Nieves Ortiz de Adler - Academia.edu (original) (raw)

Books by Nieves Ortiz de Adler

This book deals with the calculation of the solar radiation that reaches the Earth, considering e... more This book deals with the calculation of the solar radiation that reaches the Earth, considering each and every one of the processes involved, whether astronomical, physical or chemical. It begins with the calculation of the energy that reaches the edge of the Atmosphere, and then introduces the phenomenon of attenuation of the radiation that passes through it until it reaches the Earth's surface. In order to simplify the analysis, the simplest case is first treated, an atmosphere without clouds, ideal to then enable the calculation with real atmospheres, but without clouds. Finally, the most complex case is presented, real atmospheres with clouds and the prediction of very short-term ground irradiance data, based on the processing of series of images captured by satellites or generated by cameras at ground.

Papers by Nieves Ortiz de Adler

Geofisica Internacional, 2004

Utilizando datos ionosféricos de los meses de marzo y septiembre, registrados en Okinawa (26°N, 1... more Utilizando datos ionosféricos de los meses de marzo y septiembre, registrados en Okinawa (26°N, 128°E), otro autor encontró una asociación entre la varianza de la frecuencia crítica de la capa F2, foF2var, y la oscilación cuasibienal de la media mensual del viento zonal (MMZW). En este trabajo se extiende este análisis, utilizando datos horarios mensuales de foF2 (entre las 12 y las 19 TL) para el periodo 1957-1989, para una estación ubicada en la cresta sur de la anomalía ecuatorial (Tucumán, 27ºS; 65ºW), para otra en el ecuador magnético (Huancayo, 12ºS; 75ºW) y otra estación de alta latitud (Slough, 51ºN; 0.6ºW). El coeficiente de correlación entre foF2var y MMZW es 0.05, 0.16 y 0.20 para Tucumán, Huancayo and Slough respectivamente, lo que indicaría que no hay asociación. Sin embargo dada la alta correlación encontrada en Okinawa (r=0.65), y en Tucumán cuando sólo se considera el período 1958-1968 (r=0.67), no descartamos completamente la posibilidad que la QBO del MMZW module la ionosfera en las crestas de la anomalía ecuatorial, sin buscar antes una explicación sobre la falta de correlación para Tucumán a partir de 1968. El análisis espectral de las tres estaciones muestra una significativa oscilación de alta frecuencia en foF2var (2.5-3.3 años) muy cercana, pero no coincidente con la QBO del MMZW, que también merece ser estudiada. PALABRAS CLAVE: Oscilación cuasibienal, frecuencia crítica de la capa F2, media mensual del viento zonal, efecto dínamo.

Geofísica Internacional, 2004

En este trabajo se busca una relación entre la anomalía de la temperatura estratosférica tropical... more En este trabajo se busca una relación entre la anomalía de la temperatura estratosférica tropical a 10 hPa (~30 km), durante el período 1964-1996 y el flujo solar F10.7 cm. De las cuatro series estacionales y de la serie anual, se filtró la tendencia de largo plazo y la influencia de la oscilación de casi dos años (QBO). El coeficiente de correlación lineal r entre la temperatura y F10.7 para cada una de las cinco series está entre 0.02 y 0.31, lo que llevaría a pensar que la asociación entre la temperatura y el ciclo solar es débil. Sin embargo, si los datos de cada serie son agrupados de acuerdo con el ciclo solar al que pertenecen, la temperatura en función de F10.7 presenta un comportamiento no aleatorio, similar a una histéresis. El sentido de rotación, el eje y el área de cada histéresis varía segun el ciclo solar. El área, proporcional al desfasaje entre la temperatura y el F10.7, se hace más grande desde el ciclo 20 al 22. Para la serie anual r es 0.83 en el ciclo 20, decrec...

Radio Science, 1989

The technique used at present to obtain Faraday electron content from polarimeter ground measurem... more The technique used at present to obtain Faraday electron content from polarimeter ground measurements of beacon signals is briefly reviewed and its basic assumptions are pointed out. A new alternative method is described. This method obviates the knowledge of the orientation of the transmitted electrical field and removes the so‐called ambiguity problem and may be useful in the case of interrupted polarimeter records. It makes use of electron density profiles obtained from an ionosonde located near the subionospheric point. Numerical comparisons of this method with the conventional one give good agreement. This was made using the combination of data from geostationary satellites with ionogram records. The relative advantages of both techniques are pointed out.

