Incoherent Scatter Radar Data Research Articles

Climatology of polar ionospheric density profile in comparison with mid-latitude ionosphere from long-term observations of incoherent scatter radars: A review

Although the horizontal density structures of the polar ionosphere have been extensively studied mostly using the F-region peak density or total electron content, there are relatively few studies on the vertical density structures. In this review, we present the climatology of the polar ionospheric density not only in the F-region but also in the E-region and topside ionosphere, in comparison with the mid-latitude ionosphere, using long-term incoherent scatter radar (ISR) observations at Millstone Hill, Tromsø, and Svalbard. The ISR data during the period of 1995–2015 are analyzed to study on the variations with local time, season, and solar/geomagnetic activity. The diurnal variations of the F-region density are much smaller in the polar region than in the mid-latitude, particularly in summer. At Svalbard, there is a characteristic double-peak structure in the diurnal variation of the polar ionosphere in winter only for high solar activity. The diurnal variation of hmF2 decreases with increasing latitude and eventually disappears at Svalbard for low solar activity but the hmF2 and its diurnal variations in the polar ionosphere are remarkably enhanced for high solar activity. The distinctive irregularity in the mid-latitude F1-layer nearly disappears in the polar region, especially at Svalbard. The anomalous seasonal variations of the F-region density are less evident in the polar ionosphere especially for low solar activity and for high magnetic activity conditions. The polar E-region density shows characteristic nighttime peaks induced by auroral precipitation but it does not necessarily increase with solar activity. The topside ionospheric density variations are much stronger in the polar region for high solar activity. Finally, it is found that the polar ionospheric density profiles more strongly respond to increasing solar activity as well as the magnetic activity compared with the mid-latitude ionosphere.

Equatorial F‐Region Plasma Waves and Instabilities Observed Near Midnight at Solar Minimum During the NASA Too WINDY Sounding Rocket Experiment

AbstractRadar and sounding rocket observations of plasma irregularities in the F‐region ionosphere acquired on 19 June 2019 during NASA experiment Too WINDY on Kwajalein Atoll are presented. The experiment was conducted near local midnight during a period of low solar flux and quiet geomagnetic conditions. Plasma density irregularities were seen by the rocket and also in the incoherent scatter radar data to emerge and persist mainly in the topside. Density irregularities in the bottomside remained very small by comparison throughout the observations. Zonal plasma drifts measured by the rocket were highly structured in the topside. Patches of coherent scatter entrained in the large‐scale topside density irregularities appeared to propagate slowly westward in a narrow flow channel detected by the rocket. Broadband ELF emissions were also detected in the topside. Some of the characteristics of the topside irregularities are typical of postsunset equatorial F‐region irregularities observed frequently by coherent scatter radars, and some of the common features in the coherent scatter database are reviewed. Two scenarios that have been proposed to account for postmidnight spread F are tested computationally. One involves unseasonably large background zonal electric fields, and the other involves forcing from below by neutral waves and turbulence. Neither scenario appears to be able to account for the Too WINDY observations and the preponderance of topside irregularities without bottomside precursors in particular.

Plasma Cavity Formation During Ionospheric Heating at Arecibo

AbstractThe formation of an anomalous, high‐altitude plasma cavity was observed during the 11–15 June 2019 ionospheric heating campaign at Arecibo Observatory. The cavity was induced by interactions of the transmitted 5.125‐MHz heater wave with the ionospheric plasma. Simultaneous ion line and plasma line measurements were taken by the Arecibo Incoherent Scatter Radar (ISR). We used a novel experimental technique, enabling rapid pulsing of the heater, to collect ISR spectral data of the heated ionosphere without high frequency (HF)‐induced enhanced ion line (HFIL), simplifying the analysis. ISR data were analyzed using Tikhonov regularization, revealing that the cavity was confined to a very narrow altitude range around 350 km and constituted a deep depletion of the electron density, along with strong electron temperature enhancement, and ion temperature enhancement. We report on the details of these observations, and the possibility for unique combinations of physical interactions to explain the underlying mechanisms.

