The physical origin of the intraseasonal variability of the tropical convection is still a subject of debate, in particular for the role of the air-sea interaction in the development and the evolution of these perturbations. The object of the present analysis is to precisely characterize intraseasonal convective events and their associated perturbation of the dynamic fields and of the Sea surface Temperature (SST). Time series of the Outgoing Longwave Radiation (OLR) are first analyzed using an original approach (the Local Mode Analysis) in order to extract the spatio-temporal structure of two strong intraseasonal perturbations during winter 1998-99.  The first mode is centered on the 21st of January and is almost symmetrical relative to the equator, while the second mode, centered on the 6th of March is stronger in the latitude band 7°S-15°S-. The individual convective systems forming the perturbation are extracted from the Meteosat-5 infrared imagery. It is shown that the smallest OLR in the intraseasonal envelope is associated with only a few large convective systems that are preceded a few (3-4) days before by numerous small convective systems. This analysis also shows that, for the Indian Ocean, the propagation of the individual convective systems, within the eastward propagating convective envelope, do not follow the classical westward scheme found over the Pacific. Time series of the low-level (850hPa) winds are further used to document the link between the low-level dynamics and the OLR perturbation. Finally, the variation of the SST field at relatively high spatial and temporal resolutions is investigated thanks to the SST estimated from TRMM-TMI measurements. According to this data set, the perturbation of the SST field associated to the convective perturbation may be up to 3.5K over large areas of the ocean both in January and March but may also remain small for other regions. Quantitative physical arguments will be presented to explain these regional differences and to investigate the potential feedback of these SST perturbations on the characteristics of the intraseasonal perturbations.