Anomalous variations in the structure of the ionospheric <Emphasis Type="Italic">F</Emphasis><Subscript>2</Subscript> region at geomagnetic midlatitudes of the Southern and Northern hemispheres in going from summer to winter conditions at high solar activity

The structure and dynamics of the ionosphere and plasmasphere at high solar activity under quiet geomagnetic conditions of June 2–3, 1979, and January 5–6, 1980, over Millstone Hill station and Argentine Islands ionosonde, the locations of which are approximately magnetically conjugate, have been theoretically calculated. The plasma drift velocity, determined by comparing the calculated and measured heights of the F ₂ layer maximum (hmF2), and the correction of [N₂] and [O₂], found in the NRLMSISE-00 model, make it possible to coordinate the electron densities (NmF2) calculated at the hmF2 height and the measured anomalous variations in NmF2 over the Argentine Islands ionosonde as well as the calculated and measured NmF2 and electron temperature at the hmF2 height over Millstone Hill station. It has been shown that, if the interference of the diffusion velocities of O⁺(⁴S) and H⁺ ions is taken into account, the additional heating of plasmaspheric electrons leads to an increase in the flux of O⁺(⁴S) ions from the topside ionosphere to lower F ₂ layer altitudes, as a result of which an anomalous nighttime increase in NmF2 6, observed on January 6, 1980, over Millstone Hill station, is mainly produced. The second component of the formation of anomalous night-time NmF2 is the plasma drift along the magnetic field caused by the neutral wind, which shifts O⁺(⁴S) ions to higher altitudes where the recombination rate of O⁺(⁴S) with N₂ and O₂ is lower and slows down a decrease in NmF2 in the course of time. It has been shown that the influence of electronically excited O⁺ ions and vibrationally excited N₂ and O₂ molecules on electron density (N _e ) considerably differs under winter and summer conditions. This difference forms significant part of the winter anomaly in N _e at heights of the F ₂ region and topside ionosphere over Millstone Hill station.     

Anomalous variations in the ionospheric <Emphasis Type="Italic">F</Emphasis><Subscript>2</Subscript>-layer structure at geomagnetic midlatitudes of the Southern and Northern hemispheres at the transition from summer to winter conditions under low solar activity

The structure and dynamics of the ionosphere and plasmasphere at low solar activity under quiet geomagnetic conditions on January 15–17, 1985, and July 10–13, 1986, over Millstone Hill station and Argentine Islands ionosonde, the locations of which are approximately magnetically conjugate, have been theoretically calculated. The detected correction of the model input parameters makes it possible to coordinate the measured and calculated anomalous variations in the electron density NmF2 at the height hmF2 of the ionospheric F2 layer over Argentine Islands ionosonde as well as the calculated and measured values of NmF2 and electron temperature at the hmF2 height over Millstone Hill station. It has been shown that vibrationally excited N₂ and O₂ molecules almost do not influence the formation of the winter anomaly under the conditions of low solar activity. A difference between the influence of electronically excited O⁺ on N _e ions under winter and summer conditions forms not more than 11% of the N _e winter anomaly event in the F ₂ layer and topside ionosphere. The model without electronically excited O⁺ ions reduces the duration of the N _e winter anomaly event. It has been shown that the seasonal variations in the composition of the neutral atmosphere form mainly the NmF2 winter anomaly event over the Millstone Hill radar at low solar activity.     