Temporal and Spatial Variations of Total Electron Content Enhancements During a Geomagnetic Storm on 27 and 28 September 2017

AbstractTemporal and spatial evolutions of total electron content (TEC) and electron density in the ionosphere during a geomagnetic storm that occurred on 27 and 28 September 2017 have been investigated using global TEC data obtained from many Global Navigation Satellite System stations together with the ionosonde, geomagnetic field, Jicamarca incoherent scatter and Super Dual Auroral Radar Network (SuperDARN) radar data. Our analysis results show that a clear enhancement of the ratio of the TEC difference (rTEC) first occurs from noon to afternoon at high latitudes within 1 hr after a sudden increase and expansion of the high‐latitude convection and prompt penetration of the electric field to the equator associated with the southward excursion of the interplanetary magnetic field. Approximately 1–2 hr after the onset of the hmF2 increase in the midlatitude and low‐latitude regions associated with the high‐latitude convection enhancement, the rTEC and foF2 values begin to increase and the enhanced rTEC region expands to low latitudes within 1–2 hr. This signature suggests that the ionospheric plasmas in the F2 region move at a higher altitude due to local electric field drift, where the recombination rate is smaller, and that the electron density increases due to additional production at the lower altitude in the sunlit region. Later, another rTEC enhancement related to the equatorial ionization anomaly appears in the equatorial region approximately 1 hr after the prompt penetration of the electric field to the equator and expands to higher latitudes within 3–4 hr.

Validation of Ionospheric Electron Density Measurements Derived From Spire CubeSat Constellation

AbstractCommercial Global Navigation Satellite System radio occultation ionospheric measurements collected by the Spire CubeSat constellation could significantly improve the determination of the global ionospheric state. However, the systematic validation work is needed before using the Spire data for scientific and assimilative purposes. In this work, the electron density profiles retrieved from Spire total electron content measurements using Abel inversion corrected by horizontal asymmetry are compared to digisonde measurements and Arecibo incoherent scatter radar data. Four events when the radio occultation measurements occurred close to three digisondes showed a strong agreement between these independent measurements. The comparison of 2 layer peak and height obtained from Spire data to digisonde measurements at 34 stations around the globe from Global Ionospheric Radio Observatory network also showed a strong agreement. Additionally, a good agreement was obtained in the comparison of Spire profiles with Arecibo electron density measurements.

First Incoherent Scatter Measurements and Adaptive Suppression of Field-Aligned Irregularities by the PANSY Radar at Syowa Station, Antarctic

The Program of the Antarctic Syowa Mesosphere–Stratosphere–Troposphere/Incoherent Scatter (PANSY) radar is a large atmospheric radar located at the Antarctic Syowa Station (69.01°S, 39.59°E). The PANSY radar performed the first incoherent scatter (IS) measurements in the Antarctic region in 2015. Several specific observations were undertaken in 2017 including a 24-h observation of the ionosphere using a peripheral antenna array to suppress interference from the field-aligned irregularities (FAIs). This paper presents the preliminary results derived from the IS measurements using the PANSY radar and the adaptive signal processing techniques to suppress FAIs. The norm-constrained and directionally constrained minimization of power (NC-DCMP) algorithm was applied to the 24-h ionosphere observations by the PANSY radar with a weighting applied to the directional constraint based on the gain differences of the subarrays. When compared with the conventional nonadaptive approach, the number of usable power profiles was increased by about 24% by the gain-weighted NC-DCMP algorithm, suggesting its effectiveness for FAI clutter suppression in ionosphere observations. Furthermore, detection of FAIs using the dedicated antenna array was found valuable in assessing the reliability of estimations of electron density based on VHF-band IS radar data.

Merging of Storm Time Midlatitude Traveling Ionospheric Disturbances and Equatorial Plasma Bubbles

AbstractPostsunset midlatitude traveling ionospheric disturbances (TIDs) and equatorial plasma bubbles (EPBs) were simultaneously observed over American sector during the geomagnetic storm on 8 September 2017. The characteristics of TIDs are analyzed by using a combination of the Millstone Hill incoherent scatter radar data and 2‐D detrended total electron content (TEC) from ground‐based Global Navigation Satellite System receivers. The main results associated with EPBs are as follows: (1) stream‐like structures of TEC depletion occurred simultaneously at geomagnetically conjugate points, (2) poleward extension of the TEC irregularities/depletions along the magnetic field lines, (3) severe equatorial and midlatitude electron density (Ne) bite outs observed by Defense Meteorological Satellite Program and Swarm satellites, and (4) enhancements of ionosphere F layer virtual height and vertical drifts observed by equatorial ionosondes near the EPBs initiation region. The stream‐like TEC depletions reached 46° magnetic latitudes that map to an apex altitude of 6,800 km over the magnetic equator using International Geomagnetic Reference Field. The formation of this extended density depletion structure is suggested to be due to the merging between the altitudinal/latitudinal extension of EPBs driven by strong prompt penetration electric field and midlatitude TIDs. Moreover, the poleward portion of the depletion/irregularity drifted westward and reached the equatorward boundary of the ionospheric main trough. This westward drift occurred at the same time as the sudden expansion of the convection pattern and could be attributed to the strong returning westward flow near the subauroral polarization stream region. Other possible mechanisms for the westward tilt are also discussed.

