Geomagnetic Activity Conditions Research Articles

Reconstruction of geomagnetic activity and near-Earth interplanetary conditions over the past 167 yr – Part 3: Improved representation of solar cycle 11

Abstract. Svalgaard (2014) has recently pointed out that the calibration of the Helsinki magnetic observatory's H component variometer was probably in error in published data for the years 1866–1874.5 and that this makes the interdiurnal variation index based on daily means, IDV(1d), (Lockwood et al., 2013a), and the interplanetary magnetic field strength derived from it (Lockwood et al., 2013b), too low around the peak of solar cycle 11. We use data from the modern Nurmijarvi station, relatively close to the site of the original Helsinki Observatory, to confirm a 30% underestimation in this interval and hence our results are fully consistent with the correction derived by Svalgaard. We show that the best method for recalibration uses the Helsinki Ak (H) and aa indices and is accurate to ±10%. This makes it preferable to recalibration using either the sunspot number or the diurnal range of geomagnetic activity which we find to be accurate to ±20%. In the case of Helsinki data during cycle 11, the two recalibration methods produce very similar corrections which are here confirmed using newly digitised data from the nearby St Petersburg observatory and also using declination data from Helsinki. However, we show that the IDV index is, compared to later years, too similar to sunspot number before 1872, revealing independence of the two data series has been lost; either because the geomagnetic data used to compile IDV has been corrected using sunspot numbers, or vice versa, or both. We present corrected data sequences for both the IDV(1d) index and the reconstructed IMF (interplanetary magnetic field). We also analyse the relationship between the derived near-Earth IMF and the sunspot number and point out the relevance of the prior history of solar activity, in addition to the contemporaneous value, to estimating any "floor" value of the near-Earth interplanetary field.

Impact of active geomagnetic conditions on stimulated radiation during ionospheric second electron gyroharmonic heating

Recently, narrowband emissions ordered near the H+ (proton) gyrofrequency (fcH) were reported in the stimulated electromagnetic emission (SEE) spectrum during active geomagnetic conditions. This work presents new observations and theoretical analysis of these recently discovered emissions. These emission lines are observed in the stimulated electromagnetic emission (SEE) spectrum when the transmitter is tuned near the second electron gyroharmonic frequency (2fce) during recent ionospheric modification experiments at the High Frequency Active Auroral Research (HAARP) facility near Gakona, Alaska. The spectral lines are typically shifted below and above the pump wave frequency by harmonics of a frequency roughly 10% less than fcH (≈ 800 Hz) with a narrow emission bandwidth less than the O+ gyrofrequency (≈ 50 Hz). However, new observations and analysis of emission lines ordered by a frequency approximately 10% greater than fcH are presented here for the first time as well. The interaction altitude for the heating for all the observations is in the range of 160 km up to 200 km. As described previously, proton precipitation due to active geomagnetic conditions is considered as the reason for the presence of H+ ions known to be a minor background constituent in this altitude region. DMSP satellite observations over HAARP during the heating experiments and ground‐based magnetometer and riometer data validate active geomagnetic conditions. The theory of parametric decay instability in multi‐ion component plasma including H+ ions as a minority species described in previous work is expanded in light of simultaneously observed preexisting SEE features to interpret the newly reported observations. Impact of active geomagnetic conditions on the SEE spectrum as a diagnostic tool for proton precipitation event characterization is discussed.

Correction to “Oxygen and hydrogen ion abundance in the near‐Earth magnetosphere: Statistical results on the response to the geomagnetic and solar wind activity conditions”

[1] The composition of ions plays a crucial role for the fundamental plasma properties in the terrestrial magnetosphere. We investigate the oxygen-to-hydrogen ratio in the near-Earth magnetosphere from −10 RE 274 keV O+ ion intensities, relative to the corresponding hydrogen intensities; (3) In contrast to ∼10 keV ions, the >274 keV O+ions show the strongest acceleration during growth phase and not during the expansion phase itself. This suggests a connection between the energy input to the magnetosphere and the effective energization of energetic ions during growth phase; (4) The ratio between quiet and disturbed times for the intensities of ion ionospheric outflow is similar to those observed in the near-Earth magnetosphere at >274 keV. Therefore, the increase of the energetic ion intensity during disturbed time is likely due to the intensification and the effective acceleration of the ionospheric source. In conclusion, the energization process in the near-Earth magnetosphere is mass dependent and it is more effective for the heavier ions.

