El Arenosillo Research Articles

Effects of geomagnetic storms on the ionospheric regions over the Southwest of Europe. An approach to the influence of the G condition on ionospheric values

The effects of three geomagnetic storms on the ionospheric F region and the influence of the G condition on TEC estimates have been analysed by using ionospheric data from INTA El Arenosillo Atmospheric Sounding Station (37.1N, 353.3E) and GPS TEC measurements obtained at the IGS station of San Fernando (36.5N, 353.8E). The results stress the importance of these perturbations and the need of using edited ionograms.

Intercomparison of aerosol optical depth measurements in the UVB using Brewer Spectrophotometers and a Li‐Cor Spectrophotometer

The first Iberian UV radiation intercomparison was held at “El Arenosillo”‐Huelva station of the Instituto Nacional de Técnica Aeroespatial (INTA) from September 1 to 10, 1999. During this campaign, seven Brewer spectrophotometers and one Li‐Cor spectrophotometer measured the total column aerosol optical depth (AOD) at 306, 310, 313.5, 316.75 and 320 nm. The AOD calibration of one Brewer was transferred to all other Brewers using one day of intensive measurements. The remaining days were used to observe the stability and reproducibility of the AOD measurements by the different instruments. All Brewer spectrophotometers agreed to within an AOD of 0.03 during the whole measurement campaign. The differences in AOD between the Li‐Cor spectrophotometer and the Brewer spectrophotometers were between −0.07 and +0.02 at 313.5, 316.75, and 320 nm. This investigation demonstrates the possibility of using the existing worldwide Brewer network as a global UV aerosol network for AOD monitoring.

Monitoring of biologically effective UV irradiance at El Arenosillo (INTA), Andalucia, in Spain.

Biological UV (ultraviolet) dosimetry was applied using the biofilm-technique (DLR patent) to determine the UV levels weighted of biologically weighted UV radiation at the INTA Sounding Station of El Arenosillo at Huelva, Spain (37 degrees 06'N, 6 degrees 44'W, 50 m a s 1=above sea level) on 2 days in 1997 [correction of 1977] (April 1, and May 5). Exposure periods were calculated for clear sky days using a radiative transfer model for erythemal doses to reach 1.3 to 1.5 MED (minimal erythemal dose). Reliability of the radiative transfer model was demonstrated by the doses registered by a Yankee-UV biometer for the same exposure periods as used for the biosensor. This work presents the methodology employed (biofilm-technique utilized [correction of utiliced], calculation of exposing periods with radiative transfer model, etc) and the results obtained with the Yankee biometer and the biofilm. At noon, the ratio of biofilm measurements (Ieff, W/m2=biological effective irradiance, in W/m2) to the UV Biometer data (in MED/h) was 3-4.

A method for f0F2 monitoring over Spain using the El Arenosillo digisonde current observations

Ionosphere monitoring implies: observations, prediction and mapping of ionospheric parameters. A case with one available (El Arenosillo) ionosonde is considered. Some statistical methods for f0F2 short-term (1-24 h in advance) prediction are compared. The analysis of multi-dimensional regression for Df0F2 (relative deviation from running median) with Ap, F10.7 and previous Df0F2 observations has shown that inclusion of additional terms with Ap and F10.7 improves the prediction accuracy for lead time more than 15 h. For lead time 1-6 h a linear regression with earlier observed Df0F2 provides the f0F2 forecast with Relative Mean Deviation (RMD) 6-11%. This is acceptable from a practical point of view. A 24-h forecast can be done with RMD 10-11%. Multi-regressional methods provide better prediction accuracy than the usual 10-day running median or quasi-inertial method based on such median. Hourly f0F2 values may be used to calculate the effective index R12eff used as input to the ITU-R monthly median model. This allows the ITU-R model to "breathe" following hour-to-hour f0F2 variations. Then standard surfering methods may be applied for f0F2 mapping over the whole area. The f0F2 mapping accuracy based on the hourly R12eff index is shown to be 9-11% depending on solar activity level.

