The Contrasting Features of Winter Circulation During Surplus and Deficient Precipitation Over Western Himalayas

Contrasting features associated with surplus and deficient precipitation years are studied to examine atmospheric circulation characteristics during the winter season viz., December, January February and March (DJFM) to assess the wintertime synoptic weather system affecting the western Himalayas. Large-scale balances of kinetic energy, vorticity, angular momentum, heat and moisture fields are analyzed. Winter circulations are studied over the domain 15°S–45°S and 30°E–120°E. This domain is considered particularly to illustrate the distribution of precipitation due to wintertime eastward moving synoptic weather systems called western disturbances. Surplus and deficient years of seasonal (DJFM) precipitation are identified using±20% departure from mean from uninitialized daily reanalysis data of fourty (1958–1997) years of the National Center for Environmental Prediction (NCEP), USA. The years 1965–1969, 1973 and 1991 are found to be surplus years and years 1962, 1963, 1971, 1977 and 1985 are found to be deficient years. Composites of these two categories are made. Comparative study is made using Students t-test of significance. Examining the aspects associated with energetics during the two extreme categories of winter seasonal precipitation years, higher heat flux convergence in excess years in the area of study of precipitation takes place. Diabatic heating shows cooling. Higher flux of convergence of kinetic energy and higher dissipation of kinetic energy are observed during surplus years.     

Extreme rainfall events over the Himalayas between 1871 and 2007

Abstract

Currently there is much discussion regarding the impact of climate change and the vagaries of the weather, in particular extreme weather events. The Himalayas form the main natural water resource of the major river systems of the Indian region. We present a brief review of the available information and data for extreme rainfall events that were experienced in different sectors of the Himalayas during the last 137 years (1871–2007). Across the entire Himalayas, from east to west, there are now 822 rainfall stations. There was an increase in the rainfall station network from 1947 onwards, especially in the Nepal and Bhutan Himalayas. Extreme one-day rainfall has been picked out for each station irrespective of the period for which data are available. The decadal distribution of these extreme one-day rainfalls shows that there is a considerable increase in the frequencies during the decades 1951–1960 to 1991–2000, whereas there is a sudden decrease in the frequencies in the present decade during 2001–2007, indicating the need to understand the response of the systems to global change and the associated physical and climatological changes. This is essential in terms of preserving this natural resource and to encourage environmental management and sustainable development of mountain regions.

Citation Nandargi, S. & Dhar, O. N. (2011) Extreme rainfall events over the Himalayas between 1871 and 2007. Hydrol. Sci. J. 56(6), 930–945.     

On the Validity of ECHAM-Simulated Daily Extreme Temperatures

Three-dimensional global circulation models (GCMs) are state-of-the-art tools for projecting possible changes in climate. GCM simulations have frequently been validated against observations in terms of time-averaged variables while daily time series have not been studied extensively. In this paper, 30-year simulations of daily extreme temperatures are compared with the 30-year series recorded in Moravia. Attention is focused on the annual cycles, trimmed characteristics and average interdiurnal variability which are calculated for the average simulated series (4 gridpoints) and the average time series recorded in Moravia (5 stations). It is shown that daily extreme temperature variability is underestimated in the simulations, maximum (minimum) temperatures being underestimated (overestimated). Generally, the persistence of the simulated series is much higher, and small day-to-day changes are observed more frequenly than those in reality. The model is unable to reflect large changes between two consecutive days.     

Generation of Magnetic Fields During the Protogalactic Collapse

Large-scale galactic magnetic fields are probably caused by some magnetic field amplification mechanism starting from a seed field. This seed field is still enigmatic. In this contribution it is shown that macroscopic sheared relative velocities of the charged and neutral components of a protogalactic partially ionized plasma generate magnetic fields during the protogalactic collapse. Plasma-neutral gas fluid simulations are performed in order to illustrate this magnetic field-self generation mechanism.     