Reconstruction of geomagnetic activity and near-Earth interplanetary conditions over the past 167 yr – Part 2: A new reconstruction of the interplanetary magnetic field

Abstract. We present a new reconstruction of the interplanetary magnetic field (IMF, B) for 1846–2012 with a full analysis of errors, based on the homogeneously constructed IDV(1d) composite of geomagnetic activity presented in Part 1 (Lockwood et al., 2013a). Analysis of the dependence of the commonly used geomagnetic indices on solar wind parameters is presented which helps explain why annual means of interdiurnal range data, such as the new composite, depend only on the IMF with only a very weak influence of the solar wind flow speed. The best results are obtained using a polynomial (rather than a linear) fit of the form B = χ · (IDV(1d) − β)α with best-fit coefficients χ = 3.469, β = 1.393 nT, and α = 0.420. The results are contrasted with the reconstruction of the IMF since 1835 by Svalgaard and Cliver (2010).

Reconstruction of geomagnetic activity and near-Earth interplanetary conditions over the past 167 yr – Part 1: A new geomagnetic data composite

Abstract. We present a new composite of geomagnetic activity which is designed to be as homogeneous in its construction as possible. This is done by only combining data that, by virtue of the locations of the source observatories used, have similar responses to solar wind and IMF (interplanetary magnetic field) variations. This will enable us (in Part 2, Lockwood et al., 2013a) to use the new index to reconstruct the interplanetary magnetic field, B, back to 1846 with a full analysis of errors. Allowance is made for the effects of secular change in the geomagnetic field. The composite uses interdiurnal variation data from Helsinki for 1845–1890 (inclusive) and 1893–1896 and from Eskdalemuir from 1911 to the present. The gaps are filled using data from the Potsdam (1891–1892 and 1897–1907) and the nearby Seddin observatories (1908–1910) and intercalibration achieved using the Potsdam–Seddin sequence. The new index is termed IDV(1d) because it employs many of the principles of the IDV index derived by Svalgaard and Cliver (2010), inspired by the u index of Bartels (1932); however, we revert to using one-day (1d) means, as employed by Bartels, because the use of near-midnight values in IDV introduces contamination by the substorm current wedge auroral electrojet, giving noise and a dependence on solar wind speed that varies with latitude. The composite is compared with independent, early data from European-sector stations, Greenwich, St Petersburg, Parc St Maur, and Ekaterinburg, as well as the composite u index, compiled from 2–6 stations by Bartels, and the IDV index of Svalgaard and Cliver. Agreement is found to be extremely good in all cases, except two. Firstly, the Greenwich data are shown to have gradually degraded in quality until new instrumentation was installed in 1915. Secondly, we infer that the Bartels u index is increasingly unreliable before about 1886 and overestimates the solar cycle amplitude between 1872 and 1883 and this is amplified in the proxy data used before 1872. This is therefore also true of the IDV index which makes direct use of the u index values.