Assessing Ionospheric Convection Estimates From Coherent Scatter From the Radio Aurora

AbstractCoherent radar backscatter spectra from auroral E region plasma irregularities can be measured with great precision and accuracy. The Doppler spectra obtained from those measurements can be used to estimate auroral convection patterns using an empirical model. These estimates are consistent with rocket, optical, and incoherent scatter radar data, but direct comparison between the different data sets is not straightforward. In order to establish the quality of the empirical model, alternative approaches are then needed. In this work, we use the electrostatic nature of the convection electric field to assess the physical consistency of the empirical model: The model will be satisfactory to the extent that the convection patterns derived from them are incompressible. The incompressibility criteria were assessed for the estimated convection patterns obtained from the substorm of 20 December 2015. Two different approaches were used for this assessment. First, an electrostatic potential was fitted to the convection pattern produced by the empirical model. A good fit implies that there exists an incompressible convection pattern consistent with the Doppler spectra measurements. Second, the uncertainties on the Doppler spectral estimates where propagated through the empirical model to calculate the expected uncertainties on the divergence of the convection field obtained directly from the empirical model. The convection field will be incompressible if its divergence lies within the uncertainty estimates. Both approaches indicate that the evaluated convection patterns are consistently incompressible.

Improvement of the IRI Model Using F2 Layer Parameters Derived From GPS/COSMIC Radio Occultation Observations

AbstractIn this study, an improved ionospheric model is presented by applying self‐specified F2 layer parameters and an adaptive topside model into the International Reference Ionosphere (IRI) model. Three F2 layer parameters, the critical frequency (foF2), peak height (hmF2), and the scale height (Hsc) obtained from Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) observations, are modeled by spherical harmonics expansion. The empirical orthogonal functions are used to construct the associated parameters in the adaptive topside model. The improved model is validated by incoherent scatter radar (ISR) data of Millstone station and the Global Ionospheric Maps. Results show that the NmF2 and hmF2 of improved model have better agreement with ISR measurements. The vertical total electron content deviation compared with Global Ionospheric Map is discussed in different seasons and levels of solar activity. With radio occultation‐based parameters, the accuracy of original IRI model is improved by 1 total electron content unit globally on average.

A Polar‐Cap Patch Detection Algorithm for the Advanced Modular Incoherent Scatter Radar System

AbstractWe introduce an algorithm to detect polar‐cap patches in an Advanced Modular Incoherent Scatter Radar data set, using the Resolute Bay Incoherent Scatter Radar—North. Patches are detected by comparing plasma density (ne) measurements along each radar beam to a 30‐min running average of the median ne within the field‐of‐view. The algorithm is tested and shown to be an effective tool for polar‐cap patch studies. It is then used to conduct a survey of patches over Resolute Bay for two separate periods of time centered on March and December of 2010. The survey shows that polar‐cap patches are almost always present in both sunlit and nighttime conditions. However, the population is subdued during the day. The patch densities are found to vary by as much as an order of magnitude throughout the day. Their ion temperature is relatively constant, only varying by 100 K between the sunlit and nighttime conditions. By contrast, their electron temperature is very sensitive to the solar zenith angle and changes dramatically around sunrise.

Modulation of Low‐Altitude Ionospheric Upflow by Linear and Nonlinear Atmospheric Gravity Waves

