Observation of a Summer Tropopause Fold by Ozonesonde at Changchun,China:Comparison with Reanalysis and Model Simulation

Tropopause folds are one of the key mechanisms of stratosphere-troposphere exchange （STE） in extratropical regions, transporting ozone-rich stratospheric air into the middle and lower troposphere. Although there have been many studies of tropopause folds that have occurred over Europe and North America, a very limited amount of work has been carried out over northeastern Asia. Ozonesondes produced by the Institute of Atmospheric Physics were launched in Changchun （43.9°N, 125.2° E）, Northeast China, in June 2013, and observed an ozone-enriched layer with thickness of 3 km and an ozone peak of 180 ppbv at 6 km in the troposphere. The circulation field from the European Centre for Medium-Range Weather Forecasts Interim Reanalysis （ERA-Interim） dataset shows that this ozone peak was caused by a tropopause fold associated with a jet stream at the eastern flank of the East Asian trough. By analyzing the ozone data from the ozone monitoring instrument and Weather Research and Forecasting model with Chemistry （WRF-Chem） simulations, it was found that a high ozone concentration tongue originating from the lower stratosphere at high latitude （near central Siberia） intruded into the middle troposphere over Changchun between 5 and 8 km on 12 June 2013. The high-resolution WRF-Chem simulation was capable of describing events such as the tropopause fold that occurred on the cyclonic shear side of the jet stream. In addition, the TRAJ3D trajectory model was used to trace the origin of measured secondary ozone peaks in the middle troposphere back, for example, to stratospheric intrusion through the tropopause fold.

Development and Preliminary Evaluation of a Double-cell Ozonesonde

Ozonesondes are widely used to obtain ozone concentration profiles from the surface to the upper atmosphere.A kind of double-cell ozonesonde has been developed at the Institute of Atmospheric Physics （IAP）,Chinese Academy of Sciences （named the ＂IAP ozonesonde＂） based on previous experience over the past 20 years of developing the singlecell GPSO3 ozonesonde.The IAP ozonesonde is of the Electrochemical Concentration Cell （ECC） type.A detailed description of the IAP ozonesonde is firstly provided in the present paper,followed by a presentation of results from a series of launches carried out to evaluate its performance.The analysis involved comparing its observations with measurements from the GPSO3 and ECC ozonesondes （Model type ENSCI-Z） as well as a Brewer spectrophotometer.The results showed that the IAP ozonesonde is a vast improvement over the GPSO3 ozonesonde,able to capture vertical ozone structures very well and in good agreement with ECC ozonesonde measurements.The average difference in the ozone partial pressure between the IAP and ECC ozonesondes was 0.3 mPa from the surface to 2.5 km,close to zero from 2.5 to 9 km and generally less than 1 mPa for layers higher than 9 km.The apparent deviation is likely caused by a decreasing pump flow rate in the IAP ozonesonde which needs further improvement.The total ozone amounts measured by the IAP ozonesonde profiles were highly comparable with the Brewer data with a relative difference of 6％.The development of the IAP ozonesonde and its strong performance will surely accelerate the process of conventional observations of ozone profiles over China in the near future as well as provide more data for ozone research in general.

The Impact of Cut-off Lows on Ozone in the Upper Troposphere and Lower Stratosphere over Changchun from Ozonesonde Observations

In situ measurements of the vertical structure of ozone were made in Changchun （43.53°N, 125.13°E）, China, by the Institute of Atmosphere Physics, in the summers of 2010-13. Analysis of the 89 validated ozone profiles shows the vari- ation of ozone concentration in the upper troposphere and lower stratosphere （UTLS） caused by cut-off lows （COLs） over Changchun. During the COL events, an increase of the ozone concentration and a lower height of the tropopause are observed. Backward simulations with a trajectory model show that the ozone-rich airmass brought by the COL is from Siberia. A case study proves that stratosphere-troposphere exchange （STE） occurs in the COL. The ozone-rich air mass transported from the stratosphere to the troposphere first becomes unstable, then loses its high ozone concentration. This process usually happens during the decay stage of COLs. In order to understand the influence of COLs on the ozone in the UTLS, statistical analysis of the ozone profiles within COLs, and other profiles, are employed. The results indicate that the ozone concentrations of the in-COL profiles are significantly higher than those of the other profiles between ±4 km around the tropopause. The COLs induce an increase in UTLS column ozone by 32% on average. Meanwhile, the COLs depress the lapse-rate tropopause （LRT）/dynamical tropopause height by 1.4/1.7 km and cause the atmosphere above the tropopause to be less stable. The influence of COLs is durable because the increased ozone concentration lasts at least one day after the COL has passed over Changchun. Furthermore, the relative coefficient between LRT height and lower stratosphere （LS） column ozone is -0.62, which implies a positive correlation between COL strength and LS ozone concentration.