Five Years of Stereo Magnetospheric Imaging by TWINS

Two Wide-angle Imaging Neutral-atom Spectrometers (TWINS) is the first stereoscopic magnetospheric imager. TWINS is a NASA Explorer Mission of Opportunity performing simultaneous energetic neutral atom (ENA) imaging from two widely-separated Molniya orbits on two different spacecraft, and providing nearly continuous coverage of magnetospheric ENA emissions. The ENA imagers observe energetic neutrals produced from global ion populations, over a broad energy range (1–100 keV/u) with high angular (4∘×4∘) and time (about 1-minute) resolution. TWINS distinguishes hydrogen ENAs from oxygen ENAs. Each TWINS spacecraft also carries a Lyman-α geocoronal imager to monitor the cold exospheric hydrogen atoms that produce ENAs from ions via charge exchange. Complementing the imagers are detectors that measure the local charged particle environment around the spacecraft. During its first five years of science operations, TWINS has discovered new global properties of geospace plasmas and neutrals, fostered understanding of causal relationships, confirmed theories and predictions based on in situ data, and yielded key insights needed to improve geospace models. Analysis and modeling of TWINS data have: (1) obtained continuous (main phase through recovery) global ion spectra, (2) revealed a previously unknown local-time dependence of global pitch angle, (3) developed quantitative determination of ion fluxes from low altitude ENAs (4) determined dynamic connections between local pitch angle and global ion precipitation, (5) confirmed local-time dependence of precipitating ion temperature, (6) imaged global dynamic heating of the magnetosphere, (7) explained why the oxygen ring current survives longer into recovery than hydrogen, and (8) revealed new global exospheric density features and their influence upon ring current decay rates. Over the next several years of the solar cycle, TWINS observations of three-dimensional (3D) global ion dynamics, composition, origins and destinies are crucial to capture the system-level view of geospace over the full range of geomagnetic and solar activity conditions.

On the non‐conjugacy of nightside aurora and their generator mechanisms

AbstractWe have investigated a data set of 19 h of simultaneous global conjugate auroral imaging from space. The data set consists of 10 sequences with durations from 1 to 5 h during active geomagnetic conditions (average AE ∼ 400 nT). We have identified 15 features (including two presented earlier) of auroral forms that appear mainly in one hemisphere, and we define this as non‐conjugate aurora. Three generator mechanisms has been suggested for producing interhemispheric currents and non‐conjugate aurora: (1) Hemispherical differences in solar wind dynamo efficiency due to interplanetary magnetic field (IMF) Bx and dipole tilt angle leading to asymmetric region 1 currents in the two polar hemispheres, (2) interhemispheric currents induced by the penetration of IMF By into the closed nightside magnetosphere, and (3) hemispheric differences in ionospheric conductivity controlled by the dipole tilt angle inducing interhemispheric currents on closed field‐lines. We want to find out if our observations are consistent with these mechanisms. Our analysis shows that five features were consistent with the IMF By penetration mechanism, seven features consistent with the solar wind dynamo mechanism, three features consistent with the conductivity mechanism, and two features could not be explained by any of the three suggested mechanisms. Because two features were consistent with two different mechanisms, the numbers add up to 17 although the total number of features is 15. The analysis also shows the expected correlation between the magnitude of the longitudinal shift of conjugate points, ΔMLT, and the occurrence of non‐conjugate aurora consistent with the By mechanism.

Statistics of whistler mode waves in the outer radiation belt: Cluster STAFF‐SA measurements

AbstractELF/VLF waves play a crucial role in the dynamics of the radiation belts and are partly responsible for the main losses and the acceleration of energetic electrons. Modeling wave‐particle interactions requires detailed information of wave amplitudes and wave normal distribution over L‐shells and over magnetic latitudes for different geomagnetic activity conditions. We performed a statistical study of ELF/VLF emissions using wave measurements in the whistler frequency range for 10 years (2001–2010) aboard Cluster spacecraft. We utilized data from the STAFF‐SA experiment, which spans the frequency range from 8 Hz to 4 kHz. We present distributions of wave magnetic and electric field amplitudes and wave normal directions as functions of magnetic latitude, magnetic local time, L‐shell, and geomagnetic activity. We show that wave normals are directed approximately along the background magnetic field (with the mean value of θ—the angle between the wave normal and the background magnetic field, about 10°–15°) in the vicinity of the geomagnetic equator. The distribution changes with magnetic latitude: Plasmaspheric hiss normal angles increase with latitude to quasi‐perpendicular direction at ∼35°–40° where hiss can be reflected; lower band chorus are observed as two wave populations: One population of wave normals tends toward the resonance cone and at latitudes of around 35°–45° wave normals become nearly perpendicular to the magnetic field; the other part remains quasi‐parallel at latitudes up to 30°. The observed angular distribution is significantly different from Gaussian, and the width of the distribution increases with latitude. Due to the rapid increase of θ, the wave mode becomes quasi‐electrostatic, and the corresponding electric field increases with latitude and has a maximum near 30°. The magnetic field amplitude of the chorus in the day sector has a minimum at the magnetic equator but increases rapidly with latitude with a local maximum near 12°–15°. The wave magnetic field maximum is observed in the night sector at L>7 during low geomagnetic activity (at L∼5 for Kp>3). Our results confirm the strong dependence of wave amplitude on geomagnetic activity found in earlier studies.

