Air Surge Research Articles

Meteorological Analysis of the Pacific Northwest June 2021 Heatwave

Abstract During the last week of June 2021, the Pacific Northwest region of North America experienced a record-breaking heatwave of historic proportions. All-time high temperature records were shattered, often by several degrees, across many locations, with Canada setting a new national record, the state of Washington setting a new record, and the state of Oregon tying its previous record. Here we diagnose key meteorology that contributed to this heatwave. The event was associated with a highly anomalous midtropospheric ridge, with peak 500-hPa geopotential height anomalies centered over central British Columbia. This ridge developed over several days as part of a large-scale wave train. Back trajectory analysis indicates that synoptic-scale subsidence and associated adiabatic warming played a key role in enhancing the magnitude of the heat to the south of the ridge peak, while diabatic heating was dominant closer to the ridge center. Easterly/offshore flow inhibited marine cooling and contributed additional downslope warming along the western portions of the region. A notable surface thermally induced trough was evident throughout the event over western Oregon and Washington. An eastward shift of the thermal trough, following the eastward migration of the 500-hPa ridge, allowed an inland surge of cooler marine air and dramatic 24-h cooling, especially along the western periphery of the region. Large-scale horizontal warm-air advection played a minimal role. When compared with past highly amplified ridges over the region, this event was characterized by much higher 500-hPa geopotential heights, a stronger thermal trough, and stronger offshore flow.

A cold wave of winter 2021 in central South America: characteristics and impacts.

The online version contains supplementary material available at 10.1007/s00382-023-06701-1.

Shortterm Outcome Air Plombage Thoracoplasty of Empyema Thoracis at Pulmonary Tuberculosis

Pulmonary tuberculosis (pulmonary TB) is a type of infectious disease caused by the bacterium Mycobacterium tuberculosis. A male patient aged 40 years, came to the hospital with complaints of shortness of breath, severe shortness of breath for 1 week before coming to the hospital, the patient had a history of having WSD installed, on palpation the left vocal fremitus was stronger than the right, percussion was found to be dim in the basal area. lung, hyperresonance in the medial-apex area pulmo dextra and sonor on pulmo sinistra, decreased vesicular auscultation in the right lung, chest X-ray found pleural effusion. The patient was treated with air surge therapy. After surgery and evaluated for 4 days in the hospital and repeated follow-up on patients where the results of the examination did not find recurrent effusions.

A 1600-year record of eolian activity from Jili Lake in northern Xinjiang

Eolian activity determines the magnitude of dust emission. However, geological records of eolian activity are scarce due to strong wind erosion in the dust source areas. Northern Xinjiang is recognized as a major dust source region in arid central Asia. Here we present a lacustrine record of eolian activity over the past 1600 years from Jili Lake, in northern Xinjiang, which acts a natural trap for airborne materials. Based on the stratigraphic variability of two sedimentary sequences and 20 radiocarbon dates, we infer that Jili Lake initially developed in the southwestern part of the lake basin during the mid-Holocene and then expanded to close to its modern surface area until 1600 years ago. Grain-size analyses of materials from different parts of the lake sedimentary system, including lake surface sediments, lake catchment deposits, and airborne sand and dust collected from near the lakeshore, demonstrate that the coarse silt and fine sand fraction (40–200 μm) of the lake sediments was transported primarily by strong winds and can be regarded as an indicator of changes in eolian activity. We argue that wind strength played an important role in lifting and transporting the coarse particles, although an arid climate cannot be entirely excluded out as a factor favoring eolian activity. The most intensive eolian activity occurred from ∼910 to 1300 AD, roughly corresponding to the Medieval Warm Period (MWP), whereas eolian activity was weak during the Little Ice Age (LIA, ∼1300 to 1760 AD). However, this pattern is inconsistent with other dust records from central Asia. Eolian dust activity reflects the coupling of dust-generating windstorms and dust source areas which were swept by cold air surges. The spatial differentiation of eolian dust activity in arid central Asia may thus be causally linked to the intensity and extent of the Siberian High (SH), given that intense cyclogenesis always occurs on the southwestern periphery of the SH in springtime. Changes in the SH can be further ascribed to atmospheric circulation modulated by phase alternations of the North Atlantic Oscillation (NAO) due to large-scale thermal contrasts. Our results suggest that the dynamics of Asian dust emission are closely linked with the spatial variability of the SH. Nonetheless, more records of eolian activity are needed to further elucidate the forcing mechanisms of dust entrainment in the source area of Asian dust.