基于非相干散射雷达和GPS观测研究Millstone Hill地区等离子体层电子含量

本文尝试结合非相干散射雷达和GPS TEC观测数据提取等离子体层总电子含量(PTEC).我们首先描述所用的技术方法,然后具体利用了Millstone Hill台站的观测数据研究该地区上空等离子体层总电子含量(PTEC)的变化情况.我们采用变化标高的Chapman函数对非相干散射雷达测得的电子浓度剖面数据进行拟合,然后通过对剖面积分得到100 km到1000 km高度范围的电离层总电子含量.GPS提供的TEC数据为高度达20200 km的总电子含量,两者之差可近似看成等离子体层的电子含量.本文分别选取太阳活动高年(2000, 2002年)和太阳活动低年(2005,2008年)Millstone Hill台站的静日数据进行研究.结果表明,等离子体层电子含量及其所占GPS TEC的比例具有明显的周日变化.PTEC含量在白天高于夜间,而所占GPS TEC的百分比,夜间明显高于白天.太阳活动高年所选月份等离子体层电子含量在4~14 TECU (1TECU=10¹⁶el/m²) 范围内变化,夜间所占比例可达60%左右.太阳活动低年所选月份等离子体层电子含量在3~7 TECU范围内变化,所占比例夜间最高可达80%左右.我们所得到的结果与前人基于其它观测手段所得结果在变化趋势上一致,在量级上也大致相当.因此,这从一个侧面证明了我们所用方法的可靠性.非相干散射雷达能够探测包括F2层峰值以下及以上高度的电子浓度,利用这一设备所观测得到的资料来推算电离层电子含量将比前人基于电离层垂测仪观测资料进行的推算更具真实性,由此得到的等离子体层电子含量也将更为接近真实情况.     

Comparison of the measured and modelled electron densities and temperatures in the ionosphere and plasmasphere during 20/30 January, 1993

We present a comparison of the electron density and temperature behaviour in the ionosphere and plasmasphere measured by the Millstone Hill incoherent-scatter radar and the instruments on board of the EXOS-D satellite with numerical model calculations from a time-dependent mathematical model of the Earths ionosphere and plasmasphere during the geomagnetically quiet and storm period on 20/30 January, 1993. We have evaluated the value of the additional heating rate that should be added to the normal photoelectron heating in the electron energy equation in the daytime plasmasphere region above 5000 km along the magnetic field line to explain the high electron temperature measured by the instruments on board of the EXOS-D satellite within the Millstone Hill magnetic field flux tube in the Northern Hemisphere. The additional heating brings the measured and modelled electron temperatures into agreement in the plasmasphere and into very large disagreement in the ionosphere if the classical electron heat flux along magnetic field line is used in the model. A new approach, based on a new effective electron thermal conductivity coefficient along the magnetic field line, is presented to model the electron temperature in the ionosphere and plasmasphere. This new approach leads to a heat flux which is less than that given by the classical Spitzer-Harm theory. The evaluated additional heating of electrons in the plasmasphere and the decrease of the thermal conductivity in the topside ionosphere and the greater part of the plasmasphere found for the first time here allow the model to accurately reproduce the electron temperatures observed by the instruments on board the EXOS-D satellite in the plasmasphere and the Millstone Hill incoherent-scatter radar in the ionosphere. The effects of the daytime additional plasmaspheric heating of electrons on the electron temperature and density are small at the F-region altitudes if the modified electron heat flux is used. The deviations from the Boltzmann distribution for the first five vibrational levels of N₂(v) and O₂(v) were calculated. The present study suggests that these deviations are not significant at the first vibrational levels of N₂ and O₂ and the second level of O₂, and the calculated distributions of N₂(v) and O₂(v) are highly non-Boltzmann at vibrational levels v > 2. The resulting effect of N₂(v > 0) and O₂(v > 0) on NmF2 is the decrease of the calculated daytime NmF2 up to a factor of 1.5. The modelled electron temperature is very sensitive to the electron density, and this decrease in electron density results in the increase of the calculated daytime electron temperature up to about 580 K at the F2 peak altitude giving closer agreement between the measured and modelled electron temperatures. Both the daytime and night-time densities are not reproduced by the model without N₂(v > 0) and O₂(v > 0), and inclusion of vibrationally excited N₂ and O₂ brings the model and data into better agreement.     

