Abstract. We investigate the seasonal and longitude dependence of the daytime, vertical E×B drift velocities, on a day-to-day basis, using a recently-developed technique for inferring realistic E×B drifts from ground-based magnetometer observations. We have chosen only quiet days, A_p<10, from January 2001 through December 2002, so that the main contribution to the variability is due to the variability in the tidal forcing from below. In order to study the longitude dependence in daytime E×B drift velocities, we use appropriately-placed magnetometers in the Peruvian, Philippine, Indonesian and Indian longitude sectors. Since we are particularly interested in quantifying the E×B drift velocities associated with the 4-cell, non-migrating tidal structure, we compare the seasonal and longitude E×B drift structure with TOPEX satellite observations of Total Electron Content (TEC). We outline a plan to establish the magnitude of the longitude gradients that exist in the daytime, vertical E×B drift velocities at the boundaries of the observed 4-cell patterns and to theoretically identify the physical mechanisms that account for these sharp gradients. The paper demonstrates that sharp gradients in E×B drift velocities exist at one of the 4-cell boundaries and outlines how the C/NOFS IVM and VEFI sensor observations could be used to establish the E×B drift longitude gradients at the boundaries of each of the 4 cells. In addition, the paper identifies one of the theoretical, atmosphere/ionosphere models that could be employed to identify the physical mechanisms that might explain these observations.