Response of the Ionosphere-Plasmasphere System to Periodic Forcing

The role of different mechanisms for generating periodic variability in the ionosphere and plasmasphere is studied in this dissertation. The impact of vertically propagating waves of lower atmospheric origin on introducing periodic spatial and temporal variability in the ionosphere and plasmasphere is first investigated. This is comprised of several different aspects. Initial focus is on the seasonal, local time, and altitude dependence of longitude variations due to nonmigrating tides in the F-region and topside ionosphere/plasmasphere using a combination of observations and numerical models. This is facilitated by the development of a new method for mitigating the effect of multipath on low-Earth orbit (LEO) satellite Global Positioning System (GPS) observations. The impact of large-scale changes in tropospheric convection due to the El-Nino Southern Oscillation on the ionosphere is also explored observationally. The influence of nonmigrating tides on the global ionosphere is revealed through study of the longitude variations in the solar quiet current system. Periodic temporal variability in the ionosphere due to planetary waves originating in the lower atmosphere is also investigated. The response of the global ionosphere to the quasi-16 day planetary wave is first presented. This is followed by observational evidence demonstrating that the nonlinear interaction between planetary waves and tides is the primary mechanism responsible for low-latitude ionospheric variability during sudden stratospheric warmings. Periodic temporal variability in the ionosphere and plasmasphere of solar origin is also studied. During the declining phase of solar cycle 23, near-Earth geospace was routinely disturbed due to high-speed solar wind streams emanating from solar coronal holes. The nature of the coronal holes was such that the Earth\u27s upper atmosphere exhibited periodic behavior due to recurrent geomagnetic activity. A study of the latitude and local time response of the ionosphere to recurrent geomagnetic activity is performed herein. A method for estimating the location of the plasmapause from LEO GPS observations is also developed and applied to study periodic oscillations in the plasmapause

Infrastructure needs on latitudinal and longitudinal chains of co-located ground-based observations

The generation, propagation, and dissipation of atmospheric planetary waves (PW), tides, and gravity waves (GW) constitute the primary mechanism that transfers energy and momentum from the atmosphere to space. While single-location ground-based observations have been making successful measurements of such waves over the past decades, NSF funded ground-based observations are not yet systematically distributed at the same latitude or the same longitude, despite the importance of latitudinal and longitudinal dependence of dynamical processes like large scale wave propagation, interaction, and dissipation. This white paper discusses the significance and potential of coordinating a chain of ground-based instruments with the current large facilities to extend the latitudinal and longitudinal observational coverage in the American sector (both South and North America). We further discuss the benefits of co-locating heterogeneous instruments with different techniques and different temporal/spatial resolution/coverage, for instance, radio instruments (e.g., ISR, HF radar, meteor radar), optical instruments (e.g., FPI, lidar, airglow imager), magnetometers, ionosondes, sounding rockets and so on

Interannual Variability of Winds in the Antarctic Mesosphere and Lower Thermosphere Over Rothera (67°S, 68°W) During 2005–2021 in Meteor Radar Observations and WACCM‐X

The mesosphere and lower thermosphere (MLT) plays a critical role in linking the middle and upper atmosphere. However, many General Circulation Models do not model the MLT and those that do remain poorly constrained. We use long-term meteor radar observations (2005–2021) from Rothera (67°S, 68°W) on the Antarctic Peninsula to evaluate the Whole Atmosphere Community Climate Model with thermosphere-ionosphere eXtension (WACCM-X) and investigate interannual variability. We find some significant differences between WACCM-X and observations. In particular, at upper heights, observations reveal eastwards wintertime (April–September) winds, whereas the model predicts westwards winds. In summer (October–March), the observed winds are northwards but predictions are southwards. Both the model and observations reveal significant interannual variability. We characterize the trend and the correlation between the winds and key phenomena: (a) the 11-year solar cycle, (b) El Niño Southern Oscillation, (c) Quasi-Biennial Oscillation and (d) Southern Annular Mode using a linear regression method. Observations of the zonal wind show significant changes with time. The summertime westwards wind near 80 km is weakening by up to 4–5 ms−1 per decade, whilst the eastward wintertime winds around 85–95 km are strengthening at by around 7 ms−1 per decade. We find that at some times of year there are significant correlations between the phenomena and the observed/modeled winds. The significance of this work lies in quantifying the biases in a leading General Circulation Model and demonstrating notable interannual variability in both modeled and observed winds

Development of Data Assimilation Systems for the Ionosphere, Thermosphere, and Mesosphere

