Analysis of South Asian Monsoons within the Context of Increasing Regional Black Carbon Aerosols

South Asian monsoons were analyzed within the context of increasing emissions of black carbon(BC) aerosols using a global atmospheric general circulation model.The BC aerosols were allowed to increase only over the south Asian domain to analyze the impacts of regional black carbon over the climatological patterns of monsoons.The black carbon significantly absorbed the incoming short wave radiation in the atmosphere,a result that is consistent with previous studies.Pre-monsoon(March-April-May) rainfall showed positive anomalies,particularly for some coastal regions of India.The summer(June-July-August) rainfall anomalies were negative over the northern Himalayas,Myanmar,southern China,and most of the regions below 20°N due to the decrease in temperature gradients induced by the absorption of radiation by BC aerosols.The vertical wind speed anomalies indicated that these regions experienced less convection,which reduces the precipitation efficiency of the monsoon system in South Asia.     

Influence of ridges on hydrographic parameters in the Southwest Indian Ocean

The objective of the paper is to use the data collected along two meridional sections (45° E and 57°30′ E) during the austral summer (January–March) 2004 to understand the influence of seabed topography across the Madagascar and Southwest Indian Ridges on hydrographic parameters. The study was supplemented by World Ocean Circulation Experiment (WOCE) Conductivity-Temperature-Depth data collected during February–March 1996 along 30° E, as well as Levitus climatology. A southward shift of 2° latitude (between 45° E and 57°30′ E) was recorded for the two predominant frontal structures, i.e., the Agulhas Return Front and Southern Subtropical Front, which is attributed to the influence of seabed topography on hydrographic parameters. No significant spatial variation of these fronts was noted between the 30° E and 45° E meridional sections. Between latitudes 31° S and 42° S, the temperature and salinity structures show deepening over the ridges. The Antarctic Circumpolar Current core was detected between 40°15′ S and 43° S.     

Storminess and surges in the South-Western Approaches of the eastern North Atlantic: the synoptic climatology of recent extreme coastal storms

The climatology of intense winter cyclone events in the eastern North Atlantic responsible for high magnitude surge generation (top 1% of events) within the region of the South-Western Approaches to northwest France and southwest England is extracted from daily sea-level and 500-hPa level atmospheric pressure analyses. Cluster analysis yields discrete cyclone track regimes linked to upper airflow patterns being responsible for the generation of intense storms (central pressure at sea-level ≤990 hPa) which promote severe surge events ≥60 cm along the French coast of the South-Western Approaches. Fluctuations in storminess are strongly influenced by the southward intrusion and strengthening of the jet stream in mid-Atlantic. These occurrences are often associated with negative sea surface temperature (SST) anomalies near Newfoundland and a strengthening of the thermal gradient across the Atlantic well to the south of its normal position. Resultant cyclogenesis promotes storms displaying a delay in minimum central pressure attainment until well east of 14°W, encouraging enhancement of surge flow. Stepwise multiple regression analysis indicates that the most influential variables in promoting severe surge events in the South-Western Approaches are trans-Atlantic sea surface temperature gradients. The most important influence is the prevailing west–east sea surface temperature gradient during the month of the storm, followed by that for the prior month of the storm and thirdly, the north–south sea surface temperature gradient prevailing during the month of the event. Other influential variables reflect the character of the cyclone, storm duration, mean deepening rate of storm central pressure, the value of the outermost closed isobar around the storm centre, and the longitudinal position of the outermost closed isobar to the right of the cyclone track. In contrast, the North Atlantic Oscillation (NAO) is not very effective as a discriminator of surge activity. This may reflect the greater intra-month volatility of parameters used to derive the NAO index than of other monthly variables considered in the study. The lack of resolvability at the individual storm level probably also arises because of the monthly detailing of the NAO against storms of 2–3 days duration. This behavioural model of extreme storminess in the South-Western Approaches to northwest France provides the basis by which extremes of coastal susceptibility can be calibrated.     