Physics and Chemistry of the Earth, Parts A/B/C, 2002

The trend of the peak height of the ionospheric F2 layer, hmF2, during three solar cycles (1957-1... more The trend of the peak height of the ionospheric F2 layer, hmF2, during three solar cycles (1957-1986) at Tucuman (26.9°S, 65.4°W), station located at the southern peak of the equatorial anomaly, has been estimated. hmF2 was calculated from M(3000), foE and foF2 records at 12 LT using Bilitza equation, which has been tested with real height values obtained from more than 200 rescaled ionograms. The anomalies, hmF2A, calculated as the deviation of experimental hmF2 values from that calculated assuming a linear dependence between hmF2 and the sunspot number, were estimated. The cumulated periodogram of hmF2A indicates a non-random behavior, within a 95% confidence level. After removing the effect of solar cycle variations and periodicities of less than 5 years, hmF2A shows a mean decrease of 0.2 km/yr (6 km in 30 years). A decrease of 14% in the maximum ionospheric electron density, NmF2, was also observed at the same station for the same period in a previous work of the authors. The lowering of hmF2 and NmF2 observed at Tucuman, are greater than that expected from the theory of a sinking of the upper atmosphere, due to a cooling in the thermosphere produced by the increase in CO 2 concentration.

Radio Science, 1992

A method to obtain the total electron content (TEC) of the ionosphere over Tucumán (26.9° S; 65.4... more A method to obtain the total electron content (TEC) of the ionosphere over Tucumán (26.9° S; 65.4° W), from ionogram data alone, is reported. To accomplish this, two Chapman profile expressions for the electron density (n) distribution in the F region are assumed, and a characteristic point of the n profile, called F region base point, is required. This method allows the TEC for a given particular time (not average) to be obtained. The results suggest that it could be a new method to calibrate polarimeter records used to measure TEC, and it could also allow the determination of TEC at predawn hours where only ionosounder data are available.

Radio Science, 1994

The total electron content (TEC) of the ionosphere is a parameter of great importance for the sys... more The total electron content (TEC) of the ionosphere is a parameter of great importance for the systems which use transionospheric radiowaves and for the checking of the validity of ionospheric models. It is known that the highest TEC values in the world occur at the peaks of the equatorial anomaly (EA) regions at ~15 ø either side from the magnetic equator. In this paper, TEC measurements obtained with Faraday technique at three stations placed near both peaks of the EA are used to check the validity of three ionospheric models to predict TEC in these regions. The TEC data of the southern peak of the EA were obtained at Tucumfin (26.9øS, 294.6øE) in 1982, and those corresponding to the northern peak were obtained at Palehua (21.4øN, 203.2øE) in 1978 and Delhi (28.6øN, 77.2øE) in 1968. Ionosonde data from Tucum,4n, Delhi, and Maui, (20.8øN, 203.5øE) are also used. Two widely used models are considered, namely: the international reference ionosphere and the semiempirical low-latitude ionospheric model. The third model considered is a Chapman layer with scale height equal to atomic oxygen scale height (CHOEA). In general, the models underestimate TEC during daylight hours at Tucum,4n suggesting that the real electron density profiles are larger in electron density magnitudes than those given by the models. For Palehua and Delhi the models' predictions are better than those for Tucum,4n, and a very good agreement among calculated and measured TEC values at Palehua for some months is observed. Taking into account the simplicity of the TEC calculus with CHOEA, this model would be an adequate alternative to predict TEC at stations placed near the northern crest of the EA, at least for the considered solar activity. This model allows also to calculate TEC at the southern crest of the EA with a similar degree of accuracy of those values obtained with the other models.

Physics and Chemistry of the Earth, Parts A/B/C, 2006

Long-term trends in the electron density of the ionosphere for the period 1957-1986 is studied us... more Long-term trends in the electron density of the ionosphere for the period 1957-1986 is studied using foF2 monthly median hourly data measured at Tucuman (26.9°S, 65.4°W), a station located at the southern crest of the equatorial anomaly. The linear trend for each hour and each month is estimated after filtering out the effects of solar activity. For the intervals 0-2 LT and 9-23 LT, during equinoxes and summer solstice, the trend is negative. Statistically null or slightly positive trends are observed for the interval 3-8 LT for every season, and for every hour of winter months. The daily amplitude of foF2 decreases since 1957 due to the decreasing trend in the maximum daily values and almost null-trended minimum daily values. A rough estimate, based on the dip angle trend (which in Tucuman has increased during the 30-year interval at a rate of 0.35%/year), indicates that negative foF2 trends should be expected during daytime hours, and positive trends during night-time hours, behaviour observed in the foF2 data here analyzed.