Comparison of models and data at Millstone Hillduring the 5–11 June 1991 storm

We compare measurements of the ionospheric F region at Millstone Hillduring the severe geomagnetic disturbances of 5–11 June 1991 with results from the IZMIRANand FLIP time-dependent mathematical models of the Earths ionosphere and plasmasphere. Somecomparisons are also made with the Millstone Hill semi-empirical model which was previouslyused to model this storm. New rate coefficients from recent laboratory measurements of the O⁺+N₂ and O⁺+O₂ loss rates are included in theIZMIRAN and Millstone Hill models. The laboratory measurements show that vibrationallyexcited N₂ and O₂ (N₂(v) and O₂(v)) are both important at high temperatures such as found in the thermosphere during disturbedconditions at summer solar maximum. Increases in the O⁺+N₂ loss ratedue to N₂(v) result in a factor ∼2 reduction in the daytime F₂ peak electron density. On some days inclusion of N₂(v) improves theagreement between the models and the data, and on other days it worsens it. In the present workwe show for the first time the significant effect that the increase in the O⁺recombination rate due to O₂(v) may have on the calculated NmF₂. There are considerable uncertainties in the model calculations during the unusual,extremely disturbed conditions found during the daytime on 6 June. The results illustratedifficulties involved and the current state of the art in modelling severe disturbances, and thusprovide a benchmark against which future progress can be gauged.     

Day-to-day thermosphere parameter variation as deduced from Millstone Hill incoherent scatter radar observations during March 16-22, 1990 magnetic storm period

A self-consistent method for day-time F2-region modelling was applied to the analysis of Millstone Hill incoherent scatter observations during the storm period of March 16-22, 1990. The method allows us to calculate in a self-consistent way neutral composition, temperature and meridional wind as well as the ionized species height distribution. Theoretically calculated N_e(h) profiles fit the observed daytime ones with great accuracy in the whole range of heights above 150 km for both quiet and disturbed days. The overall increase in T_ex by 270 K from March 16 to March 22 reflects the increase of solar activity level during the period in question. A 30% decrease in [O] and a twofold increase in [A^] are calculated for the disturbed day of March 22 relative to quiet time prestorm conditions. Only a small reaction to the first geomagnetic disturbance on March 18 and the initial phase of the second storm on March 20 was found in [O] and [N₂] variations. The meridional neutral wind inferred from plasma vertical drift clearly demonstrates the dependence on the geomagnetic activity level being more equatorward on disturbed days. Small positive F2-layer storm effects on March 18 and 20 are totally attributed to the decrease in the northward neutral wind but not to changes in neutral composition. A moderate (by a factor of 1.5) O/ N₂ ratio decrease relative to the MSIS-83 model prediction is required to describe the observed N_mF2 decrease on the most disturbed day of March 22, but virtually no change of this ratio is needed for March 21.     

Anomalous electron density events in the quiet summer ionosphere at solar minimum over Millstone Hill

This study compares the observed behavior of the F region ionosphere over Millstone Hill with calculations from the IZMIRAN model for solar minimum for the geomagnetically quiet period 23–25 June 1986, when anomalously low values of hmF2(<200 km) were observed. We found that these low values of hmF2 (seen as a G condition on ionograms) exist in the ionosphere due to a decrease of production rates of oxygen ions resulting from low values of atomic oxygen density. Results show that determination of a G condition using incoherent scatter radar data is sensitive both to the true concentration of O⁺ relative to the molecular ions, and to the ion composition model assumed in the data reduction process. The increase in the O⁺ + N₂ loss rate due to vibrationally excited N₂ produces a reduction in NmF2 of typically 5–10%, but as large as 15%, bringing the model and data into better agreement. The effect of vibrationally excited NO⁺ ions on electron densities is negligible.     

Morphological analysis of the winter nighttime ionosphere at mid-latitudes of the Asian region

We present a study of peculiarities of the winter nighttime maximum in the critical frequencies f ₀ F2 at mid-latitudes of the Asian region. The data of stations located at different longitudes and close latitudes have been used in the analysis: Novosibirsk (54.8°N, 83.2°E), Irkutsk (52.5°N, 104.0°E), and Khabarovsk (48.5°N, 135.1°E). It has been found that the nighttime maximum in f ₀ F2 is observed after midnight (∼0200–0400 LT) and is a stable feature of the quiet ionosphere from the middle of October to the middle of March at low solar activity (SA) at all analyzed stations. This interval decreases with increasing SA. The difference between the maximal and minimal f ₀ F2 values in nighttime hours is the largest in December–January, and its amplitude is almost independent of SA. Variations in the critical frequency of the h _m F2 layer are inversely related to those in the height of the maximum. We have studied periods when the difference between the daytime and nighttime values of f ₀ F2 is less than 2 MHz. The intervals of observations of such events at different longitudes do not coincide. No dependence of the winter nighttime maximum amplitude on magnetic activity has been found.     

