Solar Minimum Years Research Articles

The Midlatitude Summer Night Anomaly as observed by CHAMP and GRACE: Interpreted as tidal features

AbstractThis paper presents a description of the Midlatitude Summer Night Anomaly (MSNA) in terms of solar tidal signatures, based on in situ observations from CHAMP (CHAllenging Minisatellite Payload) and GRACE (Gravity Recovery and Climate Experiment) during the solar minimum years 2008 and 2009. Our analysis is focusing on 40° to 60° magnetic latitude ranges in both hemispheres, where the reversed diurnal variations of the electron density are strongest. The results revealed that in the Southern Hemisphere the longitudinally symmetric tide D0 is particularly strong during December solstice. The well‐known Weddell Sea Anomaly is caused by a simultaneous constructive interference of three components D0, DW2, and SPW1. During June solstice the eastward propagating tide DE1 is the strongest in the Northern Hemisphere, which causes a wave‐2 longitudinal pattern. The two crests of the wave‐2 pattern at nighttime correspond well with the MSNA feature in the Northern Hemisphere. The MSNA feature over the USA continent is particularly strong, which can be explained by the combined contributions of the components DE1, D0, and DW2. The diurnally varying difference in electron density between the USA East and West Coast can also be explained by the phase propagation of the DE1. A similar effect has also been observed in the Asian region. The peak electron densities of the tidal component D0 appear around 0700 LT and 2000 LT in the Southern and Northern Hemispheres, respectively. The time shift suggests that the two hemispheres move in antiphase up and down. The planetary wave SPW1 exhibits an electron density crest near longitude sectors where the dip equator reaches far into the summer hemisphere.

GPS derived TEC and foF2 variability at an equatorial station and the performance of IRI-model

The ionosphere induces a time delay in transionospheric radio signals such as the Global Positioning System (GPS) signal. The Total Electron Content (TEC) is a key parameter in the mitigation of ionospheric effects on transionospheric signals. The delay in GPS signal induced by the ionosphere is proportional to TEC along the path from the GPS satellite to a receiver. The diurnal monthly and seasonal variations of ionospheric electron content were studied during the year 2010, a year of extreme solar minimum (F10.7=81 solar flux unit), with data from the GPS receiver and the Digisonde Portable Sounder (DPS) collocated at Ilorin (Geog. Lat. 8.50°N, Long. 4.50°E, dip −7.9°). The diurnal monthly variation shows steady increases in TEC and F2-layer critical frequency (foF2) from pre-dawn minimum to afternoon maximum and then decreases after sunset. TEC show significant seasonal variation during the daytime between 0900 and 1900UT (LT=UT+1h) with a maximum during the March equinox (about 35 TECU) and minimum during the June solstice (about 24 TECU). The GPS-TEC and foF2 values reveal a weak seasonal anomaly and equinoctial asymmetry during the daytime. The variations observed find their explanations in the amount of solar radiation and neutral gas composition. The measured TEC and foF2 values were compared with last two versions of the International Reference Ionosphere (IRI-2007 and IRI-2012) model predictions using the NeQuick and CCIR (International Radio Consultative Committee) options respectively in the model. In general, the two models give foF2 close to the experimental values, whereas significant discrepancies are found in the predictions of TEC from the models especially during the daytime. The error in height dependent thickness parameter, daytime underestimation of equatorial drift and contributions of electrons from altitudes above 2000km have been suggested as the possible causes.

Quasi‐two‐day wave structure, interannual variability, and tidal interactions during the 2002–2011 decade