Journal of Geophysical Research, 1997

A correlation has been found between the peak electron density of the ionospheric F 2 layer, Nmax... more A correlation has been found between the peak electron density of the ionospheric F 2 layer, Nmax, and the temperature of the lower stratosphere. The electron density anomaly, Nma, dl, and the 12-month running mean of the lower stratospheric temperature anomaly (LSTA) are correlated. Nma,,A is the residual of the linear regression of Nmax on the sunspot number, Rz; and LSTA is the difference between the lower stratospheric temperature and its mean value. Monthly median values at 1200 LT of Nmax measured at Yamagawa, Kodaikanal, Okinawa, and Manila ionospheric stations are considered, covering the period 1979-1994. The lower stratospheric temperature corresponds to monthly mean values of the period January 1979 to December 1993. Since solar EUV and UV radiation affect the F 2 layer ionization and the stratospheric heating respectively, the part of the EUV and UV flux time variation that is not dependent on Rz has also been analyzed. This has been done using the photoelectron current (Ipe) measured with a Langmuir Probe on the Pioneer Venus Orbiter as indicator of the EUV flux, and the Mg II core-towing ratio as indicator of the UV flux. The temporal variations of Nma x independent of Rz are found to be similar to LSTA variations. The temporal variations, not dependent on Rz, of the solar EUV and UV energy output, are also similar.

Journal of Atmospheric and Solar-Terrestrial Physics, 1997

It is established that ionospheric parameters are linearly related to the sunspot number, RZ, and... more It is established that ionospheric parameters are linearly related to the sunspot number, RZ, and the solar flux at 2800 MHz, F10. 7. These solar activity parameters provide a measure of the EUV radiation variability which is responsible for most of the ionospheric ionization. ...

Journal of Atmospheric and Solar-Terrestrial Physics, 2006

It is well known that the Earth magnetic field, as well as geomagnetic activity, presents long-te... more It is well known that the Earth magnetic field, as well as geomagnetic activity, presents long-term variations. Both phenomena affect the height of the F2 layer peak, hmF2, and the maximum electron concentration estimated by foF2. Experimental data of three mid-high latitude stations (Argentine Islands, Slough and Uppsala) were used to estimate foF2 long-term trends. These trends were compared with

Journal of Atmospheric and Solar-Terrestrial Physics, 2006

Results of various authors on long-term trends in foF2, which is equivalent to the maximum electr... more Results of various authors on long-term trends in foF2, which is equivalent to the maximum electron density in the ionosphere, and their interpretation do not reveal a consistent pattern. Therefore, a joint analysis of one carefully selected dataset was performed by six teams, which used different approaches to trend determination. High-quality data of station Juliusruh (54.61N, 13.41E) for noon (average from 10 to 14 UT) were used for the period of two solar cycles from minimum to minimum (1976-1996). Juliusruh is relatively sensitive to geomagnetic activity as an almost subauroral station, which might play some role in interpretation of trend results. Various methods provide results, which differ to some extent, even when one co-author applies different methods. Another source of differences is application of various ways of removal (or at least large suppression) of the effect of solar (and geomagnetic) activity. Nevertheless finally most teams obtained quite comparable results. Interpretation of the observed trends is not unique-co-authors consider either the long-term change in geomagnetic activity, or anthropogenic effects to be predominantly responsible for trends. There is some generally accepted output from the joint analysis. All trends are either negative or insignificant. Data corrections with sunspot number (R), F10.7 adjusted to the Sun-Earth distance, observed F10.7, adjusted E10.7 and observed E10.7 result in somewhat different trends; the observed F10.7 and E10.7 appear to be the best correcting factor. The trends in foF2 are very small, of the order of À0.01 MHz/year, much smaller than the solar cycle effect and, therefore, sensitive to the solar activity correction. The Juliusruh dip angle increased very little over the period 1976-1996 and the possible impact of that increase on trends is negligibly small.

