Solar Flux Units Research Articles

Changes in solar quiet magnetic variations since the Maunder Minimum: A comparison of historical observations and model simulations

AbstractMagnetic measurements going back to the eighteenth century offer a unique opportunity to study multicentennial changes in the upper atmosphere. We analyzed measurements from Rome and Mannheim from May 1782 to May 1783 and measurements from Greenwich, St. Helena, Cape of Good Hope, and Singapore from May 1841 to May 1842. A comparison of the daily magnetic variations in these historical data with modern‐day observations from 2010 at nearby stations (where available) showed notable differences in the amplitude and/or phase of the X and Y components. Model simulations indicated that these can be explained at least to some extent by changes in the Earth's main magnetic field. Changes in the main field strength and the northwestward movement of the magnetic equator, in particular in the region of the South Atlantic Anomaly, have caused changes in the positioning, shape, and strength of the equivalent current vortices in the ionosphere that result in the magnetic perturbations on the ground. Differences in solar activity between the historical and modern epochs, which were all near solar minima, were too small to have a notable effect on the ground magnetic perturbations. However, in regions where main magnetic field changes have been relatively small for the last ~400 years, e.g., in Singapore, the effects of a long‐term increase in solar activity from Maunder Minimum conditions to normal solar minimum conditions (an increase in F10.7 of ~35 solar flux units) were comparable to the effects of geomagnetic main field changes.

Ozone and temperature decadal responses to solar variability in the stratosphere and lower mesosphere, based on measurements from SABER on TIMED

Abstract. We have derived ozone and temperature responses to solar variability over a solar cycle, from 2002 to 2014 at 20–60 km and 48° S–48° N, based on data from the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on the Thermosphere–Ionosphere–Mesosphere Energetics and Dynamics (TIMED) satellite. Simultaneous results for ozone and temperature with this kind of spatial coverage have not been previously available, and they provide the opportunity to study correlations between ozone and temperature responses. In previous studies, there has not been general agreement on the details or, at times, even the broad behavior of the responses to decadal solar variability. New results from a different dataset should supply new information on this important and interesting subject. A multiple regression is applied to obtain responses as a function of the solar 10.7 cm flux. Positive responses mean that they are larger at solar maximum than at solar minimum of the solar cycle. Both ozone and temperature responses are found be positive or negative, depending on location. Generally, from ∼ 25 to 60 km, the ozone and temperature responses are mostly out of phase (negatively correlated) with each other as a function of solar variability, with some exceptions in the lower altitudes. These negative correlations are maintained even though the individual ozone (temperature) responses can change signs as a function of altitude and latitude, because the corresponding temperature (ozone) responses change signs in step with each other. From ∼ 50 to 60 km, ozone responses are relatively small, varying from ∼ −1 to ∼ 2 % 100 sfu−1 (solar flux units), while temperature responses can approach ∼ 2 °K 100 sfu−1. From ∼ 25 to ∼ 40 km, the ozone responses have become mostly positive at all latitudes and approach a maximum of ∼ 5 % 100 sfu−1 near the Equator and ∼ 30–35 km. In contrast, at low latitudes, the temperature responses have become negative but also reach a local maximum (near 32 km) in magnitude. The ozone and temperature responses remain mostly out of phase, with isolated exceptions at midlatitudes between ∼ 25 and 45 km. The general negative correlations are consistent with the idea that photochemistry is more in control in the upper stratosphere and lower mesosphere. The correlation coefficients between the solar 10.7 cm flux and the ozone and temperature themselves from 2002 to 2014 are positive (negative) in regions where the responses are positive (negative). This supports our results since the correlations are independent of the multiple regression used to derive the responses. We also compare with previous results.

Long-term (2004–2015) tendencies and variabilities of tropical UTLS water vapor mixing ratio and temperature observed by AURA/MLS using multivariate regression analysis

