Evolutionary Features of Marine Atmospheric Boundary Layer (MABL) over the Arabian Sea and the Onset of Monsoon over Kerala during ARMEX-2003

In this study an attempt has been made to examine the evolutionary features of the dynamic and thermodynamic characteristics of the marine atmosphere over the South-East Arabian Sea near 9.22°N, 74.51°E just two to three days prior to the onset of southwest monsoon over Kerala during 2003 and seek the linkages with the large-scale flow in the lower and middle troposphere at that time over the region. The marine meteorological data collected onboard ORV Sagarkanya as part of the experiment ARMEX-2003 for 4–8 June, 2003 are used. The monsoon onset over Kerala occurred on 8 June, 2003. The observed changes in the marine atmospheric boundary layer (MABL) characteristics just two days prior to the onset are discussed. It is observed that the MABL increased in height up to 4 km on 6 June from an initial height 2.8 km on 5 June. The top of the MABL dried up (Relative Humidity RH ~ 30–40%) with weak and variable winds throughout the day on 6 June while the air at 850 hPa is relatively humid (RH ~ 50–80%) but not saturated. A sequential increase in RH is associated with a change in the winds from southwesterly to westerly from 6 June onwards until the onset date. The changes in the lower and middle troposphere flow patterns over the Arabian Sea and Indian region are highlighted.     

A Diagnostic Study of the Cyclonic Storm over the Arabian Sea during June 1994

—Based on the NCMRWF analysis over the Arabian Sea, a complete energy cycle of the severe cyclonic storm that formed in the beginning of June 1994 in the east central Arabian Sea is carried out, using the in-house developed energy package. Both barotropic and baroclinic energy conversions are responsible for the maintenance of the system, however dominance of one over the other is noticed at different stages of the system at different heights. Dynamical characteristics of synoptic scale monsoon flow surrounding the cyclonic storm are also investigated. By examining the generation and dissipation terms, it is observed that both zonal and eddy components of the synoptic scale flow act as source of energy for the cyclonic storm, both in the predeveloped and developed stages.     

Understanding how physical-biological coupling influences harmful algal blooms,low oxygen and fish kills in the Sea of Oman and the Western Arabian Sea

In the last decade, green Noctiluca scintillans with its symbiont and other dinoflagellates such as Cochlodinium polykrikoides, Prorocentrum micans and Scrippsiella trochoidea have become the dominant HABs, partially replacing the previously dominant diatoms and red Noctiluca scintillans, especially during the northeast monsoon. Fish kills in the Sea of Oman are linked to a slow seasonal decline in oxygen concentration from January to November, probably due to the decomposition of a series of algal blooms and the deep, low oxygen waters periodically impinging the Omani shelf. In the western Arabian Sea, cyclonic eddies upwell low oxygen, nutrient-rich water and the subsequent algal bloom decays and lowers the oxygen further and leads to fish kills. Warming of the surface waters by 1.2 °C over the last 5 decades has increased stratification and resulted in a shoaling of the oxycline. This has increased the probability and frequency of upwelling low oxygen water and subsequent fish kills.     

Dynamical mechanism of the stratospheric quasibiennial oscillation impact on the South China Sea Summer Monsoon

The National Center for the Atmospheric Research (NCAR) middle atmospheric model is used to study the effects of the quasi-biennial oscillation in the stratosphere (QBO) on the tropopause and uppe troposphere, and the relationship between the QBO and South China Sea Summer Monsoon (SCSSM is explored through NCEP (the National Centers for Environmental Prediction)/NCAR, ECMWF (Euro pean Centre for Medium-Range Weather Forecasts) monthly mean wind data and in situ sounding data The simulations show that the QBO-induced residual circulations propagate downwards, and affect the tropopause and upper troposphere during the periods of mid-late QBO phase and phase transition Meanwhile, diagnostic analyses indicate that anomalous circulation similar to SCSSM circulation is generated to strengthen the SCSSM during the easterly phase and anomalous Hadley-like circulation weakens the SCSSM during the westerly. Though the QBO has effects on the SCSSM by meridiona circulation, it is not a sole mechanism on the SCSSM TBO mode.     