Annales Geophysicae, 2008

Noon foF2 monthly median values for equinoctial months of solar cycles 20, 21 and 22, were analyz... more Noon foF2 monthly median values for equinoctial months of solar cycles 20, 21 and 22, were analyzed for 37 worldwide stations. For each solar cycle and for a given R z , the difference between foF2 in the falling branch of the cycle and the corresponding value of the rising branch is evaluated. The maximum difference, considered as the hysteresis magnitude, varies systematically with geomagnetic latitude. The pattern is similar for every cycle, with greater hysteresis magnitudes for stronger solar cycles. It is positive between 45 • S and 45 • N, with minimum values at equatorial latitudes and maximum at around 25 •-30 • on either side of the equator. For latitudes greater than 50 • negative values are observed. At around 25 •-30 • and at high latitudes the hysteresis magnitude reaches 2 MHz for solar cycle with high activity levels, which represents around 20% of foF2. The effects of foF2 hysteresis on the analysis of long-term data sequences is analyzed. In the case of long-term trend analysis, the hysteresis behavior may induce spurious trends as a consequence of the filtering processes applied to foF2 time series previous to trend values estimation. This problem may be solved by considering time series covering several solar cycles.

Se estima radiación solar global sobre una superficie horizontal, para cielo todo el día sin nube... more Se estima radiación solar global sobre una superficie horizontal, para cielo todo el día sin nubes, de 3 localidades de los Valles Calchaquíes: Colalao del Valle, Amaicha del Valle y Santa María, Noroeste de Argentina. Se usa un modelo semi empírico de fácil implementación en PC, que requiere: latitud, longitud, altura sobre el nivel del mar, heliofanía efectiva, día del año y el factor de turbidez de Linke. Para cada día del año se calcula, cada 15 minutos, la irradiancia global. Los valores son integrados con un método numérico, obteniéndose los máximos valores posibles de irradiación, determinando las expectativas de valores de radiación, siempre por debajo de esta cota. Con datos de nubosidad de Santa María se realiza una estimación gruesa de la atenuación de radiación por efectos de nubosidad. Los valores de irradiación anuales así obtenidos, son 1.91 MWhm-2, 1.95 MWhm-2 y 1.92 MWhm-2, para Colalao del Valle, Amaicha del Valle y Santa María, respectivamente. Para San Carlos, Sa...

This book deals with the calculation of the solar radiation that reaches the Earth, considering e... more This book deals with the calculation of the solar radiation that reaches the Earth, considering each and every one of the processes involved, whether astronomical, physical or chemical. It begins with the calculation of the energy that reaches the edge of the Atmosphere, and then introduces the phenomenon of attenuation of the radiation that passes through it until it reaches the Earth's surface. In order to simplify the analysis, the simplest case is first treated, an atmosphere without clouds, ideal to then enable the calculation with real atmospheres, but without clouds. Finally, the most complex case is presented, real atmospheres with clouds and the prediction of very short-term ground irradiance data, based on the processing of series of images captured by satellites or generated by cameras at ground.

Geofisica Internacional, 2004

Utilizando datos ionosféricos de los meses de marzo y septiembre, registrados en Okinawa (26°N, 1... more Utilizando datos ionosféricos de los meses de marzo y septiembre, registrados en Okinawa (26°N, 128°E), otro autor encontró una asociación entre la varianza de la frecuencia crítica de la capa F2, foF2var, y la oscilación cuasibienal de la media mensual del viento zonal (MMZW). En este trabajo se extiende este análisis, utilizando datos horarios mensuales de foF2 (entre las 12 y las 19 TL) para el periodo 1957-1989, para una estación ubicada en la cresta sur de la anomalía ecuatorial (Tucumán, 27ºS; 65ºW), para otra en el ecuador magnético (Huancayo, 12ºS; 75ºW) y otra estación de alta latitud (Slough, 51ºN; 0.6ºW). El coeficiente de correlación entre foF2var y MMZW es 0.05, 0.16 y 0.20 para Tucumán, Huancayo and Slough respectivamente, lo que indicaría que no hay asociación. Sin embargo dada la alta correlación encontrada en Okinawa (r=0.65), y en Tucumán cuando sólo se considera el período 1958-1968 (r=0.67), no descartamos completamente la posibilidad que la QBO del MMZW module la ionosfera en las crestas de la anomalía ecuatorial, sin buscar antes una explicación sobre la falta de correlación para Tucumán a partir de 1968. El análisis espectral de las tres estaciones muestra una significativa oscilación de alta frecuencia en foF2var (2.5-3.3 años) muy cercana, pero no coincidente con la QBO del MMZW, que también merece ser estudiada. PALABRAS CLAVE: Oscilación cuasibienal, frecuencia crítica de la capa F2, media mensual del viento zonal, efecto dínamo.