In this paper we employ Thermosphere Ionosphere Mesosphere Energetics Dynamics/Sounding of the Atmosphere using Broadband Emission Radiometry temperature measurements from 20 to 120 km and between about ±72° latitude to investigate several aspects of the quasi‐two‐day wave (QTDW) during the 2002–2011 decade, including interannual variability of its seasonal‐latitudinal structure, its penetration into the lower thermosphere, and various wave‐wave interactions. We focus on two components of the QTDW: the westward‐propagating component with zonal wave number s=3 (TDW3), and the eastward‐propagating component with s=−2 (TDE2). TDW3(TDE2) has maximum amplitudes during 2003, 2004, and 2011(2006 and 2011) and both waves have their lowest amplitudes during the deep solar minimum years of 2008–2009. TDW3 and to some degree TDE2 penetrate with significant amplitudes up to 120 km altitude, well into the region where neutral winds generate electric fields through the dynamo mechanism. A new “longitude subdivision method (LSM)” is presented that enhances temporal resolution of TDW3 and enables the determination of 9.6 h and 16 h waves that result from nonlinear interaction between TDW3 and/or TDE2 and diurnal migrating (DW1) and semidiurnal migrating (SW2) tides. Evidence is presented for westward‐propagating 9.6 h and 16 h waves with s=5 and s=4, respectively, and a zonally symmetric (s=0) 9.6 h wave. The s=5(s=0) wave only occurs as a result of nonlinear interaction between SW2 and TDW3(TDE2), whereas the s=4 wave can result from interaction of TDW3 with DW1 or of TDE2 with SW2. We payed special attention to possible aliasing between different waves.

Equatorial Ionospheric Anomaly (EIA) and comparison with IRI model during descending phase of solar activity (2005–2009)

The ionospheric variability at equatorial and low latitude region is known to be extreme as compared to mid latitude region. In this study the ionospheric total electron content (TEC), is derived by analyzing dual frequency Global Positioning System (GPS) data recorded at two stations separated by 325km near the Indian equatorial anomaly region, Varanasi (Geog latitude 25°, 16/N, longitude 82°, 59/E, Geomagnetic latitude 16°, 08/N) and Kanpur (Geog latitude 26°, 18/N, longitude 80°, 12/E, Geomagnetic latitude 17°, 18/N). Specifically, we studied monthly, seasonal and annual variations as well as solar and geomagnetic effects on the equatorial ionospheric anomaly (EIA) during the descending phase of solar activity from 2005 to 2009. It is found that the maximum TEC (EIA) near equatorial anomaly crest yield their maximum values during the equinox months and their minimum values during the summer. Using monthly averaged peak magnitude of TEC, a clear semi-annual variation is seen with two maxima occurring in both spring and autumn. Results also showed the presence of winter anomaly or seasonal anomaly in the EIA crest throughout the period 2005–2009 only except during the deep solar minimum year 2007–2008. The correlation analysis indicate that the variation of EIA crest is more affected by solar activity compared to geomagnetic activity with maximum dependence on the solar EUV flux, which is attributed to direct link of EUV flux on the formation of ionosphere and main agent of the ionization. The statistical mean occurrence of EIA crest in TEC during the year from 2005 to 2009 is found to around 12:54LT hour and at 21.12°N geographic latitude. The crest of EIA shifts towards lower latitudes and the rate of shift of the crest latitude during this period is found to be 0.87°N/per year. The comparison between IRI models with observation during this period has been made and comparison is poor with increasing solar activity with maximum difference during the year 2005.

Impact of tropospheric tides on the nitric oxide 5.3 μm infrared cooling of the low‐latitude thermosphere during solar minimum conditions

This paper explores the impact of diurnal tides that begin near the surface as heat is released by evaporation and condensation on Earth's upper atmosphere natural thermostat: the nitric oxide (NO) infrared cooling of the thermosphere at 5.3 μm. Equatorial NO volume emission rate measurements from 100 to 180 km made by Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) on TIMED during the solar minimum year 2008 are analyzed on two important nonmigrating tides, the DE2 and DE3 components. DE3 (DE2) amplitudes maximize around 125 km altitude and, depending on season, are on the order of 0.18 (0.16) nW/m3. This represents a substantial modulation of the mean NO emission that maximizes in the same altitude range with a value of about 0.8 nW/m3. Tropospheric tides are therefore important not only for the dynamics and electrodynamics of the ionosphere‐thermosphere system but also for modulating the thermospheric energy budget. Supporting photochemical tidal modeling indicates that the main tidal coupling mechanism is the temperature dependence of the collisional excitation of the NO (ν=1) vibrational state. However, the response to vertical tidal advection is also important. It is in‐phase with the response to temperature and contributes as much as 50% to the NO tides at and above the emission maximum. Neutral density tidal variations contribute about 25% but with a 9 h phase offset resulting in a net damping. These results imply that NO 5.3 μm emissions are a suitable proxy for studying tidal dynamics in the thermosphere where no global temperature measurements are available.

Are ionospheric storms the same during different solar cycles?

