Because of the dawn-dusk electric field Edd, plasma in the magnetotail convects from the lobe toward the central plasma sheet (CPS). In the absence of space or velocity diffusion due to plasma turbulence, convection would yield a steady state distribution function f=V-2/3g(v2V2/3), where V is the flux tube volume. Starting with such a distribution function and a plasma beta which varies from &bgr;>1 in the CPS to &bgr;≪1 in the lobe, we study the evolution of the ion distribution function considering the combined effects of ion diffusion by kinetic Alfv¿n waves (KAW) in the ULF frequency range (1--10 mHz) and convection due to Edd¿B drift in the plasma sheet boundary layer (PSBL) and outer central plasma sheet (OCPS). Our results show that during the early stages after launching the KAWs, a beamlike ion distribution forms in the PSBL and at the same time the plasma density and temperature decrease in the OCPS. Following this stage, ions in the beams convect toward the CPS resulting in an increase of the plasma temperature in the OCPS. We also discuss the effects on the polytropic index &ggr; by simultaneous convection and wave-induced diffusion, both in the PSBL and CPS. We find that &ggr; is less than the adiabatic value (&ggr;ad=2/3) in the OCPS but approaches the adiabatic value in the CPS and in the PSBL. ¿1991 American Geophysical Union