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The dynamics and morphology of the thermosphere and ionosphere is strongly controlled by thermospheric neutral winds. However, direct observations of thermospheric winds are historically limited both temporally and spatially. For example, interferometric methods for measuring thermospheric winds are restricted to nighttime observations and cloudless conditions and are limited to relatively few locations. Space-based observations made by cross-track measurements from accelerometers as well as onboard interferometers and spectrometers provide valuable information of thermospheric winds, but coverage is sparse over a given location for all local times. Ionospheric observations, on the hand, are abundant and embed information about the underlying thermosphere. Data assimilation is a technique that combines information from observations with a physical model. Observed data are assimilated into the model as a constraint for the physical equations that describe the dynamics of the system, which allows estimates of unobserved driving forces, e.g., the thermospheric neutral wind. The Global Assimilation of Ionospheric Measurements Full Physics (GAIM-FP) model can assimilate a multitude of ionospheric observations to estimate magnetic meridional winds at low- and mid-latitudes. The Thermospheric Wind Assimilation Model (TWAM) combines these magnetic meridional wind estimates with the equation of motion of the neutral gas using a Kalman filter technique to provide estimates of the thermospheric wind components. We will present the month-to-month progression of the TWAM thermospheric wind estimates for an entire year and compare our estimates with those obtained from the climatological Horizontal Wind Model (HWM14)., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

During geomagnetic storm, the energy transfer from solar wind to magnetosphere-ionosphere system adversely affects the communication and navigation systems. Quantifying storm impacts on TEC (Total Electron Content) and assessment of modeling capability of reproducing storm impacts on TEC are of importance to specifying and forecasting space weather. In order to quantify storm impacts on TEC, we considered several parameters: TEC changes compared to quiet time (the day before storm), TEC difference between 24-hour intervals, and maximum increase/decrease during the storm. We investigated the spatial and temporal variations of the parameters during the 2006 AGU storm event (14-15 Dec. 2006) using ground-based GPS TEC measurements in the selected 5 degree eight longitude sectors. The latitudinal variations were also studied in two longitude sectors among the eight sectors where data coverage is relatively better. We obtained modeled TEC from various ionosphere/thermosphere (IT) models. The parameters from the models were compared with each other and with the observed values. We quantified performance of the models in reproducing the TEC variations during the storm using skill scores. This study has been supported by the Community Coordinated Modeling Center (CCMC) at the Goddard Space Flight Center. Model outputs and observational data used for the study will be permanently posted at the CCMC website (http://ccmc.gsfc.nasa.gov) for the space science communities to use.

Total electron content (TEC) measurements from ground stations to Global Positioning System (GPS) satellites provide a rich source of information about the Earth's ionosphere. These data comprise a significant part of the typical data set used by various data ingestion and assimilation models of the ionosphere. For example, the Utah State University (USU) Global Assimilation of Ionospheric Measurements (GAIM) data assimilation model uses slant TEC, along with various other types of data, to obtain a global reconstruction of the ionosphere. There are presently two different USU GAIM models: the Gauss‐Markov Kalman Filter (GAIM‐GM), which is operational at the NASA Community Coordinated Modeling Center and the Air Force Weather Agency; and the Full‐Physics Kalman Filter (GAIM‐FP), which is presently run for scientific studies. TEC is the integrated electron density along the path from the ground to the GPS satellites, which orbit at approximately 20,200 km. The GAIM‐FP modeled space ranges up to 30,000 km in altitude, so the entire TEC raypath is contained within the model space. Many ionosphere models do not model this entire region. For example, the GAIM‐GM extends up to an altitude of 1400 km. It is necessary to account for the portion of TEC that is not modeled by some means. There are basically two simple techniques that are in common use: (1) correct the measured TEC by using a model of the upper ionosphere and plasmasphere to subtract their contributions, or (2) ignore the effect and assign the full measured TEC to the ionosphere within the assimilation model space. We present the effect of assimilating TEC measurements into the GAIM‐GM using both the techniques mentioned above. It is found that derived quantities such as N m F 2 are significantly degraded by ignoring the upper ionospheric contribution to TEC. This degradation is seen at all local times. The effect is most pronounced at night, when the F region densities are small and the upper ionospheric contribution to TEC is relatively large.