Long-term variabilities and tendencies in the tropical (30°N–30°S)monthly averaged zonal mean water vapor mixing ratio (WVMR) and temperature in the upper troposphere and lower stratosphere (UTLS), obtained from the Microwave Limb Sounder (MLS) instrument onboard Earth Observing System (EOS) satellite for the period October 2004-September 2015, are studied using multivariate regression analysis. It is found that the WVMR shows a decreasing trend of 0.02–0.1ppmv/year in WVMR below 100hPa while the trend is positive (0.02–0.035ppmv/year) above 100hPa. There is no significant trend at 121hPa. The WVMR response to solar cycle (SC) is negative below 21hPa. However, the magnitude decreases with height from 0.13ppmv/100sfu(solar flux unit) at 178hPa to 0.07ppmv/100sfuat 26hPa. The response of WVMR to multivariate El Niño index (MEI), which is a proxy for El Niño Southern Oscillation (ENSO), is positive at and below 100hPa and negative above 100hPa. It is negative at 56–46hPa with maximum value of 0.1ppmv/MEI at 56hPa. Large positive (negative) quasi-biennial oscillation (QBO) in WVMR at 56–68hPa reconstructed from the regression analysis coincide with eastward (westward) to westward (eastward) transition of QBO winds at that level. The trend in zonal mean tropical temperature is negative above 56hPa with magnitude increasing with height. The maximum negative trend of 0.05K/year is observed at 21–17hPa and the trend insignificant around tropopause. The response of temperature to SC is negative in the UTLS region and to ENSO is positive below 100hPa and mostly negative above 100hPa. The negative response of WVMR to MEI in the stratosphere is suggested to be due to the extended cold trap of tropopause temperature during El Niño years that might have controlled the water vapor entry into the stratosphere. The WVMR response to residual vertical velocity at 70hPa is positive in the stratosphere, whereas the temperature response is positive in the UTLS region and negative above 56hPa. Besides, the interannual variability and the response of the WVMR to the different parameters are explained based on the response of temperature at 100hPa (proxy for tropopause) to those parameters.

The response of the temperature of cold‐point mesopause to solar activity based on SABER data set

AbstractThe thermal structure and energy balance of upper atmosphere are dominated by solar activity. The response of cold‐point mesopause (CPM) to solar activity is an important form. This article presents the response of the temperature of CPM (T‐CPM) to solar activity using 14 year Sounding of the Atmosphere using Broadband Emission Radiometry data series over 80°S–80°N regions. These regions are divided into 16 latitude zones with 10° interval, and the spatial areas of 80°S–80°N, 180°W–180°E are divided into 96 lattices with 10°(latitude) × 60°(longitude) grid. The annual‐mean values of T‐CPM and F10.7 are calculated. The least squares regression method and correlation analysis are applied to these annual‐mean series. First, the results show that the global T‐CPM is significantly correlated to solar activity at the 0.05 level of significance with correlation coefficient of 0.90. The global solar response of T‐CPM is 4.89 ± 0.67 K/100 solar flux unit. Then, for each latitude zone, the solar response of T‐CPM and its fluctuation are obtained. The solar response of T‐CPM becomes stronger with increasing latitude. The fluctuation ranges of solar response at middle‐latitude regions are smaller than those of the equator and high‐latitude regions, and the global distribution takes on W shape. The corelationship analysis shows that the T‐CPM is significantly correlated to solar activity at the 0.05 level of significance for each latitude zone. The correlation coefficients at middle‐latitude regions are higher than those of the equator and high‐latitude regions, and the global distribution takes on M shape. At last, for each grid cell, the response of T‐CPM to solar activity and their correlation coefficient are presented.

Solar activity variations of nocturnal thermospheric meridional winds over Indian longitude sector

The night time F-layer base height information from ionosondes located at two equatorial stations Trivandrum (TRV 8.5°N, 77°E) and Sriharikota (SHAR 13.7°N, 80.2°E) spanning over two decades are used to derive the climatology of equatorial nocturnal Thermospheric Meridional Winds (TMWs) prevailing during High Solar Activity (HSA) and Low Solar Activity (LSA) epochs. The important inferences from the analysis are 1) Increase in mean equatorward winds observed during LSA compared to HSA during pre midnight hours; 25m/s for VE (Vernal Equinox) and 20m/s for SS (Summer Solstice), AE (autumnal Equinox) and WS (Winter Solstice). 2) Mean wind response to Solar Flux Unit (SFU) is established quantitatively for all seasons for pre-midnight hours; rate of increase is 0.25m/s/SFU for VE, 0.2m/s/SFU for SS and WS and 0.08m/s/SFU for AE. 3) Theoretical estimates of winds for the two epochs are performed and indicate the role of ion drag forcing as a major factor influencing TMWs. 4) Observed magnitude of winds and rate of flux dependencies are compared to thermospheric wind models. 5) Equinoctial asymmetry in TMWs is observed for HSA at certain times, with more equatorward winds during AE. These observations lend a potential to parameterize the wind components and effectively model the winds, catering to solar activity variations.