Transient Simulation of Underground Pumped Storage Hydropower Plants Operating in Pumping Mode

The increasing penetration of variable renewable energies (VRE) in the European electricity mix requires flexible energy storage systems (ESS), such as pumped storage hydropower (PSH). Disused mining voids from deep closed mines may be used as subsurface reservoirs of underground pumped-storage hydropower (UPSH) plants. Unlike conventional PSH plants, the air pressure in UPSH plants is variable and it differs from the atmospheric conditions. In this paper, the hydraulic transient process of an UPSH plant operating in pumping mode was investigated and a preliminary thermodynamic analysis of the closed surge tank was carried out. Analytical and CFD three-dimensional numerical simulations based on the volume of fluid (VOF) model with two-phase flow have been performed for analyzing the transient process. In the transient simulation, air and water are considered as ideal gas and compressible liquid, respectively. Different guide vanes closing schemes have been simulated. The obtained results show that the dimensioning of underground reservoir, surge tank, and air ducts is essential for ensuring the hydraulic performance and optimizing the operation of UPSH plants. The static pressure in the air duct, surge tank and lower reservoir reaches −1.6, 112.8 and −4 kPa, respectively, while a heat flux of −80 W was obtained through the surge tank walls.

Case Study of a Convective Cluster Over the Rain Shadow Region of Western Ghats Using Multi-platform Observations and WRF Model

Unique observational features of a convective cluster, occurred on 12-Sept-2015, over the rain shadow region in the leeward side of Western Ghats have been presented in this study. The synoptic environment had preconditioned the formation of a convergence zone over the study area. Moisture transport from the Arabian Sea was responsible for the moistening in the lower layers. Boundary layer convective thermals contributed to middle level moistening and subsequent onset of the cloud cluster was accompanied by a sudden surge of moist and warm air into the middle troposphere, and subsequent lifting of freezing level (FL) and wet bulb temperature zero (WBT0) levels. Sudden changes in the FL and WBT0 levels in association with the gust front prior to the initiation of the cloud system has been documented with high-resolution measurements using microwave radiometer and wind profiler. Thermodynamical parameters from radiometer illustrate the percussive conditions for formation of the cloud system. The cloud cluster had resulted in 25.50 mm rainfall, attributing to ~ 91% of convective rain. Intense fall velocity (10–12 ms−1) was noted up to ~ 7 km during the convective rain and the fall velocity was reduced to ~ 7 ms−1 (below the melting layer) during the stratiform counterpart. The cloud system was forecasted using WRF model (version 3.6.1), which was reproduced reasonably well as in the observations and the model output has been analyzed to understand the morphology of the system. The features such as formation of a cold pool, initiation of convective rainfall from the system were well forecasted by the model. Microphysical characteristics of the cloud cluster have also been examined. Riming was the dominant microphysical process within the convective regime. A major contribution to precipitation was from melting of ice hydrometeors especially graupel and snow was noted. Deep warm layer and associated production of supercooled liquid by the lifting of liquid water above the freezing level in updrafts exceeding 15 ms−1 was important for the production of a mixed-phase cloud system. Vapor deposition and aggregation process was noted in the stratiform/anvil counterpart, which also contained mixed phase hydrometeors, primarily of snow.

