Nighttime Enhancements Research Articles

Winter Nighttime Enhancement of the Midlatitude Ionosphere: Contribution From the Diffusive and Wind‐Driven Plasma Transport

AbstractThe characteristics of winter nighttime enhancement (WNE) of the midlatitude ionosphere at 300, 550, and 750 km altitude are presented, based on the radio occultation data from the Constellation Observing System for Meteorology, Ionosphere, and Climate. WNE at 750 km altitude has earlier start time and larger increasing rate than that at 550 km, possibly due to the downward plasma diffusion from above that dominates the most upper part of the ionosphere. Theoretical calculation of the plasma transport at 300 km altitude reveals the largest effect of downward diffusion at 45° geomagnetic latitude, consistent with the latitudinal distribution of WNE. Meanwhile, the wind‐driven plasma transport also contributes to WNE, at 30°W–180°W geographic longitude in the Southern Hemisphere. The strength and end time of WNE vary with longitude, and are correlated with the longitudinal variations of the enhancement in the conjugate (summer) hemisphere. This may be attributed to the transport processes in the interhemispheric geomagnetic flux tubes, which redistribute and balance the plasma between the conjugate hemispheres at night. The plasma flux from above is hence an important plasma source for further understanding of both the winter and summer nighttime enhancements.

Ionospheric Nighttime Enhancements in the Equatorial Region as Revealed by the Beidou Geostationary TEC Observations

AbstractIonospheric electron density enhancement at nighttime has been widely studied in the past decades. However, the mechanisms of this anomalous nighttime enhancement are not fully understood. In this study, we took advantage of the fidelity of geostationary total electron contents (GEO TECs) combined with the observations from three equatorial ionosondes to examine the morphology of equatorial ionospheric nighttime enhancements in the Asian‐Australian sector. The equatorial ionospheric nighttime enhancements from GEO TECs during 2016–2018 can be characterized by three categories. Each of these categories showed similar seasonal variations, with the maximal occurrence in the equinoxes. Interestingly, there was a strong correlation between the pre‐reversal enhancement (PRE) of the eastward equatorial electric field and these three types of equatorial ionospheric nighttime enhancements that were mostly accompanied by PRE inferred from foF2 and h'F2 from ionograms around dusk. Nevertheless, the formations of equatorial ionospheric nighttime enhancements could be associated with other factors, such as the equatorial electric fields and neutral winds, as well as associated plasma transports. This study provides a new perspective to explore the variations and the underlying physical processes of ionospheric nighttime enhancements.

Simultaneous Detection of Signatures of Conjugate Photoelectrons in the Ionosphere and Thermosphere.

We investigate the impact of conjugate photoelectrons (CPEs) on the topside (∼600 km altitude) ionosphere at low and midlatitudes using measurements of the ion temperature, density, and composition from the first Republic of China satellite during a period of the high to moderate solar activity (March 1999 to June 2004). Elevated ion temperatures and densities are observed in the dark Northern American‐Atlantic sector during the December solstice and in the Australian sector during the June solstice. The oxygen ion fraction and density are also elevated at these locations. These observations indicate that photoelectrons from the conjugate hemisphere heat the local ionospheric plasma. The morphology of the ion temperature in the winter hemisphere is well represented by the solar zenith angle in the sunlit conjugate hemisphere. The CPE hypothesis for the observed ionospheric heating is confirmed by coincident nighttime enhancements of the far ultraviolet airglow measured by the Global Ultraviolet Imager onboard the Thermosphere Ionosphere Mesosphere Energetics and Dynamics satellite.

Comparison of Ionospheric Response to Two Types of Electron Concentration Disturbances

Based on the data of vertical sounding of the ionosphere in Almaty in 2000–2008, the paper deals with the response of the F2-layer to the passage of large-scale traveling ionospheric disturbances (LSTIDs) and the formation of the nighttime enhancements in the electron concentration of the F2-layer. For these two types of perturbations, we compared behavior in the time of the following layer parameters: the height of maximum of the layer (hmF), the height of the bottom of the layer (hbotF), the half-thickness of the layer (Δh = hmF − hbotF), the electron concentration at fixed heights and at the maximum of the layer (NmF), the height profiles of the nighttime enhancement peak-to-peak value of the F2-layer (A), and the height hAm corresponding to the maximum enhancement amplitude. The parameters hmF, hbotF and Δh demonstrate similar dependences associated with the temporal expansion and upward rise of the ionospheric layer and its lowering, accompanied by layer compression, giving an NmF peak at the moment of maximum compression. The common features of the profiles of two types of disturbances are found: the height hAm is always below hmF, there is a good correlation between hAm and hmF, and the difference between hAm and hmF increases linearly with hmF.