Solar activity dependence of nightside aurora in winter conditions

AbstractThe dependence of the nightside (21:00–03:00 MLT; magnetic local time) auroral energy flux on solar activity was quantitatively studied for winter/dark and geomagnetically quiet conditions. Using data combined from Thermosphere, Ionosphere, Mesosphere Energetics and Dynamics/Global Ultraviolet Imager and Defense Meteorological Satellite Program/Special Sensor Ultraviolet Spectrographic Imager observations, we separated the effects of geomagnetic activity from those of solar flux on the nightside auroral precipitation. The results showed that the nightside auroral power was reduced by ~42% in solar maximum (F10.7 = 200 sfu; solar flux unit 1 sfu = 10−22 W m−2 Hz−1) with respect to that under solar minimum (F10.7 = 70 sfu) for the Kp = 1 condition, and this change rate became less (~21%) for the Kp = 3 condition. In addition, the solar cycle dependence of nightside auroral power was similar with that from both the premidnight (21:00–23:00 MLT) and postmidnight (01:00–03:00 MLT) sectors. These results indicated that as the ionospheric ionization increases with the enhanced auroral and geomagnetic activities, the solar activity dependences of nightside auroral power become weaker, at least under geomagnetically quiet conditions.

The responses of the nightglow emissions observed by the TIMED/SABER satellite to solar radiation

AbstractThe responses of four nightglow emissions, NO emission at 5.3 µm, O2 infrared atmospheric band at 1.27 µm, and OH emissions at 2.0 µm and 1.6 µm (referred to as OH2 and OH1 in this study), to solar radiation are studied and compared based on the data observed by the Sounding of the Atmosphere using Broadband Emission Radiometry instrument over 13 years. The quantitative relationships between the nightglow emissions and solar radiation are obtained by a linear regression fit using the F10.7 index. The intensities and the peak heights of the 13 year average global mean NO, O2, OH2, and OH1 nightglows are 270.0 ± 42.8 kR, 106.9 ± 2.2 kR, 133.2 ± 1.6 kR, 217.5 ± 2.4 kR, 123.6 ± 0.2 km, 89.8 ± 0.05 km, 88.1 ± 0.02 km, and 86.6 ± 0.02 km, respectively. Among the four nightglow emissions, the influence of solar radiation on the ones at lower heights is weaker than the ones higher above. The responses of the global mean NO, O2, OH2, and OH1 nightglow intensities to solar radiation are 176.3 ± 4.8%/100 solar flux units (sfu), 22.2 ± 1.4%/100 sfu, 12.9 ± 1.1%/100 sfu, and 11.4 ± 1.3%/100 sfu, respectively. The intensities and peak emission rates of the four global mean nightglow emissions are highly correlated to solar radiation. The response of the height of the global mean O2 nightglow peak emission rate to solar radiation is 0.51 ± 0.08 km/100 sfu. The responses of NO, OH2, and OH1 nightglow peak heights to solar radiation are not obvious. In addition, the responses of nightglow emissions to solar radiation change with latitude.

Ozone and temperature decadal responses to solar variability in the mesosphere and lower thermosphere, based on measurements from SABER on TIMED

Abstract. We have derived ozone and temperature responses to solar variability over a solar cycle, from June 2002 through June 2014, 50 to 100 km, 48° S to 48° N, based on data from the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on the Thermosphere-Ionosphere-Mesosphere-Energetics and Dynamics (TIMED) satellite. Results with this extent of coverage in the mesosphere and lower thermosphere have not been available previously. A multiple regression is applied to obtain responses as a function of the solar 10.7 cm flux (solar flux units, sfu). Positive responses mean that they are larger at solar maximum than at solar minimum of the solar cycle. From ∼ 80 to 100 km, both ozone and temperature responses are positive for all latitudes and are larger than those at lower altitudes. From ∼ 80 to 100 km, ozone responses can exceed 10 % (100 sfu)−1, and temperature responses can approach 4 °K. From 50 to ∼ 80 km, the ozone responses at low latitudes ( ∼ ±35°) are mostly negative and can approach ∼ negative 3 % (100 sfu)−1. However, they are mostly positive at midlatitudes in this region and can approach ∼ 2 % (100 sfu)−1. In contrast to ozone, from ∼ 50 to 80 km, the temperature responses at low latitudes remain positive, with values up to ∼ 2.5 K (100 sfu)−1, but are weakly negative at midlatitudes. Consequently, there is a systematic and robust relation between the phases of the ozone and temperature responses. They are positively correlated (in phase) from ∼ 80 to 100 km for all latitudes and negatively correlated (out of phase) from ∼ 50 to 80 km, also for all latitudes. The negative correlation from 50 to 80 km is maintained even though the ozone and temperature responses can change signs as a function of altitude and latitude, because the corresponding temperature responses change signs in step with ozone. This is consistent with the idea that dynamics have the larger influence between ∼ 80 and 100 km, while photochemistry is more in control from ∼ 50 to 75 km. The correlation coefficients between the solar 10.7 cm flux and the ozone and temperature themselves from 2012 to 2014 are positive (negative) in regions where the responses are positive (negative). This supports our results since the correlations are independent of the multiple regression used to derive the responses. We also compare with previous results.