On the Structure and Formation of UTLS PV Dipole/Jetlets in Tropical Cyclones by Convective Momentum Surges

AbstractThe structure and origin of mesoscale jets and associated potential vorticity (PV) dipoles in the upper troposphere and lower stratosphere (UTLS) in tropical cyclones (TCs) are investigated. UTLS PV dipole/jetlets, which occurred in Talas (2011), Edouard (2014), and Ita (2014), are simulated with the University of Wisconsin Nonhydrostatic Modeling System (UWNMS). PV dipoles are confined to the UTLS, where the jetlets oppose the ambient anticyclonic flow. They form ~100–250 km from the eye in convective asymmetries and are characterized by surges of air that accelerate in the updraft, overshoot, and extend radially outward. In these cases, the outflow jet merges with the subtropical westerly jet. Analysis of the structure of UTLS PV dipole/jetlets led to a new physical interpretation for their formation, based on the difference in momentum between the updraft and air in the UTLS: the convective momentum transport hypothesis. This view is complementary to the vorticity tilting hypothesis. A jetlet will form whenever an updraft carries horizontal winds to a level with different wind. Schematic diagrams show how to predict jetlet orientation based on horizontal speeds in the updraft and UTLS ambient air. In TCs, horizontal winds in the updraft are cyclonic, so a UTLS jetlet will be cyclonic and oppose the ambient flow. Each jetlet creates an anticyclonic, inertially unstable PV member, which lies radially outward. Estimates of terms in the PV conservation equation support the hypothesis that the dipoles arise from the curl of shear stress. Convective asymmetries associated with PV dipole/jetlets can significantly modify TC evolution by local thermodynamic acceleration.

Water Hammer Phenomenon: Analysis and Solutions ظاھرة الطرق المائى : التحلیل والحلول

تعتبر المطرقة المائية ظاھرة معقدة يجب التعرف على تأثيرھا الضار حتى نجدالحلول المناسبة لمنع ھذه الاضرار وتنشأ المطرقة المائية نتيجة التغيرالمفاجى فى سرعة المياه داخل الأنابيب نتيجة انقطاع المغذى لمحرکاتالطلمبات فجاة أو القفل المفاجئ للمحابس أثناء التشغيل وينتج عنھا ارتفاعوانخفاض مفاجئ فى الضغط وظھور موجة ضغط موجبة وسالبة تتحرکبسرعة الصوت مما يسبب أضرار بالغة مثل ( انفجار المواسير – تدميرالطلمبات – تدمير المحابس .... ) وتھدف الدارسة إلى تحليل ووضع الحلوللظاھرة الطرق المائى أو منعھا عن طريق ترکيب أجھزة الحماية مثل( خزاناتالفائض – خزانات المياه والھواء – محابس الأمان – محابس الھواء ) تناولالبحث تطبيق عملى على أحدى منظومات محطات الرى فى مشروع الصالحيةالزراعى حوالى ۳۳٥٥۱ فدان ( محافظة الاسماعيلية ) واشتمل العمل علىالقياسات العملية للتصرفات والضغوط داخل المواسير فى حالة السريانالمنتظم وتم تسجيل أعلى ضغط وأقل ضغط على اللوحة الرئيسية للتشغيل عندانقطاع التيار وفى وجود خزان المياه والھواء تم التحليل باستخدام الطريقةللحصول على النتائج التسجيل وأسفرت ( AFT impulse ) النظرية الحسابيةالنتائج إلى أن استخدام أجھزة الحماية مثل خزانات المياه والھواء أو خزاناتالفائض تؤدى إلى حماية منظومة الرى من ظاھرة الطرق المائى کذلک کانتلحل مشاکل الطرق المائى CFD من النتائج أھمية وسھولة الطرق الحسابيةبالمقارنة إلى التحليل النظرى أو العملى AFT Impulse باستخدام برنامجتطابقت النتائج العملية والنظرية والحاسبية إلى حد کبير .Abstract: Water hammer (hydraulic transient) is a complex phenomenon. The cause of a hydraulic transient is the rapid change in the velocity of the flow in a closed pipe due to sudden power failure or sudden valve closure which generates high and low pressure waves transmit through the pipe line with a speed of sound. The generated waves can cause serious problems in the pipeline system such as pipe burst, pumps and valves failure. The aim of the study is to analyze experientially, theoretically and computationally to find out a solution for this phenomenon. This was done through applying some practical methods techniques of water hammer control devices used in irrigation pumping systems. In Salhia Agriculture Project site, Ismailia 33551 feddan were selected to carry out the water hammer investigation. The steady state calculation was first executed to measure the flow rate and the head, unsteady state flow calculation was carried out to identify the maximum and minimum pressure during the sudden pump trips. The results showed that the control devices such as the air vessels or surge tanks would mitigate the pressure rise and prevent the formation of negative pressure. Water hammer analysis using AFT impulse program is an effective and reliable tool to choose the required surge protection device. Installation of surge control device in the system such as one air vessel 50 m3 air volumes provides an acceptable level of protection to the irrigation pumping systems, as there are no cavitations at the pipeline and the maximum pressure reduces from 11 bars to 6 bars. A good a agreement among the experimental, theoretical and computational associated results was found.