Vertical exchange due to horizontal density gradients in lakes; the case of Lake Lucerne

Recent field investigations have shown that differential mixing causes a significant density driven exchange between the two eastern basins of Lake Lucerne, Gersauersee and Urnersee. The long term vertical mixing characteristics during the winter mixing period and the influence of the resulting exchange flow on water quality are examined through the analysis of ten years (1964 to 1974) of monthly limnological data. Vertical homogenization of the state variables (temperature, electric conductivity and density) occurred on average once every two years in Urnersee, but not once in Gersauersee where the ten year average winter mixed-layer depth extended to 120 m. In Urnersee intense mixing was evident over the whole water column for every year. In contrast intense mixing in the deeper layers of Gersauersee occurred approximately once every four years. A three layer model shows that theT/ ₂₀ signature of the Gersauersee intermediate water correlates best with the Urnersee deep water confirming the regular occurrence of a density driven exchange. For the lower layers the oxygen consumption rate in Urnersee was approximately twice that for Gersauersee. It appears the exchange flow can act either as a source or sink for the oxygen balance of Urnersee deep water. The larger rate in Urnersee hypolimnion might also be associated with the larger sediment input to this system. Density driven exchange resulting from differential mixing is probably an important contribution to the vertical water replenishment in many lakes.     

Effects of ionospheric horizontal gradients on differential GPS

This paper outlines the effect of horizontal ionospheric gradients on transionospheric path propagation such as for the case of GPS signals. The total electron content (TEC) is a function of time of day, and is much influenced by solar activity and also the receiving station location. To make the model applicable for long baselines, for which the ionosphere is not generally well correlated between receiving stations, the ionospheric gradients should be taken into account. In this work the signal path is determined using a modified ray-tracing technique together with a homing-in method. Results show that horizontal gradients can have a significant effect on GPS positioning for both single station positioning and differential GPS. For differential GPS, the ionospheric delay can, however, be either increased or decreased compared with the case of no gradient, depending on the gradient direction.     

Estimating the internal pressure gradient errors in a σ-coordinate ocean model for the Nordic Seas

Internal pressure gradient estimation is problematic in σ-coordinate ocean models and models based on more generalised topography following coordinate systems. Artificial pressure gradients in these models may create artificial flow. In recent literature, several methods for reducing the errors in the estimated internal pressure gradients are suggested. A basin with a bell-shaped seamount in the middle has often been applied as a test case. To supplement the findings from these more idealised experiments, the internal pressure gradient errors in a σ-coordinate ocean model for the Nordic Seas are discussed in the present paper. Three methods for estimating internal pressure gradients are applied in these experiments. The sensitivity of the results to the subtraction of background stratification and to the horizontal viscosity are also investigated. For the extended Nordic Seas case, basin scale modes dominate after a few days of simulation. The errors in the transports across some sections may be larger than 1 Sv (1 Sv = 10⁶ m³ s^− 1) in these studies with 16-km grid resolution. The order of magnitude of the errors in the transports of Atlantic water into the Nordic Seas is approximately 0.5 Sv or between 5 and 10 % of recent transport estimates based on measurements. The results do not indicate that the errors are generally reduced if the background stratification is subtracted when estimating internal pressure gradients in terrain following models. However, the results from the experiments initialised with the background stratification show that the erroneous flows may be reduced considerably by using more recent techniques for estimating internal pressure gradients, especially for higher values of horizontal viscosity.     

莫桑比克罗非鱼在降温过程中与呼吸有关的血糖和乳酸含量变化的研究

在海水中养殖的莫桑比克罗非鱼(Oreochromis mossambicus),水温从20℃开始,以1℃/小时速度下降到10℃为终止温度时发现随着温度的逐渐下降,呼吸次数逐渐减少,水温降至14℃以下时,明显地表现出机能的衰竭。本文对与鱼类体温调节有关的血糖和乳酸的含量,在不同的温度梯度下进行了测定。并对以上两种供能物质的变动情况与呼吸机能衰竭的相互关系进行了分析和讨论。     

基于启动压力梯度的低渗透砂岩储层分类研究

利用大庆杏树岗油田的取芯资料、论述了低渗透储层的岩性、物性、含油性以及渗流特征。通过测试不同渗透率岩芯样品的启动压力梯度．得出了启动压力梯度与渗透率之间具有明显的相关性．不同渗透率储层的启动压力梯度变化率的数量级不同,并依此建立了低渗透砂岩储层分类的新方法。按照该方法重新确定了低渗透储层的渗透率上限．并将低渗透储层划分为3种类型。