The total ozone and UV solar radiation over Stara Zagora,Bulgaria

The results from direct ground-based solar UV irradiance measurements and the total ozone content (TOC) over Stara Zagora (42° 25′N, 25° 37′E), Bulgaria are presented. During the period 1999–2003 the TOC data show seasonal variations, typical for the middle latitudes – maximum in the spring and minimum in the autumn. The comparison between TOC ground-based data and Global Ozone Monitoring Experiment (GOME) satellite-borne ones shows a seasonal dependence of the differences between them.A strong negative relationship between the total ozone and the 305 nm wavelength irradiance was found. The dependence between the two variables is significant (r = −0.62 ± 0.18) at 98% confidence level.The direct sun UV doses for some specific biological effects (erythema and eyes) are obtained. The estimation of the radiation amplification factor RAF shows that the ozone reduction by 1% increases the erythemal dose by 2.3%. The eye-damaging doses are more influenced by the TOC changes and in this case RAF = −2.7%.The amount of these biological doses depended on the solar altitude over the horizon. This dependence was not so strong when the total ozone content in the atmosphere was lower.     

Centre-to-limb variation of photospheric facular radiance and image resolution

We study the effect of the angular resolution on the determination of the angular properties of the facular radiance. We analyze photospheric intensity in the continuum, around the Ni 676.8 nm line, and longitudinal magnetic field along the line of sight, measured by the MDI instrument aboard SOHO with two spatial resolutions, 4″ and 1.2″ (2″ and 0.6″ pixels, respectively). The effect of the limited photometric sensitivity of the instrument and the limited information on the angular structure of the magnetic field tubes are considered. Our study of the high-resolution data shows that intensity contrast of magnetic features between 80 and 600 Gauss increases from centre to limb up to a maximum that occurs at higher heliocentric angles (θ) when obtained with higher resolution data than for lower resolution data. There is a suggestion that at heliocentric angles below about 75° there is only a monotonic increase in the contrast as one goes from cos (θ) = 1 to cos (θ) = 0.2.     

On solar 5.7 GHz subsecond burst source sizes

Due to the narrow bandwidth and the small size of the subsecond microwave pulses, we can use them as probe sources for study of propagation effects in the low corona. More than 160 microwave bursts with subsecond pulses (SSP) have been observed with the Siberian Solar Radio Telescope at 5.7 CHz for the period 2000–2004. Working with a large dataset of homogeneous observational material (spatial resolution from 15″ to 20″, temporal resolution 14 mc), we estimated sizes of SSP and studied relation between SSP sizes and sense of the polarization and their position on the Sun. Our results are in accordance with those obtained during the 22nd solar cycle. The apparent sizes of SSP increase toward the solar limb. The obtained dependence is in agreement with Bastian‘s (Bastian, T.S. Angular scattering of solar radio emission by coronal turbulence. ApJ 426, 774, 1994.) model calculations. The center-to-limb variation of the source size is explained by scattering on plasma turbulence along the ray path in the solar corona. The most events with high polarization occur near the central meridian (±30°). The polarization sense corresponds mainly to the ordinary mode.     

Ground-based measurement of strato–mesospheric CO by a FTIR spectrometer over Poker Flat,Alaska

Upper atmospheric CO above 24 km has been observed over Poker Flat (147°W, 65°N, altitude 0.61 km), Alaska using ground-based solar absorption infrared spectroscopy. This is the first reported detection of stratospheric–mesospheric CO using this method from the ground. The results clearly indicate that there is a seasonal variation of the CO profile with enhanced abundances in spring while remaining low from May onwards.The Poker Flat Research Range is one of the many measurement sites that constitute the Network for the Detection of Stratospheric Change (NDSC). The method used in this work, estimating the CO partial column abundances above the middle stratosphere, can be applied to spectra observed using FTIR spectrometry at many other NDSC sites. This suggests the availability of this established technique as a new method for CO measurements in the upper atmosphere.     