Geofísica Internacional, 2004

En este trabajo se busca una relación entre la anomalía de la temperatura estratosférica tropical... more En este trabajo se busca una relación entre la anomalía de la temperatura estratosférica tropical a 10 hPa (~30 km), durante el período 1964-1996 y el flujo solar F10.7 cm. De las cuatro series estacionales y de la serie anual, se filtró la tendencia de largo plazo y la influencia de la oscilación de casi dos años (QBO). El coeficiente de correlación lineal r entre la temperatura y F10.7 para cada una de las cinco series está entre 0.02 y 0.31, lo que llevaría a pensar que la asociación entre la temperatura y el ciclo solar es débil. Sin embargo, si los datos de cada serie son agrupados de acuerdo con el ciclo solar al que pertenecen, la temperatura en función de F10.7 presenta un comportamiento no aleatorio, similar a una histéresis. El sentido de rotación, el eje y el área de cada histéresis varía segun el ciclo solar. El área, proporcional al desfasaje entre la temperatura y el F10.7, se hace más grande desde el ciclo 20 al 22. Para la serie anual r es 0.83 en el ciclo 20, decrec...

Radio Science, 1989

The technique used at present to obtain Faraday electron content from polarimeter ground measurem... more The technique used at present to obtain Faraday electron content from polarimeter ground measurements of beacon signals is briefly reviewed and its basic assumptions are pointed out. A new alternative method is described. This method obviates the knowledge of the orientation of the transmitted electrical field and removes the so‐called ambiguity problem and may be useful in the case of interrupted polarimeter records. It makes use of electron density profiles obtained from an ionosonde located near the subionospheric point. Numerical comparisons of this method with the conventional one give good agreement. This was made using the combination of data from geostationary satellites with ionogram records. The relative advantages of both techniques are pointed out.

Physics and Chemistry of the Earth, Parts A/B/C, 2002

The trend of the peak height of the ionospheric F2 layer, hmF2, during three solar cycles (1957-1... more The trend of the peak height of the ionospheric F2 layer, hmF2, during three solar cycles (1957-1986) at Tucuman (26.9°S, 65.4°W), station located at the southern peak of the equatorial anomaly, has been estimated. hmF2 was calculated from M(3000), foE and foF2 records at 12 LT using Bilitza equation, which has been tested with real height values obtained from more than 200 rescaled ionograms. The anomalies, hmF2A, calculated as the deviation of experimental hmF2 values from that calculated assuming a linear dependence between hmF2 and the sunspot number, were estimated. The cumulated periodogram of hmF2A indicates a non-random behavior, within a 95% confidence level. After removing the effect of solar cycle variations and periodicities of less than 5 years, hmF2A shows a mean decrease of 0.2 km/yr (6 km in 30 years). A decrease of 14% in the maximum ionospheric electron density, NmF2, was also observed at the same station for the same period in a previous work of the authors. The lowering of hmF2 and NmF2 observed at Tucuman, are greater than that expected from the theory of a sinking of the upper atmosphere, due to a cooling in the thermosphere produced by the increase in CO 2 concentration.

Radio Science, 1992

A method to obtain the total electron content (TEC) of the ionosphere over Tucumán (26.9° S; 65.4... more A method to obtain the total electron content (TEC) of the ionosphere over Tucumán (26.9° S; 65.4° W), from ionogram data alone, is reported. To accomplish this, two Chapman profile expressions for the electron density (n) distribution in the F region are assumed, and a characteristic point of the n profile, called F region base point, is required. This method allows the TEC for a given particular time (not average) to be obtained. The results suggest that it could be a new method to calibrate polarimeter records used to measure TEC, and it could also allow the determination of TEC at predawn hours where only ionosounder data are available.

