In this paper,an explosive extratropical cyclone(EC)over the Northern Atlantic from 14 to 20 June 2006 was investigated by using the ERA5 reanalysis data provided by European Centre for Medium-Range Weather Forecasts(ECMWF),as well as the infrared satellite imagery provided by Cooperative Institute for Meteorological Satellite Studies(CIMSS).Tropical Storm Alberto underwent an extratropical transition(ET)process and then developed into an explosive cyclone.It was the EC case with maximum deepening rate of central pressure among the ECs that occurred over the Northern Atlantic during the 17 summers from 2000 to 2016.The evolutionary process of this cyclone might be classified into four stages initial,developing,mature and decaying stages.The cloud characteristics associated with this EC at its different stages were documented.The upper-and lower-level circulations as well as the interaction between upper-and lower-level during the explosive intensification of this cyclone were also investigated.It is shown that lower-level atmospheric baroclinicity caused by intense cold and warm advections was a significant environmental condition for the cyclone’s intensification.The positive advection of relative vorticity in the front of 500 hPa trough might provide dynamic forcing for the development of this cyclone.The downward transmission of anomalous upper-level potential vorticity might contribute to the rapid deepening of this cyclone.The latent heat release(Q2/CP)which was mainly located in the middle and lower troposphere,seemed to be conducive to the development of this cyclone.In terms of the Zwack-Okossi equation,the contribution of the absolute vorticity advection term and the diabatic term was always positive during the development of this cyclone.Diabatic heating was the dominan factor which promoted the rapid development of this cyclone.While the temperature advection term and the adiabatic term acted to inhibit development.