Temperature–topographic elevation relationship for high mountain terrain: an example from the southeastern Tibetan Plateau

ABSTRACTThis study quantifies the spatial–temporal distribution of the near‐surface temperature lapse rate (TLR) on the southeastern Tibetan Plateau (SETP) on the northern slopes of the eastern Himalayas, using the jackknife regression model. A 20‐year (1985–2004) climatic data set of 16 stations between the elevation range of 3553–4801 m asl was used for this investigation. Controls for the spatial–temporal variation on TLRs and causes of higher mean square error (MSE) from the jackknife regressions were also analysed. Dry convection due to increasing sensible heating at lower elevations associated with clear skies, the effect of cold air surges, cloud/fog, as well as pronounced long‐wave radiation loss due to snow cover at higher elevation, results in the super‐dry adiabatic TLR in the dry winter. In response to the effects of high rainfall and humidity, intense latent heating at higher elevation due to moist adiabatic cooling causes TLRs to decrease significantly in summer. The variation in net radiation due to differences in moisture, rainfall, cloud cover and air mass between higher (fewer) and lower (higher) elevations further contributes to reducing TLRs values in this season. Observed steeper values of TLRs at higher elevations and more shallow values at lower elevations are due to the thermal contrast between snow‐free ground and snow‐covered mountain terrain, as well as the effect of variations in air mass and moisture. Based on derived values, this article also estimates near‐surface temperature at higher elevations and analyses the precision of estimated values. Measurement of the lowest discrepancy (bias) between observed and estimated values from this study suggests that the estimation skills of the model are good enough. More precisely, including the smallest MSE from the jackknife regression and biases of the estimated values can be made for summer, perhaps due to the moisture controlled throughout the SETP, i.e. associated with the Indian monsoon. Higher MSE and biases are observed during winter and are due to the substantial effects of westerlies, as well as the station's geographical coordinate, local topography and microclimate. The MSE and the estimated biases are lowest at high‐elevation stations and are associated with the lower contaminating effects of the surface. This estimation model, using derived values from this investigation, could be useful for glacier‐hydro‐climatic and ecological modelling in this region.

Electromagnetic Bridge Energy Harvester Utilizing Bridge’s Vibrations and Ambient Wind for Wireless Sensor Node Application

This paper presents novel electromagnetic bridge energy harvesters (BEHs) utilizing bridge vibrations and ambient wind surges to power wireless sensor nodes used for bridges’ health monitoring. The developed BEHs are cantilever-type and are comprised of a wound coil, permanent magnet, an airfoil, cantilever beam, and a support. Harvesters are characterized in-lab under different vibration levels and are subjected to variable speed air surges. The harvesters exhibit multiresonant frequencies; prototype I has resonant frequencies of 3.6, 14.9, and 17.6 Hz. However, 7.6, 33, and 45 Hz are the resonant frequencies for prototype II. Under vibration testing, prototype I produced a maximum voltage of 206 mV and an optimum power of 354.51 μW at a frequency of 3.6 Hz and 0.4g acceleration. However, at a frequency of 7.6 Hz and 0.6g acceleration, prototype II showed the capability of generating a maximum voltage of 430 mV and an optimum power of 2214.32 μW. Moreover, when BEHs are characterized under variable speed air surges, prototype I generated a load voltage of 19 mV and a power of 7.84 μW at an air speed of 9 m/s; however, 22 mV and 9.14 μW load voltage and power, respectively, are developed by prototype II at 6 m/s air speed.