Radio Science, 1994

The total electron content (TEC) of the ionosphere is a parameter of great importance for the sys... more The total electron content (TEC) of the ionosphere is a parameter of great importance for the systems which use transionospheric radiowaves and for the checking of the validity of ionospheric models. It is known that the highest TEC values in the world occur at the peaks of the equatorial anomaly (EA) regions at ~15 ø either side from the magnetic equator. In this paper, TEC measurements obtained with Faraday technique at three stations placed near both peaks of the EA are used to check the validity of three ionospheric models to predict TEC in these regions. The TEC data of the southern peak of the EA were obtained at Tucumfin (26.9øS, 294.6øE) in 1982, and those corresponding to the northern peak were obtained at Palehua (21.4øN, 203.2øE) in 1978 and Delhi (28.6øN, 77.2øE) in 1968. Ionosonde data from Tucum,4n, Delhi, and Maui, (20.8øN, 203.5øE) are also used. Two widely used models are considered, namely: the international reference ionosphere and the semiempirical low-latitude ionospheric model. The third model considered is a Chapman layer with scale height equal to atomic oxygen scale height (CHOEA). In general, the models underestimate TEC during daylight hours at Tucum,4n suggesting that the real electron density profiles are larger in electron density magnitudes than those given by the models. For Palehua and Delhi the models' predictions are better than those for Tucum,4n, and a very good agreement among calculated and measured TEC values at Palehua for some months is observed. Taking into account the simplicity of the TEC calculus with CHOEA, this model would be an adequate alternative to predict TEC at stations placed near the northern crest of the EA, at least for the considered solar activity. This model allows also to calculate TEC at the southern crest of the EA with a similar degree of accuracy of those values obtained with the other models.

Physics and Chemistry of the Earth, Parts A/B/C, 2006

Long-term trends in the electron density of the ionosphere for the period 1957-1986 is studied us... more Long-term trends in the electron density of the ionosphere for the period 1957-1986 is studied using foF2 monthly median hourly data measured at Tucuman (26.9°S, 65.4°W), a station located at the southern crest of the equatorial anomaly. The linear trend for each hour and each month is estimated after filtering out the effects of solar activity. For the intervals 0-2 LT and 9-23 LT, during equinoxes and summer solstice, the trend is negative. Statistically null or slightly positive trends are observed for the interval 3-8 LT for every season, and for every hour of winter months. The daily amplitude of foF2 decreases since 1957 due to the decreasing trend in the maximum daily values and almost null-trended minimum daily values. A rough estimate, based on the dip angle trend (which in Tucuman has increased during the 30-year interval at a rate of 0.35%/year), indicates that negative foF2 trends should be expected during daytime hours, and positive trends during night-time hours, behaviour observed in the foF2 data here analyzed.

Journal of Geophysical Research, 1997

A correlation has been found between the peak electron density of the ionospheric F 2 layer, Nmax... more A correlation has been found between the peak electron density of the ionospheric F 2 layer, Nmax, and the temperature of the lower stratosphere. The electron density anomaly, Nma, dl, and the 12-month running mean of the lower stratospheric temperature anomaly (LSTA) are correlated. Nma,,A is the residual of the linear regression of Nmax on the sunspot number, Rz; and LSTA is the difference between the lower stratospheric temperature and its mean value. Monthly median values at 1200 LT of Nmax measured at Yamagawa, Kodaikanal, Okinawa, and Manila ionospheric stations are considered, covering the period 1979-1994. The lower stratospheric temperature corresponds to monthly mean values of the period January 1979 to December 1993. Since solar EUV and UV radiation affect the F 2 layer ionization and the stratospheric heating respectively, the part of the EUV and UV flux time variation that is not dependent on Rz has also been analyzed. This has been done using the photoelectron current (Ipe) measured with a Langmuir Probe on the Pioneer Venus Orbiter as indicator of the EUV flux, and the Mg II core-towing ratio as indicator of the UV flux. The temporal variations of Nma x independent of Rz are found to be similar to LSTA variations. The temporal variations, not dependent on Rz, of the solar EUV and UV energy output, are also similar.

Journal of Atmospheric and Solar-Terrestrial Physics, 1997

It is established that ionospheric parameters are linearly related to the sunspot number, RZ, and... more It is established that ionospheric parameters are linearly related to the sunspot number, RZ, and the solar flux at 2800 MHz, F10. 7. These solar activity parameters provide a measure of the EUV radiation variability which is responsible for most of the ionospheric ionization. ...