AbstractThe ionosphere's response to geomagnetic storms has been studied since the earliest days of terrestrial space physics. In terms of temporal coverage, the largest data sets used extensively have been from the global network of ionosondes. Many previous investigations examined the behavior of the F layer's maximum electron density (Nmax)—often contrasting the difference seen between storms that occur during solar maximum years versus those during solar minimum years. We report on the first attempt to study systematically the patterns of ionospheric disturbance seen during different solar cycles. We select two midlatitude sites with long‐term consistency in data: Wallops Island (Virginia) and Hobart (Tasmania)—stations with comparable geographic and geomagnetic coordinates—but in different hemispheres and widely separated longitude sectors. We compare average ionospheric storm patterns using over 200 moderate to severe geomagnetic storms within each of solar cycle #20 (October 1964 to June 1976) and cycle #23 (May 1996 to December 2008). We compute average patterns of ΔNmax(%), measured with respect to monthly mean conditions, following storm and local time. The overall results show remarkable consistency in characteristic patterns of an ionospheric storm: a short positive phase that occurs during the daytime hours on the first day of a storm, with a prolonged negative phase on subsequent days. Statistical differences occur in the overall magnitudes and longevities of these patterns, consistently showing that cycle #23 had less severe ionospheric storms. An analysis of geomagnetic indices shows that degrees of disturbance were, in fact, lower during solar cycle #23 than cycle #20.

Quiet time equatorial mass density distribution derived from AMPTE/CCE and GOES using the magnetoseismology technique

An inversion technique for estimating the properties of the magnetospheric plasma from the harmonic frequencies of the toroidal standing Alfvén waves has been used to derive the global equatorial mass density covering radial distances from 4 to 9 Earth radii (RE), within the local time sector spanning from 0300 to 1900 h. This broad range of L shell extending to the outer magnetosphere allows us to examine the local time and radial dependence of the quiet time equatorial mass density during solar minimum and thereby construct a global distribution of the equatorial mass density. The toroidal Alfvén waves were detected with magnetometers on the Active Magnetospheric Particle Tracer Explorers (AMPTE)/Charge Composition Explorer (CCE) during the nearly 5 year interval from August 1984 to January 1989 and on the Geostationary Operational Environmental Satellites (GOES) (10, 11, and 12) for 2 years from 2007 to 2008, both of which were operating during solar minimum years. The derived equatorial mass density, ρeq, at geosynchronous orbit (GEO) monotonically increases with increasing magnetic local time (MLT) from the nightside toward the dusk sector. At other radial distances, ρeq has the same MLT variation as that of GEO, while the magnitude logarithmically decreases with increasing L value. An investigation of the Dst and Kp dependence shows that the median value of ρeq varies little in the daytime sector during moderately disturbed times, which agrees with previous studies. ρeq calculated from the F10.7 dependent empirical model shows good agreement with that of CCE but overestimates that of GOES probably due to the extreme solar cycle minimum in years 2007–2008.

The solar cycle variation of plasma parameters in equatorial and mid latitudinal areas during 2005–2010

Based on the ISL data detected by DEMETER satellite, the solar cycle variation in electron density (Ne) and electron temperature (Te) were studied separately in local daytime 10:30 and nighttime 22:30 during 2005–2010 in the 23rd/24th solar cycles. The semi-annual, annual periods and decreasing trend with the descending solar activity were clearly revealed in Ne. At middle and high latitudes, there exhibited phase shift and even reversed annual variation over Southern and Northern hemisphere, and the annual variation amplitudes were asymmetrical at both hemispheres in local daytime. In local nighttime, the annual variations of Ne at south and north hemispheres were symmetrical at same latitudes, but the annual variation amplitudes at different latitudes differed largely, showing obviously zonal features. As for Te, the phase shift in annual variations was not as apparent as Ne with the increase of latitudes at Southern and Northern hemisphere in local daytime. While in local nighttime the reversed annual variations of Te were shown at low latitudinal areas, not at high latitudes as those in Ne. The correlation study on Ne and Te illustrated that, in local daytime, Ne and Te showed strong negative correlation at equator and low latitudes, but during the solar minimum years the correlation between Ne and Te changed to be positive at 25–30° latitudes in March 2009. The correlation coefficient R between Ne and Te also showed semi-annual periodical variations during 2005–2010. While in local nighttime, Ne and Te exhibited relatively weak positive correlation with R being about 0.6 at low latitudes, however no correlation beyond latitudes of 25° was obtained.