The past decade saw the development of several data assimilation systems for the ionosphere, thermosphere, and mesosphere (ITM). To fully realize the capabilities of ITM data assimilation systems for both scientific investigations and operations, several critical advances are needed. This white paper outlines some of the outstanding challenges facing ITM data assimilation that need to be addressed in the coming decade in order to achieve robust, high-quality, ITM data assimilation systems. Benefits to both the scientific and operational communities of advancing ITM data assimilation capabilities are also provided. These include, but are not limited to, providing the framework for investigating ITM predictability, scientific investigations into day-to-day ITM variability driven by the lower atmosphere and geomagnetic storms, as well as advancing space weather forecasting capabilities

Improving ionospheric predictability requires accurate simulation of the mesospheric polar vortex

The mesospheric polar vortex (MPV) plays a critical role in coupling the atmosphere-ionosphere system, so its accurate simulation is imperative for robust predictions of the thermosphere and ionosphere. While the stratospheric polar vortex is widely understood and characterized, the mesospheric polar vortex is much less well-known and observed, a short-coming that must be addressed to improve predictability of the ionosphere. The winter MPV facilitates top-down coupling via the communication of high energy particle precipitation effects from the thermosphere down to the stratosphere, though the details of this mechanism are poorly understood. Coupling from the bottom-up involves gravity waves (GWs), planetary waves (PWs), and tidal interactions that are distinctly different and important during weak vs. strong vortex states, and yet remain poorly understood as well. Moreover, generation and modulation of GWs by the large wind shears at the vortex edge contribute to the generation of traveling atmospheric disturbances (TADs) and traveling ionospheric disturbances (TIDs). Unfortunately, representation of the MPV is generally not accurate in state-of-the-art general circulation models (GCMs), even when compared to the limited observational data available. Models substantially underestimate eastward momentum at the top of the MPV, which limits the ability to predict upward effects in the thermosphere. The zonal wind bias responsible for this missing momentum in models has been attributed to deficiencies in the treatment of GWs and to an inaccurate representation of the high-latitude dynamics. Such deficiencies limit the use of these models to study the role of the MPV in the transport of constituents and in wave-mean flow interactions, and to elucidate the mechanisms by which the atmosphere-ionosphere system is interconnected. In the coming decade, simulations of the MPV must be improved. This can be accomplished by constraining the model temperature and wind fields in the mesosphere and lower thermosphere (MLT) with a more extensive suite of satellite and ground-based observations. In addition, improvements to current model GW parameterizations are required to more accurately simulate the processes that govern the generation, propagation, and dissipation of GWs

Intercomparison of middle atmospheric meteorological analyses for the Northern Hemisphere winter 2009-2010

Detailed meteorological analyses based on observations extending through the middle atmosphere (&sim;&thinsp;15 to 100&thinsp;km altitude) can provide key information to whole atmosphere modeling systems regarding the physical mechanisms linking day-to-day changes in ionospheric electron density to meteorological variability near the Earth's surface. However, the extent to which independent middle atmosphere analyses differ in their representation of wave-induced coupling to the ionosphere is unclear. To begin to address this issue, we present the first intercomparison among four such analyses, JAGUAR-DAS, MERRA-2, NAVGEM-HA, and WACCMX+DART, focusing on the Northern Hemisphere (NH) 2009&ndash;2010 winter, which includes a major sudden stratospheric warming (SSW). This intercomparison examines the altitude, latitude, and time dependences of zonal mean zonal winds and temperatures among these four analyses over the 1&nbsp;December 2009 to 31&nbsp;March 2010 period, as well as latitude and altitude dependences of monthly mean amplitudes of the diurnal and semidiurnal migrating solar tides, the eastward-propagating diurnal zonal wave number 3&nbsp;nonmigrating tide, and traveling planetary waves associated with the quasi-5&thinsp;d and quasi-2&thinsp;d Rossby modes. Our results show generally good agreement among the four analyses up to the stratopause (&sim;&thinsp;50&thinsp;km altitude). Large discrepancies begin to emerge in the mesosphere and lower thermosphere owing to (1) differences in the types of satellite data assimilated by each system and (2) differences in the details of the global atmospheric models used by each analysis system. The results of this intercomparison provide initial estimates of uncertainty in analyses commonly used to constrain middle atmospheric meteorological variability in whole atmosphere model simulations. </div

Improving ionospheric predictability requires accurate simulation of the mesospheric polar vortex

The mesospheric polar vortex (MPV) plays a critical role in coupling the atmosphere-ionosphere system, so its accurate simulation is imperative for robust predictions of the thermosphere and ionosphere. While the stratospheric polar vortex is widely understood and characterized, the mesospheric polar vortex is much less well-known and observed, a short-coming that must be addressed to improve predictability of the ionosphere. The winter MPV facilitates top-down coupling via the communication of high energy particle precipitation effects from the thermosphere down to the stratosphere, though the details of this mechanism are poorly understood. Coupling from the bottom-up involves gravity waves (GWs), planetary waves (PWs), and tidal interactions that are distinctly different and important during weak vs. strong vortex states, and yet remain poorly understood as well. Moreover, generation and modulation of GWs by the large wind shears at the vortex edge contribute to the generation of traveling atmospheric disturbances and traveling ionospheric disturbances. Unfortunately, representation of the MPV is generally not accurate in state-of-the-art general circulation models, even when compared to the limited observational data available. Models substantially underestimate eastward momentum at the top of the MPV, which limits the ability to predict upward effects in the thermosphere. The zonal wind bias responsible for this missing momentum in models has been attributed to deficiencies in the treatment of GWs and to an inaccurate representation of the high-latitude dynamics. In the coming decade, simulations of the MPV must be improved

