Bian Jianchun

A nonlinear regional prediction experiment on a short‐range climatic process of the atmospheric ozone

A regional prediction experiment on the distribution of the atmospheric ozone column over China is performed by means of a spatiotemporal artificial neural network system (STANNS) built by using the monthly mean values of Total Ozone Mapping Spectrometer (TOMS) data from the Nimbus 7 satellite. The experiment region is situated from 72.5°E to 128.75°E and from 22°N to 49°N and divided into a rectangular grid net of 16×10. The data used cover 174 months from November 1978 to April 1993; those from the first 150 months were used to construct STANNS, and those from the last 24 months were used to test the prediction ability. The experiment results are encouraging. All the values of the correlation coefficient between the prediction and the actual fields for 24 or more samples exceed 90% at the lead time of not more than 6 months. This shows that there exists a good agreement between the prediction and the actual fields. In addition, some important features in the ozone distribution, such as the unusual depletion area over the Tibetan Plateau in summer, are also predicted very well. The results also show that, in a rough sense, the prediction accuracy decreases with the increasing of lead time.

The Impact of the South Asia High Bimodality on the Chemical Composition of the Upper Troposphere and Lower Stratosphere

Abstract The South Asia High (SAH) is the dominant feature of the circulation in the upper troposphere and lower stratosphere (UTLS) during the boreal summer, and the upper tropospheric anticyclonic circulation extends into the lower stratosphere. The preferred locations of the center of the SAH occur in two different regions, and the center can be located over the Iranian Plateau or over the Tibetan Plateau. This bimodality has an impact on the distribution of chemical constituents in the UTLS region. We analyzed water vapor (H2O), carbon monoxide (CO), and ozone (O3) data derived from the Aura Microwave Limb Sounder (MLS) and total column ozone data from the Ozone Monitoring Instrument (OMI). For the Iranian Plateau mode of the SAH, the tropospheric tracers exhibited a positive anomaly over the Iranian Plateau and a negative anomaly over the Tibetan Plateau, whereas the stratospheric tracer exhibited a negative and a positive anomaly over the Iranian Plateau and the Tibetan Plateau, respectively. For the Tibetan Plateau mode, however, the distribution of the anomaly was the reverse of that found for the chemical species in the UTLS region. Furthermore, the locations of the extrema within the anomaly seemed to differ across chemical species. The anomaly extrema for H2O occurred in the vicinity of the SAH ridgeline, whereas CO and O3 exhibited a northward shift of 4–8 degrees. These impacts of the variation in the SAH on the chemical constitutes in the UTLS region can be attributed in part to the dynamical structure delineated by the tropopause field and the temperature field at 100 hPa.

Statistics of gravity waves in the lower stratosphere over Beijing based on high vertical resolution radiosonde

The seasonal variation of inertia gravity-wave activity in the lower stratosphere (17―24 km) over Beijing is studied based on the high vertical resolution radionsonde observations (from December 2001 to February 2003) of Beijing Observatory (116―28―∄E, 39∄48∄∄N). Some of the important gravity-wave parameters, such as intrinsic frequency, and propagation direction, are estimated according to the polarized relation among gravity-wave wind components and temperature. Time series of wave energy show that the largest wave amplitudes occur during the winter and the least during the summer, and the average of the KE:PE ratios is about 2.6. Zonal and meridional wind perturbations have almost the same roots of mean variances, which shows that the wave energy in the lower stratosphere is isotropic horizontally. The motion and temperature fields are dominated by waves with vertical wavelengths of 1.5―3 km, which occupy above 80% samples, with a mean value of about 2.3 km. The horizontal wavelengths are mainly distributed between 100―800 km, averaging 445 km. The ratio of the mean horizontal to vertical wavelength is about 200:1, which indicates that the wave propagates nearly horizontally, with a very small vertical angle. The intrinsic frequency is estimated by fitting a polarized ellipse to the wind perturbations after band-filtering waves with a wavelength of 1.5―3 km, and the results show that the intrinsic frequency is dominated by 1f―3.5f, with an averaging value of 2f, corresponding to an intrinsic time period of 9 hours. Wave energy is found to propagate mainly upward, and in the horizontal direction, there is clear azimuthal anisotropy, with predominate northwest propagation against the prevailing wind.

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 of Cloud Detection Methods Using CFH, GTS1, and RS80 Radiosondes

The accuracies of three instruments in measuring atmospheric column humidity were assessed during an upper troposphere and lower stratosphere observation campaign conducted from 7 to 13 August 2009 in Kunming, China. The three instruments are a cryogenic frost-point hygrometer (CFH), a Vaisala RS80 radiosonde (RS80), and a GTS1 radiosonde (GTS1). The accuracy of relative humidity (RH) measurements made by the CFH, GTS1, and RS80 was similar between the surface and 500 hPa (∼5.5 km above sea level). However, above 500 hPa, the errors in RH measurements made by the RS80, relative to measurements made by the CFH, are much less than those detected with the GTS1. Three different retrieval methods for determining cloud boundaries from CFH, RS80, and GTS1 measurements were developed and take into account the differences in accuracy among the three instruments. The method for the CFH is based on RH thresholds at all levels, which demands high accuracy. Given that the accuracy of RH measurements decreases at higher altitudes, the cloud detection methods for RS80 and GTS1 are different for different altitude ranges. Below 5 km, the methods for the RS80 and the GTS1 are similar to that of the CFH; above 5 km, the methods for the RS80 and the GTS1 are both developed based on the second-order derivatives of temperature and RH with respect to height, but with different criteria applied. Comparisons of cloud-layer retrievals derived from the three measurements are also made.

ENSO Signals in Tropospheric Temperature Simulated by an AGCM GAMIL

Abstract Using reanalysis data as a benchmark, the authors evaluate the performance of an Atmospheric General Circulation Model (AGCM) named GAMIL (Grid-point Atmospheric Model of LASG/IAP). GAMIL is used to simulate the tropospheric temperature anomalies associated with the El Niño-Southern Oscillation (ENSO) in boreal winters for the period 1980–99. The results show that the symmetrical components of temperature anomalies simulated by GAMIL closely resemble those in the reanalysis data in spatial patterns, especially in the Northern Hemisphere. The limitation of the model is that the simulated cold anomaly over South Asia is located to the east of the reanalysis. The observed temperature anomalies in the South Pacific and the high latitudes of the Southern Hemisphere are not evident in the simulation. The maximum value is 0.8 K smaller and the minimum value is –0.4 K smaller than the reanalysis. The difference between the simulation and the reanalysis is more evident in the regional features of the asymmetrical components of the temperature anomalies. Our results demonstrate that the previously discovered weak response of the GAMIL model to specified sea surface temperature forcing is dominated by the symmetric (asymmetric) component in the tropics (extra-tropics).

Interdecadal variations of phase delays between two Niño indices at different time scales

Phase delays between two Niño indices—sea surface temperatures in Niño regions 1+2 and 3.4 (1950–2001)—at different time scales are detected by wavelet analysis. Analysis results show that there are two types of period bifurcations in the Niño indices and that period bifurcation points exist only in the region where the wavelet power is small. Interdecadal variation features of phase delays between the two indices vary with different time scales. In the periods of 40–72 months, the phase delay changes its sign in 1977: Niño 1+2 indices are 2–4 months earlier than Niño 3.4 indices before 1977, but 3–6 months later afterwards. In the periods of 20–40 months, however, the phase delay changes its sign in another way: Niño 1+2 indices are 1–4 months earlier before 1980 and during 1986–90, but 1–4 months later during 1980–83 and 1993–2001.