Investigating the performance of simplified neutral‐ion collisional heating rate in a global IT model

AbstractThe Joule heating rate has usually been used as an approximate form of the neutral‐ion collisional heating rate in the thermospheric energy equation in global thermosphere‐ionosphere models. This means that the energy coupling has ignored the energy gained by the ions from collisions with electrons. It was found that the globally averaged thermospheric temperature (Tn) was underestimated in simulations using the Joule heating rate, by about 11% when F10.7=110 solar flux unit (sfu, 1 sfu = 10−22 W m−2 Hz−1) in a quiet geomagnetic condition. The underestimation of Tn was higher at low latitudes than high latitudes, and higher at F region altitudes than at E region altitudes. It was found that adding additional neutral photoelectron heating in a global IT model compensated for the underestimation of Tn using the Joule heating approximation. Adding direct photoelectron heating to the neutrals compensated for the indirect path for the energy that flows from the electrons to the ions then to the neutrals naturally and therefore was an adequate compensation over the dayside. There was a slight dependence of the underestimation of Tn on F10.7, such that larger activity levels resulted in a need for more compensation in direct photoelectron heating to the neutrals to make up for the neglected indirect heating through ions and electrons.

A new topside profiler based on Alouette/ISIS topside sounding

A new empirical model of the topside ionospheric density was developed to describe the measured topside profile accurately. This profiler is a composite of two separate layers of different ion species in the topside ionosphere, the O+ layer and the light-ions (H+ and He+) layer. The light-ions layer is characterized by an α-Chapman function with a linearly increasing scale height with altitude. This new model appears to perform the best as compared to five other typical topside profilers in representing data from ISIS-1&2 and Alouette-1&2 observations. We also analyzed the magnetic latitude dependence, seasonal variation, and day–night difference of the characteristic parameters of the light-ions layer during the magnetic quiet (Kp<4) and low solar activity (f107<120 solar flux unit, sfu) period within magnetic latitudes from −60° to 90°. The statistical results show the expected different behaviors of light-ions and O+ parameters. In addition, the portion of the light-ion components contributing to the topside-ionospheric total electron content (TTEC) was studied also. The results suggest that the light ions make a great contribution to the TTEC, especially in magnetic low- and middle-latitudes at night.

Climatologies of nighttime thermospheric winds and temperatures from Fabry‐Perot interferometer measurements: From solar minimum to solar maximum

AbstractWe present a climatology of quiet time thermospheric winds and temperatures estimated from high‐resolution Fabry‐Perot interferometer measurements of the 630.0 nm airglow emission spectral line shape. Three locations are examined in this long‐term study: northeastern Brazil (August 2009 to August 2014), a midlatitude site in North Carolina, USA (June 2011 to December 2014), and a midlatitude site in Morocco (November 2013 to December 2014). We discuss the day‐to‐day, seasonal, and solar cycle trends and variations of thermospheric meridional winds, zonal winds, neutral temperatures, and for the first time vertical winds. Observations made from solar minimum to solar maximum (with F10.7 values ranging from ∼70 to ∼159 solar flux units) confirm that neutral temperatures have a strong solar cycle dependence. However, this data set shows that the neutral winds are more closely tied to the seasonal variation, rather than the solar cycle. We also present comparisons between the two midlatitude sites and include neutral wind comparisons to the updated Horizontal Wind Model 14.