Journal of Atmospheric and Solar-Terrestrial Physics, 2006

It is well known that the Earth magnetic field, as well as geomagnetic activity, presents long-te... more It is well known that the Earth magnetic field, as well as geomagnetic activity, presents long-term variations. Both phenomena affect the height of the F2 layer peak, hmF2, and the maximum electron concentration estimated by foF2. Experimental data of three mid-high latitude stations (Argentine Islands, Slough and Uppsala) were used to estimate foF2 long-term trends. These trends were compared with

Journal of Atmospheric and Solar-Terrestrial Physics, 2006

Results of various authors on long-term trends in foF2, which is equivalent to the maximum electr... more Results of various authors on long-term trends in foF2, which is equivalent to the maximum electron density in the ionosphere, and their interpretation do not reveal a consistent pattern. Therefore, a joint analysis of one carefully selected dataset was performed by six teams, which used different approaches to trend determination. High-quality data of station Juliusruh (54.61N, 13.41E) for noon (average from 10 to 14 UT) were used for the period of two solar cycles from minimum to minimum (1976-1996). Juliusruh is relatively sensitive to geomagnetic activity as an almost subauroral station, which might play some role in interpretation of trend results. Various methods provide results, which differ to some extent, even when one co-author applies different methods. Another source of differences is application of various ways of removal (or at least large suppression) of the effect of solar (and geomagnetic) activity. Nevertheless finally most teams obtained quite comparable results. Interpretation of the observed trends is not unique-co-authors consider either the long-term change in geomagnetic activity, or anthropogenic effects to be predominantly responsible for trends. There is some generally accepted output from the joint analysis. All trends are either negative or insignificant. Data corrections with sunspot number (R), F10.7 adjusted to the Sun-Earth distance, observed F10.7, adjusted E10.7 and observed E10.7 result in somewhat different trends; the observed F10.7 and E10.7 appear to be the best correcting factor. The trends in foF2 are very small, of the order of À0.01 MHz/year, much smaller than the solar cycle effect and, therefore, sensitive to the solar activity correction. The Juliusruh dip angle increased very little over the period 1976-1996 and the possible impact of that increase on trends is negligibly small.

Annales Geophysicae, 2008

Noon foF2 monthly median values for equinoctial months of solar cycles 20, 21 and 22, were analyz... more Noon foF2 monthly median values for equinoctial months of solar cycles 20, 21 and 22, were analyzed for 37 worldwide stations. For each solar cycle and for a given R z , the difference between foF2 in the falling branch of the cycle and the corresponding value of the rising branch is evaluated. The maximum difference, considered as the hysteresis magnitude, varies systematically with geomagnetic latitude. The pattern is similar for every cycle, with greater hysteresis magnitudes for stronger solar cycles. It is positive between 45 • S and 45 • N, with minimum values at equatorial latitudes and maximum at around 25 •-30 • on either side of the equator. For latitudes greater than 50 • negative values are observed. At around 25 •-30 • and at high latitudes the hysteresis magnitude reaches 2 MHz for solar cycle with high activity levels, which represents around 20% of foF2. The effects of foF2 hysteresis on the analysis of long-term data sequences is analyzed. In the case of long-term trend analysis, the hysteresis behavior may induce spurious trends as a consequence of the filtering processes applied to foF2 time series previous to trend values estimation. This problem may be solved by considering time series covering several solar cycles.

Se estima radiación solar global sobre una superficie horizontal, para cielo todo el día sin nube... more Se estima radiación solar global sobre una superficie horizontal, para cielo todo el día sin nubes, de 3 localidades de los Valles Calchaquíes: Colalao del Valle, Amaicha del Valle y Santa María, Noroeste de Argentina. Se usa un modelo semi empírico de fácil implementación en PC, que requiere: latitud, longitud, altura sobre el nivel del mar, heliofanía efectiva, día del año y el factor de turbidez de Linke. Para cada día del año se calcula, cada 15 minutos, la irradiancia global. Los valores son integrados con un método numérico, obteniéndose los máximos valores posibles de irradiación, determinando las expectativas de valores de radiación, siempre por debajo de esta cota. Con datos de nubosidad de Santa María se realiza una estimación gruesa de la atenuación de radiación por efectos de nubosidad. Los valores de irradiación anuales así obtenidos, son 1.91 MWhm-2, 1.95 MWhm-2 y 1.92 MWhm-2, para Colalao del Valle, Amaicha del Valle y Santa María, respectivamente. Para San Carlos, Sa...