Papers by Larisa Goncharenko
The Tonga volcano eruption at 04:14:45 UT on 2022-01-15 released enormous amounts of energy into ... more The Tonga volcano eruption at 04:14:45 UT on 2022-01-15 released enormous amounts of energy into the atmosphere, triggering very significant geophysical variations not only in the immediate proximity of the epicenter but also globally across the whole atmosphere. This study provides a global picture of ionospheric disturbances over an extended period for at least 4 days. We find traveling ionospheric disturbances (TIDs) radially outbound and inbound along entire Great-Circle loci at primary speeds of ∼300–350 m/s (depending on the propagation direction) and 500–1,000 km horizontal wavelength for front shocks, going around the globe for three times, passing six times over the continental US in 100 h since the eruption. TIDs following the shock fronts developed for ∼8 h with 10–30 min predominant periods in near- and far- fields. TID global propagation is consistent with the effect of Lamb waves which travel at the speed of sound. Although these oscillations are often confined to the troposphere, Lamb wave energy is known to leak into the thermosphere through channels such as atmospheric resonance at acoustic and gravity wave frequencies, carrying substantial wave amplitudes at high altitudes. Prevailing Lamb waves have been reported in the literature as atmospheric responses to the gigantic Krakatoa eruption in 1883 and other geohazards. This study provides substantial first evidence of their long-duration imprints up in the global ionosphere. This study was enabled by ionospheric measurements from 5,000+ world-wide Global Navigation Satellite System (GNSS) ground receivers, demonstrating the broad implication of the ionosphere measurement as a sensitive detector for atmospheric waves and geophysical disturbances.
<p>During Sudden Stratospheric Warming events, the ionosphere exhibits phase-shifte... more <p>During Sudden Stratospheric Warming events, the ionosphere exhibits phase-shifted semi-diurnal perturbations, which are typically attributed to vertical coupling associated with the semi-diurnal lunar tide (M2). Our understanding of ionospheric responses to M2 is limited. This study focuses on fundamental vertical coupling processes associated with the latitudinal extent and hemispheric asymmetry of ionospheric M2 signatures, using total electron content data from the eastern Asian and American sectors. Our results illustrate that the asymmetry maximizes at around 15°N and 20°S magnetic latitudes. In the southern hemisphere, the M2-like signatures extend deep into midlatitude and, in the American sector, encounter the Weddell Sea Anomaly. The M2 amplitude is larger in the northern hemisphere and such asymmetry is more distinct in the eastern Asian sector. The hemispheric asymmetry of M2 signatures in the low latitude can be primarily explained by the trans-equatorial wind modulation of the equatorial plasma fountain. Other physical processes could also be relevant, including hemispheric asymmetry of the M2 below the F region, the ambient thermospheric composition and ionospheric plasma distribution, and the geomagnetic field configuration.</p>
Journal of Geophysical Research: Space Physics
Journal of Geophysical Research: Space Physics
One of the most important requirements for the space weather community is to improve ionospheric ... more One of the most important requirements for the space weather community is to improve ionospheric predictions for HF radio communications. During geomagnetic storm periods, the ionosphere undergoes dramatic variations including both increases and decreases of electron density compared with quiet days. A key component of understanding the observed ionospheric variations is to also understand the neutral thermosphere variations. In this
Japan Geoscience Union, 2017
Travelling ionospheric disturbances (TIDs) represent a key dynamic process of energy transfer in ... more Travelling ionospheric disturbances (TIDs) represent a key dynamic process of energy transfer in horizontal and vertical directions, and one of the important sources of ionospheric variability. Acoustic gravity waves (AGWs) play a key role in coupling of different atmospheric regions through momentum and energy transfer, and TIDs are thought to be the manifestations of AGWs at ionospheric heights. The incoherent scatter method is well suited for TID studies as it enables TIDs detection in multiple ionospheric parameters (electron density, ion and electron temperatures, plasma velocity), and thus provides critical information needed to examine different hypothesis about association of TIDs with their sources. In 2016, two coordinated measuring campaigns have been held near the vernal equinox and summer solstice using Kharkiv (49.6 N, 36.4 E) and Millstone Hill (42.6 N, 288.5 E) IS radars. The goal of joint observations was to detect TIDs and estimate their characteristics during thes...
Midlatitude Ionospheric Dynamics and Disturbances
ABSTRACT A strong positive storm phase was observed by both the Millstone Hill and Arecibo incohe... more ABSTRACT A strong positive storm phase was observed by both the Millstone Hill and Arecibo incoherent scatter radars during a moderate geomagnetic storm on 10 September 2005. The positive storm phase featured an interesting UT–altitude profile of the F region electron density enhancement that closely resembles the Greek letter L. The radar measurements showed that the uplift of the electron density peak height corresponded to a strong upward ion drift, whereas the subsequent falling of the peak height coincided with a downward ion drift. Using realistic, time-dependent ionospheric convection and auroral precipitation as input, the thermosphere– ionosphere electrodynamics general circulation model (TIEGCM) is able to reproduce the same L-like structure in the electron density profile, along with many large-scale features in electron temperature and vertical ion drift as observed by the radars. Over the 3-day period of 8–10 September, our simulation results show an error of 1%–4% for hmF2, electron, and ion temperatures at both radar locations. The estimated error for NmF2 is about 9% at Millstone Hill and 19% at Arecibo. However, the simulated vertical ion drifts are less accurate, with the normalized root-mean-square errors of 72% at Millstone Hill and 52% at Arecibo, due largely to model’s inability to capture the large temporal fluctuations measured by the radars. However, it reproduces reasonably well the overall large-scale variations during the 3-day period, including the storm-time-enhanced upward ion drift that is responsible for the interesting F region density profile. The model is also able to reproduce the temporal and spatial total electron content variations as shown in the global GPS maps. The comparison with the GUVI O/N2 is less satisfactory, although there is a general agreement in terms of relative O/N2 changes during the storm in the longitudinal sector between 60°W and 80°W where the radars are located. The detailed data–model comparison carried out in this study is helpful not only to validate the model but also to interpret the complex observations. The TIEGCM simulations reveal that it is the enhanced meridional neutral wind, not the penetration electric field, that is the primary cause of the L structure of the F region electron density profile.