Satellite reentry predictions for the Italian civil protection authorities

In just 5 months, from September 2011 to January 2012, three campaigns of reentry predictions were carried out in support of the Italian civil protection authorities. The satellites involved were UARS, ROSAT and Fobos-Grunt, which received widespread attention for the marginal risk on the ground associated with their uncontrolled reentry. From the technical point of view, the three reentry campaigns offered the occasion to compare some semi-empirical thermospheric density models under varying solar and geomagnetic activity conditions, dealing with spacecraft characterized by quite different configurations, shapes, masses and attitude control. However, what made the experience substantially different from usual reentry test campaigns was the strict interaction with the civil protection community and the public. In fact, in order to provide understandable and unambiguous information useful for civil protection planning and applications, the nominal reentry time predictions were of no use, while a particular care was devoted to the definition of appropriate reentry uncertainty windows. The attention of the civil protection authorities was focused, of course, on the Italian territory, so the relevant question for any planning was the following: given a certain uncertainty window, where and when a fragment might have crossed the national airspace and hit the ground? In order to meet this demand, during the last 3–4 days of satellite residual lifetime, reentries where simulated over Italy to obtain quite accurate ground tracks, debris swaths and air space crossing time windows associated with the critical passes over the national territory still included in the current uncertainty window. This information was updated, if needed, but remained relatively stable and accurate until the reentry, not much affected by the actual trajectory evolution due to the varying air drag. In other words, it was easy to understand for people not familiar with orbital dynamics, unambiguous and remarkably stable, all qualities that made it very useful for civil protection applications. This paper presents the work done, the information issued to the Italian authorities, the results obtained and the lesson learned during the three above mentioned campaigns. They might be of some help and offer useful insights on reentry predictions for civil protection applications if really dangerous space objects were to decay from orbit without control in the future.

A Simulation Study of the Effect of Geomagnetic Activity on the Global Circulation in the Earth’s Middle Atmosphere

To investigate how geomagnetic activity affects the formation of the large-scale global circulation of the middle atmosphere, the non-hydrostatic model of the global wind system of the Earth’s atmosphere, developed earlier in the Polar Geophysical Institute, is utilized. The model produces three-dimensional global distributions of the zonal, meridional, and vertical components of the wind velocity and neutral gas density in the troposphere, stratosphere, mesosphere, and lower thermosphere. Simulations are performed for the winter period in the northern hemisphere (16 January) and for two distinct values of geomagnetic activity (Kp = 1 and Kp = 4). The simulation results indicate that geomagnetic activity ought to influence considerably on the formation of global wind system in the stratosphere, mesosphere, and lower thermosphere. The influence on the middle atmosphere is conditioned by the vertical transport of air from the lower thermosphere to the mesosphere and stratosphere and vice versa. This transport may be rather distinct under different geomagnetic activity conditions.