A comparison of f0F hmE model calculations with El Arenosillo digisonde observations. Seasonal variations

Seasonal variations of hmE and f0F2 are analyzed using El Arenosillo digisonde observations during solar minimum (1995-1996). Unlike some widely used empirical models daytime hmE show seasonal variations with winter hmE being higher than summer ones and seasonal differences increase with solar zenith angle. Model calculations enable us to reproduce the observed hmE seasonal variations but the calculated daytime f0E values are too low if conventional EUV fluxes and dissociative recombination rate constants are used. A reduction of a (NO+ ) by taking into account Te > Tn in the E-region as it follows from probe measurements seems to be a plausible solution. The E-region ion composition corresponding to rocket observations may be obtained in model calculations using an appropriate [NO] height distribution. Calculated summer concentrations of [NO] are by a factor of 3-4 larger than winter ones at the hmE-heights.

Ionospheric despatch centre in Europe

Ionospheric Despatch Centre in Europe — IDCE operates in the frame of the European COST 251 IITS project (Improved Quality of Ionospheric Telecommunication Systems Planning and Operation) since January 1997 in Heliogeophysical Prediction Service of the Space Research Centre of Polish Academy of Sciences (Regional Warning Centre Warsaw of the International Space Environment Service — ISES). IDCE provides solar-geophysical data for COST 251 participants, putting stress on the ionospheric data particularly from the European ionospheric stations. Some of data are available worldwide. Data and special messages are accessible on ftp.cbk.waw.pl, as well as on IDCE home page http://www.cbk.waw.pl/rwc/idce.html. Messages are prepared on the base of local measurements and daily messages from RWC's: Boulder, Meudon, Moscow, Praha, Sydney, Tokio, Beijing and also special messages obtained directly from observatories: El Arenosillo, Juliusruh, Lannion, Lunping, Ondrejov, Sofia, Tortosa, Uppsala and Chilton. Data and global review are available from the last few days and forecast for some days in advance. Daily message describes the solar, magnetic and ionospheric activity, sudden ionospheric disturbances, gives solar-geophysical situation review and forecast. Some ionospheric parameters are collected from the whole current and preceding month -hourly vertical-incidence ionosonde data. Catalogues of disturbed and quiet days, as well as the list of disturbed periods of few hours duration are provided for the whole year since January 1997.

Correlation in f0F2 and M(3000) F2 variations in South-West Europe

A statistical analysis of the variations of the hourly daily values of the M(3000)F2 with the corresponding values of critical frequencies f0F2 was provided for two similar ionosondes (Digisonde-256) located in El Arenosillo and Geophysical Observatory Ebro (both in Spain). Data for winter 1993/1994 and summer 1993 are presented. It is shown that for hour-to-hour variations (both seasons) and for day-to-day variations in summer the correlation is poor and contradictory but for the day-to-day variations in winter months the correlation is significantly higher and positive.

Large-scale structures in hydroxyl rotational temperatures during DYANA

Comparison of nightly means of OH ∗ rotational temperatures measured at Yakutsk, Kiruna, Andoya, Biscarrosse, and El Arenosillo during the DYANA campaign reveals information about dynamics in the 86 km altitude region that includes relatively short-range temperature gradients at high latitudes associated with a stratospheric warming, and long-range oscillations with periods from about 2 to more than 30 days that can be attributed to travelling or quasi-stationary planetary waves. The DYANA campaign averages terrd to exceed zonal mean temperatures of the CIRA 86 model by up to 15 K.

Simultaneous observation of the quasi-two-day variations in the lower and upper ionosphere over Europe

The large scale character of the observed quasi-two-day fluctuations in the whole ionosphere (from D- up to F-region maximum) over Europe is shown. The study is based on the lower and upper ionospheric data obtained in Sofia (42.9°, 23.4°E), Ebre Observatory (40.9°N, 0.5°E) and El Arenosillo (37.1°N, 6.7°W) during two summer intervals: June–August 1980 and 1983. The obtained prevailing periods for the F-region fluctuations are 52–55 h and the mean amplitude is higher than 1 MHz. It was found that the fluctuations propagate westward with a mean phase velocity between 4.6 and 6° /h. The quasi-two-day variations in the F-region maximum are probably generated by flucutations in the mesospheric, neutral wind. During the time when well developed quasi-two-day fluctuations exist in the mesospheric neutral wind, similar variations are observed in the lower ionosphere also. Possible mechanisms for generating the D- and F-region electron density fluctuations from these oscillations in the neutral wind are proposed.