Influence of Solar-Geophysical Factors on the State of the Stratospheric Polar Vortex

Geomagnetism and Aeronomy - The stratospheric polar vortex is one of the most important connecting links between solar activity and circulation of the lower atmosphere at extratropical latitudes....     

Large-Scale Environmental Influences on the Onset, Maintenance, and Dissipation of Six Sea Fog Cases over the Yellow Sea

Sea fog is typically formed and developed under a set of favorable environmental conditions, which are associated with the station pressure changes, sea level pressure, winds, temperature, water vapor supply, and sea surface temperature. Understanding of these environmental factors during the evolution of a sea fog episode is crucial for forecasting the occurrence and severity of sea fogs over the ocean and adjacent coastal areas. In this study, the large-scale environment variability of six fog events over the Yellow Sea was investigated. It was realized in the present study that the northwest Pacific Ocean high (NPH) is vital to fog formation over the Yellow Sea. In our study, six fog cases can be basically divided into two types: (1) pressure-weakening type, (2) pressure-strengthening type. The former type happened in spring and the latter type in summer. Prevailing southerly winds, accompanied with the well-positioned NPH, may supply a large amount of warm water vapor for the fog formation and maintenance. The intensity of the air temperature inversion is stronger in summer cases than that in spring ones. The wind direction change from south to north and the unstable lower atmosphere may lead to fog’s dissipation. This study may provide a comprehensive understanding of sea fog’s onset, maintenance, and dissipation over the Yellow Sea.     

Dynamics behind warming of the southeastern Arabian Sea and its interruption based on in situ measurements

A study of the inter-annual variability of the warming of the southeastern Arabian Sea (SEAS) during the spring transition months was carried out from 2013 to 2015 based on in situ data from moored buoys. An attempt was made to identify the roles of the different variables in the warming of the SEAS (e.g., net heat flux, advection, entrainment, and thickness of the barrier layer during the previous northeast monsoon season). The intense freshening of the SEAS (approximately 2 PSU) occurring in each December, together with the presence of a downwelling Rossby wave, supports the formation of a thick barrier layer during the northeast monsoon season. It is known that the barrier layer thickness, varying each year, plays a major role in the spring warming of the SEAS. Interestingly, an anomalously thick barrier layer occurred during the northeast monsoon season of 2012–2013. However, the highest sea surface temperature (31 °C) was recorded during the last week of April 2015, while the lowest sea surface temperature (29.7 °C) was recorded during the last week of May 2013. The mixed layer heat budget analysis during the spring transition months proved that the intense warming has been mainly supported by the net heat flux, not by other factors like advection and entrainment. The inter-annual variability analysis of the net heat flux and its components, averaged over a box region of the SEAS, showed a substantial latent heat flux release and a reduction in net shortwave radiation in 2013. Both factors contributed to the negative net heat flux. Strong breaks in the warming were also observed in May due to the entrainment of cold sub-surface waters. These events are associated with the cyclonic eddy persisting over the SEAS during the same time. The entrainment term, favoring the cooling, was stronger in 2015 than that in 2013 and 2014. The surface temperatures measured in 2013 were lower than those in 2014 and 2015 despite the presence of a thick barrier layer. The substantial decrease in net heat flux along with entrainment cooling has been identified as causes for this behavior.     

Influence of the Planetary Boundary Layer Physics on Medium-range Prediction of Monsoon over India

—The present study emphasizes the importance of proper representation of boundary layer physics in a general circulation model. The Turbulent Kinetic Energy (TKE) closure scheme incorpo rates important processes of the Planetary Boundary Layer (PBL) compared to a simplistic first-order closure model. Hence the model which has the TKE closure scheme is capable of simulating important weather systems associated with summer monsoon, such as monsoon depressions and lows that form over the Indian subcontinent quite well compared to the first-order closure model. The present study indicates better performance of the global model with the TKE scheme in the prediction of the monsoon circulation, including the tracks of the depressions over the Indian subcontinent. Medium-range weather prediction has also improved with the use of the TKE closure. However further studies are necessary to improve the forecast, with emphasis on boundary layer processes.     