Ionospheric Nighttime Enhancements at Low Latitudes Challenge Performance of the Global Ionospheric Maps

In this study, two ionospheric nighttime enhancement (INE) events at low latitudes are selected to investigate their spatial features through the observations from Global Navigation Satellite System (GNSS) receivers and ionosondes. For the first time, we present the detailed spatial pictures of premidnight and postmidnight INEs under geomagnetically quiet conditions. The two INE events have the maximum extents of about 11° × 34° and 17° × 25° (longitude × latitude), respectively. Dramatic latitudinal and longitudinal features are revealed in the two INEs. We perform a comparison between the products of Global Ionospheric Maps (GIMs) and total electron content (TEC) measurement from GNSS receivers. However, GIMs fail to capture the TEC distribution during INEs owing to their limited spatial and temporal resolution. Considering the extent of INEs from the observations, the spherical harmonic (SH) expansion adopted by the GIM models needs to upgrade the degree and order to 36. The pixel-based methods developed from two GIM models are required to reduce their grid size for higher spatial resolution. The recommended time interval is shorter than 30 min. Among seven GIMs, CODG and JPLG maps generally have the best performance in reproducing the latitudinal structure of the ionosphere.

Lunar Tide Effects on Ionospheric Solar Eclipse Signatures: The August 21, 2017 Event as an Example

AbstractThe ionospheric total electron content (TEC) derived from dense ground‐based Global Navigation Satellite System receivers over the continental United States and those from global ionosphere maps are utilized to find the ionosphere response to the August 21, 2017 total solar eclipse. Maximum obscurations and their associated TEC major depressions appear simultaneously at midlatitudes, while major depressions elongate toward the magnetic equator with some delays in the equatorial ionization anomaly (EIA) region. The former is due to the photochemical loss process, while the latter is caused by the plasma transport of E×B drifts and lunar gravitation forces. TECs of predawn reductions, morning enhancements, afternoon reductions, and nighttime enhancements reveal that the semidiurnal lunar tide are essential. Since a solar eclipse always occurs on a new moon day, the lunar tide results in the early EIA appearance and major depressions being underestimated/diminished before and overestimated/enhanced after about 14:00 local time.

Nighttime enhancements in the VTEC at anomaly crest region Bhopal: Solar and magnetic activity effects

Nighttime enhancement in the Vertical Total Electron Content (VTEC) of the ionosphere near equatorial ionization anomaly crest region in the Indian ionospheric sector has been studied during May 2016 to August 2017, a solar minimum period. VTEC data is obtained from a multi-frequency multi-constellation global navigation satellite system (GNSS) receiver installed at Bhopal (23.2°N, 77.4°E & MLAT 14.2°N). Only those enhancements which show VTEC enhancement ≥ 10% compared to the background has been considered in the study. Out of the total 105 cases of enhancement recorded during this period, 86 events occurred during pre-midnight and 19 during post-midnight hours. Enhancements in VTEC occurred in all seasons; more frequent however during summer than winter and equinox months. Some of the nighttime enhancements in VTEC resulted in the scintillations in the satellite signals as well. Peak amplitude of the enhancement maximizes in summer whereas its half amplitude duration maximizes during equinox month. The number of occurrences of nighttime enhancement in VTEC shows negative correlation with peak amplitude while they are positively correlated with half amplitude duration. We have found that the peak amplitude of nighttime enhancements in VTEC shows strong positive correlation while percentage occurrence shows strong negative correlation with solar and magnetic activities respectively. Other characteristics like half amplitude duration, time of peak and occurrence time of nighttime enhancement in VTEC show positive correlation with solar activity while they are insignificant with magnetic activity. The peak amplitude of pre-midnight enhancements in VTEC is highly correlated with the strength of equatorial electrojet strength. The results are compared with the earlier observations and possible mechanism is also discussed.

