Global trends of tropopause folds in recent decades

对流层顶折卷是平流层-对流层物质交换的主要机制.本研究采用三维标记方法,利用1979-2020年间的ERA5再分析数据,分析了对流层顶折卷的时空变化特征及机理.研究结果表明,全球对流层顶折卷的多年变化趋势存在明显的季节性和区域性差异.总体上,对流层顶折卷呈增加趋势,其中北半球的春季,夏季和冬季,对流层顶折卷主要沿副热带急流区呈现明显增加的趋势.进一步分析表明,对流层顶折卷发生频率的增加与大气斜压性增大导致的锋生增强有关,而经向位温梯度的增大使得次级环流增强,也可能促进了对流层顶折卷活动的增多.

The Influence of Meridional Variation in North Pacific Sea Surface Temperature Anomalies on the Arctic Stratospheric Polar Vortex

This study examines the dependence of Arctic stratospheric polar vortex(SPV)variations on the meridional positions of the sea surface temperature(SST)anomalies associated with the first leading mode of North Pacific SST.The principal component 1(PC1)of the first leading mode is obtained by empirical orthogonal function decomposition.Reanalysis data,numerical experiments,and CMIP5 model outputs all suggest that the PC1 events(positive-minus-negative PC1 events),located relatively northward(i.e.,North PC1 events),more easily weaken the Arctic SPV compared to the PC1 events located relatively southward(i.e.,South PC1 events).The analysis indicates that the North PC1-related Aleutian low anomaly is located over the northern North Pacific and thus enhances the climatological trough,which strengthens the planetary-scale wave 1 at mid-to-high latitudes and thereby weakens the SPV.The weakened stratospheric circulation further extends into the troposphere and favors negative surface temperature anomalies over Eurasia.By contrast,the South PC1-related Aleutian low anomaly is located relatively southward,and its constructive interference with the climatological trough is less efficient at high latitudes.Thus,the South PC1 events could not induce an evident enhancement of the planetary-scale waves at high latitudes and thereby a weakening of the SPV on average.The Eurasian cooling associated with South PC1 events(positive-minus-negative PC1 events)is also not prominent.The results of this study suggest that the meridional positions of the PC1 events may be useful for predicting the Arctic SPV and Eurasian surface temperature variations.

Nutrient-regulated dynamics of chondroprogenitors in the postnatal murine growth plate

Longitudinal bone growth relies on endochondral ossification in the cartilaginous growth plate,where chondrocytes accumulate and synthesize the matrix scaffold that is replaced by bone.The chondroprogenitors in the resting zone maintain the continuous turnover of chondrocytes in the growth plate.Malnutrition is a leading cause of growth retardation in children;however,after recovery from nutrient deprivation,bone growth is accelerated beyond the normal rate,a phenomenon termed catch-up growth.Although nutritional status is a known regulator of long bone growth,it is largely unknown whether and how chondroprogenitor cells respond to deviations in nutrient availability.Here,using fate-mapping analysis in Axin2CreERT2 mice,we showed that dietary restriction increased the number of Axin2+chondroprogenitors in the resting zone and simultaneously inhibited their differentiation.Once nutrient deficiency was resolved,the accumulated chondroprogenitor cells immediately restarted differentiation and formed chondrocyte columns,contributing to accelerated growth.Furthermore,we showed that nutrient deprivation reduced the level of phosphorylated Akt in the resting zone and that exogenous IGF-1 restored the phosphorylated Akt level and stimulated differentiation of the pooled chondroprogenitors,decreasing their numbers.Our study of Axin2CreERT2 revealed that nutrient availability regulates the balance between accumulation and differentiation of chondroprogenitors in the growth plate and further demonstrated that IGF-1 partially mediates this regulation by promoting the committed differentiation of chondroprogenitor cells.

Impact of intensity variability of the Asian summer monsoon anticyclone on the chemical distribution in the upper troposphere and lower stratosphere

亚洲夏季风期,平流层-对流层物质交换过程能显著影响上对流层下平流层化学成分的浓度变化和空间分布.然而,亚洲夏季风反气旋强度的季节内变化对其内部和周围地区化学成分水平分布的影响尚不清楚.本文将亚洲夏季风反气旋划分为季节内强周期和弱周期,发现当亚洲夏季风反气旋更强时,100 hPa O_(3)低值区的面积更大,O_(3)浓度更低.但是这种影响主要体现在6月份,7,8月的O_(3)水平分布还受东南亚地区深对流的影响.这些结果表明亚洲夏季风反气旋强度和深对流的季节内变化可以显著影响亚洲夏季风期上对流层下平流层的化学分布.

Impacts of the atmospheric apparent heat source over the Tibetan Plateau on summertime ozone vertical distributions over Lhasa

青藏高原(TP)是一个对气候变化敏感的地区,其上空的臭氧分布影响着青藏高原及其周边地区的大气环境.北半球夏季青藏高原上空臭氧柱总量相对较低的现象,及其时空变化受到广泛关注.本研究利用北半球夏季5年的拉萨上空臭氧的气球测量数据,研究高原上空大气视热源(Q1)对臭氧垂直分布的影响并探讨了该过程的机制.结果表明,当TP上空对流层整体的Q1相对较高时,拉萨上空对流层臭氧浓度下降.大气更强的上升运动伴随着TP主体区域上空的Q1的增大.因此,当夏季Q1较高时,由于近地表低浓度臭氧空气向上输送,拉萨上空的对流层臭氧浓度下降.