Stratospheric electric field measurements with transmediterranean balloons

The horizontal component of the stratospheric electric field was measured using a balloon in the ODISEA Campaign of Transmediterranean Balloon Program. The balloon flew between Trapani (Sicily) and El Arenosillo (Huelva, Spain) along the 39 o N parallel at a height between 34 Km and 24 Km. The high values found for the field on fair-weather and its quasi turbulent variation, both in amplitude and direction, are difficult to explain with the classical electric field sources. A new source, first described by Holzworth /1/, is considered as possibly causing them.

Altitude distribution of vibrationally excited states of atmospheric hydroxyl at levels v = 2 to v = 7

An instrument for the measurement of three different infrared regions of the OH Meinel system was launched in night conditions from El Arenosillo Sounding Rocket Range (Spain). The instrument covered transitions between vibrational states from v = 2to v = 7 in the first overtone sequence. The altitude profiles of the concentration of OH ∗ in the vibrational levels 2 to 7 are deduced. The individual profiles show that there is a dependence of the characteristics of the layers (altitude of the peak and half width) on the vibrational level. The lower levels extend to lower altitude than the higher ones. The obtained profiles are used, on the basis of a photochemical model, to investigate the values for the rate constants of the production and the chemical and collisional deactivation of atmospheric OH ∗.

A scale analysis of the D region winter anomaly

A scale analysis, i.e., an estimation of typical values of important atmospheric and ionospheric parameters and time scales is performed for the meteorological type of winter anomaly at medium latitudes (40°N). An interpretative model of the winter anomaly is developed by a correlation analysis on the basis of data obtained from the Western European Winter Anomaly Campaign 1975/76 at El Arenosillo, Spain, and a simultaneous winter anomaly campaign at Wallops Island, U.S.A large number of rocket experiments performed in six previous winters in Spain are also analyzed and found to support the model. The model explains the buildup and decay of the winter anomaly by combined action of temperature, turbulent downward transport of nitric oxide, and horizontal transport of nitric oxide by winds. The horizontal wind direction is not important for the picture. Mechanisms involved are fast enough to explain the rapid variations of the winter anomaly. Large‐scale winter anomaly structure is linked to planetary wave number 2. The model picture is found to be compatible with quite a number of experimentally known features of the winter anomaly. There are hints to a more general validity of the model.

Ion production and effective loss rate in the mesosphere and lower thermosphere during the Western European Winter Anomaly Campaign 1975/76

As part of a campaign to study the middle latitude ionosphere during winter anomaly conditions, rocket ‘salvoes’ were launched from ‘El Arenosillo’, Spain, on 4 and 21 January 1976. On each of these days the rocket instrumentation measured solar X-ray and H-Lyman-α intensities, energetic particle precipitation, and also the height distribution of the minor constituents NO and O 2( 1Δ g) . On this basis the ion production q( h) in the height range 50–120 km was estimated. The main contribution to q( h) were X-rays (above 90 km), H-Lyman-α (70–90 km), ionization of O 2( 1Δ g (80–90 km), particles, and galactic cosmic rays (below 70 km). Combining the ion production with simultaneously measured values of electron density N ϵ ( h) an estimate of the effective electron loss rate ψ(h) = q N ϵ 2 was obtained. On both days, ψ( h) showed a characteristic rapid decrease from values about 10 −11–10 −10 m 3s −1 below 78 km to values in the range 2 × 10 −13–3 × 10 −12m 3s −1 above this height.

An integrated GBR campaign for the study of the D-region winter anomaly in western Europe 1975/76

An integrated rocket, balloon and ground observation campaign for the study of the D- region winter anomaly was performed in Western Europe from December 1975 to February 1976. A total of 22 experimenter groups with 38 different types of experiment participated in the campaign. Forty-seven rockets and 23 balloons were successfully launched from the range of ‘El Arenosillo’, Spain. Various coordinated groundbased experiments were performed in Spain, France, Great Britain, Italy, Austria and Germany. The structure of the campaign, the relevant geophysical background data, and a survey on the kind of data obtained is presented in this introductory paper. Specific scientific aspects and the respective results are covered by 12 subsequent papers.