Subseasonal Variations of Wintertime North Pacific Evaporation, Cold Air Surges, and Water Vapor Transport

This study addresses subseasonal variations of oceanic evaporation E over the North Pacific during winter and the connection with the cold air surges (CASs) and atmospheric water vapor transport using the OAFlux and ERA-Interim daily data. By performing an empirical orthogonal function (EOF) analysis, two dominant modes of subseasonal evaporation anomaly E′ are identified: a zonal wave train–like pattern (EOF1) and an east negative–west positive dipolar pattern (EOF2) in the midlatitude basin. Further analyses yield the following conclusions. 1) The Siberian high (SH)-related CAS has a crucial role in generation of the EOF1 mode of E′. When the dry and cold air mass passes the region of the warm Kuroshio and its extension [Kuroshio–Oyashio Extension (KOE)], the increased air–sea temperature and moisture differences and intensified wind speed lead to the above-normal oceanic E, and vice versa. 2) The Aleutian low (AL)-related CAS contributes to the EOF2 mode of E′. The intensified AL transports a dramatically colder and drier air mass toward the KOE region and a slightly warmer and wetter one toward the west coast of North America, leading to the east negative–west positive structure of E′ in the midlatitude basin. 3) A quasi-linear relationship exists between E′ and divergent water vapor transport anomalies over the KOE region. Positive (negative) E′ is generally accompanied by anomalous vapor source (sink). 4) The divergent water vapor transport anomalies associated with the two EOFs are preliminarily decided by their individual lower-level wind field anomalies and second by the meridional inhomogeneity of subseasonal specific humidity anomalies. Hydroclimate effects on precipitation over the pan–North Pacific region are also discussed.

Upgrading of a Norwegian pressurized sand trap combined with an open air surge tank

AbstractIn 1988 the Tonstad power plant (Norway) was upgraded from 640 to 960 MW. The headrace system to the reservoirs was not upgraded except for an additional pressure shaft, surge tank and an additional sand trap. Even with about 50 % higher discharge in the main tunnel, the sand traps worked adequately after the commissioning. However, in recent years, higher flexibility of demand is challenging the power plant and has resulted in events with flushing of sediments to the turbines. Higher flexibility demands also challenge the current surge tank design. During one event, free surface flow is believed to have occurred in the sand trap since severe damage to two of the turbines was observed. This contribution presents the background of the power system situation at the Tonstad power plant and the current flexibility demands of the power market and its challenges for the hydraulic system, as well as the proposals to solve the sand trap issues and the oscillation demands for the surge tank. The paper discusses the possibility of utilizing a model predictive controller with real‐time flow simulations to solve the challenges without structural reconstruction, and possible options should structural reconstruction be necessary. The contribution compares analysed options for improving the efficiency of sand traps. Finally, an outlook is offered to future demands for flexibility in hydropower plants with increasing supply of renewable power sources.

アンモニア燃焼ガスタービン発電用の低NOx燃焼器開発のための試験設備

Ammonia is focused as a hydrogen energy carrier and carbon free fuel. National Institute of Advanced Industrial Science and Technology (AIST) collaborated with Tohoku University successfully performed an ammonia combustion gas turbine power generation in 2015. However, the weakness of the facilities was that they required large-size Selective Catalytic Reduction (SCR) equipment in order to suppress a high concentration of NOx. Although NOx reduction in the combustion process is desirable, low NOx combustion technology is difficult because ammonia had been thought of as a source of fuel-NO. AIST prepared a combustor test rig to test combustor alone without a compressor or turbine. Sharing with a 1-ton ammonia cylinder, a vaporizer and a gas compressor, combustor test rig was added two engine compressors, air surge tanks, and a high temperature SCR. A regenerator was used to preheat combustion air. Combustor test rig can achieve the same combustion condition as the gas turbine that was successfully demonstrated.

