The Buoyancy Frequency Of The Atmosphere: Its Temporal And Spatial Distribution And Influencing Factors

We have studied the temporal and spatial distribution,influencing factors of the buoyancy frequency(N),as well as its impact on climates.When presenting its characteristics of temporal and spatial distribution(calculated with the NCEP/NCAR reanalysis),we take the examples of the particular year,months and dates and intend to obtain figures that can reflect the distribution of buoyancy frequency of diurnal,daily and monthly scales.We find that the N~2 can be negative when the time scale is small,and when the time scale gets larger,it tends to take positive values which have slight spatial variations.As is for these time scales,we find high value centers in the extratropical troposphere in the winter hemisphere and tropical stratosphere.We also notice that the distribution of the buoyancy frequency relates to the latitudes and heights,ocean and land,coastal and mountains.The buoyancy frequency can further be expressed as a function of the mean and the difference of the temperatures at two adjacent levels.With the data collected from the samples of different temporal or spatial scales,statistical relationships between buoyancy frequency and these two factors are established with linear regression.The relative contributions of the two factors in the temporal-spatial variations of buoyancy frequency are compared.It is shown that for the interannual sample,the variation of buoyancy frequency on the lower level is dominated by temperature difference;while on the higher level,it is affected by both temperature and temperature difference.Relatively,in the seasonal variations of the buoyancy frequency,their influences change remarkably.On the lower level in the troposphere,the changes take place over plateaus and mountains;on the higher level,they take place in the high latitudes areas.As is for the spatial samples,the influence of temperature will not increase noticeably until stratosphere.We also find that the buoyancy frequency can also affect climates and weathers in remote areas.Analysis shows that it may have direct effects on the moisture rather than the precipitations.