New Features of the Enhancements in Electron Density at Low Latitudes

AbstractIn this study, we present some new features of the enhancements of electron density in the ionospheric F region at low latitudes. The peak parameters of the ionosphere were recorded by Sanya (109.6°E, 18.3°N) ionosonde and electron density profiles analyzed were measured by the Qujing (103.8°E, 25.6°N) incoherent scatter radar. The peak electron density of the F2 layer (NmF2) is found to be enhanced in the afternoon and sunset hours. Common features in the cases demonstrate that the NmF2 increases at low latitudes are characterized by a descent of the peak height (hmF2). Meanwhile, the electron density at Qujing shows an increase at the bottom of the ionosphere and a depression at topside altitudes. It is consistent with those of the ionosonde measurements at Sanya, for both the daytime and nighttime enhancements. Cross correlation analyses reveal a lag of NmF2 to hmF2 in the cases. After taking time shifts some events of the enhancements in NmF2 are still associated with a downwelling hmF2, confirming the processes which drive a lower hmF2 and a convergence of plasma flux may possibly bring about a rise in NmF2.

Global ionospheric maps with a high temporal resolution

A new approach is proposed for the global ionospheric modeling using epoch-by-epoch estimation. The GIMs with a high temporal resolution are greatly useful for studying the climatology and weather of the ionosphere, including ionospheric variations, such as noon-time bite-outs and nighttime enhancements.

Total electron content and scintillations over Maseno, Kenya, during high solar activity year

Proper characterization of total electron content (TEC) and scintillation is very important to global positioning system (GPS) users in communication, navigation, ionospheric or atmospheric studies. Quiet time variation of TEC is useful in the estimation and removal of ionospheric delay for global navigation satellite systems single-frequency positioning. During geomagnetic storms, the variations of ionosphere deviate from their quiet day pattern and can cause significant effects on short-term prediction of various ionospheric parameters. The dynamics of the ionosphere change from region to region; therefore, in order to evaluate and improve the performance of global models of the ionosphere, numerous studies of variations using measured ionospheric parameters from stations globally are useful. This paper presents for the first time variations in the TEC and scintillation at Maseno University (geomagnetic coordinates, 9.64°S, 108.59°E), Kenya, investigated using a NovAtelGSV400B GPS receiver for the high solar activity year 2014. The GPS-measured TEC values were compared with the modeled TEC values by the latest International Reference Ionosphere model (IRI-2016), with a view to evaluate the performance of this version of the model. The largest TEC values were observed from 1300 to 1500 h local time throughout the year with the largest diurnal values occurring in March equinox and smallest during June solstice. The largest TEC values are attributed to extreme ultraviolet radiation coupled with upward $$\vec{E} \times \vec{B}$$ plasma drift velocity. Nighttime enhancements in TEC attributed to the ‘fountain’ effect occurred during some months. Scintillation correlated with depletions in TEC occurred in the period between 1600 h local time to 1900 h local time (post-sunset) sector during some months, with the strongest value of − 0.91 being experienced in March equinox. Scintillation was absent during geomagnetic storms studied mainly as a result of the time of onset of the recovery phases of the storms. In addition, the geomagnetic storms were manifested in GPS-measured TEC as negative ionospheric storms. The IRI-2016 model gave a good prediction of measured values except for its overestimation of measured TEC in the months of May and June. Further, a new insight shown by the results is the ability of the IRI-2016 model to predict post-sunset TEC enhancements during some months contrary to previous versions reported by other researchers in East Africa. However, model is not quickly sensitive to transitions from one season to another. This result contributes to the improvement of the current IRI model by recommending the introduction of an input into the model that is sensitive to transitions in seasons in future versions of the model.

The formation of nitro-aromatic compounds under high NO<sub><i>x</i></sub> and anthropogenic VOC conditions in urban Beijing, China