In order to study the effects of ionospheric plasma densities on the thermosphere, the electron and O+ densities in the Thermosphere Ionosphere Nested Grid (TING) model were replaced by electron densities from the Global Assimilation of Ionospheric Measurements (GAIM) model at pressure level z = 0 (about 210 ~ 230 km altitude) and above. This GAIM-derived TING model (G-TING) was then run for the period 1–4 April 2004. The TING model was also run as a stand-alone coupled model (S-TING), without using the GAIM electron densities, for the same period. The resulting thermospheric responses from the two simulations were compared at around the F region peak altitude. There was an extended quiet period during this interval followed by a moderate geomagnetic storm (Kp ~ 6.0). The ingestion of the GAIM electron densities had little effect on the neutral temperature and composition during the quiet period before the storm, but there were noticeable global effects on the neutral winds, mainly as a result of changes in the ion drag force. During disturbed periods, changed electron densities produced much more significant effects on the global thermosphere. The increased auroral electron densities enhanced the Joule heating rate, in addition to the ion drag, which resulted in significant global changes not only in the neutral winds, but also in the neutral temperature and composition. The results of our study confirm that having correct ionospheric plasma densities is critical to accurately predicting the thermosphere in the coupled thermosphere-ionosphere model.

The Utah State University (USU) Global Assimilation of Ionospheric Measurements (GAIM) program is developing assimilation models to specify ionospheric weather. In this study the Gauss Markov Kalman Filter (GMKF) GAIM model was used. The period 20 March through 19 April 2004, which spanned the Climate and Weather of the Sun-Earth-System (CAWSES) first study period, has been extensively studied to validate the performance of the GAIM model. Although the USU-GAIM model has both regional and global capabilities and can assimilate data from a wide variety of ionospheric observations, for this study the GMKF model was run in a global mode using data only from 162 ground-based GPS slant total electron content (TEC) stations and in situ measurements from three satellites. Using measurements from the 11 ionosonde stations of the Australian Department of Defence sounder network as an independent bottomside ground-truth, the International Reference Ionosphere (IRI), Ionospheric Forecast Model (IFM), and GMKF were compared for (1) monthly mean climatology and (2) the day-to-day weather during the 31 day period. A skill score was developed for the day-to-day weather by defining the IRI as the reference model. IFM is found to be a 10% improvement, while the GMKF is 39% more capable to capture weather variability. However, the study also identifies that this global version of GMKF has difficulty around sunrise, during which time the GMKF performance can be poorer than IRI. Excluding this interval from the skill score analysis increases the GMKF ability to track weather to 48%. The use of more data and different data types should further increase the GMKF's ability to capture weather variations.

Physics-based data assimilation models of the ionosphere were developed at Utah State University as part of a DoD Multidisciplinary University Research Initiative (MURI) program. The USU effort was called Global Assimilation of Ionospheric Measurements (GAIM). One of the USU Data assimilation models has been selected for operational use at the Air Force Weather Agency (AFWA in Omaha, Nebraska. This model is a Gauss-Markov Kalman Filter model, and it uses a physic-based model of the global ionosphere and a Kalman filter as a basis for assimilating a diverse set of real-time (or near real-time) measurements. The model has been designed to be modular and flexible. It can assimilate four different data types from an arbitrary number of stations. Quality control algorithms are an integral part of the model and latent data of up to three hours can be taken into account. The Gauss-Markov modell can also be applied to just a region (e.g., North America or Europe) with a simple change to the setup file. The configuration of the model and its current status are presented.

International audience; We use incoherent scatter radar measurements from Millstone Hill and Saint Santin to study the midlatitude F region electrodynamic plasma drifts during geomagnetically quiet and active periods. We present initially a local time, season, and solar flux dependent analytical model of the quiet time zonal and meridional ExB drifts over these stations. We discuss, for the first time, the Saint Santin drift patterns during solar maximum. We have used these quiet time models to extract the geomagnetic perturbation drifts which were modeled *s * function of the time history of the auroral electrojet indices. Our results illustrate the evolution of the disturbance drifts driven by the combined effects of prompt penetration *nd longer lasting perturbation electric fields. The meridion*l electrodynamic disturbance drifts have largest amplitudes in the midnight-noon sector. The zonal drifts *re predominantly westward, with largest amplitudes in the dusk-midnight sector *nd, following a decrease in the high-latitude convection, they dec*y more slowly th*n the meridional drifts. The prompt penetration *nd steady state zonal disturbance drifts derived from radar measurements *re in good agreement with results obtained from both the ion drift meter data on board the Dynamics Explorer 2 (DE 2) satellite *nd f?om the Rice Convection Model.