Neutral atmospheric composition measurements daring the Western European Winter Anomaly Campaign 1975/76

The neutral atmospheric composition and structure were determined over ‘El Arenosillo’ (37°6′N, 6°44′W) during the Western European Winter Anomaly Campaign 1975/76 by mass spectrometric measurements. Two different types of mass spectrometers were launched on 4 and 21 January 1976 around 1430 and 1530 UT, on both days measuring the number density profiles of N 2, O 2, O, Ar, and CO 2 in the altitude range from about 80 to 117 km. The 2 days are characterized by high radio wave absorption. The main result is an enhancement of atomic oxygen densities by factors of 3–5 on 4 January compared with 21 January in the altitude region of 80–110 km. The N 2 and O 2 density profiles on both days show structures with deviations from CIRA (1972) up to 50%.

Relationships between the local dynamical structure of the atmosphere and ionospheric absorption during the Western European Winter Anomaly Campaign 1975/76

During the period December 1975–mid-February 1976 of the Western European Winter Anomaly Campaign, the local dynamical and thermal structure of the stratosphere and mesosphere was determined by some 31 rocket launches at El Arenosillo, Spain, while the mesospheric thermal structure in the winter (northern) hemisphere was derived from Nimbus 6 satellite observations. An analysis of these data is presented here. As determined by the A3 technique and the parameter L d[= L 0 (n +1) ] , ionospheric absorption is significantly correlated with many features of the dynamical and thermal structure of the atmosphere. The strongest correlations are, on this occasion, with local winds, at a level between 85 and 92 km altitude, the sense being that high absorption corresponds to northward and eastward wind tendencies, while low absorption corresponds to southward and westward wind tendencies. Additionally, there is a significant correlation with local temperature above 60 km, high absorption corresponding to high mesospheric temperatures. These local variations are corroborated by data obtained from the PMR 3000 channel of the Nimbus 6 satellite (centred about 80km). A trivariate analysis of absorption ( L d ), temperature (40° latitude) and meridional temperature gradient along the 0° longitude meridian, which corresponds to the pressure gradient driving a ‘geostrophic’ zonal wind, shows extremely high significance. High ionospheric absorption in Spain is associated with disruption of the normally strong winter vortex around a warm winter mesospheric pole. As the polar temperature decreases, temperatures at low- and mid-latitudes increase and, responding to a decrease of meridional temperature gradient, the mid-latitude zonal and meridonal wind regime changes. Disturbances of the winter mesospheric polar vortex are triggered by the upward propagation of earlier perturbations within the troposphere and/or stratosphere. Delays of 2–4 days are indicated between the onset of stratospheric circulation disturbances, perturbation of the mesospheric polar vortex, and the consequent dynamical and thermal effects in the mid-latitude mesosphere which are associated with anomalously high ionospheric absorption.

Silicon ions below 100 km: A case for SiO2+

Silicon ions are normally detected at altitudes above 100 km and within sporadic‐E layers. Traces have rarely been observed within the more permanent metallic layer near 93 km. This is surprising since silicon is an important constituent of chondritic meteorites, which ablate material in this region to provide a primary source of the metallic species observed there. In this work, we present evidence that Si+ ions form SiO2+ at the lower altitudes, and exist in this ionic state prior to recombination. A rocket launched from El Arenosillo, Spain, on 3 July 1972, at 0743 LMT (χ = 57.1°), during the predicted period of the β Taurids meteor shower, passed through a continuous belt of metallic ions that began near 85 km, ended near 115 km, and exhibited an order of magnitude increase in the form of a layer near 114 km. Si+ was measured in and below the ledge down to 103 km. It showed a rapid decrease below this height. A comparison of the isotopic ratio for nickel, [60Ni]/[58Ni], with the measured ions shows too large a ratio for the ions below 100 km, suggesting contribution to 60+ from other sources. A prime candidate is SiO2+, since Si+ is observed to decrease in the region where the ratio becomes too large. No evidence for SiO+ (44+) is present in the data, indicating that Si+ forms SiO2+ either directly or through SiO+ in a short‐lived state. Radiative association is offered as a primary mechanism for SiO2+ production and yields a calculated reaction rate of 2×10−16 cm3 sec−1.