Global characteristics of Pc1 magnetic pulsations during solar cycle 23 deduced from CHAMP data

Abstract. We present a global climatology of Pc1 pulsations as observed by the CHAMP satellite from 2000 to 2010. The Pc1 center frequency and bandwidth are about 1 and 0.5 Hz, respectively. The ellipticity is mostly linear with the major axis almost aligned with the magnetic zonal direction. The diurnal variation of Pc1 occurrences shows a primary maximum early in the morning and a secondary maximum during pre-midnight hours. The annual variations of the occurrence rates exhibit a clear preference for local summer. The solar cycle dependence of the occurrence rate reveals a maximum at the declining phase (2004–2005). Neither magnetic activity nor solar wind velocity controls the Pc1 occurrence rate significantly. Pc1 occurrence rate peaks at subauroral latitudes, but the steep cutoff towards higher latitudes is due to auroral field-aligned currents masking the Pc1 pulsations. The center frequency of Pc1 pulsations does not show a clear dependence on latitude. The global distribution of Pc1 exhibits highest occurrence rates near the longitude sector of the South Atlantic Anomaly. Pc1 events at auroral latitudes, although they are rarely detected, show a clear occurrence peak around local noon. A majority of the auroral Pc1 events are observed during solar minimum years.

Effect of Interplanetary Disturbances and Geomagnetic Activities on Relativistic Electrons at Geosynchronous Orbit

AbstractUsing hourly averaged data of > 2 MeV electron fluxes measured with GOES 7/9/10/11 satellites during 1988–2010, this paper investigates statistically conditions of solar wind and geomagnetic activities during relativistic electrons flux (Fe) enhancements, and describes the dependence of relativistic electrons at geosynchronous orbit (GEO) on local time, magnetic storms. The results are as follows: (1) The local time dependence of GEO relativistic electrons is influenced by solar wind and geomagnetic activities. The noon/midnight electron flux ratio grows with increasing solar wind velocity (Vsw). On conditions of the Dst index above −50 nT, relativistic electrons show regular variation with local time, while during storms with Dst< −50 nT, the maximum electrons flux may not be measured at local noon. During the declining phase of a solar cycle relativistic electron fluxes approaching maximum, Vsw, the Kp index and the cube root of solar wind density (N) show better correlations with electron fluxes after 39∼57 h, 57∼80 h and 12∼24 h, respectively. (2) Before about two years of solar minimum and near the equinoxes, occurrence frequencies of intense relativistic electron flux enhancement events, in which the daily maximum relativistic electron flux Femax ≥ 104 pfu increased, while weaker events with 104 > Femax ≥ 103 pfu exhibited no such solar cycle and seasonal dependences. For most intense events, relativistic electron fluxes begin to increase during main phases of magnetic storms, while for weaker events, relativistic electron fluxes tend to increase during recovery phases. (3) The solar wind density shows as a good indicator of subsequent relativistic electron activities. For most electron flux enhancement events, relativistic electron flux decreased to its minimum after 0∼1 days of the maximum solar wind density, Nmax, while approaching the maximum after 0∼2 days of the minimum solar wind density, Nmin. (4) Above 90% of relativistic electron events occurred on conditions of high‐speed solar wind and geomagnetic disturbances, which are as follows: Vswmax > 516 km/s, Dstmin < −31 nT, Nmin < 2.8 cm−3, Nmax > 14.1 cm−3, Bzmin < −2.9 nT, AEmax > 698 nT. (5) For all magnetic storms, occurrence probability of daily maximum electron flux above 103 pfu after Dstmin, is about 53%, the percent of intense, weak events being 36%, 64%, respectively, which is hardly affected by intensities of storms. During storms, solar wind velocity, density, and the AE index are important indicators for subsequent relativistic electron activities.

