International audienceAs part of the African Monsoon Multidisciplinary Analysis (AMMA) field campaign, rain Drop Size Distribution (DSD) measurements were carried out in Benin, in the Sudanese climatic zone, with optical disdrometers, over 3 rainy seasons. The observed DSDs are well modelled by a gamma distribution, with the value of the shape parameter (μ) close to 5. The average normalized intercept parameter (N0*) is close to 103 mm−1m−3. After classification of the convective and stratiform spectra, it is shown that for a given rain rate the proportion of the bigger drops is higher in the stratiform spectra, consistent with the observed occurrences of ‘N0 jumps' within the squall lines. Specific reflectivity-rain rate (Z-R) relationships were derived for the whole data set, for the squall lines and for the convective and stratiform regions
During the International Equatorial Electrojet Year, high resolution vertical HF coherent radar experiments were performed in the Ivory Coast (9°24′62″N, 5°37′38″W) at frequencies in the range 1–8 MHz. Kilometric scale irregularities were observed in the E and F regions of the daytime equatorial ionosphere. These irregularities constitute a large sporadic E layer within the altitude range 100 to 150 km, larger than the width of the equatorial electrojet. The higher part of this irregular region is detached in the morning and evening forming an intermediate region at 150–160 km. These 150 km echoes overtakes the E region electrojet echoes at 100–120 km at noon. The echolocation shows that the reflections arise from the vertical direction up to 150 km with a significant contribution of reflections from East West directions above 110 km. The F1 region irregularities are characterized by time and height scales significantly larger than the E region irregularities scales. As in the E region, the F1 region reflections arise from the vertical and from East West directions when the reflection distance increases. The variations of the Doppler frequency versus the observation distance at several sounding frequencies are well explained by a horizontal motion of the irregular plasma flow both in the E and F regions with velocities of 100 m/s and 130 m/s respectively.
Abstract. Geomagnetic storm-time variations often occur coherently at high latitude and the day-side dip equator where they a ect the normal eastward Sq ®eld. This paper presents an analysis of ground magnetic ®eld and ionospheric electrodynamic data related to the geomagnetic storm which occured on 27 May 1993 during the International Equatorial Electrojet Year (IEEY) experiment. This storm-signature analysis on the auroral, mid-latitude and equatorial ground ®eld and ionospheric electrodynamic data leads to the identi®cat-ion of a sensitive response of the equatorial electrojet (EEJ) to large-scale auroral return current: this response consists in a change of the eastward electric ®eld during the pre-sunrise hours (0400±0600 UT) coherently to the high-, mid-, and equatorial-latitude H decrease and the disappearance of the EEJ irregularities between the timeinterval 0800±0950 UT. Subsequent to the change in h'F during pre-sunrise hours, the observed foF2 increase revealed an enhancement of the equatorial ionization anomaly (EIA) caused by the high-latitude penetrating electric ®eld. The strengthening of these irregularities attested by the Doppler frequency increase tracks the H component at the equator which undergoes a rapid increase around 0800 UT. The DH variations observed at the equator are the sum of the following components: S R , DP, DR, DCF and DT.
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