Abstract. Nitro-aromatic compounds (NACs), as important contributors to the light absorption by brown carbon, have been widely observed in various ambient atmospheres; however, their formation in the urban atmosphere was little studied. In this work, we report an intensive field study of NACs in summer 2016 at an urban Beijing site, characterized by both high-NOx and anthropogenic VOC dominated conditions. We investigated the factors that influence NAC formation (e.g., NO2, VOC precursors, RH and photolysis) through quantification of eight NACs, along with major components in fine particulate matter, selected volatile organic compounds, and gases. The average total concentration of the quantified NACs was 6.63 ng m−3, higher than those reported in other summertime studies (0.14–6.44 ng m−3). 4-Nitrophenol (4NP, 32.4 %) and 4-nitrocatechol (4NC, 28.5 %) were the top two most abundant NACs, followed by methyl-nitrocatechol (MNC), methyl-nitrophenol (MNP), and dimethyl-nitrophenol (DMNP). The oxidation of toluene and benzene in the presence of NOx was found to be a more dominant source of NACs than primary biomass burning emissions. The NO2 concentration level was found to be an important factor influencing the secondary formation of NACs. A transition from low- to high-NOx regimes coincided with a shift from organic- to inorganic-dominated oxidation products. The transition thresholds were NO2 ∼ 20 ppb for daytime and NO2∼25 ppb for nighttime conditions. Under low-NOx conditions, NACs increased with NO2, while the NO3- concentrations and (NO3-)/NACs ratios were lower, implying organic-dominated products. Under high-NOx conditions, NAC concentrations did not further increase with NO2, while the NO3- concentrations and (NO3-)/NACs ratios showed increasing trends, signaling a shift from organic- to inorganic-dominated products. Nighttime enhancements were observed for 3M4NC and 4M5NC, while daytime enhancements were noted for 4NP, 2M4NP, and DMNP, indicating different formation pathways for these two groups of NACs. Our analysis suggested that the aqueous-phase oxidation was likely the major formation pathway of 4M5NC and 3M5NC, while photo-oxidation of toluene and benzene in the presence of NO2 could be more important for the formation of nitrophenol and its derivatives. Using the (3M4NC+4M5NC) ∕ 4NP ratios as an indicator of the relative contribution of aqueous-phase and gas-phase oxidation pathways to NAC formation, we observed that the relative contribution of aqueous-phase pathways increased at elevated ambient RH and remained constant at RH > 30 %. We also found that the concentrations of VOC precursors (e.g., toluene and benzene) and aerosol surface area acted as important factors in promoting NAC formation, and photolysis as an important loss pathway for nitrophenols.

Variation of the TEC at a dip equatorial station, Trivandrum and a mid latitude station, Hanle during the descending phase of the solar cycle 24 (2014–2016)

Morphological variations in the Total Electron Content (TEC) of the ionosphere at a dip equatorial station, Trivandrum (8.47°N, 76.91° E) and a mid latitude station, Hanle (32.78° N, 78.95° E) during the period 2014–2016 is studied using the GPS TEC measurements from the InSWIM (Indian Network for Space Weather Impact Monitoring) network of stations. The variation of the TEC at Hanle, which is located in the same longitude sector as that of Trivandrum, is presented here for the first time. At Hanle, the TEC peaks at local noontime while its peak appears with a delay (1600 LT) at Trivandrum. The minima in the TEC at both stations appear during the early morning hours. Nighttime enhancements in the TEC are seen at Trivandrum during the equinoctial months while at Hanle they appear in the summer months. The TEC at both the stations exhibit semi-annual anomaly and equinoctial asymmetry. However, the winter anomaly is seen only at Trivandrum. The TEC at both Trivandrum and Hanle is seen to display strong solar activity dependence with the average TEC decreasing as solar activity decreases. We surmise that the observed diurnal/seasonal/annual variations in the TEC at the dip equatorial station, Trivandrum is controlled by the processes induced by electrodynamics while the TEC variations at the mid latitude station, Hanle is mostly affected by the neutral dynamical processes. The morphological comparison between the TEC at Trivandrum derived from the IRI 2012 model and GPS TEC measurements shows only a qualitative agreement. The IRI 2012 model is found to overly underestimate the daytime as well as nighttime TEC at the dip equatorial station, Trivandrum while it is well in agreement with the TEC measurements at the mid latitude station, Hanle.

Nighttime Enhancements in the Midlatitude Ionosphere and Their Relation to the Plasmasphere

AbstractIn situ electron density measurements by the CHAllenging Minisatellite Payload and the Defense Meteorological Satellites Program F17 satellites show that the midlatitude ionization at altitudes of ∼350 and 850 km is enhanced in the late evening. The enhancements increase to maximum around midnight and are clearly observed till early morning as the equatorial ionization decays to minimal level. They appear in the winter hemisphere during June and December solstices and in both hemispheres during equinox. The enhancements are well confined between ±30° and ±50° magnetic latitude, with the magnetic flux tubes of L = 1.3 − 2.4 connecting to the plasmasphere. Furthermore, coincident longitudinal variations exist in both the ionospheric enhancements and the plasmaspheric total electron content, especially during the solstice months. The coincidence may suggest essential plasma transport between the ionosphere and the plasmasphere. These facts support the idea that the plasmasphere provides extra plasma to the midlatitude ionosphere through downward plasma influx along the magnetic field lines to form the nighttime ionization enhancements when the sunlight is absent.