Long‐periodic strong radar echoes in the summer polar D region correlated with oscillations of high‐speed solar wind streams

We report long‐periodic oscillations of polar mesospheric summer echoes (PMSEs) correlated with high‐speed solar wind streams (HSSs) as observed between 1 June and 8 August in the solar minimum years 2006 and 2008. PMSEs (80–90 km altitudes) were observed by 52 MHz VHF radar measurements at Esrange, Sweden (67.8°N, 20.4°E). Correlations between PMSE volume reflectivity/counts, HSSs, and AE index are primarily found at 7‐day, 9‐day, and 13‐day periodicities as well as 9‐day and 13.5‐day periodicities in 2006 and 2008, respectively. The observations show that the effects of HSSs appear in PMSEs. During corotating interaction region (CIR)‐induced HSSs, the long‐lasting enhancement of PMSEs, geomagnetic disturbances, and D‐region ionization suggests that a favorable condition in generating PMSEs can be provided by the precipitating energetic electrons (>30 keV), which are frequently multiplied in the magnetosphere during HSSs.

Linear scaling and periodicity on the measures of global and local scale complexities of total electron content dynamics

[1] In this paper, we compare the local and global dynamics of total electron content (TEC) by analyzing Lyapunov exponents and correlation dimensions. The internal structure of the underlying system is studied using TEC data from the solar minimum years 2007–2008. The mutual information, false nearest neighbors, and space-time separation of both local and global snapshots are estimated and analyzed. It indicates that although the internal dynamics changes with season, the pattern of variation over the seasons remains identical for both the years, suggesting that the characteristics of these changes might be predictable. We report the evidence of a linear scaling with slope 0.00187 and a periodicity with period of 1 year on measures of global and local scale complexities of TEC dynamics. This behavior appears to be a universal phenomenon unaffected by change of cycles and amount of information influencing the complexity, since they are almost constant over the 2 years. The global Lyapunov exponent increases linearly over a year, whereas the local Lyapunov exponent increases up to the middle of the year, attains greatest local complexity, and then decreases. This suggests that local prediction is more reliable than the global one. The estimated invariants characterize the complex dynamics as it evolve from local time to global time and also provide information to the system's heterogeneity. The features such as presence of multiple attractors, linear scaling, and nearly regular seasonal periodicity may have practical consequences and could yield insights into the internal dynamics of TEC and the modeling of its variations.

High‐speed stream impacts on the equatorial ionization anomaly region during the deep solar minimum year 2008

To demonstrate high‐speed stream effects during the recent deep solar minimum year 2008, we have analyzed manually scaledfoF2 and hmF2 at Jicamarca and total electron content (TEC) in the equatorial ionization anomaly (EIA) region over the America longitudinal sector. Our results reveal that a prominent 9 day oscillation appears in the hmF2 and foF2 at the dip equator. The 9 day oscillation amplitudes of foF2are not always positively correlated with TEC in the equatorial ionosphere, and they show nonlinear dependence on the intensity of geomagnetic disturbances. With the outputs of Fejer and Scherliess's (1997) empirical model, we found that this periodicity is also present in equatorial vertical drifts caused by disturbance dynamoelectric field (DDEF) but absent in the drifts due to prompt penetration electric field (PPEF). DDEF effects on the equatorial periodic variations alone are not sufficient to explain the observed phenomena; other mechanisms, such as thermal expansion/contraction and neutral composition changes, are also the plausible causes of the periodic oscillation in the equatorial ionosphere. Further, the complicated patterns appear in the 9 day band‐pass‐filtered TEC perturbations in the EIA region, and they are quite different from the patterns of global coherent thermospheric oscillations triggered by high‐speed streams. We also found that the latitudinal variations of band‐passed‐filtered TEC present different behaviors involving tilt latitudinal configuration, antiphased correlation between the crests and trough, and south‐north asymmetry, which vary as a function of season, local time, or even from event to event.

Global S4 index variations observed using FORMOSAT‐3/COSMIC GPS RO technique during a solar minimum year

