Recent research has shown that the occurrence frequency and brightness of polar mesospheric clouds(PMCs)have been gradually increasing since first recorded in 1883;the trend is likely related to global warming and associated anthropogenic activity.The increasing trend is somewhat under debate,however,as not all studies on the subject have reached similar conclusions.Analysis of the thermodynamic mechanism remains necessary to confirm the impact of climate change and the surrounding atmosphere on this trend.Upward-propagating atmospheric gravity waves(GWs)are a thermodynamic process with significant effect on the upper mesosphere,which were addressed in this work by examining characteristics of perturbations induced by small-scale GWs on the ice particle size distribution(PSDs)of PMCs. Using the level_2albedo images and particle effective radius data of both North(NH)and South (SH)hemispheres during 20072008from the cloud imaging and particle size(CIPS)experiment, 6489GW events were distinguished to calculate the corresponding PSDs.The differences of PSDs in the mean clouds formed in GW areas were employed to determine the effect of GWs with regard to latitude and throughout the PMCs seasons.Additionally,the amplitudes in particle radius and wavelength of GWs were used to explore the relationship between the GWs and clouds. The mean radius and width of PSDs in GW areas were 2.5nm and 6.1nm,respectively;less than those of mean clouds in the NH season.The differences were 1.1nm and 7.9nm in the SH season.The radius perturbations induced by GWs were almost negative at latitudes below 80°for both hemispheres,and the absolute values decreased as latitude increased.These distributions reversed at latitudes above 80°.Similarly,the absolute width decreased as latitude increased.Both the mean radius and width were dominated by negative perturbations during the starting and ending stages of the seasons,but increased to positive values in the middle of the seasons.These characteristics are consistent with the distributions of amplitude in particle size induced by GWs regarding latitude and season.GW wavelengths also decreased as latitude increased,reaching larger values during the starting and ending stages but smaller values in the middle of both seasons.The magnitude of variations in the SH season was considerably larger than that in the NH season,and the change rate of perturbation amplitude in particle size varied with wavelength at 0.207nm·km~(-1) in the SH season and 0.163nm·km~(-1) in the NH season. According to our results and those found in the literature,we deduced that the parameters of PSDs in GW areas have direct relationship with GW properties(e.g.,amplitude and wavelength.) Large amplitude and wavelength create large negative perturbation for the mean radius and width.The results presented here further suggest that the micro physical processes under the effect of GWs on ice crystals can be further studied via the cloud micro physical model.