can have a considerable effect on the ionospheric plasma condition (Kazimirovsky, ; Lastovicka, ; Yiğit et al, ). For example, equatorial ionosphere variability related to low atmosphere temperature changes is shown to be up to a half of the solar‐induced one (Mukhtarov & Pancheva, ).…”

Section: Introductionmentioning

confidence: 96%

Variations in Ionospheric Peak Electron Density During Sudden Stratospheric Warmings in the Arctic Region

Yasyukevich

2018

The focus of the paper is the ionospheric disturbances during sudden stratospheric warming (SSW) events in the Arctic region. This study examines the ionospheric behavior during 12 SSW events, which occurred in the Northern Hemisphere over 2006–2013, based on vertical sounding data from DPS‐4 ionosonde located in Norilsk (88.0°E, 69.2°N). Most of the addressed events show that despite generally quiet geomagnetic conditions, notable changes in the ionospheric behavior are observed during SSWs. During the SSW evolution and peak phases, there is a daytime decrease in NmF2 values at 10–20% relative to background level. After the SSW maxima, in contrast, midday NmF2 surpasses the average monthly values for 10–20 days. These changes in the electron density are observed for both strong and weak stratospheric warmings occurring at midwinter. The revealed SSW effects in the polar ionosphere are assumed to be associated with changes in the thermospheric neutral composition, affecting the F2‐layer electron density. Analysis of the Global Ultraviolet Imager data revealed the positive variations in the O/N2 ratio within the thermosphere during SSW peak and recovery periods. Probable mechanisms for SSW impact on the state of the high‐latitude neutral thermosphere and ionosphere are discussed.