Formation mechanisms of the midlatitudinal <Emphasis Type="Italic">NmF2</Emphasis> semiannual anomaly under daytime quiet geomagnetic conditions at low solar activity

The F-region peak electron densities NmF2 measured during daytime quiet geomagnetic conditions at low solar activity on January 22, 2008, April 8, 1997, July 12, 1986, and October 26, 1995, are compared. Ionospheric parameters are measured by the ionosonde and incoherent scatter radar at Millstone Hill and calculated with the use of a 1D nonstationary ionosphere–plasmasphere model of number densities and temperatures of electrons and ions at middle geomagnetic latitudes. The formation of the semiannual anomaly of the midlatitudinal NmF2 under daytime quiet geomagnetic conditions at low solar activity is studied. The study shows that the semiannual NmF2 anomaly occurs due to the total impact of three main causes: seasonal variations in the velocity of plasma drift along the geomagnetic field due to the corresponding variations in the components of the neutral wind velocity; seasonal variations in the composition and temperature of the neutral atmosphere; and the dependence of the solar zenith angle on a number of the day in the year at the same solar local time.     

The role of vibrationally excited nitrogen in the formation of the mid-latitude negative ionospheric storms

Millstone Hill ionospheric storm time measurements of the electron density and temperature during the ionospheric storms (15-16 June 1965; 29–30 September 1969 and 17–18 August 1970) are compared with model results. The model of the Earth’s ionosphere and plasmasphere includes interhemispheric coupling, the H⁺, O⁺(⁴S), O⁺(²D), O⁺(²P), NO⁺, O⁺₂ and N⁺₂ ions, electrons, photoelectrons, the electron and ion temperature, vibrationally excited N₂ and the components of thermospheric wind.In order to model the electron temperature at the time of the 16 June 1965 negative storm, the heating rate of the electron gas by photoelectrons in the energy balance equation was multiplied by the factors 5–30 at he altitude above 700 km for the period 4.50-12.00 LT, 16 June 1965. The [O]/[N₂] MSIS-86 decrease and vibrationally excited N₂ effects are enough to account for the electron density depressions at Millstone Hill during the three storms. The factor of 2 (for 27–30 September 1969 magnetic storm) and the & actor 2.7 (for 16–18 August 1970 magnetic storm) reduction in the daytime peak density due to enhanced vibrationally excited N₂ is brought about by the increase in the O⁺+N₂ rate factor.     

Comparison of model electron densities and temperatures with Millstone Hill observations during undisturbed periods and the geomagnetic storms of 16–23 March and 6–12 April 1990

Measurements of F-region electron density and temperature at Millstone Hill are compared with results from the IZMIRAN time-dependent mathematical model of the Earths ionosphere and plasmasphere during the periods 16–23 March and 6–12 April 1990. Each of these two periods included geomagnetically quiet intervals followed by major storms. Satisfactory agreement between the model and the data is obtained during the quiet intervals, provided that the recombination rate of O⁺(⁴S) ions was decreased by a factor of 1.5 at all altitudes during the nighttime periods 17–18 March, 19–20 March, 6–8 April and 8–9 April in order to increase the NmF2 at night better to match observations. Good model/data agreement is also obtained during the storm periods when vibrationally excited N₂ brings about factor-of-2-4 reductions in daytime NmF2. Model calculations are carried out using different expressions for the O⁺ – O collision frequency for momentum transfer, and the best agreement between the electron-density measurements and the model results is obtained when the CEDAR interim standard formula for the O⁺ – O collision frequency is used. Deviations from the Boltzmann distribution for the first five vibrational levels of NI were calculated. The calculated distribution is highly non-Boltzmann at vibrational levels j > 2, and the Boltzmann distribution assumption results in the increase of 10–30% in calculated NmF2 during the storm-time periods. During the March storm at solar maximum the model results obtained using the EUVAC solar flux model agree a little better with the observations in comparison with the EUV94 solar flux model. For the April storm period of moderate solar activity the EUV94X model results agree better with the observations in comparison to the EUVAC model.     