New type of ensemble of quasi-periodic, long-lasting VLF emissions at the auroral zone

Abstract. A new type of the series of quasi-periodic (QP) very low frequency (VLF) emissions in frequency range of 1–5 kHz, and not associated with geomagnetic pulsations, has been discovered at auroral latitudes (L = 5.3) during the Finnish VLF campaign (held in December 2011). At least five unusually spectacular events, each with a duration of several hours, have been observed during the night under conditions of quiet geomagnetic activity (Kp = 0–1), although QPs usually occur during the daytime. Contrary to the QP emissions typically occurring during the day, the spectral structure of these QP events represented an extended, complicated sequence of repeated discrete rising VLF signals. Their duration was about 2–3 min each, with the repetition periods ranging from ~1 min to ~10 min. Two such nighttime non-typical events are reported in this paper. The fine structure of the separated QP elements may represent a mixture of the different frequency band signals, which seem to have independent origins. It was found that the periodic signals with lower frequency appear to trigger the strong dispersive upper frequency signals. The temporal dynamics of the spectral structure of the QPs studied were significantly controlled by some disturbances in the solar wind and interplanetary magnetic field (IMF). This finding is very important for future theoretical investigations because the generation mechanism of this new type of QP emissions is not yet understood.

Oxygen and hydrogen ion abundance in the near‐Earth magnetosphere: Statistical results on the response to the geomagnetic and solar wind activity conditions

The composition of ions plays a crucial role for the fundamental plasma properties in the terrestrial magnetosphere. We investigate the oxygen‐to‐hydrogen ratio in the near‐Earth magnetosphere from −10 RE < XGSE < 10 RE. The results are based on seven years of ion flux measurements in the energy range ∼10 keV to ∼955 keV from the RAPID and CIS instruments on board the Cluster satellites. We find that (1) hydrogen ions at ∼10 keV show only a slight correlation with the geomagnetic conditions and interplanetary magnetic field changes. They are best correlated with the solar wind dynamic pressure and density, which is an expected effect of the magnetospheric compression; (2) ∼10 keV O+ ion intensities are more strongly affected during disturbed phase of a geomagnetic storm or substorm than >274 keV O+ ion intensities, relative to the corresponding hydrogen intensities; (3) In contrast to ∼10 keV ions, the >274 keV O+ions show the strongest acceleration during growth phase and not during the expansion phase itself. This suggests a connection between the energy input to the magnetosphere and the effective energization of energetic ions during growth phase; (4) The ratio between quiet and disturbed times for the intensities of ion ionospheric outflow is similar to those observed in the near‐Earth magnetosphere at >274 keV. Therefore, the increase of the energetic ion intensity during disturbed time is likely due to the intensification and the effective acceleration of the ionospheric source. In conclusion, the energization process in the near‐Earth magnetosphere is mass dependent and it is more effective for the heavier ions.

Comparison between SuperDARN flow vectors and equivalent ionospheric currents from ground magnetometer arrays

Equivalent ionospheric currents obtained with the spherical elementary current systems (SECS) method and derived from nearly 100 ground magnetometers spread over North America and Greenland are compared with ionospheric flow vectors measured by the SuperDARN radars during both the summer and winter seasons. This comparison is done over a range of spatial separations, magnetic latitudes, magnetic local times, and auroral electrojet activity to investigate under what conditions the vectors are anti-parallel to one another. Our results show that in general the equivalent ionospheric currents are anti-parallel to the flows and the best results are achieved within the auroral oval during active geomagnetic conditions in the dawn, dusk and noon sectors in the northern hemisphere summer. These results indicate the best anti-parallel alignment occurs when the currents and flows are large and well defined. Factors that may influence the alignment include ionospheric conductivity gradients and quiet time backgrounds. Our results can be used to approximate the macroscopic (∼1000 km) ionospheric convection patterns. The SECS maps represent a value-added product from the raw magnetometer database and can be used for contextual interpretation; they can help with our understanding of magnetosphere-ionosphere coupling mechanisms using ground arrays and the magnetospheric spacecraft data, and they can be used as input for other techniques.