Coronal Mass Ejections in September 2017 from Monitoring of Interplanetary Scintillations with the Large Phased Array of the Lebedev Institute of Physics

Results of monitoring of interplanetary scintillations with the Large Phased Array of the Pushchino Radio AstronomyObservatory at 111 MHz during a period of flare activity of the Sun in the first ten days of September 2017 are presented. Enhancements of scintillations associated with interplanetary coronal mass ejections propagating after limb flares have been recorded. The propagation velocities are estimated to be about 2000 km/s for an ejection on September 7 and about 1000 km/s for an ejection on September 6. It is shown that, during the propagation from the Sun, the lateral part of the ejections decelerates faster than its leading part. Night-time enhancements of second-timescale scintillations during periods of high geomagnetic activity have an ionospheric origin.

TEC behavior over the Mexican region

With the advent of the Navigation Satellites the Total Electron Content (TEC) has become one of the main parameters of the ionosphere. This is the result of a continuous TEC monitoring and rather dense network of GPS receivers. For Mexican region having no ionosondes the use of TEC for ionospheric conditions studies and monitoring has a special value. To study the behaviour of TEC and for its applied aspects two types of source-files are used worldwide: IONEX (global maps) and RINEX (local data) depending on the task solved. Magnetometer and satellite data from CHAMP and DMSP were involved in the analysis. First, benefits and limitations of TEC derived from both types of files are discussed in regard to the estimation of the ionosphere state in the Mexican region. Second, using both methods the specific features of diurnal, seasonal and annual patterns in TEC behaviour over Mexico were revealed, among which are the shift of the diurnal maximum to 14 LT, dependence on solar activity, high probability of night-time enhancements, presence of annual and winter anomalies. Third, it was revealed that the positive short-lived TEC enhancements are characteristic for Mexican region. They may occur even under quiet conditions. The answer is given what part of the ionosphere is responsible for TEC change during these positive disturbances. The results for Mexico were compared to the neighboring regions and South-East zone.

An Artificial Neural Network‐Based Ionospheric Model to Predict NmF2 and hmF2 Using Long‐Term Data Set of FORMOSAT‐3/COSMIC Radio Occultation Observations: Preliminary Results

AbstractArtificial Neural Networks (ANNs) are known to be capable of solving linear as well as highly nonlinear problems. Using the long‐term and high‐quality data set of Formosa Satellite‐3/Constellation Observing System for Meteorology, Ionosphere, and Climate (FORMOSAT‐3/COSMIC, in short F3/C) from 2006 to 2015, an ANN‐based two‐dimensional (2‐D) Ionospheric Model (ANNIM) is developed to predict the ionospheric peak parameters, such as NmF2 and hmF2. In this pilot study, the ANNIM results are compared with the original F3/C data, GRACE (Gravity Recovery and Climate Experiment) observations as well as International Reference Ionosphere (IRI)‐2016 model to assess the learning efficiency of the neural networks used in the model. The ANNIM could well predict the NmF2 (hmF2) values with RMS errors of 1.87 × 105 el/cm3 (27.9 km) with respect to actual F3/C; and 2.98 × 105 el/cm3 (40.18 km) with respect to independent GRACE data. Further, the ANNIM predictions found to be as good as IRI‐2016 model with a slightly smaller RMS error when compared to independent GRACE data. The ANNIM has successfully reproduced the local time, latitude, longitude, and seasonal variations with errors ranging ~15–25% for NmF2 and 10–15% for hmF2 compared to actual F3/C data, except the postsunset enhancement in hmF2. Further, the ANNIM has also captured the global‐scale ionospheric phenomena such as ionospheric annual anomaly, Weddell Sea Anomaly, and the midlatitude summer nighttime anomaly. Compared to IRI‐2016 model, the ANNIM is found to have better represented the fine longitudinal structures and the midlatitude summer nighttime enhancements in both the hemispheres.

