Supercooled water in austral summer in Prydz Bay,Antarctica

Supercooled water with temperatures below freezing point, was identified from hydrographic data obtained by Chinese and Australian expeditions to Prydz Bay, Antarctica, during the austral summer. The study shows that most supercooled waters occurred at depths of 63-271 m in the region north of the Amery Ice Shelf （AIS） front. The maximum supercooling was 0.16℃ below the in-situ freezing point. In temperature and salinity ranges of-2.14 - -1.96℃ and 34.39-34.46, respectively, the water was colder and fresher than peripheral shelf water. The supercooled water had less variability in the vertical profiles compared to shelf water. Based on analysis of their thermohaline features and spatial distribution, as well as the circulation pattern in Prydz Bay, we conclude that these supercooled waters originated from a cavity beneath the AIS and resulted from upwelling just outside of the AIS front. Water emerging from the ice shelf cools to an extremely low temperature （about -2.0℃） by additional cooling from the ice shelf, and becomes buoyant with the addition of melt water from the ice shelf base. When this water flows out of the ice shelf front, its upper boundary is removed, and thus it rises abruptly. Once the temperature of this water reaches below the freezing point, supercooling takes place. In summer, the seasonal pycnocline at -100 m water depth acts as a barrier to upwelling and supercooling. The upwelling of ice shelf outflow water illuminates a unique mid-depth convection of the polar ocean.

THE CCA BETWEEN 500 hPa GEOPOTENTIAL HEIGHT FIELDS OVER NORTHERN HEMISPHERE AND RAINFALL OF CHINA IN MAY

Based on the theory of Canonical Correlation Analysis (CCA), the correlation between 500 hPa geopotential height (H) fields over the Northern Hemisphere (NH) and a 15-region rainfall (R) field of China in May is studied. The results indicate that: (1) there is a strong relationship between the H fields in January / May and the R field in China, (2) the variation of the general circulation over the whole NH (especially the 500 hPa H field over Europe and Asia) can affect the R in China, (3) in January and February the atmospheric general circulation can affect the R mainly by means of planetary waves, while in April and May the main control mechanism can be due to some teleconnections, and (4) the characteristic vectors for R in May and H from January to May have wave train structure, alternating sign from south to north.

Interdecadal Variability in Surface Solar Radiation over Northwest China and Its Possible Cause

The present study investigates the interdecadal variability of seasonal mean surface solar radiation over Northwest China using station observations from 1961-2003. Spring and summer surface solar radiation over Northwest China was lower in the late 1970s through 1990s than in the 1960s through the mid-1970s, and fall and winter surface solar radiation displayed similar patterns. These results indicate that the decrease in spring and summer surface solar radiation may be associated with increased low-cloud cover over Northwest China. Rainfall anomalies were closely related to the low-cloud cover over Northwest China and with the Northern Hemisphere circumglobal teleconnection in spring, summer, and winter.

Origins of intraseasonal rainfall variations over the southern South China Sea in boreal winter

This study investigates the origins of intraseasonal rainfall variations over the southern South China Sea（SCS） region in boreal winter.It is found that intraseasonal rainfall variations over the southern SCS have different origins on the 10-20-day and 30-60-day time scales.On the 10-20-day time scale,large rainfall anomalies over the southern SCS are preceded by strong northerly wind anomalies associated with the East Asian winter monsoon（EAWM）,by about two days.On the 30-60-day time scale,the strong EAWM-related northerly wind anomalies almost appear simultaneously with large rainfall anomalies over the southern SCS.In addition,obvious large rainfall anomalies occur over the southeastern tropical Indian Ocean about one week before the peak southern SCS rainfall anomalies.It indicates that the convection and related circulation anomalies with origins over the tropical Indian Ocean may play an important role in inducing intraseasonal rainfall variations over the southern SCS on the 30-60-day time scale,but not on the 10-20-day time scale.

Numerical Research of the Influences of the Outer Raceway Curvature Radii on the EHL Properties of Ball Bearing

Based on numerical simulation, the influences of outer raceway curvature radii on some EHL properties of deep groove ball bearing were studied in detail. It was found that the second peak film pressure value decreases with the increase of curvature radius Ry. The minimal film thickness increases at first and then decreases with the increase of curvature radius Ry. The minimum film thickness reaches the maximal value when curvature radius Ry is about 1.7r. Film thickness becomes thinner with the increase of Rx with keeping other parameters constant. The conclusions obtained in this paper are very helpful to practical design of ball bearings.