In this paper, presented for the first time the three‐dimensional global morphology and seasonal variations of scintillation index (S4 index) measured from the signal‐to‐noise ratio (SNR) intensity fluctuations of L1 channel of GPS radio occultation (RO) signals using FORMOSAT‐3/COSMIC (in short, F3/C) satellites for a low solar activity year 2008. The S4 index, which confined around ±30° magnetic latitudes, is found to start around post‐sunset hours (1900 MLT, magnetic local time) and often persists till post‐midnight hours (0300 MLT) between 150 and 350 km altitudes during equinox and northern winter seasons while no activity is observed during southern winter season. However, high latitudes are characterized with no scintillation activity beyond 150 km during any season, which implying that in the solar minimum period the drives of instabilities in the auroral, cusp and polar cap regions, namely the gradient drift and velocity shear, are absent. The S4 index at F region altitudes during magnetically quiet times is more intense and extends to higher latitudes than that observed during disturbed time consistent with earlier studies. The equatorial S4 index appears below the peak of F2 layer (hmF2) during most of the seasons although the associated intensities and the time of maximum occurrences are relatively higher and earlier during vernal equinox followed by autumn equinox. This equinoctial asymmetry could be primarily attributed to the asymmetries in eastward drift velocities, thermospheric meridional winds and plasma densities. Further, the global maps of S4 index at E region altitudes (between 75 and 125 km) show strong seasonal variations with highest activity during northern and southern summer solstice in the middle latitudes while it appears on both sides of magnetic equator with less or no activity at and around the equator during equinox seasons. The absence of S4 index along the equator can be understood in terms of the vanishing vertical component of the magnetic field lines that can inhibit the vertical movement and layered deposition of ionized particles of thin irregular electron density layers such as Es‐layers. Keeping in view the importance of these valuable database, we would like to emphasize that the F3/C GPS RO technique can be used to study the ionospheric irregularities at GHz frequency globally directly from the high‐rate L1 data, which reiterating its importance as a powerful tool to explore the terrestrial ionosphere on a global scale.

Revealing the classes of ionospheric disturbances on the basis of multiyear data on the critical frequency of the F2 layer

The bases of the classification method of ionospheric disturbances caused by solar-geomagnetic activity on the basis of the critical frequency of the F2 layer are developed. Data for the total solar activity cycle from 1975 to 1986 were used for studying variations in the critical frequency of the ionospheric F2 layer. The critical frequency was measured at the Moscow ionospheric observatory (55°45′N, 37°37′E) at an interval of 1 h. The gaps in the critical frequency values were filled in by the cubic interpolation method. The solar activity level was estimated using the F10.7 index. The geomagnetic disturbance was determined using the Kp · 10, Dst, and AE indices. According to the developed classification, an index of ionospheric activity is introduced. An analysis of the obtained values of the index for years of solar activity minimum and maximum shows that an increase in the absolute values of the index as a rule occurs at an increase in global geomagnetic and/or auroral disturbances. This fact indicates the sufficient information content of the developed index for characterizing ionospheric activity in any season. Moreover, using the sign of the index, one can form an opinion regarding an increase or decrease in the concentration of the ionospheric F2 layer, because the values of the considered index correspond to real oscillations in the critical frequency of the midlatitude ionosphere.

A Study of the Periodic Variations of Solar Magnetic Fields During Maxima and Minima of Solar Activity

By using the solar magnetic field data of Wilcox Observatory from 1975 to 2010, the short-time periodicities of solar mean magnetic fields during solar maximum and minimum years are analyzed. The results reveal that the solar magnetic fields mainly exhibit the approximate periods of 9 d, 13 d, and 27 d. During maximal solar activity the period about 27 d is most conspicuous, while during minimal solar activity the most evident period is approximately 13.5 d (except the solar minimum in the years 1984-1986). These results imply that solar active regions exhibit evidently different distributions in the periods of maxima and minima of solar activity.

Equatorial vertical plasma drifts and the measured and IRI model-predicted F 2-layer parameters above Ouagadougou during solar minimum

In this paper, hourly median value of ionosonde measurements: peak height F2-layer (hmF2), F2-layer critical frequency ( foF2) and propagation factor M(3000)F2 made at near-equatorial dip latitude, Ouagadougou, Burkina Faso (12°N, 1.5°W; dip: 1.5°N) and relevant F2-layer parameters: thickness parameter (Bo), electron temperature (Te), ion temperature (Ti), total electron content (TEC) and electron density (Ne) (at the fixed altitude of 300 km) provided by the International Reference Ionosphere (IRI) model for the longitude of Ouagadougou are contrasted with the IRI vertical drift model to explore in detail the monthly climatological behavior of equatorial ionosphere and the effects of equatorial electrodynamics on the diurnal structure of F2-layer parameters. The analysis period covers four months representative of solstitial and equinoctial seasonal periods during solar minimum year of 1987 for geomagnetically quiet-day. It is demonstrated that the month-by-month morphological patterns between vertical E × B drifts and F2-layer parameters range from worst to reasonably good and are largely seasonally dependent. A cross-correlation analysis conducted between equatorial drift and F2-layer characteristics yield statistically significant correlations for equatorial vertical drift and IRI-Bo, IRI-Te and IRI-TEC, whereas little or no acceptable correlation is obtained with observational evidence. Examination of the association between measured foF2, hmF2 and M(3000)F2 illustrates consistent much more smaller correlation coefficients with no systematic linkage.