Bright 30 THz impulsive solar bursts

AbstractImpulsive 30 THz continuum bursts have been recently observed in solar flares, utilizing small telescopes with a unique and relatively simple optical setup concept. The most intense burst was observed together with a GOES X2 class event on 27 October 2014, also detected at two subterahertz (sub‐THz) frequencies, Reuven Ramaty High Energy Solar Spectroscopic Imager X‐rays and Solar Dynamics Observatory/Helioseismic and Magnetic Imager and EUV. It exhibits strikingly good correlation in time and in space with white‐light flare emission. It is likely that this association may prove to be very common. All three 30 THz events recently observed exhibited intense fluxes in the range of 104 solar flux units, considerably larger than those measured for the same events at microwave and submillimeter wavelengths. The 30 THz burst emission might be part of the same spectral burst component found at sub‐THz frequencies. The 30 THz solar bursts open a promising new window for the study of flares at their origin.

Unique latitudinal shape of ion upper transition height (HT) surface during deep solar minimum (2008–2009)

AbstractThe ionospheric upper transition height (HT) is found to increase dramatically by ~100 km from 2008–2009 to 2010 only for a marginal increase in solar activity (F10.7) by 11.76 solar flux units. The latitudinal variation of HT surface during 2008–2009 period exhibits a local minimum at equatorial latitudes and increase at low latitudes. Further, the HT at equatorial latitudes exhibits slower rate of increase than at low latitudes. These interesting features are new and different from those reported in literature. A quick loss of O+ and increase in H+ ions are observed around ~550 to 650 km indicating that the charge exchange reaction is responsible for the slower rate of increase and lowered HT at equatorial latitudes. These new aspects of HT are more conspicuously observed during this deep solar minimum period where the resonant charge exchange reaction is taking place at altitudes as low as ~550 km.

Annual Fluctuations (~10&amp;lt;sup&amp;gt;-12&amp;lt;/sup&amp;gt; W•m&amp;lt;sup&amp;gt;-2&amp;lt;/sup&amp;gt;) in Ground Level Photon Power Densities: Quantitative Evidence for Possible Modulation From the Galactic Center

The numbers of photons per second for more than a year (2013-2014) recorded every ~2.5 s by a digital photomultiplier unit was maximum during August to October and minimum during February through April. The peak-to-peak difference in quantity for the classical, smooth variation was 2.4 x 10-12 W m-2. This value is within the order of magnitude for a photon source from the galactic center with a power of 1059 J from a spherical surface with a radius defined for a singularity that could be equivalent to the galactic mass. The calculated change in photon flux density from such a source for the annual change in the earth’s distance around the sun relative to the distance to galactic center was ~10-21 W m-2 or equivalent to 10 Solar Flux Units (SFU). Data obtained for daily SFU for the years 2009 through 2013 indicated that an average difference was 8 to 10 SFU higher for September-October when the earth would be closer to the galactic center than March-April. The most likely source of the amplitude of the annual variation is consistent with modification by the earth’s position in the solar mass field with respect to the galactic center. These data suggest that at least a subset set of background photon emissions on the earth’s surface display a clear annual variation whose source could originate from a singularity at the distance of the center of the Milky Way.

Performance assessment of GPS receivers during the September 24, 2011 solar radio burst event

The sudden outburst of in-band solar radio noise from the Sun is recognized as one of the potential Radio Frequency Interference (RFI) sources that directly impact the performance of Global Navigation Satellite System (GNSS) receivers. On September 24, 2011, the solar active region 1302 unleashed a moderate M7.1 soft X-ray flare associated with a very powerful radio burst at 1415 MHz. The Solar Radio Burst (SRB) event spanned over three distinct episodes of solar radio noise emission that reached the maximum radio flux density of 114,144 Solar Flux Units (SFU) at 13:04:46 UTC. This paper analyzes the impact of September 24, 2011 SRB event on the performance of a significant subset of NAVSTAR Global Positioning System (GPS) receivers located in the sunlit hemisphere. The performance assessment is carried out in terms of Carrier-to-Noise power spectral density ratio (C /N 0 ) degradation, dual-frequency pseudorange measurements availability, pseudorange residual errors, and dual-frequency positioning errors in the horizontal and vertical dimensions. We observed that during the SRB event the GPS C /N 0 is reduced at most by 13 dB on L1 and 24 dB on L2. The C /N 0 degradation caused the loss of lock on GPS L1 and L2 signals and significant code-tracking errors. We noticed that many stations experienced less than four satellite measurements, which are the minimum required number of measurements for position estimation. The deteriorated satellite-receiver geometry due to loss of signal lock and significant code-tracking errors during the solar radio burst event introduced large positioning errors in both the horizontal and vertical dimensions. Rise in vertical positioning error of 303 m and rise in horizontal positioning of 55 m could be noticed during the solar radio burst event.