Magnetic and Electric Fields Produced in the Sea During Geomagnetic Disturbances

— To understand geomagnetic effects on systems with long conductors it is necessary to know the electric field those systems experience. For surface conductors such as power systems and pipelines this can easily be calculated from the magnetic field variations at the surface using the surface impedance of the earth. However, for calculating the electric fields in pipelines and submarine cables at the seafloor it is necessary to take account of the attenuating effect of the conducting seawater. Assuming that the fields are vertically propagating plane waves, we derive the transfer functions between the electric and magnetic fields at the seafloor and the magnetic field variations at the sea surface. These transfer functions are then used, with surface magnetic field data, to determine the power spectra of the seafloor magnetic and electric fields in a shallow sea (depth 100 m) and in the deep ocean (depth 5 km) for different values of the Kp magnetic activity index. For the period range considered (2 min to 3 hrs) the spectral characteristics of the seafloor magnetic and electric fields for a 100 m deep sea are very similar to those of the surface fields. For the deep ocean the seafloor spectra show a faster decrease in spectral density with increasing frequency compared to the surface fields. The results obtained are shown to be consistent with seafloor observations. Assessment of the seafloor electric fields produced by different levels of geomagnetic activity can be useful in the design of the power feed equipment for submarine cables and cathodic protection for undersea pipelines.     

Modeling hydrothermal fluid circulation and gravity signals at the Phlegraean Fields caldera

The Phlegraean Fields caldera is an active volcanic system where episodes of ground deformation are accompanied by significant changes in geochemical and geophysical parameters monitored at the surface. These changes derive from a complex interaction between magmatic system and hydrothermal fluid circulation. We calculate the gravity changes associated with the variable density of hydrothermal fluids. We simulate the multi-phase and multi-component fluid circulation triggered by a pulsating magma degassing, periodically increasing the discharge of CO₂-enriched fluids into the shallow hydrothermal system. The simulated evolution of the hydrothermal system successfully reproduces the observed composition of gas discharged at the surface. At the same time, results indicate that changes in average fluid density generate a detectable gravity signal that is of the same order of magnitude of the observed changes. This contribution to gravity changes can explain the peculiar behavior of gravity data collected at Solfatara, where surface hydrothermal phenomena are present. Simultaneous fitting of two independent sets of monitoring data (gas composition and gravity changes) confirms the conceptual model proposed for the hydrothermal system at Solfatara, and it provides new insights for the interpretation of gravity data.     

Mid-Mountain Clouds at Whistler During the Vancouver 2010 Winter Olympics and Paralympics

A comprehensive study of mid-mountain clouds and their impacts on the Vancouver 2010 Winter Olympics and Paralympics is presented. Mid-mountain clouds were frequently present on the Whistler alpine venue, as identified in an extensive archive of webcam images over a 45-day period from February 5 to March 21, 2010. These clouds posed serious forecast challenges and had significant impacts on some Olympic and Paralympic alpine skiing competitions. Under fair weather conditions, a diurnal upslope (anabatic) flow can work in concert with a diurnal temperature inversion aloft to produce a localized phenomenon known as “Harvey’s Cloud” at Whistler. Two detailed case studies in this paper suggest that mid-mountain clouds can also develop in the area as a result of a moist valley flow interacting with a downslope flow descending from the mountaintop. A southerly inflow through the Sea-to-Sky corridor can be channeled by the local topography into a westerly upslope flow toward Whistler Mountain, resulting in orographic clouds on the alpine venue. Under favorable circumstances, these clouds are trapped to the mid-mountain zone by the leeward subsidence of an elevated southerly flow. The presence of the downslope subsidence was manifested by a distinguished dry layer observed on the top of the mid-mountain clouds in both cases. It is the subsidence-induced adiabatic warming that imposes a strong buoyant suppression to trap the mid-mountain cloud. On the other hand, the subsidence-induced dry layer has the potential to trigger evaporative instability to periodically breakup the mid-mountain cloud.     

Seasonal upwelling on the Western and Southern Shelves of the Gulf of Mexico

An 8-year database of sea surface temperature (SST), 7 years of Sea-viewing Wide Field-of-view Sensor (SeaWiFS) ocean color images, wind fields, and numerical model results are analyzed to identify regions and periods of coastal upwelling on the western and southern shelves of the Gulf of Mexico. On the seasonal scale, it is found that on the Tamaulipas, Veracruz, and southwestern Texas–Louisiana shelves there are upwelling favorable winds from April to August, when southeasterly winds are dominant and cold SST anomalies associated with upwelling are observed along their coasts. However, during summer, values of chlorophyll-a concentration are lower than those in autumn and winter, which are high due to advection of old bloom biological material from upstream. During winter, there is a cold front on the Tamaulipas shelf produced by advection of cold water from the Texas–Louisiana shelf and not due to upwelling. On the eastern Campeche Bank, persistent upwelling is observed due to favorable winds throughout the year with cold SST and large chlorophyll-a content along the inner shelf from May to September. On the Tamaulipas shelf, the summer upwelling delays the annual SST peak until September, while in most of the Gulf SST peaks in August. This difference is due to the end of the upwelling favorable wind conditions and the September seasonal current reversal.     