AbstractThis study examines how thermospheric motions due to gravity waves (GWs) drive ion upflow in the F region, modulating the topside ionosphere in a way that can contribute to ion outflow. We present incoherent scatter radar data from Sondrestrom, from 31 May 2003 which showed upflow/downflow motions, having a downward phase progression, in the field‐aligned velocity, indicating forcing by a thermospheric GW. The GW‐upflow coupling dynamics are investigated through the use of a coupled atmosphere‐ionosphere model to examine potential impacts on topside ionospheric upflow. Specifically, a sequence of simulations with varying wave amplitude is conducted to determine responses to a range of transient forcing reminiscent of the incoherent scatter radar data. Nonlinear wave effects, resulting from increases in amplitude of the modeled GW, are shown to critically impact the ionospheric response. GW breaking deposits energy into smaller scale wave modes, drives periods of large field‐aligned ion velocities, while also modulating ion densities. Complementary momentum transfer increases the mean flow and, through ion‐neutral drag, can increase ion densities above 300 km. Ionospheric collision frequency (cooling) and photoionization effects (heating), both dependent on ionospheric density, modify the electron temperature; these changes conduct quickly up geomagnetic field lines driving ion upflow at altitudes well above initial disturbances. This flow alters ion populations available for high‐altitude acceleration processes that may lead to outflow into the magnetosphere. We have included a representative source of transverse wave heating which, when supplemented by our GWs, illustrates strengthened upward fluxes in the topside ionosphere.

Comments on “Long‐Term Variations of Exospheric Temperature Inferred From foF1 Observations: A Comparison to ISR Ti Trend Estimates” by Perrone and Mikhailov

AbstractPerrone and Mikhailov (2017, https://doi.org/10.1002/2017JA024193) and Mikhailov et al. (2017, https://doi.org/10.1002/2017JA023909) have recently examined thermospheric and ionospheric long‐term trends using a data set of four thermospheric parameters (Tex, [O], [N2], and [O2]) and solar EUV flux. These data were derived from one single ionospheric parameter, foF1, using a nonlinear fitting procedure involving a photochemical model for the F1 peak. The F1 peak is assumed at the transition height ht with the linear recombination for atomic oxygen ions being equal to the quadratic recombination for molecular ions. This procedure has a number of obvious problems that are not addressed or not sufficiently justified. The potentially large ambiguities and biases in derived parameters make them unsuitable for precise quantitative ionospheric and thermospheric long‐term trend studies. Furthermore, we assert that Perrone and Mikhailov (2017, https://doi.org/10.1002/2017JA024193) conclusions regarding incoherent scatter radar (ISR) ion temperature analysis for long‐term trend studies are incorrect and in particular are based on a misunderstanding of the nature of the incoherent scatter radar measurement process. Large ISR data sets remain a consistent and statistically robust method for determining long term secular plasma temperature trends.

Refraction and Faraday rotation in the incoherent scatter radar technique

AbstractIn this paper we consider the radiolocation equation for the incoherent scatter radar (ISR) method; the equation accounts for refraction effect and Faraday rotation in the VHF frequency domain. Our research shows that we cannot ignore refraction in processing the incoherent scatter data when lag‐product is used to obtain the ionospheric characteristics. Effect of refraction can explain some uncertainties that arise during processing and interpretation of the ISR data. This effect shows that together with the “ion line” of incoherent scatter spectrum, a relatively small “electron line” also plays a significant role in forming the ionosphere response. The “electron line” behaves as an additional “radar induced” wideband radiolocation signal affected by refraction and Faraday rotation; it depends on the ionosphere temperature and ion composition. The presence of a wideband “electron line” produces specific distortions of the ISR spectrum during 3D‐forming of the ionosphere response inside the ISR antenna diagram pattern. During testing, we found that the signal from the ISR “electron line” can be measured at much higher altitudes comparing to the “ion line.” Hence, to improve the incoherent scatter technique, we can take the “electron line” and refraction into account.

Ionospheric‐thermospheric UV tomography: 3. A multisensor technique for creating full‐orbit reconstructions of atmospheric UV emission

AbstractWe present the Volume Emission Rate Tomography (VERT) technique for inverting satellite‐based, multisensor limb and nadir measurements of atmospheric ultraviolet emission to create whole‐orbit reconstructions of atmospheric volume emission rate. The VERT approach is more general than previous ionospheric tomography methods because it can reconstruct the volume emission rate field irrespective of the particular excitation mechanisms (e.g., radiative recombination, photoelectron impact excitation, and energetic particle precipitation in auroras); physical models are then applied to interpret the airglow. The technique was developed and tested using data from the Special Sensor Ultraviolet Limb Imager and Special Sensor Ultraviolet Spectrographic Imager instruments aboard the Defense Meteorological Satellite Program F‐18 spacecraft and planned for use with upcoming remote sensing missions. The technique incorporates several features to optimize the tomographic solutions, such as the use of a nonnegative algorithm (Richardson‐Lucy, RL) that explicitly accounts for the Poisson statistics inherent in optical measurements, capability to include extinction effects due to resonant scattering and absorption of the photons from the lines of sight, a pseudodiffusion‐based regularization scheme implemented between iterations of the RL code to produce smoother solutions, and the capability to estimate error bars on the solutions. Tests using simulated atmospheric emissions verify that the technique performs well in a variety of situations, including daytime, nighttime, and even in the challenging terminator regions. Lastly, we consider ionospheric nightglow and validate reconstructions of the nighttime electron density against Advanced Research Project Agency (ARPA) Long‐range Tracking and Identification Radar (ALTAIR) incoherent scatter radar data.