Solar cycle variation of plasma mass density in the outer magnetosphere: Magnetoseismic analysis of toroidal standing Alfvén waves detected by Geotail

AbstractWe study the variation of plasma mass density in the outer magnetosphere over a solar cycle using mass density estimated from the frequency of fundamental toroidal standing Alfvén waves observed by the Geotail spacecraft. We identify wave events using ion bulk velocity data covering 1995–2006 and use events in the 0400–0800 magnetic local time sector for statistical analysis. We find that the F10.7 index is a dominant controlling factor of the mass density. For the equatorial mass density that is normalized to the value at L = 11, we obtain an empirical formula , where the units of and F10.7 are amu cm−3 and solar flux units (sfu; 1 sfu =10−22 W m−2 Hz−1), respectively. This formula indicates that changes by a factor of 1.8, if F10.7 changes from 70 sfu (solar minimum) to 210 sfu (solar maximum). A formula derived in a similar manner using GOES magnetometer data indicates that, for the same range of F10.7, the mass density at L ∼ 7 varies by a factor of 4.1 We attribute the smaller factor at L = 11 to the lower O+/H+ number density ratio at higher L, the stronger F10.7 dependence of the O+ outflow rate than the H+ outflow rate, and entry of solar wind H+ ions to the outer magnetosphere.

Solar cycle dependence of middle atmosphere temperatures

AbstractSounding of the Atmosphere using Broadband Emission Radiometry (SABER) temperature data during 2002 through 2013 and covering 20–110 km altitude between ±83° latitude are analyzed to determine the dependence of middle atmosphere temperatures on solar flux, as parameterized by a linear relation with 81 day mean values of the 10.7 cm solar radio flux, F10.7a. The basic data analyzed are 60 day mean values, which represent zonal and local‐time means. Analysis is conducted on both fixed altitude and fixed pressure levels. Below 70 km, the sensitivity of SABER annual mean temperatures is of order 1–2 K per 100 solar flux units (100 sfu) when data are analyzed on fixed altitude levels. At 85 km this increases to 3–6 K/100 sfu between ±60°latitude. At 95 km, values of order 4–6 K/100 sfu are found over the latitude range ±50° with values of order 10–14 K/100 sfu at higher latitudes in both hemispheres; these values increase to 5–11 K/100 sfu and 13–29 K/100 sfu, respectively, at 105 km. Comparisons are made with similarly analyzed temperatures from the National Center for Atmospheric Research Whole Atmosphere Community Climate Model (WACCM). At 85 km, the WACCM response is similar to observed but above that level WACCM predicts a lower response by a factor of about 2 at 95 km. On the other hand, below 70 km, the sensitivity of WACCM annual mean temperatures is stronger than SABER (∼3 K/100 sfu). When analysis is instead performed on pressure levels, the response in the lower thermosphere increases, especially at 105 km where changes of 29 to 51 K/100 sfu are seen in SABER annual mean temperatures.

Long‐term trends and the effect of solar cycle variations on mesospheric winter temperatures over Longyearbyen, Svalbard (78°N)

AbstractThis paper gives an update on the long‐term trend in hydroxyl (OH*) airglow winter temperatures measured by a 1 m Ebert‐Fastie spectrometer in Longyearbyen, Svalbard (78°N, 16°E), from 1983 to 2013. The temperatures are derived through synthetic fits of measured airglow spectra of the OH*(6‐2) vibrational state. The data set is corrected for seasonal variations by subtracting the mean climatology. Also, solar cycle dependence is investigated. A solar response coefficient of 3.6 K ± 4.0 K/100 solar flux units (SFU) is calculated from F10.7 cm solar radio flux data. After subtraction of the climatology and solar response, the remaining long‐term trend is a near‐zero trend, −0.2 K ± 0.5 K/decade. Trend analysis of monthly temperatures indicates positive trends for November, January, and February and a negative trend for December, but the uncertainties are high.

THz photometers for solar flare observations from space

Fil: Kaufmann, Pierre. Universidade Estadual de Campinas; Brasil. Universidade Presbiteriana Mackenzie; Brasil

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.