Optical properties of dust and the opacity of the Martian atmosphere

Particulate component of the Mars atmosphere composed by micron-sized products of soil weathering and water ice clouds strongly affects the current climate of the planet. In the absence of a dust storm so-called permanent dust haze with τ ≈ 0.2 in the atmosphere of Mars determines its thermal structure. Dust loading varies substantially with the season and geographic location, and only the data of mapping instruments are adequate to characterize it, such as TES/MGS and IRTM/Viking. In spite of vast domain of collected data, no model is now capable to explain all observed spectral features of dust aerosol. Several mineralogical and microphysical models of the atmospheric dust have been proposed but they cannot explain the pronounced systematic differences between the IR data (τ = 0.05–0.2) and measurements from the surface (Viking landers, Pathfinder) which give the typical “clear” optical depth of τ ≈ 0.5 from one side, and ground-based observations in the UV–visible range showing much more transparent atmosphere, on the other side. Also the relationship between τ₉ and the visible optical depth is not well constrained experimentally so far. Future focused measurements are therefore necessary to study Martian aerosol.     

Brazilian Decimetre Array (Phase-1): Initial solar observations

An East–West one-dimensional radio interferometer array consisting of 5 parabolic dish antennas has been set-up at Cachoeira Paulista, Brazil (Longitude: 45°0′20″W, Latitude: 22°41′19″S) for observations of Sun and some of the strong sidereal sources by the Instituto Nacional de Pesquisas Espaciais (INPE), Brazil. This is Phase-1 of the proposed Brazilian Decimetre Array (BDA) and can be operated at any frequency in the range 1.2–1.7 GHz. The instrument is functional since November 2004 onwards at 1.6 GHz. The angular and temporal resolution at the above frequency range are ∼3′ and 100 ms, respectively. We present here the initial solar observations carried out with this array.     

A spectroscopic measurement of high velocity spray plasma from an M-class flare and coronal mass ejection

The M1.5-class flare and associated coronal mass ejection (CME) of 16 February 2011 was observed with the Extreme ultraviolet Imaging Spectrometer on board the Hinode spacecraft. Spray plasma associated with the CME is found to exhibit a Doppler blue-shift of 850 km s^?1 – one of the largest values reported from spectroscopy of the solar disk and inner corona. The observation is unusual in that the emission line (Fe xii 193.51 Å) is not observed directly, but the Doppler shift is so large that the blue-shifted component appears in a wavelength window at 192.82 Å, intended to observe lines of O v, Fe xi and Ca xvii. The Fe xii 195.12 Å emission line is used as a proxy for the rest component of 193.51 Å. The observation highlights the risks of using narrow wavelength windows for spectrometer observations when observing highly-dynamic solar phenomena. The consequences of large Doppler shifts for ultraviolet solar spectrometers, including the upcoming Multi-slit Solar Explorer (MUSE) mission, are discussed.     

On the 27-day variations of the galactic cosmic ray anisotropy and intensity for different periods of solar magnetic cycle

The average amplitude of the 27-day variation of the galactic cosmic ray anisotropy calculated based on the neutron monitors experimental data is larger in the qA > 0 period than in the qA < 0 period of solar magnetic cycle. The amplitudes of the 27-day variation of the galactic cosmic rays anisotropy do not depend on the tilt angles of the heliospheric neutral sheet for different the qA > 0 and the qA < 0 periods of solar magnetic cycle. A good correlation has been revealed between the changes of the amplitudes of the 27-day variations of the galactic cosmic ray anisotropy and intensity versus the qA > 0 and the qA < 0 periods of solar magnetic cycle.     

Evaluation of solar proton spectra using balloon cosmic ray observations and Monte Carlo simulation results

We have developed a method to evaluate the spectrum of solar energetic protons at the top of the Earth’s atmosphere from the measurements of our balloon cosmic ray experiment. By using the Monte Carlo PLANETOCOSMICS code based on Geant4 we compute the interaction of solar protons [10 MeV–10 GeV] with the Earth’s atmosphere. We obtain the angular and energy distributions of secondary particles (p, e⁻, e⁺, photons, muons) at different atmospheric levels as a function of primary proton spectra. By comparing the calculated depth dependence of the particle flux with the data obtained by our balloon experiment we can deduce the parameters of the solar proton spectrum that best fit the observations. In this paper we discuss our solar proton spectrum estimation method, and present results of its application to selected solar proton events from 2001 to 2005.     