Investigating the ionosphere response to exhaust products of “Progress” cargo spacecraft engines on the basis of Irkutsk Incoherent Scatter Radar data

The FSUE Central Research Institute of Machine Building (TsNIIMash), Rocket and Space Corporation “Energia”, and Institute of Solar-Terrestrial Physics of Siberian Branch of Russian Academy of Sciences (ISTP SB RAS) jointly conducted the active space experiment “Radar-Progress” in 2007–2015. During this experiment, we used the Irkutsk Incoherent Scatter Ra-dar to study space-time characteristics of ionospheric disturbances generated by exhaust products of “Pro-gress” cargo spacecraft engines. As the basic effect dur-ing exhaust product injection we consider the formation of new centers for recombination of ambient iono-spheric ions O+ on molecules of water and carbon diox-ide. This produces an ionization “hole” in the region of injection. In nighttime conditions when the majority of experiments were performed, this hole was filled by hydrogen ions from the plasmasphere, thus the ion composition in the vicinity of the hole and incoherent scatter spectra were changed. For successful obser-vation of the ionization hole dynamics, the critical fac-tors are the degree of radar antenna diagram filling by exhaust products and the velocity of the thermospheric neutral wind, which makes exhaust gases move from the antenna diagram. These two factors lead to poor repeatability of successful experiments. Successful experiments recorded a decrease in electron density up to 35 % in the hole that existed for 30 min. The lifetime of the region with high concentration of H+ ions can be as long as one hour.

Variations in energy, flux, and brightness of pulsating aurora measured at high time resolution

Abstract. High-resolution multispectral optical and incoherent scatter radar data are used to study the variability of pulsating aurora. Two events have been analysed, and the data combined with electron transport and ion chemistry modelling provide estimates of the energy and energy flux during both the ON and OFF periods of the pulsations. Both the energy and energy flux are found to be reduced during each OFF period compared with the ON period, and the estimates indicate that it is the number flux of foremost higher-energy electrons that is reduced. The energies are found never to drop below a few kilo-electronvolts during the OFF periods for these events. The high-resolution optical data show the occurrence of dips in brightness below the diffuse background level immediately after the ON period has ended. Each dip lasts for about a second, with a reduction in brightness of up to 70 % before the intensity increases to a steady background level again. A different kind of variation is also detected in the OFF period emissions during the second event, where a slower decrease in the background diffuse emission is seen with its brightness minimum just before the ON period, for a series of pulsations. Since the dips in the emission level during OFF are dependent on the switching between ON and OFF, this could indicate a common mechanism for the precipitation during the ON and OFF phases. A statistical analysis of brightness rise, fall, and ON times for the pulsations is also performed. It is found that the pulsations are often asymmetric, with either a slower increase of brightness or a slower fall.

Observability of ionospheric space‐time structure with ISR: A simulation study

AbstractThe sources of error from electronically steerable array (ESA) incoherent scatter radar (ISR) systems are investigated both theoretically and with use of an open‐source ISR simulator, developed by the authors, called Simulator for ISR (SimISR). The main sources of error incorporated in the simulator include statistical uncertainty, which arises due to nature of the measurement mechanism and the inherent space‐time ambiguity from the sensor. SimISR can take a field of plasma parameters, parameterized by time and space, and create simulated ISR data at the scattered electric field (i.e., complex receiver voltage) level, subsequently processing these data to show possible reconstructions of the original parameter field. To demonstrate general utility, we show a number of simulation examples, with two cases using data from a self‐consistent multifluid transport model. Results highlight the significant influence of the forward model of the ISR process and the resulting statistical uncertainty on plasma parameter measurements and the core experiment design trade‐offs that must be made when planning observations. These conclusions further underscore the utility of this class of measurement simulator as a design tool for more optimal experiment design efforts using flexible ESA class ISR systems.