The effect of carbon dioxide cooling on trends in the F2-layer ionosphere

The effect of carbon dioxide (CO₂) cooling on trends of h_mF₂ and N_mF₂ are investigated using a coupled thermosphere and ionosphere general circulation model. Model simulations indicate that CO₂ cooling not only causes contraction of the upper atmosphere and changes of neutral and ion composition but also changes dynamics and electrodynamics in the thermosphere/ionosphere. These changes determine the altitude dependence of ionospheric trends and complex latitudinal, longitudinal, diurnal, seasonal, and solar cycle variations of trends of h_mF₂ and N_mF₂. Under the CO₂ cooling effect, trends of N_mF₂ are negative with magnitude from 0% to −40% for doubled CO₂, depending on location, local time, season, and solar activity. The corresponding trends of h_mF₂ are mostly negative with a magnitude from 0 to −40 km, but can be positive with a magnitude from 0 to 10 km at night, with maximum positive trends occurring after midnight under solar minimum conditions.     

Formation Mechanisms of the Spring–Autumn Asymmetry of the Midlatitudinal <Emphasis Type="Italic">NmF</Emphasis>2 under Daytime Quiet Geomagnetic Conditions at Low Solar Activity

Formation mechanism of the spring–autumn asymmetry of the F2-layer peak electron number density of the midlatitudinal ionosphere, NmF2, under daytime quiet geomagnetic conditions at low solar activity are studied. We used the ionospheric parameters measured by the ionosonde and incoherent scatter radar at Millstone Hill on March 3, 2007, March 29, 2007, September 12, 2007, and September 18, 1984. The altitudinal profiles of the electron density and temperature were calculated for the studied conditions using a one-dimensional, nonstationary, ionosphere–plasmasphere theoretical model for middle geomagnetic latitudes. The study has shown that there are two main factors contributing to the formation of the observed spring–autumn asymmetry of NmF2: first, the spring–autumn variations of the plasma drift along the geomagnetic field due to the corresponding variations in the components of the neutral wind velocity, and, second, the difference between the composition of the neutral atmosphere under the spring and autumn conditions at the same values of the universal time and the ionospheric F2-layer peak altitude. The seasonal variations of the rate of O⁺(⁴S) ion production, which are associated with chemical reactions with the participation of the electronically excited ions of atomic oxygen, does not significantly affect the studied NmF2 asymmetry. The difference in the degree of influence of O⁺(⁴S) ion reactions with vibrationally excited N₂ and O₂ on NmF2 under spring and autumn conditions does not significantly change the spring–autumn asymmetry of NmF2.     

The height of the maximum ionospheric electron density over the MU radar

Ionospheric F₂-layer peak height h_mF₂ variations, as measured over 1986–1995 by the MU radar (34.85°N, 136.1°E) and as calculated with a theoretical model, are discussed. The diurnal variations of the measured peak height for different seasons and levels of solar activity are compared with those estimated from ionosonde M3000F₂ and IRI predictions. Also given are the measured ion drift velocities and meridional neutral winds needed to understand the dynamic behavior of the F₂-layer. It is found that: (1) h_mF₂ is generally higher during periods of the solar maximum than during periods of the solar minimum, and higher in summer than in winter; (2) for the solar maximum, h_mF₂ drops markedly in the morning and in the afternoon, while, for the solar minimum, the h_mF₂ minimum occurs in the morning during summer and usually in the afternoon during winter. In general, the measured h_mF₂ is well reproduced by our model when we use the observed drift velocities and plasma temperatures as inputs. Our modeling study shows that the neutral wind contributes strongly to the diurnal variation of h_mF₂ in winter by lowering the ionization layer by day, particularly for the solar maximum; it also helps to enlarge the day–night difference of h_mF₂ in summer. The northward electromagnetic drifts that usually cancel the neutral wind effect have only a minor effect for the location of the MU radar. Other features of the observed h_mF₂ variations, e.g., the solar maximum–minimum difference, the summer–winter difference, and the morning and afternoon drops, are explained by the basic processes of O⁺ production, loss and diffusion, as influenced by the atomic oxygen concentration and neutral and plasma temperatures.     

