Larisa P. Goncharenko

The potential role of stratospheric ozone in the stratosphere-ionosphere coupling during stratospheric warmings

The recent discovery of large ionospheric disturbances associated with sudden stratospheric warmings (SSW) has challenged the current understanding of mechanisms coupling the stratosphere and ionosphere. Non-linear interaction of planetary waves and tides has been invoked as a primary mechanism for such coupling. Here we show that planetary waves may play a more complex role than previously thought. Planetary wave forcing induces a global circulation that leads to the build-up of ozone density in the tropics at 30–50 km altitude, the primary region responsible for the generation of the migrating semidiurnal tide. The increase in the ozone density reaches 25% and lasts for ∼35 days following the SSW, long after the collapse of the planetary waves. Ozone enhancements are not only associated with SSW but are also observed after other amplifications in planetary waves. In addition, the longitudinal distribution of the ozone becomes strongly asymmetric, potentially leading to the generation of non-migrating semidiurnal tides. We report a persistent increase in the variability of ionospheric total electron content that coincides with the increase in stratospheric ozone and we suggest that the ozone fluctuations affect the ionosphere through the modified tidal forcing.

The neutral dynamics during the 2009 sudden stratosphere warming simulated by different whole atmosphere models

The present study compares simulations of the 2009 sudden stratospheric warming (SSW) from four different whole atmosphere models. The models included in the comparison are the Ground-to-topside model of Atmosphere and Ionosphere for Aeronomy, Hamburg Model of the Neutral and Ionized Atmosphere, Whole Atmosphere Model, and Whole Atmosphere Community Climate Model Extended version (WACCM-X). The comparison focuses on the zonal mean, planetary wave, and tidal variability in the middle and upper atmosphere during the 2009 SSW. The model simulations are constrained in the lower atmosphere, and the simulated zonal mean and planetary wave variability is thus similar up to ∼1 hPa (50 km). With the exception of WACCM-X, which is constrained up to 0.002 hPa (92 km), the models are unconstrained at higher altitudes leading to considerable divergence among the model simulations in the mesosphere and thermosphere. We attribute the differences at higher altitudes to be primarily due to different gravity wave drag parameterizations. In the mesosphere and lower thermosphere, we find both similarities and differences among the model simulated migrating and nonmigrating tides. The migrating diurnal tide (DW1) is similar in all of the model simulations. The model simulations reveal similar temporal evolution of the amplitude and phase of the migrating semidiurnal tide (SW2); however, the absolute SW2 amplitudes are significantly different. Through comparison of the zonal mean, planetary wave, and tidal variability during the 2009 SSW, the results of the present study provide insight into aspects of the middle and upper atmosphere variability that are considered to be robust features, as well as aspects that should be considered with significant uncertainty.

Climatology of neutral winds in the lower thermosphere over Millstone Hill (42.6°N) observed from ground and from space

Neutral winds in the lower thermosphere at altitudes of 94-130 km were measured in 1987-2000 by the ground-based incoherent scatter radar (ISR) at Millstone Hill (42.6°N, 288.5°E) and in 1992-1997 by the space-based Wind Imaging Interferometer (WINDII) on the Upper Atmosphere Research Satellite (UARS). The data from the ISR and WINDII have been separately grouped into four seasons. The daytime wind measurements from both instruments are found to be in good agreement, with similar structures and similar magnitudes. Winds from both instruments show an annual variation with a winter minimum. Winds in spring and summer are generally about a factor of two larger than those in fall and winter. The semidiurnal winds are dominant, but diurnal tides, mainly the in situ thermospheric diurnal tide, are comparable. The tidal characteristics and the background winds (the diurnal mean) derived from WINDII data show that the amplitude of the semidiurnal tide is generally 10 ms -1 larger than that of the in situ thermospheric diurnal tide, and the zonal and meridional background winds are less than 40 ms -1 and 15 ms -1 in all seasons, respectively. The TIME-GCM simulations of wind fields at 42.5°N for the March equinox and the December solstice are in reasonable agreement with the observations, but the comparisons for the June solstice are less satisfactory. More research needs to be done to understand the cause of disagreement at the June solstice and the September equinox and to properly model the tidal effects in the lower thermosphere during those periods.