We investigate the seasonal, local solar time, and geomagnetic activity variations of the average Doppler velocity measured by an HF digital ionosonde deployed at Bundoora, Australia. The Doppler velocities were heavily averaged to suppress the short-term effects (hours) of atmospheric gravity waves, and thereby obtain the diurnal variations attributed to the tidally-driven ionospheric dynamo and electric fields generated by magnetic disturbances. The observed seasonal variations in Doppler velocity were probably controlled by variations in the lower thermospheric winds and ionospheric conductivity above Bundoora and in the magnetically conjugate location. The diurnal variations of the meridional (fieldperpendicular) drifts and their perturbations exhibited a complex structure, and were generally smaller than the variations in the zonal drifts. The latter were basically strongly westward during the evening to early morning, and weakly eastward during the late morning to just past noon. The zonal perturbations were strongly enhanced by increasing geomagnetic activity, and closely resembled the perturbation drifts measured by the incoherent scatter radar (ISR) at Millstone Hill. There was also some resemblance between the diurnal variations in the meridional drifts. Overall, the comparisons suggest that with sufficient averaging, Doppler velocities measured with digital ionosondes at mid-latitudes correspond to true ion motions driven by ionospheric electric fields. This is a useful result because apart from the ISRs located in the American-European sector, there are no ground-based instruments capable of measuring electric fields in the mid-latitude ionosphere.

We use radar observations from the Jicamarca Observatory from 1968 to 1992 to study the effects of the F region vertical plasma drift velocity on the generation and evolution of equatorial spread F. The dependence of these irregularities on season, solar cycle, and magnetic activity can be explained as resulting from the corresponding effects on the evening and nighttime vertical drifts. In the early night sector, the bottomside of the F layer is almost always unstable. The evolution of the unstable layer is controlled by the history of the vertical drift velocity. When the drift velocities are large enough, the necessary seeding mechanisms for the generation of strong spread F always appear to be present. The threshold drift velocity for the generation of strong early night irregularities increases linearly with solar flux. The geomagnetic control on the generation of spread F is season, solar cycle, and longitude dependent. These effects can be explained by the response of the equatorial vertical drift velocities to magnetospheric and ionospheric disturbance dynamo electric fields. The occurrence of early night spread F decreases significantly during equinox solar maximum magnetically disturbed conditions due to disturbance dynamo electric fields which decrease the upward drift velocities near sunset. The generation of late night spread F requires the reversal of the vertical velocity from downward to upward for periods longer than about half an hour. These irregularities occur most often at ∼0400 local time when the prompt penetration and disturbance dynamo vertical drifts have largest amplitudes. The occurrence of late night spread F is highest near solar minimum and decreases with increasing solar activity probably due to the large increase of the nighttime downward drifts with increasing solar flux.

We present the first global empirical model for the quiet time F region equatorial vertical drifts based on combined incoherent scatter radar observations at Jicamarca and Ion Drift Meter observations on board the Atmospheric Explorer E satellite. This analytical model, based on products of cubic-B splines and with nearly conservative electric fields, describes the diurnal and seasonal variations of the equatorial vertical drifts for a continuous range of all longitudes and solar flux values. Our results indicate that during solar minimum, the evening prereversal velocity enhancement exhibits only small longitudinal variations during equinox with amplitudes of about 15–20 m/s, is observed only in the American sector during December solstice with amplitudes of about 5–10 m/s, and is absent at all longitudes during June solstice. The solar minimum evening reversal times are fairly independent of longitude except during December solstice. During solar maximum, the evening upward vertical drifts and reversal times exhibit large longitudinal variations, particularly during the solstices. In this case, for a solar flux index of 180, the June solstice evening peak drifts maximize in the Pacific region with drift amplitudes of up to 35 m/s, whereas the December solstice velocities maximize in the American sector with comparable magnitudes. The equinoctial peak velocities vary between about 35 and 45 m/s. The morning reversal times and the daytime drifts exhibit only small variations with the phase of the solar cycle. The daytime drifts have largest amplitudes between about 0900 and 1100 LT with typical values of 25–30 m/s. We also show that our model results are in good agreement with other equatorial ground-based observations over India, Brazil, and Kwajalein.

We have used ion drift observations from the DE-2 satellite to determine the latitudinal variation and the temporal evolution of mid- and low-latitude prompt penetration zonal plasma drifts driven by magnetospheric electric fields. Our results indicate that sudden increases in convection lead to predominantly westward perturbation drifts which decrease equartorwards and have largest amplitudes in the dusk-midnight sector. The diurnal perturbation drift patterns shift to later local times with increasing storm time and decay to new quasi-equilibrium values in about 2 hours, as the ring current readjusts to the new polar cap potential. The daily and latitudinal variations and temporal evolution of the DE-2 prompt penetration drifts are generally in good agreement with predictions from the Rice Convection Model, although the experimental results show larger amplitudes and longer shielding time constants.