Modeling of the electron density depletion in the storm-time trough on April 20, 1985

Multi-instrument experimental data are analyzed to determine the main processes forming a deep trough in the electron density at F-peak altitudes during a strong magnetic storm (K_p⩾5). Previous attempts to explain the observations were not successful. The model we use to interpret the data includes production of vibrationally excited N₂ in the region poleward of the trough and its transport into the trough region by a southward wind. The main source of the vibrationally excited N₂ is secondary electrons created by precipitating electrons. Joule heating and dissipation of precipitating electron energy create a pressure gradient and induce the southward wind. According to the model calculations, such a system of processes can cause the very strong electron density depletion observed by the Millstone Hill incoherent scatter radar on April 20, 1985. An important additional condition for such a deep trough is a decrease in the [O]/[N₂] ratio. The total energy flux and average energy of precipitating electrons just poleward of the trough is also a factor.     

A role of the altitude gradient of the thermospheric wind velocity in ionospheric <Emphasis Type="Italic">F</Emphasis>-region dynamics

By processing the data of vertical ionospheric sounding in Almaty for 2000–2009, we obtained the distributions of the heights of the maximum (h _m F) and bottom (h _bot F) of the F2-layer, incremental changes in its semi-thickness (δh), the characteristic time of losses (τ), and the vertical displacement velocity of the node of the thermospheric wind (V) during the transitional time of the day during nighttime increases in the electron concentration at the layer maximum. The comparison of the measured V and modeled V _m velocities showed a certain discrepancy. The influence of the altitude gradient of the meridional thermospheric wind velocity on the behaviors of h _m F, h _bot F, δh, and τ during nighttime increases in the electron concentration is studied.     

Radar chain study of the May, 1995 storm

We summarize the main features of the ionospheric F region as observed bythe Sondrestrom, Millstone Hill, Arecibo, and Jicamarca incoherent scatter radars during the 1–5May, 1995 CEDAR Storm Study interval. This paper apparently represents the first study of amajor storm interval using the current incoherent scatter radar chain supported by the U.S.National Science Foundation. We focus most attention on 2–3 May, and include additional datafrom IMP-8, the St. Johns magnetometer, SuperDARN, and global total electron content (TEC)maps from GPS. Three intervals of likely penetration of magnetospheric electric field from high tolow latitude are identified on 2 May. A unique feature of this storm are the strong daytimeequatorward wind surges in the neutral meridional wind observed at Millstone Hill. The first ofthese (at 14 UT on 2 May) is apparently due to a travelling atmospheric disturbance launched byintense frictional and Joule heating as observed at Sondrestrom. An evening enhancement in NmF₂ (the dusk effect) is typically seen only on the first day of a geomagneticstorm. However, during this storm a strong dusk effect is seen at Millstone Hill on 2, 3, and 4May, associated with the equatorward wind surges. A penetrating eastward electric field alsocontributed to the dusk effect on 2 May. A large rise in hmF₂ at Arecibo near0000 UT on 3 May is due to the same eastward electric field, which penetrates to the equator,causing a strong upward plasma drift at Jicamarca. This apparently results in a polewardexpansion of the equatorial anomaly zones as seen in GPS total electron content, and an increasein NmF₂ at Arecibo to the largest value seen at midnight in several years.     

The role of vibrationally excited nitrogen and oxygen in the ionosphere over Millstone Hill during 16-23 March, 1990

