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° 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 Tucumán (26.9°S, 294.6°E) in 1982, and those corresponding to the northern peak were Obtained at Palehua (21.4°N, 203.2°E) in 1978 and Delhi (28.6°N, 77.2°E) in 1968. Ionosonde data from Tucumán, Delhi, and Maui, (20.8°N, 203.5°E) 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 Tucumán 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 Tucumán, 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.
En este trabajo se analiza la variación a largo plazo de la precipitación total y máxima diaria de verano en Tucumán, en base a datos medidos en la Estación Experimental Agroindustrial Obispo Colombres (EEAOC) durante el período 1911-2016. La precipitación total presenta tendencia lineal positiva significativa en el período completo de análisis por la presencia del salto climático de 1956. La serie de precipitación máxima diaria sólo presenta tendencia positiva significativa en el sub-periodo 1956-1994. Teniendo en cuenta que el monzón sudamericano es un fuerte determinante de los regímenes de precipitación del norte argentino, se analiza la correlación con variables de circulación asociadas: viento zonal (U) en la troposfera superior en la región de la Alta de Bolivia y viento meridional (V) en la troposfera inferior en la región de la Baja del Chaco, junto con la presión (P) y temperatura (T) en el Atlántico Sur. Hay buen acuerdo estadístico entre las series de precipitación y estas variables cuando se considera el período completo, porque todas presentan –en general- una tendencia lineal neta. En el sub-período 1960-2012, la precipitación total tiene una cuasi-periodicidad de ~20 años en fase con P, y no tiene correlación con U y V, y disminuye su correlación con T. En cambio, la precipitación máxima en este sub-período tiene buena correlación con las variables de velocidad, las cuales están ligadas a la convección regional. Se analiza también la posible asociación con algunos índices oceánicos detectándose buena correlación con la Oscilación Decadal del Pacifico (PDO)desde mediados del siglo XX. Finalmente se analiza el posible rol sobre las tendencias del aumento de CO2 global y la variación de la columna de O3 polar. Hay correlación positiva y significativa de las series de precipitación con el CO2, muy similar a la dependencia con T, debido a que ambas series de precipitación presentan una tendencia general a aumentar. Con el O3 se observa correlación negativa significativa debido a que las series coinciden en el cambio del signo de tendencia en ~1960.
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.
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