We use low- and mid-latitude zonal ion drift observations from the DE-2 satellite and auroral electrojet indices to study the temporal and latitudinal variations of F-region perturbation drifts during magnetically disturbed conditions. These perturbation drifts are driven by magnetospheric and ionospheric disturbance dynamo electric fields with time constants from less than one to several hours. We determine, initially, the drift patterns due to the prompt penetration of magnetospheric electric fields and of longer lasting disturbances. In this study, we concentrate on the properties of the longer lasting perturbations which occur with latitude-dependent time delays after enhancements in the high-latitude ionospheric currents. These perturbation drifts are predominantly westward at all latitudes with largest amplitudes in the midnight sector and smallest near noon. The daily variation of these disturbance drifts derived from the satellite data is in good agreement with results from incoherent scatter radar observations. Our results indicate that these longer lasting perturbations are due to the combined effects of ionospheric disturbance dynamo electric fields and leakage of high-latitude steady-state electric fields to lower latitudes.

We use Jicamarca radar observations of F region vertical plasma drifts and auroral electrojet indices during 1968–1988 to study the characteristics and temporal evolution of equatorial disturbance dynamo zonal electric fields. These electric fields result from the dynamo action of storm time winds and/or thermospheric composition changes driven by enhanced energy deposition into the high-latitude ionosphere during geomagnetically active conditions. The equatorial vertical drift perturbations last for periods of up to 30 hours after large increases in the high-latitude currents. On the average, this process can be described by two basic components with time delays of about 1–12 hours and 22–28 hours between the high-latitude current enhancements and the equatorial velocity perturbations. Our data indicate strong coupling between dynamo processes with different timescales. The short-term disturbance dynamo drives upward equatorial drifts (eastward electric fields) at night with largest amplitudes near sunrise and small downward drifts during the day. These perturbation drifts are in good agreement with results from the Blanc-Richmond disturbance dynamo theory. The dynamo process with time delays of about a day drives upward drift velocities at night with largest values near midnight and downward drifts in the sunrise-noon sector. In this case, the amplitudes of the disturbance drifts maximize during geomagnetically quiet times preceded by strongly disturbed conditions. We also present results of a new equatorial storm time dependent empirical model which illustrate the characteristics of the vertical disturbance dynamo drifts.

Ionospheric plasma drifts often show highly complex and variable signatures during geomagnetically active periods due to the effects of different disturbance processes. We describe initially a methodology for the study of storm time dependent ionospheric electric fields. We present empirical models of equatorial disturbance zonal electric fields obtained using extensive F region vertical plasma drift measurements from the Jicamarca Observatory and auroral electrojet indices. These models determine the plasma drift perturbations due to the combined effects of short-lived prompt penetration and longer lasting disturbance dynamo electric fields. We show that the prompt penetration drifts obtained from a high time resolution empirical model are in excellent agreement with results from the Rice Convection Model for comparable changes in the polar cap potential drop. We also present several case studies comparing observations with results obtained by adding model disturbance drifts and season and solar cycle dependent average quiet time drift patterns. When the disturbance drifts are largely due to changes in magnetospheric convection and to disturbance dynamo effects, the measured and modeled drift velocities are generally in good agreement. However, our results indicate that the equatorial disturbance electric field pattern can be strongly affected by variations in the shielding efficiency, and in the high-latitude potential and energy deposition patterns which are not accounted for in the model. These case studies and earlier results also suggest the possible importance of additional sources of plasmaspheric disturbance electric fields.

Studies of equatorial F region evening vertical plasma drifts using different measurement techniques have produced conflicting results. We examine the relationship of incoherent scatter radar and ionosonde drift observations over the Peruvian equatorial region, and AE-E satellite drifts for different geophysical conditions. Our data show that there is large day-to-day variability on the ratios of radar and ionosonde drifts, but on the average the measurements from these two techniques are in fair agreement during low and moderate solar flux conditions. For high solar activity, however, the Jicamarca evening drifts during equinox and December solstice are significantly larger than the ionosonde drifts. These results can be explained by the different height ranges of the radar and ionosonde measurements, and the increase of the upward drift velocity with height below the F region peak. This altitudinal variation is related to the longitudinal gradient of the zonal plasma drifts as a result of the curl-free electric field condition. Our results also indicate that during equinox the increase of the vertical prereversal velocity enhancement with solar activity is largely longitude independent.

We use extensive radar measurements of F region vertical plasma drifts and auroral electrojet indices to determine the storm time dependence of equatorial zonal electric fields. These disturbance drifts result from the prompt penetration of high latitude electric fields and from the dynamo action of storm time winds which produce largest perturbations a few hours after the onset of magnetic activity. The signatures of the equatorial disturbance electric fields change significantly depending on the relative contributions of these two components. The prompt electric field responses, with lifetimes of about one hour, are in excellent agreement with results from global convection models. The electric fields generated by storm time winds have longer lifetimes, amplitudes proportional to the energy input into the high latitude ionosphere, and a daily variation which follows closely the disturbance dynamo pattern of Blanc and Richmond [1980]. The storm wind driven electric fields are responsible for the larger amplitudes and longer lifetimes of the drift perturbations following sudden decreases in convection compared to those associated with sudden convection enhancements.