Comparative study of COSMIC/FORMOSAT-3, Irkutsk incoherent scatter radar, Irkutsk Digisonde and IRI model electron density vertical profiles

The long-duration continuous Irkutsk incoherent scatter radar observations allowed us to collect 337 electron density vertical profiles obtained almost simultaneously with the radar and the COSMIC in the radar vicinity. The COSMIC electron density profiles were compared with those from the radar, Digisonde, and the IRI model. The comparison included 4 seasons and 2 solar activity levels (low and moderate). The number of simultaneous cases was ∼10 times more than in the previous incoherent scatter radar comparisons. In the case of the bottomside characteristics (peak density and bottomside electron content), the deviations between the COSMIC and the ground-based facilities data may be interpreted as the COSMIC measurement errors without significant systematic biases and with root-mean-square values that are ∼1.4–1.6 times smaller those that from the IRI model prediction. In the case of the topside characteristics (topside electron content and ionospheric electron content), the IRI model overestimates the COSMIC data by 0.6–0.8tecu on average, and the COSMIC overestimates the Irkutsk incoherent scatter radar data by 1.0–1.1tecu on average. The percentage differences between the radar and COSMIC in the topside electron content can reach 80%. In terms of the root-mean-square deviation, the COSMIC and the radar agree better than each of them agrees with the IRI model.

Localized field‐aligned currents in the polar cap associated with airglow patches

AbstractAirglow patches have been recently associated with channels of enhanced antisunward ionospheric flows propagating across the polar cap from the dayside to nightside auroral ovals. However, how these flows maintain their localized nature without diffusing away remains unsolved. We examine whether patches and collocated flows are associated with localized field‐aligned currents (FACs) in the polar cap by using coordinated observations of the Swarm spacecraft, a polar cap all‐sky imager, and Super Dual Auroral Radar Network (SuperDARN) radars. We commonly (66% of cases) identify substantial FAC enhancements around patches, particularly near the patches' leading edge and center, in contrast to what is seen in the otherwise quiet polar cap. These FACs have densities of 0.1–0.2 μA/m−2 and have a distribution of width peaking at ~75 km. They can be approximated as infinite current sheets that are orientated roughly parallel to patches. They usually exhibit a Region 1 sense, i.e., a downward FAC lying eastward of an upward FAC. With the addition of Resolute Bay Incoherent Scatter radar data, we find that the FACs can close through Pedersen currents in the ionosphere, consistent with the locally enhanced dawn‐dusk electric field across the patch. Our results suggest that ionospheric polar cap flow channels are imposed by structures in the magnetospheric lobe via FACs, and thus manifest mesoscale magnetosphere‐ionosphere coupling embedded in large‐scale convection.

Observations and simulations of midlatitude ionospheric and thermospheric response to the January 2013 stratospheric sudden warming event

AbstractUsing observations from midlatitudes, we examine the ionospheric and thermospheric responses to the 2013 stratospheric sudden warming event by comparing data with four simulations performed by the Whole Atmosphere Community Climate Model eXtended (WACCM‐X), Thermosphere‐Ionosphere Mesosphere Electrodynamics General Circulation Model (TIMEGCM), and Thermosphere‐Ionosphere Electrodynamics General Circulation Model (TIEGCM). The WACCM‐X simulation was nudged by the GEOS‐5 data. The two TIMEGCM simulations were nudged by the Modern‐Era Retrospective analysis for Research and Applications data and by the aforementioned WACCM‐X outputs, respectively. The standard TIEGCM simulation was also performed. These four simulations were compared with Millstone Hill (42.6°N, 71.4°W) incoherent scatter radar data, Millstone Hill and Boulder (40.1°N, 105.2°W) upper and lower thermospheric wind data. The meteor radar data from Collm (51.3°N, 13°E) were also used to examine the zonal wave number of the semidiurnal tide (SD). We evaluate the model simulations of the mesospheric and thermospheric responses to the 2013 SSW. The TIMEGCM simulation nudged with the WACCM‐X output has suitable stratospheric input and ionospheric dynamics and can reproduce a sharp rise of hmf2 on January 12 observed by the Millstone Hill radar. The comparison of different models with the lower thermospheric SD tide yielded mixed results. The SD tide maintained mostly as a migrating tide for most of the time and matched the TIEGCM simulation very well. The WACCM‐X appeared to perform better when the observed SD tide displays the large phase shift. It also has larger and more variable SD tide amplitude. The two TIMEGCM simulations have smaller SD amplitudes in general. Observations showed complex SD tide patterns after 20 January, which was difficult to characterize as a migrating tidal mode.