We present a comparison of the observed behavior of the F region ionosphere over Millstone Hill during the geomagnetically quiet and storm period on 16/23 March, 1990, with numerical model calculations from the time-dependent mathematical model of the Earths ionosphere and plasmasphere. The effects of vibrationally excited N₂(v) and O₂(v) on the electron density and temperature are studied using the N₂(v) and O₂(v) Boltzmann and non-Boltzmann distribution assumptions. The deviations from the Boltzmann distribution for the first five vibrational levels of N₂(v) and O₂(v) were calculated. The present study suggests that these deviations are not significant at vibrational levels v = 1 and 2, and the calculated distributions of N₂(v) and O₂(v) are highly non-Boltzmann at vibrational levels v > 2. The N₂(v) and O₂(v) non-Boltzmann distribution assumption leads to the decrease of the calculated daytime NmF2 up to a factor of 1.44 (maximum value) in comparison with the N₂(v) and O₂(v) Boltzmann distribution assumption. The resulting effects of N₂(v > 0) and O₂(v) > 0) on the NmF2 is the decrease of the calculated daytime NmF2 up to a factor of 2.8 (maximum value) for Boltzmann populations of N₂(v) and O₂(v) and up to a factor of 3.5 (maximum value) for non-Boltzmann populations of N₂(v) and O₂(v). This decrease in electron density results in the increase of the calculated daytime electron temperature up to about 1040/1410 K (maximum value) at the F2 peak altitude giving closer agreement between the measured and modeled electron temperatures. Both the daytime and nighttime densities are not reproduced by the model without N₂(v > 0) and O₂(v > 0), and inclusion of vibrationally excited N2 and O2 brings the model and data into better agreement. The effects of vibrationally excited O2 and N2 on the electron density and temperature are most pronounced during daytime.     

Dynamics of North American sector ionospheric and thermospheric response during the November 2004 superstorm

We present a study of ionospheric and thermospheric response during a November 9–10, 2004 major geomagnetic storm event (DsT ～?300 nT). We utilize the North American sector longitude chain of incoherent scatter radars at Arecibo, Millstone Hill, and Sondrestrom, operating as part of a coordinated international mesosphere/lower thermosphere coupling study experiment. Total electron content (TEC) determinations from global positioning system (GPS) ground receivers, ground magnetometer traces from the Canadian CANOPUS array, Defense Meteorological Satellite Platform (DMSP) topside data, and global convection patterns from the SuperDARN radar network are analyzed to place the detailed radar data in proper mesoscale context. The plasmaspheric boundary layer (PBL) expanded greatly in the dusk sector during ring current intensification to span more than 25° of magnetic latitude, reaching as far south as 30° invariant latitude. Strong sub-auroral polarization stream velocities of more than 1 km/s were accompanied by large upwards thermal O+ fluxes to the overlying magnetosphere. The large PBL expansion subsequently exposed both Millstone Hill and Sondrestrom to the auroral convection pattern, which developed a complex multicell and reverse convection response under strongly northward IMF conditions during a period of global interplanetary electric field penetration. Large traveling atmospheric and ionospheric disturbances caused significant neutral wind and ion velocity surges in the mid-latitude and tropical ionosphere and thermosphere, with substorm activity launching equatorward neutral wind enhancements and subsequent mid-latitude dynamo responses at Millstone Hill. However, ionosphere and thermosphere observations at Arecibo point to significant disturbance propagation modification in the post-dusk sector PBL region.     

Some F2-layer effects during the January06-11,1997 cedar storm period as observed with theMillstoneHill incoherent scatter facility

An observed daytime negative storm effect on 10 January and strongpost-midnight N_m F₂ increases on 7 and 8 January followed by a steep T_e decrease down to T_n are analyzed. Daytime neutral composition and T_n(h) were inferred from incoherent scatter (IS) radar observations using aself-consistent approach to F₂ -layer modelling. Observed daytime T_e , T_i , N_e profiles were corrected for the disturbed day using the calculated ioncomposition. The main reason for the observed N_m F₂ negative storm effectis the O/(N₂ O₂ ) ratio decrease in the thermosphere. The calculated O/N₂ ratio at hm F₂ is less by a factor of 3.7 than MSIS prediction for 10January and is close to MSIS for quiet days. Strong Nm F₂ night-time increase by afactor of 3 is due to a plasma compression mechanism under the action of observed EB drift(westward E-field) moving plasma from higher L shells to lower ones and squeezing it into the F₂ -region. Moderate (1-2)10 ⁸ cm ^-2 s ^-1 O fluxes in agreement with IS observations were shown to be sufficient to account for the night-timeN_m F₂ increase. This elevation in the F₂ -region electron densityis shown to be the main reason for the observed steep Te post-midnight decrease. 1999 ElsevierScience Ltd. All rights reserved.