Global MGS TES data and Mars-GRAM validation

Mars Global Reference Atmospheric Model (Mars-GRAM 2001) is an engineering-level Mars atmosphere model widely used for many Mars mission applications. From 0 to 80 km, it is based on NASA Ames Mars General Circulation Model (MGCM), while above 80 km it is based on University of Michigan Mars Thermospheric General Circulation Model. Mars-GRAM 2001 and MGCM use surface topography from Mars Global Surveyor Mars Orbiter Laser Altimeter (MOLA). Validation studies are described comparing Mars-GRAM with a global summary data set of Mars Global Surveyor Thermal Emission Spectrometer (TES) data. TES averages and standard deviations were assembled from binned TES data which covered surface to ∼40 km, over more than a full Mars year (February 1999–June 2001, just before start of a Mars global dust storm). TES data were binned in 10° × 10° latitude–longitude bins (36 longitude bins, centered at 5°–355°, by 18 latitude bins, centered at −85° to +85°), and 12 seasonal bins (based on 30° increments of L_s angle). Bin averages and standard deviations were assembled at 23 data levels (temperature at 21 pressure levels, plus surface temperature and surface pressure). Two time-of-day bins were used: local time near 2 or 14 h. Two dust optical depth bins were used: infrared optical depth, either less than or greater than 0.25 (which corresponds to visible optical depth less than or greater than about 0.5). For interests in aerocapture and precision entry and landing, comparisons focused on atmospheric density. TES densities versus height were computed from TES temperature versus pressure, using assumptions of perfect gas law and hydrostatics. Mars-GRAM validation studies used density ratio (TES/Mars-GRAM) evaluated at data bin center points in space and time. Observed average TES/Mars-GRAM density ratios were generally 1 ± 0.05, except at high altitudes (15–30 km, depending on season) and high latitudes (>45°N), or at most altitudes in the southern hemisphere at L_s ∼ 90° and 180°. Compared to TES averages for a given latitude and season, TES data had average density standard deviation about the mean of ∼2.5% for all data, or ∼1–4%, depending on time of day and dust optical depth. Average standard deviation of TES/Mars-GRAM density ratio was 8.9% for local time 2 h and 7.1% for local time 14 h. Thus standard deviation of observed TES/Mars-GRAM density ratio, evaluated at matching positions and times, is about three times the standard deviation of TES data about the TES mean value at a given position and season.     

Reconstruction of solar UV irradiance

Understanding solar influence on the Earth’s climate requires a reconstruction of solar irradiance for the pre-satellite period. Considerable advances have been made in modelling the irradiance variations at wavelengths longer than 200 nm. At shorter wavelengths, however, the LTE approximation usually taken in such models fails, which makes a reconstruction of the solar UV irradiance a rather intricate problem. We choose an alternative approach and use the observed SUSIM UV spectra to extrapolate available models to shorter wavelengths.     

Features of the 11-year variation of galactic cosmic rays in different periods of solar magnetic cycles

Variations of galactic cosmic ray intensity have been studied based on the neutron monitors and interplanetary magnetic field experimental data for different ascending and descending epochs of solar activity. The dependence of the diffusion coefficient on the cosmic ray particles rigidity R is stronger in the maxima epoch than in the minima epoch of solar activity. For the period of 1977–1981 (qA > 0) the diffusion coefficient for the minimum epoch is, χ_min ∝ R^{0.7 ± 0.04} and for the maximum χ_max ∝ R^{1.3 ± 0.05}; for the period of 1987–1990 (qA < 0), χ_min ∝ R^{0.8 ± 0.05} and χ_max ∝ R^{1.1 ± 0.04}. The exponents ν_y and ν_z of the power spectral density of the B_y and B_z components of the IMF in the region of the frequencies (10⁻⁶– 4 × 10⁻⁶) Hz are larger for the minimum epoch of 1987 (ν_y ≈ 2.0 and ν_z ≈ 1.93) than for the maximum epoch of 1990 (ν_y ≈ 1.43 and ν_z ≈ 1.27).     

