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5. Summary of results and concluding remarksBased on the diurnal analysis under normal conditions we have found that easterlywind prevails during the whole day at all altitudes. The biggest intensities of wind are givenbetween the 0600 and the 1800 hours. The meridional component, on the other hand, there issoutherly wind prevalence between 2 and 5 km during the day, reversing at night. At higheraltitudes (5-10 km) we have observed predominant southerly winds as well as a dailyvariability in the intensity of the wind. This variability can be due to the temperature gradientfrom north to south and the unequal heating between mountains and the Sechura desert. Thespecific causes of this effect will be left for future work.About seasonal analysis in lower troposphere, the meridional wind does not maintain apredominant direction throughout the year. During the winter and the spring the southerlywind dominates all day long. The northerly wind appears only few hours in the afternoon. Onthe other hand, in the summer and autumn, the northerly wind prevails. In the middletroposphere the northerly winds dominates during all seasons and it is maximum at noon. It isnecessary to point out that both the zonal and meridional winds reached their maximumvalues in the winterDuring El Niño 1997-98, in their initial stage we have observed a significant decreaseof easterly wind above 4 km compared to normal periods (see Figure 2a). However, in theirmature and final phase at the same heights we observe a notable increase of the easterly windas height increases. On the other hand, there is an increase in the northerly wind above 4 kmDuring the event 1997-98 in the middle levels the larger differences were observed inintensities of wind along the day, however at lower heights there were significant dailychanges: Reinforcement of the east wind around 0200 and 1000 hours during the mature stageof the event and increasing the variability of meridional wind (approximately 1.5 times more)during the initial stage.We have detected possible precursors of El Niño in the behaviour of the troposphericwind. In the zonal wind there is a strong decrease of the east wind above 4 km., six monthsbefore and during initial stage of "El Niño 1997-98" (Fig. 2b). In addition, there is asignificant decrease of the northerly wind in the meridional wind between 2 and 10 km, butonly during the previous six months to the event 1997-98.More details and figures can be found in Flores et al. [2002]ReferencesFlores L. A., La Madrid J., Chau J. L., Vientos troposféricos observados con el radar VHF enPiura-Perú: condiciones normales versus “El Niño 1997-1998”, Rev. Geof. IPGH, 57, 81-110, 2002.Gage K. S., Balsley B. B., Ecklund W.L., Woodman R. F. and Avery S. K. , Wind-Profilrelatedresearch in the tropical Pacific, J.Geophys. Res., 96(Suplement), 13209-3220, 1991.Gage K. S., McAfee J. R., Colins W. G., Soderman D., Bottger H., Radford A. and Balsley B.B., A comparison of winds observed at Christmas Island using a wind-profiler Dopplerradars with NMC and ECMWF analyses, Bull. Am. Meteorol. Soc., 69, 1041-1046, 1988.Judas T. J., Ecklund W. L. And Balsley B. B., The coaxial collinear antenna. Currentdistribution from the cylindrical antenna equation, IEEE Trans. Antennas Propag., 35,327-331, 1987.Nastrom G. D., Clarck W. L., Vanzandt T. E. And Warnock J. M., Seasonal and diurnalchanges in wind variability from Flatland VHF profiler observations, Beitr. Phys.Atmosph., 69(1), 5-12, 1996.Ragaini E., Rodriguez R., Migioramento del progetto di ricerca sull’ indagine troposfericanella regione di Piura, L’ELETTROTENICA, 79(9), 863-869, 1992.Reynolds R. W. and Smith T. S., A high resolution global sea surface temperatureclimatology, J. Climate, 8, 1571-1538, 1995329