Air flow trajectory and surge avoidance of centrifugal compressor under variable pressure operation of automotive fuel cells

The compressor of an automotive proton exchange membrane fuel cell requires severe dynamic performance under normal driving patterns. Because the air flow demand of the automotive fuel cell requires steep increase/decrease, it is very important to understand the air flow trajectory of the centrifugal compressor to avoid the compressor surge. In this study, a simulation model of an automotive fuel cell system with a dynamic compressor was developed to investigate the proper trajectory of air flow rate on a performance map of an air compressor. The dynamic response of the compressor shows that the cathode inlet and exit valves have a significant effect on surge evolution. In particular, the results showed that a proper combination of valve opening areas is required to avoid compressor surge. In this study, the original two valve approach was reduced to a single cathode exit valve control with fixed cathode inlet orifice. A surge rejection algorithm was also developed, based on the comparison of surge protection envelope pressure with actual measured pressure. The results show that surge evolution is effectively avoided by controlling the cathode exit valve.

Failure Investigation of Frame 6FA Gas Turbine Compressor Blades

This investigation elucidates failure of a land based 6FA gas turbine compressor 2nd stage blade. During discussions with site officials, it was learnt that this particular compressor operated in good condition for over 20,000 h at two other sites. In this power station, this was second such failure with less operation duration. Due to failure of blades, it was requested for a detailed root cause analysis by the utility officials in order to avert such failures in future. Failed blade samples were collected from the site and cut into the suitable sizes for investigation procedures. Investigation techniques like visual observation, stereomicroscopic, metallographic, scanning electron microscopic examinations (SEM), etc. are employed to ascertain the root cause for failure. During the investigation it was noticed that there is no degradation in the material. During stereomicroscopic examination, a number of beach marks were observed to be present on the fractured surface of the blade. It was also noticed from both stereomicroscopic and SEM examinations that the blade failed due to fatigue. The cracks have originated from micro-cracks developed at the trailing edge during shot peening process in the blade root. These cracks grew as the blades have vibrated beyond their natural frequency due to air surge during operation. It was recommended to examine the air filtration mechanism of the compressor regularly.

Detection and Analysis of an Amplified Warming of the Sahara Desert

Abstract Evaluation of three reanalyses (ERA-Interim, NCEP-2, and MERRA) and two observational datasets [CRU and Global Historical Climatology Network (GHCN)] for 1979–2012 demonstrates that the surface temperature of the Sahara Desert has increased at a rate that is 2–4 times greater than that of the tropical-mean temperature over the 34-yr time period. While the response to enhanced greenhouse gas forcing over most of the globe involves the full depth of the atmosphere, with increases in longwave back radiation increasing latent heat fluxes, the dryness of the Sahara surface precludes this response. Changes in the surface heat balance over the Sahara during the analysis period are primarily in the upward and downward longwave fluxes. As a result, the warming is concentrated near the surface, and a desert amplification of the warming occurs. The desert amplification is analogous to the polar amplification of the global warming signal, which is concentrated at the surface, in part, because of the vertical stability of the Arctic atmosphere. Accompanying the amplified surface warming of the Sahara is a strengthening of both the summertime heat low and the African easterly jet and a weakening of the wintertime anticyclone and the low-level Harmattan winds. Potential implications of the desert amplification include decreases in mineral dust aerosols globally, decreases in wintertime cold air surge activity, and increases in Sahel rainfall.

Comparison of temperature lapse rates from the northern to the southern slopes of the Himalayas

ABSTRACTBased on 20‐year (1985–2004) records of surface‐air‐temperature at 16 stations between the elevations of 3553 m and 4801 m a.s.l. in the southeastern Tibetan Plateau (or the northern slopes of the eastern Himalayas), this paper examines the monthly, seasonal and annual characteristics of near‐surface temperature lapse rates (TLRs). A linear regression model was fitted for the lapse rate calculation. The annual cycle of the TLR shows a distinct seasonal pattern, i.e. steepest in winter and shallowest in summer. Results are partially consistent with those from the southern slopes of the central Himalayas, in particular in summer, and correspond to the warm, rainy and humid season. In response to the monsoonal effect, the released latent heat of water vapour condensation causes an increase in air temperature at higher elevations. Therefore, the TLR is shallowest in the summer. The considerable amount of solar radiation at higher elevations also causes a reduction of the TLR in this season. The lowest diurnal range of lapse rates for summer is associated with lower diurnal variability in net radiation due to cloud cover and relative humidity. The steepest TLR occurs in winter in association with intense cooling at higher elevations, corresponding to the continental dry and cold air surges, and considerable snow‐temperature feedback. Lower insolation, deeper snow cover and a weaker inversion effect cause a lower diurnal range of TLR in this season. The observed contrast of winter TLR from the northern to southern slopes of the Himalayas is due to differences in elevation and topography, as well as the pronounced effect of cold air surges.