A Note on the Maintenance of Asian Summer Monsoon Circulation

In this paper, the maintenance of Asian summer monsoon circulation is compared in the National Centres for Environmental Prediction/National Centre for Atmospheric Research (NCEP/NCAR) reanalysis and National Centre for Medium Range Weather Forecasting (NCMRWF), India operational analysis. The time mean summer monsoon circulation is bifurcated into stable mean and transient eddy components. The mean component of the summer monsoon circulation is elucidated through the study of large-scale balances of kinetic energy, heat and moisture. Although the balance requirements are fairly satisfied by both NCEP/NCAR and NCMRWF fields, a major difference is noticed. Strong monsoon circulation is evinced by NCEP/NCAR over the Oceanic regions and NCMRWF over the landmass. The various mean budgets under consideration indicated this feature invariably.     

A Study on Climatological Features of the Asian Summer Monsoon: Dynamics, Energetics and Variability

A continuing goal in the diagnostic studies of the atmospheric general circulation is to estimate various quantities that cannot be directly observed. Evaluation of all the dynamical terms in the budget equations for kinetic energy, vorticity, heat and moisture provide estimates of kinetic energy and vorticity generation, diabatic heating and source/sinks of moisture. All these are important forcing factors to the climate system. In this paper, diagnostic aspects of the dynamics and energetics of the Asian summer monsoon and its spatial variability in terms of contrasting features of surplus and deficient summer monsoon seasons over India are studied with reanalysis data sets. The daily reanalysis data sets from the National Centre for Environmental Prediction/National Centre for Atmospheric Research (NCEP/NCAR) are used for a fifty-two year (1948–1999) period to investigate the large-scale budget of kinetic energy, vorticity, heat and moisture. The primary objectives of the study are to comprehend the climate diagnostics of the Asian summer monsoon and the role of equatorial convection of the summer monsoon activity over India.It is observed that the entrance/exit regions of the Tropical Easterly Jet (TEJ) are characterized by the production/destruction of the kinetic energy, which is essential to maintain outflow/inflow prevailing at the respective location of the TEJ. Both zonal and meridional components contribute to the production of kinetic energy over the monsoon domain, though the significant contribution to the adiabatic generation of kinetic energy originates from the meridional component over the Bay of Bengal in the upper level and over the Somali Coast in the low level. The results indicate that the entire Indian peninsula including the Bay of Bengal is quite unstable during the summer monsoon associated with the production of vorticity within the domain itself and maintain the circulation. The summer monsoon evinces strong convergence of heat and moisture over the monsoon domain. Also, considerable heat energy is generated through the action of the adiabatic process. The combined effect of these processes leads to the formation of a strong diabatic heat source in the region to maintain the monsoon circulation. The interesting aspect noted in this study is that the large-scale budgets of heat and moisture indicate excess magnitudes over the Arabian Sea and the western equatorial Indian Ocean during surplus monsoon. On the other hand, the east equatorial Indian Ocean and the Bay of Bengal region show stronger activity during deficient monsoon. This is reflected in various budget terms considered in this study.     

A Nonlinear Model of Level Variations in the Caspian Sea

A new thermophysical mechanism of the Caspian Sea level variations is proposed. The mechanism incorporates the effect exerted on the dynamics of the water budget of the Caspian Sea by the nonlinear dependence of the evaporation rate on the moistening of the basin.     

Influence of seasonal circulation on flushing of the Irish Sea

We applied a three-dimensional general ocean and coastal circulation model to the Irish Sea in order to determine water renewal time scales in the region. The model was forced with meteorological data for 1995, a year with relatively warm summer and when extensive hydrographic surveys were conducted in the Irish Sea. We investigated intra-annual variability in the rates of net flow through the Irish Sea and carried out several flushing simulations based on conservative tracer transport. The results indicate that the net northward flow of 2.50 km³/d is seasonally highly variable and under certain conditions is reversed to southward. The variability in obtained residence times is high; baroclinic effects are significant. Obtained results point at the importance of spatial and temporal consideration for transport of pollutants in the shelf seas. Implications for management are numerous and involve activities such as transport, fishing, use of resources, nature conservation, monitoring, tourism and recreation.     