Comparison between SuperDARN flow vectors and equivalent ionospheric currents from ground magnetometer arrays

Equivalent ionospheric currents obtained with the spherical elementary current systems (SECS) method and derived from nearly 100 ground magnetometers spread over North America and Greenland are compared with ionospheric flow vectors measured by the SuperDARN radars during both the summer and winter seasons. This comparison is done over a range of spatial separations, magnetic latitudes, magnetic local times, and auroral electrojet activity to investigate under what conditions the vectors are anti‐parallel to one another. Our results show that in general the equivalent ionospheric currents are anti‐parallel to the flows and the best results are achieved within the auroral oval during active geomagnetic conditions in the dawn, dusk and noon sectors in the northern hemisphere summer. These results indicate the best anti‐parallel alignment occurs when the currents and flows are large and well defined. Factors that may influence the alignment include ionospheric conductivity gradients and quiet time backgrounds. Our results can be used to approximate the macroscopic (∼1000 km) ionospheric convection patterns. The SECS maps represent a value‐added product from the raw magnetometer database and can be used for contextual interpretation; they can help with our understanding of magnetosphere‐ionosphere coupling mechanisms using ground arrays and the magnetospheric spacecraft data, and they can be used as input for other techniques.

Modeling the properties of plasmaspheric hiss: 1. Dependence on chorus wave emission

There is increasing evidence that plasmaspheric hiss is formed by the evolution of a portion of chorus waves that are excited in the plasmatrough and propagate into the plasmasphere. Comparison between the statistical spatial distributions of these two emissions in the morning sector during active times from THEMIS over ∼3 years shows that the two emissions have comparable peak intensities but are distinct in their spatial distributions. We present a modeling study of the hiss spectrum, based on ray tracing, by taking the observed chorus source region as an input in the magnetosphere, which contains cold and suprathermal electrons. Our modeling results show that we are able to reproduce the main features of typical hiss, including the frequency spectrum, wave normal angle and spatial distribution. However, the simulated hiss intensity is weaker (∼15 dB less) than the observed intensity, which suggests some modest internal amplification inside the plasmasphere. The responses of hiss to variations in the spatial distribution, wave normal angle distribution and frequency distribution of the source chorus are examined. We find that the majority of hiss formation is due to a small portion of chorus emission originating within ∼3 RE from the plasmapause, with wave normal directions pointing toward the Earth at an angle of 30°–60°, and over a frequency range of 0.1–0.3 fce. If the chorus power is made to increase closer to the plasmapause, the hiss intensity and the peak frequency also increases, which roughly mimics active geomagnetic conditions. Variations of the chorus source distribution do not significantly affect the wave normal angle distribution and frequency distribution of hiss, but does impact the absolute intensity of the resulting hiss.

Variation of the Upper Atmospheric Density During the Quiet Period of Solar and Geomagnetic Activity (2007?2009)

在第23至第24太阳活动周的峰年之间, 太阳活动谷年具有持续时间长, 极低<em>F</em>_10.7太阳辐射通量(低至65)和超长期的零太阳黑子数记录等特点, 因此是观测和研究在这种特殊背景下热层大气变化的极好机会. 尤其是能充分理解和掌握在宁静环境下热层大气密度对弱太阳活动和小地磁扰动的响应特性. 本文利用高度650km以上星载大气密度探测器2007-2009年的连续探测数据进行分析, 结果表明, 在太阳辐射通量<em>F</em>_10.7极低值期间, 较高热层大气密度对<em>F</em>_10.7的起伏具有更显著的响应变化. 当<em>F</em>_10.7由70降至65时, 日均大气密度会有4～5倍的显著降变, 远大于通常大气模式中的降变值. 同样在<em>F</em>_10.7极低值期间, 较高热层大气密度对小地磁扰动也具有显著的响应增变, 当日Kp指数之和由23增至30时, 较高热层大气密度则会有80%～160%的强增变.

Extremely low geomagnetic activity during the recent deep solar cycle minimum

AbstractThe recent solar minimum (2008-2009) was extreme in several aspects: the sunspot number, Rz, interplanetary magnetic field (IMF) magnitude Bo and solar wind speed Vsw were the lowest during the space era. Furthermore, the variance of the IMF southward Bz component was low. As a consequence of these exceedingly low solar wind parameters, there was a minimum in the energy transfer from solar wind to the magnetosphere, and the geomagnetic activity ap index reached extremely low levels. The minimum in geomagnetic activity was delayed in relation to sunspot cycle minimum. We compare the solar wind and geomagnetic activity observed in this recent minimum with previous solar cycle values during the space era (1964-2010). Moreover, the geomagnetic activity conditions during the current minimum are compared with long term variability during the period of available geomagnetic observations. The extremely low geomagnetic activity observed in this solar minimum was previously recorded only at the end of XIX century and at the beginning of the XX century, and this might be related to the Gleissberg (80-100 years) solar cycle.

