I.A. Adimula

Rain attenuation statistics from rain cell diameters and heights

The prediction of satellite link attenuation is generally based on the point rainfall rate for 0.01 per cent of the year. The physical quantity used to determine attenuation is rain rate, whereas the 0.01 per cent point is a more complex parameter, not obviously related to the dynamics of rain structure. The dynamics of the horizontal and vertical structure of rain are directly related to rain rate, rainfall volume, local geology and climate. If attenuation is to be predicted from rain rate it would be better to use a single parameter that remains substantially the same in most environments. This is not the case with the 0.01 per cent point. It is argued in this paper that a breakpoint in the rain-rate exceedances occurs close to 105 mm/h. Rain can be divided at the breakpoint into two broad classes: below this point it is more uniformly distributed over the area of rainfall; above, it has an increasingly more complex horizontal varaiability, with intense rain columns embedded in a background of less intense rain. By replacing the climatic zone dependent 0.01 per cent point rain rate with the fixed rain rate of 105 mm/h, a model for attenuation calculation can be derived that relates the mechanics of the physical processes to rain rate and elevation angle. The model has been developed and tested against the ITU-R model using the full measured rain-rate exceedances for each site in the ITU-R data bank. Attenuation exceedances have been shown to depend on the shape of the rain-rate exceedance curve, whereas the ITU-R model generates the same curve shape for all sites, because it uses only one rain rate, R0.01. The new model performs at least as well as the ITU-R model for temperate climates and considerably better for tropical climates. For sites with no measured rain rate it is recommended that a generalized rain-rate exceedance curve be used, especially for tropical regions. Copyright

A new index to monitor temporal and long-term variations of the equatorial electrojet by MAGDAS/CPMN real-time data: EE -Index

A new index, EE-index (EDst, EU, and EL), is proposed to monitor temporal and long-term variations of the equatorial electrojet by using theMAGDAS/CPMN real-time data. The mean value of the H component magnetic variations observed at the nightside (LT = 18–06) MAGDAS/CPMN stations along the magnetic equatorial region is found to show variations similar to those of Dst; we defined this quantity as EDst. The EDst can be used as a proxy of Dst for the real-time and long-term geospace monitoring. By subtracting EDst from the H component data of each equatorial station, it is possible to extract the Equatorial Electrojet and Counter Electrojet components, which are defined as EU and EL, respectively.

Comparing the F2-layer model of IRI with observations at Ibadan

Abstract NmF2 and hmF2 of the IRI-90 model were compared with experimental data at a typical equatorial station, for high and low solar activity. For NmF2 agreement was quite generally found during 05 to 09 LT and for the other hours of the day during June solstice at low solar activity. For high activity good agreement occurs from 05 to 18 LT in the December solstice. Deviations were found at other seasons. As for hmF2 IRI gives larger values during the day at low solar activity while agreement is good in high activity. The post sunset peak that is normally seen in equatorial hmF2 is not shown in the IRI at any solar epoch.