A Study on the Performance of the NCMRWF Analysis and Forecasting System During Asian Summer Monsoon: Thermodynamic Aspects

—The thermodynamic characteristics of the Asian summer monsoon are examined with a global analysis-forecast system. In this study, we investigated the large-scale balances of heat and moisture by making use of operational analyses as well as forecast fields for June, July and August (JJA), 1994. Apart from elucidating systematic errors in the temperature and moisture fields, the study expounds the influence of these errors on the large-scale budgets of heat and moisture over the monsoon region. The temperature forecasts of the model delineate predominant cooling in the middle and lower tropospheres over the monsoon region. Similarly, the moisture forecasts evince a drying tendency in the lower troposphere. However, certain sectors of moderate moistening exist over the peninsular India and adjoining oceanic sectors of the Arabian Sea and Bay of Bengal.¶The broad features of the large-scale heat and moisture budgets represented by the analysis/forecast fields indicate good agreement with the observed aspects of the summer monsoon circulation. The model forecasts fail to retain the analyzed atmospheric variability in terms of the mean circulation, which is indicated by underestimation of various terms of heat and moisture budgets with an increase in the forecast period. Further, the forecasts depict an anomalous diabatic cooling layer in the lower middle troposphere of the monsoon region which inhibits vertical transfer of heat and moisture from the mixed layer of the atmospheric boundary layer to the middle troposphere. In effect, the monsoon circulation is considerably weakened with an increase in the forecast period. The treatment of shallow convection and the use of interactive clouds in the model can reduce the cooling bias considerably.     

CT机型与管电压对图像质量影响的体模研究

目的:使用体模评价两种CT机型两组管电压下的图像质量。方法:采用西门子SOMATOM Force CT和飞利浦IQon Spectral CT分别扫描Catphan500图像质量控制体模的CTP 528和CTP 515组件。对比研究两台机器4组图像,分别为Force_120kVp,Force_140kVp,IQon_120kvp以及IQon_140kvp图像;4组图像均为20 mGy剂量。评价指标包括高对比度分辨率[CTP 528最佳线对（1～2 lp/cm）]、低对比度分辨率[CTP 515 1％ 浓度下最小孔径（直径2～15 mm）]、图像噪声、对比噪声比（CNR）和信噪比（SNR）。结果:Force_120kVp和IQon_120kvp两组图像的高对比度分辨率最高（均为6 lp/cm）。4组图像低对比度分辨率相同（最小孔径均为5 mm）。Force_120kVp图像噪声最小（2.500±0.000）,且SNR最高（30.806±1.398）;噪声和SNR在4组图像间差异具有统计学意义。IQon_140kvp图像的CNR最高（3.325±0.300）,各组图像间差异无统计学意义。结论:不同机型不同管电压下的图像质量存在差异;两台机器120 kVp图像的对比度分辨率略好于140 kVp图像;Force CT的120 kVp图像相比140 kVp图像的图像噪声更小,而IQon Spectral CT的两组图像噪声参数无显著差别。      

关于南海北部滨海断裂带的研究

南海北部的滨海断裂带是位于南澳岛之东粤东南滨海地区的一条北东东走向的构造带。由于其所处的构造位置而一直被地球科学工作者所关注,并从不同角度作了不少研究。在广泛收集有关断裂带的资料和研究成果的基础上,对前人关于断裂带存在的依据、断裂带发育的时代、断裂带的构造属性和第四纪活动情况的认识作了简要归纳,并就断裂带的分布、构造属性等作了初步分析。     