L-band nighttime scintillations at the northern edge of the EIA along 95°E during the ascending half of the solar cycle 24

The characteristics of nighttime ionospheric scintillations measured at the L-band frequency of 1.575 GHz over Dibrugarh (27.5°N, 95°E, MLAT ～ 17°N, 43° dip) during the ascending half of the solar cycle 24 from 2010 to 2014 have been investigated and the results are presented in this paper. The measurement location is within or outside the zone of influence of the equatorial ionization anomaly depending on solar and geomagnetic activity. Maximum scintillation is observed in the equinoxes irrespective of solar activity with clear asymmetry between March and September. The occurrence frequency in the solstices shifts from minimum in the June solstice in low solar activity to a minimum in the December solstice in high solar activity years. A significant positive correlation of occurrence of scintillations in the June solstice with solar activity has been observed. However, earlier reports from the Indian zone (～75°E) indicate negative or no correlation of scintillation in June solstice with solar activity. Scintillations activity/occurrence in solstices indicates a clear positive correlation with Es recorded simultaneously by a collocated Ionosonde. In equinoxes, maximum scintillations occur in the pre-midnight hours while in solstices the occurrence frequency peaks just after sunset. The incidence of strong scintillations (S₄ ≥ 0.4) increases with increase in solar activity. Strong (S₄ ≥ 0.4) ionospheric scintillations accompanied by TEC depletions in the pre-midnight period is attributed to equatorial irregularities whereas the dusk period scintillations are related to the sporadic-E activity. Present results thus indicate that the current location at the northern edge of the EIA behaves as low as well as mid-latitude location.     

Observations of “zebra” pattern in cm-range with spatial resolution

We present the results of the first observations of the solar microwave burst with fine spectral structure of zebra type at the frequency about 5.7 GHz. The burst has been detected simultaneously by the Siberian Solar Radio Telescope and by the spectropolarimeter of the National Astronomical Observatory of China. Zebra pattern consisted of three parallel stripes with complex frequency drift. The degree of circular polarization of emission reached 100%, the polarization sense corresponded to the extraordinary wave (X-mode). We have determined the plasma parameters in the emission source: plasma density about 10¹¹ cm⁻³, magnetic field strength 60–80 G. We argue that in the given event the most probable mechanism of the zebra pattern generation is non-linear coupling of harmonics of Bernstein modes.     

Ionospheric response to the storm-time disturbance of 29 May, 2010

The Ionospheric F2-layer peak parameters response to a magnetic storm had been investigated over Ilorin, Nigeria (Lat. 8:53°N, Long. 4.5°E, dip angle, −2.96°), Jicamarca, Peru (11.95°S, 76.87°W, dip angle, 0.8°) and Hermanus, South Africa (34.42°S, 19.22°E, dip angle, −60.77°), using percentage enhancement/depletion values. Our results showed an enhancement in NmF2 at all of these stations. Averagely, pre-noon and post-noon peaks are highest at Ilorin during quiet time. The similar pattern observed for quiet condition between Ilorin and Jicamarca was due to their latitudinal positions. For disturbed NmF2 condition, Jicamarca and Ilorin recorded higher peaks at nighttime than during the daytime for the storms main phase, and the reverse over Hermanus. The nighttime and daytime increases were observed respectively at Ilorin and Hermanus during the recovery period. The hmF2 variation recorded higher enhancement at Jicamarca during the daytime and at Hermanus at nighttime during the main phase. During the recovery phase, the highest enhancement was recorded during the daytime at Jicamarca, and over Hermanus at nighttime. These observations find their explanation in the magnetospheric current, solar wind and E × B drift.     

Characterization of the semi-annual-oscillation in mesospheric temperatures at low-latitudes

Novel measurements of the seasonal variability in mesospheric temperature at low-latitudes have been obtained from Maui, Hawaii (20.8°N, 156.2°W) during a 25-month period from October 2001 to January 2004. Independent observations of the OH (6, 2) Meinel band (peak height ∼87 km) and the O₂ (0–1) atmospheric band emission (∼94 km) were made using the CEDAR Mesospheric Temperature Mapper. The data revealed a coherent oscillation in emission intensity and rotational temperature with a well-defined periodicity of 181 ± 7 days. The amplitude of this oscillation was determined to be ∼5–6 K in temperature and ∼8–9% in intensity for both the OH and O₂ data sets. In addition, a strong asymmetry in the shape of the oscillation was also observed with the spring maximum significantly larger than the fall peak. These data provide new evidence in support of a semi-annual-oscillation in mesospheric temperature (and airglow emission intensities) and help quantify its seasonal characteristics.     