Numerical Simulation of the Response of the Ocean Surface Layer to Precipitation

Numerical experiments were conducted to investigate the ocean's response to the precipitation. A squall line observed in TOGA COARE was simulated. The simulation reproduced some of the observed ocean responses to the precipitation, such as the formation of a fresh water layer, surface cooling and the variation of upper layer turbulent mixing. The precipitation-induced fresh layer can cause the vertical turbulent diffusivities to decrease from the surface to a depth of about 11–13 meters within a few hours. After the rainfall, the turbulence increases near the surface of the ocean due to the combined effect of increased shear and wind forcing, but decreases with depth due to the development of a stable layer. The main reason for the turbulence variation is the decrease in the vertical turbulence flux below the surface fresh layer because of increased static stability. Sensitivity experiments reveal that the sea-surface temperature increases faster after rainfall due to the formation of a shallow fresh water layer near the surface.     

An Experimental High-Resolution Forecast System During the Vancouver 2010 Winter Olympic and Paralympic Games

Environment Canada ran an experimental numerical weather prediction (NWP) system during the Vancouver 2010 Winter Olympic and Paralympic Games, consisting of nested high-resolution (down to 1-km horizontal grid-spacing) configurations of the GEM–LAM model, with improved geophysical fields, cloud microphysics and radiative transfer schemes, and several new diagnostic products such as density of falling snow, visibility, and peak wind gust strength. The performance of this experimental NWP system has been evaluated in these winter conditions over complex terrain using the enhanced mesoscale observing network in place during the Olympics. As compared to the forecasts from the operational regional 15-km GEM model, objective verification generally indicated significant added value of the higher-resolution models for near-surface meteorological variables (wind speed, air temperature, and dewpoint temperature) with the 1-km model providing the best forecast accuracy. Appreciable errors were noted in all models for the forecasts of wind direction and humidity near the surface. Subjective assessment of several cases also indicated that the experimental Olympic system was skillful at forecasting meteorological phenomena at high-resolution, both spatially and temporally, and provided enhanced guidance to the Olympic forecasters in terms of better timing of precipitation phase change, squall line passage, wind flow channeling, and visibility reduction due to fog and snow.     

Assimilation and High Resolution Forecasts of Surface and Near Surface Conditions for the 2010 Vancouver Winter Olympic and Paralympic Games

A dynamical model was experimentally implemented to provide high resolution forecasts at points of interests in the 2010 Vancouver Olympics and Paralympics Region. In a first experiment, GEM-Surf, the near surface and land surface modeling system, is driven by operational atmospheric forecasts and used to refine the surface forecasts according to local surface conditions such as elevation and vegetation type. In this simple form, temperature and snow depth forecasts are improved mainly as a result of the better representation of real elevation. In a second experiment, screen level observations and operational atmospheric forecasts are blended to drive a continuous cycle of near surface and land surface hindcasts. Hindcasts of the previous day conditions are then regarded as today’s optimized initial conditions. Hence, in this experiment, given observations are available, observation driven hindcasts continuously ensure that daily forecasts are issued from improved initial conditions. GEM-Surf forecasts obtained from improved short-range hindcasts produced using these better conditions result in improved snow depth forecasts. In a third experiment, assimilation of snow depth data is applied to further optimize GEM-Surf’s initial conditions, in addition to the use of blended observations and forecasts for forcing. Results show that snow depth and summer temperature forecasts are further improved by the addition of snow depth data assimilation.     

Statistical Association between Space Weather and Meteorological Variables During Winter in the Baltic Sea Region

Geomagnetism and Aeronomy - Some authors suggest that space weather events may affect daily weather variables, such as air temperature and atmospheric pressure. Associations between space weather...     