强震前海平面异常变化特征研究

使用渤海沿岸8个验潮站的海潮潮位观测资料,根据近海或沿岸地区强震前后海平面变化的实例,分析了海平面变化的前兆意义。资料证实,大部分近海大地震前局部海域存在着可以识别的海平面异常变化。通过周期分析方法和潮汐分析方法来消除各种周期及非周期因素的影响,可以显示出地壳垂直形变的变化,分析结果表明,渤海沿岸的海平面变化不仅具有丰富的地质构造活动信息,而且可能反映较大地震前后的地壳形变过程。提取海平面地壳垂直形变信息对较大地震的预报和与海洋有关灾害的预测有重要意义。     

Study of the Evaluation Model of the Earthquake Influence Field in Yunnan

In this paper,we conducted a regression analysis of the intensity distribution data of 146 earthquakes( M ≥ 5. 0) which occurred in the period from 1900 to 2014. According to previous research,Yunnan is divided into 3 tectonic regions. Then we use the data of the isoseismic lines in these 3 regions to fit the intensity-attenuation model of each region.Since there were a few M ≥ 7. 0 earthquakes in this 114-year period,the fitted intensityattenuation model of the strong earthquakes would be random or uncertain. To solve this problem,we introduce the Rupture Scale relationship to limiting our fitted intensityattenuation model of strong earthquakes. We choose the empirical relationship of magnitude and rupture-scale,which was proposed by Li Zhonghua and Qin Jiazheng,to correct the size of the influence field estimated through our intensity-attenuation model.Comparing our intensity-attenuation models with the previous ones, we find that in a certain tectonic region,the intensity isoseismals estimated through our model have average minimum error with the real intensity isoseismal decided through field investigation.Therefore,it is more advisable to choose the small-scale zone for the intensity-attenuation evaluation.     

A Study of Oil Biodegradation in the Black Sea Water

A laboratory study was conducted to examine oil biodegradation in the presence of a fouling organism community. It is shown that the majority of fouling species exhibit relatively weak tolerance to oil. Oil degradation in seawater is shown to proceed quicker and more completely in the presence of the fouling organism community than it does without such organisms. The population of specific bacterial groups is shown first to grow and next decrease as a result of accumulation in water of toxic products of their vital activity. Oil biodegradation is found to cause substantial changes in the water hydrochemical characteristics in experimental vessels.     

Impact of ATOVS Radiance on the Analysis and Forecasts of a Mesoscale Model over the Indian Region During the 2008 Summer Monsoon

Assimilation experiments are performed with the Weather Research and Forecasting (WRF) models’ three-dimensional variational data assimilation (3D-Var) scheme to evaluate the impact of directly assimilating the Advanced Television and Infrared Observation Satellite Operational Vertical Sounder (ATOVS) radiance, including AMSU-A, AMSU-B and HIRS, on the analysis and forecasts of a mesoscale model over the Indian region. The present study is, to our knowledge, the first where the impact of ATOVS radiance has been evaluated on the analysis and forecasts of a mesoscale model over the Indian region. The control (without ATOVS radiance) as well as experimental (which assimilated ATOVS radiance) run were made for 48 h starting at 0000 UTC during the entire July 2008. The impacts of assimilating the radiances from different instruments (e.g., AMSU-A, AMSU-B and HIRS) were measured in comparison to the control run. The assimilation experiments for July 2008 (30 cases) demonstrated a positive impact of the assimilated ATOVS radiance on both the analysis state as well as subsequent short-range forecasts. Relative to the control run, the moisture analysis was improved with the assimilation of AMSU-B and HIRS radiance, while AMSU-A was mainly responsible for improved temperature analysis. The comparison of the model-predicted temperature, moisture and wind with NCEP analysis indicated that a positive forecast impact is achieved from each of the three instruments. HIRS and AMSU-A radiance yielded only a slight positive forecast impact, while AMSU-B radiance had the largest positive forecast impact for moisture, temperature and wind. The comparison of model-predicted rainfall with observed rainfall indicates that ATOVS radiance, particularly AMSU-B and HIRS, impacted the rainfall positively. This study clearly shows that the improved analysis of mid-tropospheric moisture, due to the assimilation of AMSU-B radiances, is a key factor to improve the short-term forecast skill of a mesoscale model.