Ionospheric Variability during the 2020&ndash;2021 SSW: COSMIC-2 Observations and WACCM-X Simulations

Variability in the ionosphere during the 2020&ndash;2021 sudden stratospheric warming (SSW) is investigated using a combination of Constellation Observing System for Meteorology, Ionosphere, and Climate-2 (COSMIC-2) observations and the Whole Atmosphere Community Climate Model with thermosphere&ndash;ionosphere eXtension (WACCM-X) simulations. The unprecedented spatial&ndash;temporal sampling of the low latitude ionosphere afforded by COSMIC-2 enables investigating the short-term (&lt;5 days) variability in the ionosphere during the SSW event. The COSMIC-2 observations reveal a reduction in the diurnal and zonal mean ionosphere total electron content (ITEC) and reduced amplitude of the diurnal variation in the ionosphere during the SSW. Enhanced ITEC amplitudes of the semidiurnal solar and lunar migrating tides and the westward propagating semidiurnal tide with zonal wavenumber 3 are also observed. The WACCM-X simulations demonstrate that these variations are driven by variability in the stratosphere&ndash;mesosphere during the 2020&ndash;2021 SSW event. The results show the impact of the 2020&ndash;2021 SSW on the mean state, diurnal, and semidiurnal variations in the ionosphere, as well as the capabilities of the COSMIC-2 mission to observe short-term variability in the ionosphere that is driven by meteorological variability in the lower atmosphere

Medium-scale gravity wave activity in the bottomside F region in tropical regions

Thermospheric gravity waves (GWs) in the bottomside F region have been proposed to play a key role in the generation of equatorial plasma bubbles (EPBs). However, direct observations of such waves are scarce. This study provides a systematic survey of medium‐scale (<620 km) neutral atmosphere perturbations at this critical altitude in the tropics, using 4 years of in situ Gravity Field and Steady‐State Ocean Circulation Explorer satellite measurements of thermospheric density and zonal wind. The analysis reveals pronounced features on their global distribution and seasonal variability: (1) A prominent three‐peak longitudinal structure exists in all seasons, with stronger perturbations over continents than over oceans. (2) Their seasonal variation consists of a primary semiannual oscillations (SAO) and a secondary annual oscillation (AO). The SAO component maximizes around solstices and minimizes around equinoxes, while the AO component maximizes around June solstice. These GW features resemble those of EPBs in spatial distribution but show opposite trend in climatological variations. This may imply that stronger medium‐scale GW activity does not always lead to more EPBs. Possible origins of the bottomside GWs are discussed, among which tropical deep convection appears to be most plausible

Global sounding of F; region irregularities by COSMIC during a geomagnetic storm

We analyze reprocessed electron density profiles and TEC profiles of the ionosphere in September 2008 (aroundsolar minimum) and September 2013 (around solar maximum) obtained by the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC). The TEC profiles describe the total electron content along the ray path from the GPS satellite to the low Earth orbit as function of the tangent point of the ray. Some of the profiles in the magnetic polarregions show small-scale fluctuations with spatial scales<50km. Possibly the trajectory of the tangent point intersects spatial electron density irregularities in the magnetic polar region. For derivation of the morphology of the electron density and TECfluctuations, a 50 km high pass filter is applied in the s-domain where s is the distance between a reference point (bottomtangent point) and the tangent point. For each profile, the mean of the fluctuations is calculated for tangent point altitudesbetween 400 and 500 km. First at all, the global maps of∆Neand∆TEC are quite similar. However, ∆TEC might be morereliable since it is based on less retrieval assumptions. We find a significant difference if the arithmetic mean or the median is applied to the global map of September 2013. The global map of ∆TEC at solar maximum (September 2013) has stronger fluctuations than those at solar minimum (September 2008). Finally, we compare the global maps of the quiet phase and the storm phase of the geomagnetic storm of 15 July 2012. It is evident that the TEC fluctuations are increased and extended overthe Southern magnetic polar region at the day of the geomagnetic storm. The North-South asymmetry of the storm response is more pronounced in the upper ionosphere (ray tangent points h=400-500km) than in the lower ionosphere (ray tangent points h=200-300km)