Ionospheric response to the 2009 sudden stratospheric warming over the equatorial, low, and middle latitudes in the South American sector

The present study investigates the ionospheric total electron content (TEC) and F-layer response in the Southern Hemisphere equatorial, low, and middle latitudes due to major sudden stratospheric warming (SSW) event, which took place during January–February 2009 in the Northern Hemisphere. In this study, using 17 ground-based dual frequency GPS stations and two ionosonde stations spanning latitudes from 2.8°N to 53.8°S, longitudes from 36.7°W to 67.8°W over the South American sector, it is observed that the ionosphere was significantly disturbed by the SSW event from the equator to the midlatitudes. During day of year 26 and 27 at 14:00 UT, the TEC was two times larger than that observed during average quiet days. The vertical TEC at all 17 GPS and two ionosonde stations shows significant deviations lasting for several days after the SSW temperature peak. Using one GPS station located at Rio Grande (53.8°S, 67.8°W, midlatitude South America sector), it is reported for the first time that the midlatitude in the Southern Hemisphere was disturbed by the SSW event in the Northern Hemisphere.

Observations of the April 2002 geomagnetic storm by the global network of incoherent scatter radars

Abstract. This paper describes the ionospheric response to a geomagnetic storm beginning on 17 April 2002. We present the measurements of ionospheric parameters in the F-region obtained by the network of eight incoherent scatter radars. The main effects of this storm include a deep decrease in the electron density observed at high and middle latitudes in the pre-noon sector, and a minor enhancement in the density observed in the daytime sector at middle latitudes. Extreme plasma heating (>1000-3000 K) is observed at high latitudes, subsiding to 200-300K at subauroral latitudes. The western hemisphere radar chain observed the prompt penetration of the electric field from auroral to equatorial latitudes, as well as the daytime enhancement of plasma drift parallel to the magnetic field line, which is related to the enhancement in the equatorward winds. We suggest that in the first several hours after the storm onset, a negative phase above Millstone Hill (pre-noon sector) results from counteracting processes - penetration electric field, meridional wind, and electrodynamic heating, with electrodynamic heating being the dominant mechanism. At the lower latitude in the pre-noon sector (Arecibo and Jicamarca), the penetration electric field becomes more important, leading to a negative storm phase over Arecibo. In contrast, in the afternoon sector at mid-latitudes (Kharkov, Irkutsk), effects of penetration electric field and meridional wind do not counteract, but add up, leading to a small (~15%), positive storm phase over these locations. As the storm develops, Millstone Hill and Irkutsk mid-latitude radars observe further depletion of electron density due to the changes in the neutral composition.

Long‐term trends in thermospheric neutral temperature and density above Millstone Hill

Incoherent scatter radar measurements of ionospheric temperature and density collected above Millstone Hill over the years 1976–2013 are analyzed to show the long-term trends in noontime neutral temperature and neutral O density over the height region 120–500 km. Exospheric temperature cooled by 69.3 ± 6.4 K over the period, an order of magnitude greater than that expected from greenhouse gas action. The O density dropped 0.081 ± 5.6% at 400 km altitude but rose by 36.9 ± 5.0% at 120 km over this period. This trend in density at 400 km agrees with that determined from satellite drag. The increase in density at 120 km counteracts the thermal contraction of the thermosphere expected to be associated with the cooling, resulting in only a small density response at 400 km. The long-term O density increase at 120 km may be caused by a long-term descent of the turbopause height of 4.2 km. Such a descent has been documented by a series of rocket mass spectrometer measurements.

Numerical modeling of the global ionospheric effects of storm sequence on September 9–14, 2005—comparison with IRI model

This study presents the modeling of ionospheric response to geomagnetic storms of September 9–14, 2005. We examine the performance of the Global Self-Consistent Model of Thermosphere, Ionosphere and Protonosphere (GSM TIP) and International Reference Ionosphere-2000 (IRI-2000), and compare the modeling predictions with the ionosonde and incoherent scatter radar observations over Yakutsk, Irkutsk, Millstone Hill and Arecibo stations. IRI-2000 predicted well all negative foF2 disturbances. In comparison with IRI-2000, the GSM TIP better reproduced the positive phase observed during the disturbed times. We discuss the possible reasons of the differences between the GSM TIP model calculations, IRI predictions, and the observations.