Ozone Vertical Profile Characteristics over Qinghai Plateau Measured by Electrochemical Concentration Cell Ozonesondes

An analysis of 50 ozonesondings in Xining (36.43 o N, 101.45 o E , 2296 m, ASL), between April 1995 and August 1996 is presented. General vertical distribution characteristics and seasonal changing of ozone profile are reported. The analysis indicates that the stratospheric ozone concentrations of Autumn and Summer are lower than those of Spring and Winter; and the highest value of the tropospheric ozone concentrations is found in Summer; ozone concentration changing is bigger from the troposphere to the lower stratosphere altitude region, while it is stable in the middle and upper stratosphere region; there is a lower ozone concentration region in 10 -1 5 km altitude; the result why higher ozone concentration of the troposphere occurs in Summer is the ozone injecting from the middle and upper stratosphere.

INTERCOMPARISON OF OZONE VERTICAL PROFILES BETWEEN ECC OZONESONDE AND BREWER UMKEHR MADE OVER QINGHAI PLATEAU OF CHINA

From October 1995 to August 1996.a total of 50 ECC(electrochemical concentration cell) ozonesoundings were made in Xining(36.43°N,101.45°E,2296 m ASL)to study the distribution and seasonal characteristics of ozone profile,and intercompare the Brewer Umkehr ozone profiles obtained at Waliguan Baseline Station over the Qinghai Plateau.It was demonstrated that(1) Umkehr produced estimates of the ozone comparing with ECC profiles were accurate to better than 25% in the 20—38 km altitude range,and where 23—33 km region was the most accurate,within about 15% of the ECC ozonesonde:(2)higher differences between Brewer Umkehr and ECC ozonesonde occurred in the troposphere and lower stratosphere;and ozone amounts were overestimated in Umkehr layers 1,2 and 3,and were underestimated in Umkehr layers 6 and 7 by Brewer Umkehr method.

Vertical characteristics of ozone variation over the Arctic Chukchi Sea region in 1999

In 1999 summer, Chinese Arctic Research Expedition operated the Chukchi Sea. On Chinese icebreaker Xuelong, we made many high resolution ozonesonds measurements. During the period from August 18 to 24, a synoptic scale observation was taken at 75°N, 160°W. Using the above data, together with TOMS total ozone and NCEP circulation data, we showed that atmospheric ozone amount experienced a high low high variation, with low high low tropopause altitude. Correlation analysis showed a close relation between the total ozone and ozone below 13 km, while the variation of the maximum concentration at about 20 km didn't show any relation to the column ozone. In 500 hPa height maps, there was also the weak strong weak southwesterly pattern. Therefore we suggested that the synoptic system might be responsible to a low ozone advection during this ozone variation.

Characteristics of ozone vertical profile observed in the boundary layer around Beijing in autumn

In the autumn of 2008, the vertical profiles of ozone and meteorological parameters in the low troposphere （0-1000 m） were observed at two sites around Beijing, specifically urban Nanjiao and rural Shangdianzi. At night and early morning, the lower troposphere divided into two stratified layers due to temperature inversion. Ozone in the lower layer showed a large gradient due to the titration of NO. Air flow from the southwest brought ozone-rich air to Beijing, and the ozone profiles were marked by a continuous increase in the residual layer at night. The accumulated ozone in the upper layer played an important role in the next day＇s surface peak ozone concentration, and caused a rapid increase in surface ozone in the morning. Wind direction shear and wind speed shear exhibited different influences on ozone profiles and resulted in different surface ozone concentrations in Beijing.