Anthropogenic effects on the distribution of minor chemical constituents in the mesosphere/lower thermosphere – A model study

We investigate the influence that rising concentrations of methane, nitrous oxide and carbon dioxide have had upon the chemistry of the mesosphere since 1961. Calculations were performed using our global 3D-model LIMA (Leibniz-Institute Middle Atmosphere), designed for the investigation of the MLT-region (Mesosphere-Lower Thermosphere) and particularly for the extended mesopause region. LIMA utilizes observed tropospheric and lower stratospheric temperature and horizontal wind data up to 35km altitude by assimilating ECMWF/ERA-40 and ECMWF operational data. Real Lyman-α flux values are employed to determine the variable water vapor dissociation rate. Three different calculations were carried out and analyzed: (1) use of the same annual variation of the model dynamics in the chemical transport model (CTM) for all years according to the dynamics of the solar minimum year 1964 and employment of a realistic growth of the anthropogenic gases; (2) use of constant concentrations of the anthropogenic constituents at the lower border, but employment of the varying model dynamics; (3) the so-called realistic case, which considers both the long-term increase in the anthropogenic minor constituents and the varying dynamics according to LIMA calculations. The analysis of these three cases shows that the dynamics are able to counteract the impact of anthropogenic growth of minor constituents in the upper mesosphere-mesopause-lower thermosphere region in middle to high latitudes in summer. The water vapor mixing ratio increases due to rising methane concentration. The reason for this lies in a positive feedback process of autocatalytic water vapor production. The change in concentration of the minor constituents impacts both the cooling rate and the chemical heating rate. We present the relative and absolute deviations between the solar activity minimum years 1964 and 2008 for the most important minor constituents. We discuss the long-term behavior, particularly of water vapor, with regard to the impact on the NLC-region.

Averaged NmF2 of cusp-latitude ionosphere in northern hemisphere for solar minimum — Comparison between modeling and ESR during IPY

Based on the ionosphere observation data obtained by EISCAT Svalbard Radar (ESR) in solar minimum year — 2007, we analyzed diurnal variations of F2-peak electron density (NmF2) in four seasons under disturbed and quiet geomagnetic conditions. It indicated that the soft precipitation electron had an evident effect on the NmF2 increase at magnetic noon in spring, summer and autumn and the electron precipitation effects were prominent in winter. The comparison between the IRI-2007 model and the observation exhibited that the IRI (International Reference Ionosphere) model had a better NmF2 prediction when the photoionization was dominant during the polar day, but worse when the electron precipitation was dominant during the polar night. We showed that the electrons in lower energy band decreased when the geomagnetic disturbance went greater, which resulted in the lower NmF2. By analyzing the spectrum of precipitation electron under different geomagnetic conditions, it was found that this phenomenon was induced by the energy flux enhancement of precipitation electron of low energy.

Short term topological changes of coronal holes associated with prominence eruptions and subsequent CMEs

We study the short-term topological changes of equatorial and polar coronal hole (CH) boundaries, such as a variation of their area and disintegration, associated to reconnection with nearby (within 15° distance) quiescent prominence magnetic fields leading to eruptions and subsequent Coronal Mass Ejections (CMEs). The examples presented here correspond to the recent solar minimum years 2008 and 2009. We consider a temporal window of one day between the CH topological changes and the start and end times of prominence eruptions and onset of CMEs. To establish this association we took into account observational conditions related to the instability of prominence/filaments, the occurrence of a CME, as well as the subsequent evolution after the CME. We found an association between short-term local topological changes in CH boundaries and the formation/disappearance of bright points near them, as well as, between short-term topological changes within the whole CH and eruptions of nearby quiescent prominences followed by the appearance of one or more CMEs.