New radar observations of temporal and spatial dynamics of the midnight temperature maximum at low latitude and midlatitude

Presented here are several cases of midnight temperature maximum (MTM) observations using the Millstone Hill incoherent scatter radar (ISR) and Arecibo ISR. The MTM, a temperature enhancement in the upper atmosphere (at ~300 km altitude), is a poorly understood phenomenon as observations are sparse. An upward propagating terdiurnal tide and coupling between atmospheric regions may play a large part in the generation of the MTM, yet this phenomenon and its implications are not fully understood. Two nights (6 March 1989 and 12 July 1988) show clear cases of the MTM occurring between 30 and 34°N with amplitudes of ~100 K and at ~18°N with amplitudes of ~40 K. The MTMs occurred later at the higher latitude. Experiments in 2013 also show a clear MTM at 34° and 36°N from 250 to 350 km altitude. The ionospheric measurements presented here demonstrate a new application of a well-established technique to study atmospheric parameters and allow us to study the latitudinal extent of the MTM. The results provide evidence of the phenomenon occurring at latitudes and altitudes not previously sampled by radar techniques, showing that the MTM is not just an equatorial process, but one that can easily reach midlatitudes. Simultaneous measurements with a Fabry-Perot interferometer allow us to compare the neutral temperatures with the ion temperature. Overall, these are key observations that point to large-scale effects that can help constrain model outputs at different heights and latitudes.

Ionospheric effects caused by the series of geomagnetic storms of September 9–14, 2005

This study presents the ionospheric effects caused by the series of geomagnetic storms of September 9–14, 2005. The behavior of different ionospheric parameters over the Yakutsk, Irkutsk, Millstone Hill and Arecibo stations during the considered period have been numerically calculated, using a global self-consistent model of the thermosphere, ionosphere, and protonosphere (GSM TIP) developed at WD IZMI-RAN. The model calculations of disturbances of the ionospheric parameters during storms qualitatively agree with the experimental data at these midlatitude stations. We suggest that the causes of the quantitative differences between the model calculations and the observational data were the use of the 3-hour Kp index of geomagnetic activity and the dipole approximation of geomagnetic field in GSM TIP, with additional contributions from the effects of solar flares which are not considered in GSM TIP.

Ionospheric ion temperature climate and upper atmospheric long-term cooling†

It is now recognized that Earths upper atmosphere is experiencing a long-term cooling over the past several solar cycles. The potential impact of the cooling on societal activities is significant, but a fundamental scientific question exists regarding the drivers of the cooling. New observations and analyses provide crucial advances in our knowledge of these important processes. We investigate ionospheric ion temperature climatology and long-term trends using up-to-date large and consistent ground based datasets as measured by multiple incoherent scatter radars (ISRs). The very comprehensive view provided by these unique observations of the upper atmospheric thermal status allows us to address drivers of strong cooling previously observed by ISRs. We use observations from two high latitude sites at Sondrestrom (Invariant latitude 73.2°N) from 1990-2015, and Chatanika/Poker Flat (Invariant latitude 65.9°N) over the span of 1976-2015 (with a gap from 1983-2006). Results are compared to conditions at the mid-latitude Millstone Hill site (Invariant latitude 52.8°N) from 1968-2015. The aggregate radar observations have very comparable and consistent altitude dependence of long-term trends. In particular, the lower F region (< 275 km) exhibits dayside cooling trends that are significantly higher (-3 to -1K/year at 250 km) than anticipated from model predictions given the anthropogenic increase of greenhouse gases. Above 275 km, cooling trends continue to increase in magnitude but values are strongly dependent on magnetic latitude, suggesting the presence of significant downward influences from non-neutral atmospheric processes.