通常基于准地转的变换的欧拉平均框架下提出的涡动热通量近似理论计算极区平流层温度变化的动力和非绝热加热贡献， 但是这可能会带来一定的误差。本文根据Liu and Fu（2019）提出的欧拉平均框架下新形式的面积加权平均的热力学能量方程， 通过滑动累加得到逐月的温度变化方程。再利用1980 -2019年欧洲中期天气预报中心第五代再分析资料（European Centre for Medium-range Weather Forecasts fifth reanalysis data， ERA5）， 计算北半球极区低平流层100 hPa在全时段（1980 -2019年）和两个分时段（1980 -1999年、 2000 -2019年）各月温度增量、 动力加热、 非绝热加热和对流加热项（W项）的气候平均值， 进而讨论涡动热通量近似理论成立的最佳参考纬度。结果表明， 新导出的W项使得极区累积的动力和非绝热加热项之和与温度增量项之间的误差在冬春季减少了一半。在100 hPa上， W项随月份和纬度变化， 尤其在冬春季节对温度变化贡献明显， 由此得到涡动热通量近似成立的最佳参考纬度应该在W项的零等值线附近。进一步验证表明参考纬度可以取在50°N。

Stratospheric atmosphere is jointly affected by dynamical， radiative and chemical processes.Since the 1970s， the greenhouse gas emission and ozone depletion caused by anthropogenic activities have driven significant stratospheric cooling， so the tropospheric warming and the stratospheric cooling are both important criteria for global climate change.Observational and modeling studies disclosed that the formation of polar stratospheric clouds at very low stratospheric temperatures is an important condition for rapid ozone depletion.The weak polar vortex event related to the stratospheric sudden warming can even propagate downward to the troposphere and induce the tropospheric circulation anomaly， further leading to the extreme cold event in the middle and high latitude continents.Therefore， it is necessary to clearly understand the causes of stratospheric temperature changes at the background of global warming.Under quasigeostrophic scaling， the eddy heat flux approximation theory within the transformed Eulerian-mean framework is usually used to calculate the dynamical and radiative heating contributions of the Arctic stratospheric temperature changes， but this may bring certain errors.In this paper， according to a new area-weighted averaged thermodynamic equation by Liu and Fu （2019） within the Eulerian-mean framework， a monthly temperature change equation is constructed by time-sliding accumulation.Then using the European Centre for Medium-range Weather Forecasts fifth reanalysis data （ERA5） during 1980-2019， we calculate the climatological monthly temperature increment， dynamical heating， diabatic heating and convective heating term （W term） in the Arctic lower stratosphere， respectively， during the whole period 1980-2019 and two sub periods （1980-1999 and 2000-2019）， and discuss the best reference latitude for the eddy heat flux approximation theory.The results show that the newly derived W term reduces the imbalance between the Arctic temperature increment term and the sum of cumulative dynamical and diabatic heating by half in winter and spring.At 100 hPa， W term changes with month and latitude， nontrivial especially in winter and spring.Therefore， the best reference latitude for the eddy heat flux approximation should be near the zero contour line of the W term.Further verification shows that the reference latitude can be taken at 50°N.