The importance of neutral hydrogen for the maintenance of the midlatitude winter nighttime ionosphere: Evidence from IS observations at Kharkiv, Ukraine, and field line interhemispheric plasma model simulations

AbstractThis study investigates the causes of nighttime enhancements in ionospheric density that are observed in winter by the incoherent scatter radar at Kharkiv, Ukraine. Calculations with a comprehensive physical model reveal that large downward ion fluxes from the plasmasphere are the main cause of the enhancements. These large fluxes are enabled by large upward H+ fluxes into the plasmasphere from the conjugate summer hemisphere during the daytime. The nighttime downward H+ flux at Kharkiv is sensitive to the thermosphere model H density, which had to be increased by factors of 2 to 3 to obtain model‐data agreement for the topside H+ density. Other studies support the need for increasing the thermosphere model H density for all seasons at solar minimum. It was found that neutral winds are less effective than plasmaspheric fluxes for maintaining the nighttime ionosphere. This is partly because increased equatorward winds simultaneously oppose the downward H+ flux. The model calculations also reveal the need for a modest additional heat flow from the plasmasphere in the afternoon. This source could be the quiet time ring current.

Statistical features of NmF2 enhancements according to data from the Almaty station in solar cycles 23 and 24

According to frequent five-minute vertical sounding of the ionosphere in Almaty (76°55′ E, 43°15′ N) conducted in 2000–2014, the rate of occurrence of nighttime enhancements of the electron concentration at the F2-layer maximum is analyzed, the distributions of enhancement durations are obtained, and the parameters of several very large enhancements recorded at the same time in Irkutsk and Almaty are compared. During the analyzed period, 2272 observation sessions were carried out. In 1430 sessions NmF2 enhancement was observed. The high probabilities of enhancement formation (up to 90%) in January, February, November and December are distribution features that are identical for high and low solar activity. In addition, a rapid decrease in the probability from February to March and smooth increase from September to December occurs in the same manner. High solar activity is characterized by a distinct maximum frequency in the summer months, whereas low activity is characterized by a minimum frequency. The seasonal dependence of distributions of enhancement durations is shown: durations are distributed over a wide range in the autumn–winter season and in a narrow range in the spring–summer season.

Latitudinal variation of the specific local time of postmidnight enhancement peaks inFlayer electron density at low latitudes: A case study

AbstractIonospheric nighttime enhancements are manifested in an increase of the electron density at nighttime. This paper studies the latitudinal variation of the specific local time of postmidnight enhancement peaks using ionosondes distributed at low latitudes. To obtain the parameters of the ionosphere, we manually extracted ionograms recorded by ionosondes. Cases show that there are significant latitudinal variations in the observed local time of the postmidnight enhancement peaks. Results show that the lower the geomagnetic latitude, the earlier the enhancement peak occurred in the geomagnetic northern hemisphere. Additionally, the enhancement peaks occurred earlier in the geomagnetic southern hemisphere than that in the geomagnetic northern hemisphere for these present cases. We suggest that the combined effect of the geomagnetic inclination and transequatorial meridional wind might be the main driving force for latitudinal variation of the local time of the occurrence.

Midlatitude ionospheric responses to the 2013 SSW under high solar activity

AbstractIonospheric responses to sudden stratospheric warming (SSW) are not well understood, particularly in the midlatitudes and under high solar conditions. During the 2013 SSW, ionospheric disturbances were observed in eight locations on the meridional chain from 30.5°N to 42.8°N in northern China. The midlatitude ionosphere responded strongly to the SSW despite being under high solar flux. The F2 layer maximum electric density increased by more than 80%, and the peak height was elevated more than 60 km. Well‐set and organized semidiurnal variations were recorded in early and middle January during the SSW in eight observation locations. The expected foF2 decrease in the afternoon hours was not clearly discernible; however, nighttime enhancements occurred frequently. The time‐period spectra of the average foF2 and zonal winds and meridional winds at altitudes of 86–95 km presented quasi‐16 day planetary wave‐like oscillations during the warming event. The coupling between the atmosphere and ionosphere may be strengthened by the quasi‐16 day waves. The amplified diurnal, semidiurnal, and terdiurnal tides in foF2 were also recorded during the warming, in good agreement with earlier observations. Importantly, the variations in the semidiurnal tides included a 16 day periodic component, indicating that the modulated semidiurnal tides may transmit these 16 day planetary wave‐like oscillations to the F region through wind dynamo. Although the PW‐tide interaction theory is not novel, it is of significance in the midlatitude ionospheric response to SSW.