An Investigation of the Performance, Combustion, and Emission Characteristics of a CI Engine Fueled with Used Vegetable Oil Methyl Ester and Producer Gas

Biomass-derived biodiesel and producer gas are the renovated sources of renewable fuel. In the present study, experiments have been conducted with mixed fuel mode using producer gas as an inducted fuel and near to waste–used vegetable oil biodiesel as an injected fuel in a four-stroke, naturally aspirated, variable compression ratio engine. The results have been compared with single fuel and dual fuel modes of operation with an optimized compression ratio of 18 and fuel injection pressure of 200 bar. Producer gas is collected from the gasifier and stored in gas bags and then supplied to the engine through air surge tank to maintain uniform gas quality, whereas biodiesel is used in the form of B23. The result shows that the maximum brake thermal efficiency of 26.77% is comparable with the dual fuel mode of operation, ignition delay of 13.64° is less than the dual fuel mode, and smoke opacity has been reduced up to 16% compared with the conventional fossil fuel. It has been concluded that the internal combustion engine could run with all fuel modes without any modifications and the performance is found to be comparable with that of fossil diesel.

Climatology of Storm Characteristics in Costa Rica using the TRMM Precipitation Radar

Abstract Tropical Rainfall Measuring Mission Precipitation Radar precipitation features are analyzed to understand the role of storm characteristics on the seasonal and diurnal cycles of precipitation in four distinct regions in Costa Rica. The distribution of annual rainfall is highly dependent on the stratiform precipitation, driven largely by seasonal increases in stratiform area. The monthly distribution of stratiform rain is bimodal in most regions, but the timing varies regionally and is related to several important large-scale features: the Caribbean low-level jet, the ITCZ, and the Chorro del Occidente Colombiano (CHOCO) jet. The relative importance of convective precipitation increases on the Caribbean side during wintertime cold air surges. Except for the coastal Caribbean domain, most regions show a strong diurnal cycle with an afternoon peak in convection followed by an evening increase in stratiform rain. Along the Caribbean coast, the diurnal cycle is weaker, with evidence of convection associated with the sea breeze, as well as a nocturnal increase in storms. The behavior of extreme precipitation features with rain volume in the 99th percentile is also analyzed. They are most frequent from May to November, with notable differences between features at the beginning/end of the rainy season versus those in the middle, as well as between wet and dry seasons. Convective rain exceeds stratiform in winter and midsummer extreme features, while stratiform rain is larger at the beginning and end of the wet season. Given projected changes in precipitation and extreme events in Costa Rica for future climate change scenarios, the results indicate the importance of understanding both changes in total precipitation and in the storm characteristics.

Numerical study of severe downslope windstorm

Severe downslope windstorm occurred during January 11 and 12, 1972 when the observed wind in the upstream region changed little, a surge of warmer air moved across the northwestern US at 500hPa, accompanied by rapid pressure falls and strong surface cyclogenesis in the lee of the Rocky Mountains triggered the downslope windstorm. Here, the observed soundings in the upstream are used at inflow. On a non-slip surface without the effect of rotation, the simulated downslope wind decreases with time after 2–3h. If the wind at inflow is in geostrophic balance, the simulated westerly wind at z~25m remains around 33–35ms−1. If the northwesterly upper-level-jet is unbalanced by large scale pressure gradient, the inertial oscillation decreases the westerly wind and increases the northerly wind of the upper-level-jet as it approaches mountain. Convergence forms in the upper layer and forces more air to descend and results in a severe, long-lasting downslope windstorm as observed. Meanwhile, an unbalanced upper-level-southwesterly-jet decreases the downslope wind. The simulated severe downslope wind, reversed flow atop, and hydraulic jump occur simultaneously, accompanied by waves, rotors and turbulences in the upper layers and the lee side.