The Relationship between Precipitation and Airflow over the Tibetan Plateau in Boreal Summer

Based on the observation data and the reanalysis datasets, the variability and the circulation features influencing precipitation in the Tibetan Plateau (TP) are investigated. Taking into account the effects of topography, surface winds are deconstructed into flow-around and flow-over components relative to the TP. Climatologically, the flow-around component mainly represents cyclonic circulation in the TP during the summer. The transition zone of total precipitation in the summer parallels the convergence belt between the southerlies and the northerlies of the flow-over component. The leading mode of rainfall anomalies in the TP has a meridional dipole structure, and the first principal component (PC1) mainly depicts the variation of rainfall in the southern TP. The wet southern TP experiences strengthened flow-over, which in turn mechanistically favors intensified ascent forced by the flow-over component. In addition, variations in the Indian summer monsoon (ISM) have an important role in influencing the flow over the southern TP, and the ISM ultimately impacts the precipitation over southern TP.

Statistical Characteristics of Austral Summer Cyclones in Southern Ocean

Characteristics of cyclones and explosively developing cyclones (or 'bombs') over the Southern Ocean in austral summer (December, January and February) from 2004 to 2008 are analyzed by using the Final Analysis (FNL) data produced by the National Centers for Environmental Prediction (NCEP) of the United States. Statistical results show that both cyclones and explosively developing cyclones frequently develop in January, and most of them occur within the latitudinal zone between 55°S and 70°S. These cyclones gradually approach the Antarctic Continent from December to February. Generally cyclones and bombs move east-southeastward with some exceptions of northeastward movement. The lifetime of cyclones is around 2-6 d, and the horizontal scale is about 1000 km. Explosive cyclones have the lifetime of about 1 week with the horizontal scale reaching up to 3000 km. Compared with cyclones developed in the Northern Hemisphere, cyclones over the southern ocean have much higher occurrence frequency, lower central pressure and larger horizontal scale, which may be caused by the unique geographical features of the Southern Hemisphere.

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地球是个大水球

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话说世界国家的分布

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Validation of Aura Microwave Limb Sounder water vapor and ozone profiles over the Tibetan Plateau and its adjacent region during boreal summer

We present validation studies of MLS V2.2 and V3.3 water vapor(WV) and ozone profiles over the Tibetan Plateau(Naqu and Lhasa) and its adjacent region(Tengchong) respectively by using the balloon-borne Cryogenic Frost point Hygrometer and Electrochemical Concentration Cell ozonesonde. Coincident in situ measurements were selected to compare the MLS V2.2 and V3.3 WV and ozone profiles for understanding the applicability of the two version MLS products over the region. MLS V2.2 and V3.3 WV profiles respectively show their differences within ?2.2±15.7%(n=74) and 0.3±14.9%(n=75) in the stratosphere at and above 82.5 h Pa. Accordingly, at 100 h Pa, the altitude approaching the tropopuase height, differences are within 9.8± 46.0%(n=18) and 23.0±45.8%(n=17), and they are within 21.5±90.6%(n=104) and 6.0±83.4%(n=99) in upper troposphere. The differences of MLS ozone are within ?11.7±16.3%(n=135, V2.2) and 15.6±24.2%(n=305, V3.3) at and above 82.5 h Pa. At 100 h Pa, they are within ?3.5±54.4%(n=27) and ?8.7±41.6%(n=38), and within 18.0±79.1%(n=47) and 34.2±76.6%(n=160) in the upper troposphere. The relative difference of MLS WV and ozone profile has significant oscillation and scatter at upper troposphere and lower stratosphere partly due to the stronger gradients of WV and ozone concentrations here as well the linear interpolation of sonde data for the intercomparison. At and below 70 h Pa, the relative differences of MLS ozone are significantly larger over Lhasa during the Tibetan Plateau "ozone valley" season, which is also the Asian Summer Monsoon period. The MLS ozone differences over the three sites are similar in their vertical distributions during that period. A simple linear correlation analysis between MLS and sonde profiles indicates that the sensitivity of MLS profile products is related to concentrations at each pressure level. The MLS V3.3 product sensitivity is slightly improved for WV at and above 82.5 h Pa, whereas it is not obvious for ozone. The possible factors contributing to the differences of the MLS profile products of WV and ozone are discussed.

Averaged NmF2 of cusp-latitude ionosphere in northern hemisphere for solar minimum—Comparison between modeling and ESR during IPY

Based on the ionosphere observation data obtained by EISCAT Svalbard Radar (ESR) in solar minimum year-2007, we analyzed diurnal variations of F2-peak electron density (NmF2) in four seasons under disturbed and quiet geomagnetic conditions. It indicated that the soft precipitation electron had an evident effect on the NmF2 increase at magnetic noon in spring, summer and autumn and the electron precipitation effects were prominent in winter. The comparison between the IRI-2007 model and the observation exhibited that the IRI (International Reference Ionosphere) model had a better NmF2 prediction when the photoionization was dominant during the polar day, but worse when the electron precipitation was dominant during the polar night. We showed that the electrons in lower energy band decreased when the geomagnetic disturbance went greater, which resulted in the lower NmF2. By analyzing the spectrum of precipitation electron under different geomagnetic conditions, it was found that this phenomenon was induced by the energy flux enhancement of precipitation electron of low energy.