Simulation of the behavior of excited gaseous components in the atmosphere of the Earth: Hot oxygen

The existence of so-called hot oxygen in the atmosphere is substantiated by optical measurements of airglow at high altitudes. According to these observations, nonthermal oxygen concentration is maximum at an altitude of about 550 km, and its temperature is ∼4000 K. The presence of these atoms in the thermosphere causes changes in the thermodynamic conditions in the upper atmosphere of the Earth. In this work, we calculated the global distributions of hot oxygen concentrations and temperature using the Global Self-Consistent Model of Thermosphere, Ionosphere, and Protonosphere of the Earth (GSM TIP) taking into account the main photochemical and dynamic processes. Calculations were performed for moderate solar and geomagnetic activity and winter conditions of January, 2003. The hot oxygen maximum was located in latitude 60° South and at longitude 300° at 24 UT, and its temperature was ∼1500 K. This increased the general temperature of the atmosphere by 100 K in the daytime and 70 K at night. Changes in the speed of neutral gas reached 36 m/s.

A modeling study offoF2andhmF2parameters measured by the Arecibo incoherent scatter radar and comparison with IRI model predictions for solar cycles 21, 22, and 23

[1] This work presents the results of a local empirical model that describes the behavior of the ionospheric F2 region peak. The model was developed using nearly 25 years of incoherent scatter radar (ISR) measurements made at the Arecibo Observatory (AO) between 1985 and 2009. The model describes the variability of the F2 peak frequency (foF2) and F2 peak height (hmF2) as a function of local time, season, and solar activity for quiet-to-moderate geomagnetic activity conditions (Kp < 4+). Our results show that the solar activity control of hmF2 and foF2 over Arecibo can be better described by a new proxy of the solar flux (F107P), which is presented here. The variation of hmF2 parameter with F107P is virtually linear, and only a small saturation of the foF2 parameter is observed at the highest levels of solar flux. The winter anomaly and asymmetries in the variation of the modeled parameters between equinoxes were detected during the analyses and have been taken into account by the AO model. Comparisons of ISR data with international reference ionosphere (IRI) model predictions indicate that both CCIR and URSI modes overestimate foF2 during the daytime and underestimate it at night. As expected, this underestimation is not observed in the AO model. Our analyses also show that the hmF2 parameter predicted by the IRI modes shows a saturation point, which causes hmF2 to be underestimated at high solar activity. The underestimation increases with higher levels of solar activity. Finally, we also found that IRI predictions of the seasonal variability of foF2 and hmF2 over Arecibo can be improved by using a small correction that varies with solar activity and local time.

Forecast assessment of topside spread F at Jicamarca

The Jicamarca Unattended Long Term Investigations of the Ionosphere and Atmosphere (JULIA) radar operated from August 1996 through the present time, making a total of approximately 1500 nights of ionospheric irregularities associated with equatorial spread F (ESF) observations under different seasons, solar flux levels, and geomagnetic conditions. The climatology, persistence, and correlation with the phase of the Moon of premidnight and postmidnight irregularities are evaluated, and different forecasting tools are compared. During equinox, 1 day persistence information improves the forecast over climatology alone for most solar flux and geomagnetic activity conditions, with a significant improvement during periods at low solar flux. December solstice ESF observations show a high correlation with the lunar phase, with periods close to the full Moon presenting the highest probability of ESF occurrence. Using this information for geomagnetically quiet periods during December solstice, we further improve the forecast over the climatological model. For postmidnight and premidnight June solstice ESF, however, climatology still gives the best forecasting results.