Journal of Geophysical Research: Space Physics
The Ionospheric Data Assimilation Four-Dimensional (IDA4D) technique has been coupled to Sami3 is... more The Ionospheric Data Assimilation Four-Dimensional (IDA4D) technique has been coupled to Sami3 is Another Model of the Ionosphere (SAMI3). In this application, ground- and space-based GPS Total Ele...
We present a new high resolution empirical model for the ionospheric total electron content (TEC)... more We present a new high resolution empirical model for the ionospheric total electron content (TEC). TEC data are obtained from the global navigation satellite system (GNSS) receivers with a 1 x 1 sp...
Journal of Geophysical Research: Space Physics
This work conducts a statistical study of the subauroral polarization stream (SAPS) feature in th... more This work conducts a statistical study of the subauroral polarization stream (SAPS) feature in the North American sector using Millstone Hill incoherent scatter radar measurements from 1979 to 2019...
Earth and Planetary Physics
Journal of Geophysical Research: Space Physics
Solar flares provide strong impulsive radiation and energy injection to the sunlit upper atmosphe... more Solar flares provide strong impulsive radiation and energy injection to the sunlit upper atmosphere. The impact on the ionosphere is immense in spatial scale, and therefore, it is not immediately evident if dramatically elevated neutral heating can lead to excitation of acoustic gravity waves. Using primary observations from Global Navigation Satellite System differential TEC (total electron content) over the continental United States, this paper presents postflare ionospheric observations associated with three X-class flares on 6, 7, and 10 September 2017. Postflare ionospheric changes had two significant morphological characteristics: (1) A few minutes after the X9.3 flare peak on 6 September, clear traveling ionospheric disturbance (TID) fronts emanated near the sunrise terminator with alignment parallel to its direction-TIDs propagated predominantly eastward into the dayside with a 150 m/s phase speed and a ∼30-min period; (2) synchronized differential TEC oscillations over continental United States with ∼60-min periodicity and damping amplitude over time, following all three X-class flares. Postflare ionospheric oscillation spectra exhibited significantly enhanced amplitudes and changes of periodicities (including the appearance of the 60-min oscillations). The Millstone Hill incoherent scatter radar observed large ionospheric up-welling occurring nearly simultaneously as detected TIDs at the X9.3 flare peak, with up to 80 m/s enhancements in vertical drift at 500 km lasting for ∼30 min. Results suggest that significant solar flare heating and associated dynamical effects may be an important factor in TID/acoustic gravity wave excitation. Plain Language Summary A solar flare injects a sudden and strong energy input to the sunlit upper atmosphere at a range of radiation wavelengths important for ionospheric photochemistry and thermospheric dynamics. Impulsive energy inputs from flares are well known to generate sudden ionospheric density enhancements with subsequent quick decay. This study addresses another type of flare-associated ionospheric perturbation, known as traveling ionospheric disturbances (TIDs), in the form of propagating waves in space and time as well as synchronized temporal oscillations over the continental United States. Our study provides likely direct observations pointing to a previously unconfirmed TID excitation mechanism associated with solar flare impacts near the sunrise terminator. We observed TIDs with a dense network of Global Navigation Satellite System receivers, yielding detection of differential ionospheric electron content with high fidelity and excellent spatiotemporal resolution. We also used incoherent scatter radar observations at Millstone Hill to reveal ionospheric expansion/up-welling associated with flare impact. These results address fundamental questions regarding solar flare influences on initiation of atmospheric and ionospheric waves.
Space Weather
This paper presents preliminary results of a metrics-based assessment of current modeling capabil... more This paper presents preliminary results of a metrics-based assessment of current modeling capabilities in predicting the ionospheric climatology for two ionospheric characteristics, the foF2 and hmF2. This work is part of the activities of the Ionosphere Working Group of the International Forum for Space Weather Modeling Capabilities Assessment that is facilitated by the Community Coordinated Modeling Center. The results are based on the comparison between modeled and observed monthly medians of the foF2 and hmF2. Modeling formulations considered here include two empirical models (the International Reference Ionosphere [IRI] and Massachusetts Institute of Technology [MIT] Empirical model), as well as two physics-based, coupled ionosphere-thermosphere models (the Coupled Thermosphere Ionosphere Plasmasphere Electrodynamics [CTIPe] and Thermosphere-Ionosphere-Electrodynamics General Circulation Model [TIE-GCM]). The comparisons were carried out in year 2012 over seven ionospheric locations distributed worldwide in the Northern Hemisphere. Based on our findings, although significant errors are occasionally obtained from all modeling approaches, empirical models tend to provide systematically better correlation with the observed medians and follow the observed distributions more successfully, offering smaller prediction errors than the physics-based ones. In case of foF2, the averaged prediction accuracy in terms of root-mean-square error (RMSE) ranges around 1.5 MHz for physics-based models and 0.5 MHz for empirical models. In case of hmF2, it ranges around 30 and 20 km, respectively. The prediction accuracy presents strong seasonal and local time dependence, which differs for different models and ionospheric characteristics (i.e., foF2 or hmF2): it is strong for physics-based models, weaker for IRI, and very weak for MIT empirical model. This latter outcome may provide suggestive input for future improvements.
Journal of Geophysical Research: Atmospheres
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Papers by Larisa Goncharenko