The 16-day waves in the mesosphere and lower thermosphere over Wuhan (30.6°N, 114.5°E) and Adelaide (35°S, 138°E)

Winds from a meteor radar at Wuhan (30.6°N, 114.5°E) and a MF radar at Adelaide (35°S, 138°E) are used to study the 16-day waves in the mesosphere and lower thermosphere (MLT). The height range is 78–98 km at Wuhan and 70–98 km at Adelaide. By comparison, it is found that the zonal components at both sites are generally larger than the meridional ones, and eastward motion of the zonal background winds is favorable for the 16-day waves penetration to the MLT region. The zonal maximum amplitude appears in the autumn (September–October) around 86–98 km at Wuhan and in the winter months and early spring (July–October) around 72–82 km at Adelaide. Differences are found in wave amplitudes and time of appearance between the two years of 2002 and 2003. In 2003, the intensity of the wave amplitudes is relatively smaller than that for 2002 at both sites. The summer 16-day waves are comparatively weaker at Adelaide in both years, but stronger in 2002 at Wuhan near the mesopause and the lower thermosphere (86–98 km). The strong summer waves at Wuhan may come from the winter southern hemisphere.     

Storm time spatial variations in TEC during moderate geomagnetic storms in extremely low solar activity conditions (2007–2009) over Indian region

The total electron content (TEC) measurements from a network of GPS receivers were analyzed to investigate the storm time spatial response of ionosphere over the Indian longitude sector. The GPS receivers from the GPS Aided Geo Augmented Navigation (GAGAN) network which are uniquely located around the ∼77°E longitude are used in the present study so as to get the complete latitudinal coverage from the magnetic equator to low mid-latitude region. We have selected the most intense storms but of moderate intensity (−100 nT < Dst < −50 nT) which occurred during the unusually extremely low solar activity conditions in 2007–2009. Though the storms are of moderate intensity, their effects on equatorial to low mid-latitude ionosphere are found to be very severe as TEC deviations are more than 100% during all the storms studied. Interesting results in terms of spatial distribution of positive/negative effects during the main/early recovery phase of storms are noticed. The maximum effect was observed at crest region during two storms whereas another two storms had maximum effect near the low mid-latitude region. The associated mechanisms like equatorial electrodynamics and neutral dynamics are segregated and explained using the TIMED/GUVI and EEJ data during these storms. The TEC maps are generated to investigate the storm time development/inhibition of equatorial ionization anomaly (EIA).     

The temperature map of the loop and coronal sources of an occulted solar flare

An occulted solar flare occurred at about 06:07 UT on 2002, November 2. The RHESSI X-ray images show two separate parts. The lower part consists of a complete loop and the upper part a coronal source which well extends above the solar limb. The loop source shrank for about 3 min with a speed of ∼24 km s⁻¹ during the early impulsive phase and then expanded at ∼7 km s⁻¹, while the coronal source presented an upward motion at about 6 km s⁻¹. We obtained the temperature map of the loop source from RHESSI image spectrum. The temperature of the loop increases with altitude, indicating that the reconnection X-point of this flare is located above the loop source. However, the apparent coronal source is the top of another independent large-scale loop.     

Excitations of nonmigrating diurnal tides in the mesosphere and lower thermosphere simulated by the Kyushu-GCM

Excitation mechanisms of nonmigrating diurnal tides in the MLT region simulated by the Kyushu-GCM are examined. It is shown that the westward propagating diurnal tide with zonal wavenumber s = 2 is mainly excited by nonlinear interactions between the migrating diurnal tide and the stationary planetary wave with zonal wavenumber s = 1, while the nonlinear excitation of the standing diurnal tide with zonal wavenumber s = 0 is less important than the excitation by tropospheric heating. Nonlinear interactions between the migrating diurnal tide and the stationary planetary wave with zonal wavenumber s = 2 are not dominant to excite the westward propagating diurnal tide with zonal wavenumber s = 3, and it is shown that the excitation by tropospheric heating is comparable to the nonlinear excitation. It is also shown that other nonmigrating diurnal tides are excited by tropospheric heating.