Numerical Study of the Intertropical Convergence Zone Over the Indian Ocean During the 1997 and 1998 Northeast Monsoon Episodes

—?The hydrostatic Naval Research Laboratory/North Carolina State University (NRL/NCSU) model was used to study the mesoscale dynamics and diurnal variability of the Intertropical Convergence Zone (ITCZ) over the Indian Ocean in the short-range period. To achieve this objective the initial conditions from two northeast monsoon episodes (29 January, 1997 and 29 January, 1998) were run for 48-hour simulations using a triple-nested grid version of the model with 1.5°?×?1.5°, 0.5°?×?0.5° and 0.17°?×?0.17° resolutions. The 1997 case represents a typical northeast monsoon episode, while the 1998 case depicts an abnormal monsoon episode during an El Niño event.¶Comparisons between the model-produced and analyzed mean circulation, wind speed, and associated rainfall for different spatial scales are presented. During the active northeast monsoon season in 1997, the major low-level westerly winds and associated high rainfall rates between 0° and 15°S were simulated reasonably well up to 24 hours. During the 1998 El Niño event, the model was capable of simulating weak anomalous easterly winds (between 0° and 15°S) with much lower rainfall rates up to 48 hours. In both simulations, the finest grid size resulted in largest rainfall rates consistent with Outgoing Longwave Radiation data.¶The model performance was further evaluated using the vertical profiles of the vertical velocity, the specific humidity and temperature differences between the model outputs and the analyses. It is found that during a typical northeast monsoon year, 1997, the water vapor content in the middle troposphere was largely controlled by the low-level convergence determined by strong oceanic heat flux gradient. In contrast, during the 1998 El Niño year moisture was present only in the lower troposphere. Due to strong subsidence associated with Walker circulation over the central and eastern Indian Ocean, deep convection was not present. Finally, the diurnal variations of the maximum rainfall, vertical velocity and total heat flux were noticeable only during the 1997 northeast monsoon year.     

Nitrogen and Phosphorus Recovery from Human Urine by Struvite Precipitation and Air Stripping in Vietnam

A “No Mix” sanitation system was installed in a dormitory at the University of CanTho in South Vietnam, with the objective of recycling nutrients from source separated wastewater streams. This paper presents the “Yellow Water” treatment plant and its efficiency in recovering phosphorus and nitrogen from human urine. The pilot plant achieved phosphorus removal efficiencies of 98% with both diluted and undiluted urine. Phosphorus was recovered in the form of struvite, a solid mineral fertilizer with heavy metal concentrations being below the German Fertilizer Regulation's threshold limits. About 110 g of struvite could be generated after one treatment cycle, during which 50 L of urine were processed. Nitrogen removal by air stripping showed best results when circulating the urine for 3 h through the stripping column at a high flow rate (80 L/h). With these settings, more than 90% of the nitrogen could be removed from the urine, and virtually 100% of this nitrogen could be recovered in the form of liquid ammonium sulfate. In the future, treatment costs could be further reduced by making use of the solar energy that is available during daytime in South Vietnam.     

长江中游夏季降水场预报技术研究

经SVD分析,截取足够多的预报场和因子场时间系数,使其相互关系代表两场的大尺度联系,预报场时间系数与其奇异向量线性组合估计场能反映原场主要特征.借助最优化技术,选择合理的系数,建立预测公式,由因子场时间系数预测预报场时间系数,同时订正预报场时间系数心a₁ a₂ a_N本身的误差和反演过程中分析误差造成的场格点趋势预测的误差.最后将预测的预报场时间系数和对应奇异向量反演为整个场的预报.预报过程重点考虑可预报的大尺度变化,滤去不可预报的小扰动,依据两场主要耦合关系,预测预报场未来的主要变化.     

Precipitation and hydrological variations and related associations with large‐scale circulation in the Poyang Lake basin,China

Long streamflow series and precipitation data are analysed in this study with aim to investigate changing properties of precipitation and associated impacts on hydrological processes of the Poyang Lake basin. Underlying causes behind the precipitation variations are also explored based on the analysis of the National Centers for Environmental Prediction (NCEP) and the National Center for Atmospheric Research (NCAR) reanalysis data. Besides, water intrusion from the Yangtze River to the Poyang Lake basin is studied. The results indicate that (1) seasonal transitions of precipitation are observed, showing increasing precipitation in winter, slight increase and even decrease of precipitation in summer; (2) analysis of water vapour circulation indicates decreasing/increasing water vapour flux in summer/winter; in winter, water vapour flux tends to be from the Pacific. Altered water vapour flux is the major cause behind the altered precipitation changes across the Poyang Lake basin and (3) occurrence of water intrusion from the Yangtze River to the Poyang Lake basin is heavily influenced by hydrological processes of the Poyang Lake basin. Effects of the hydrological processes from the middle Yangtze River on the occurrence of water intrusion events are not significant. The results of this study indicate that floods and droughts should share the same concerns from the scholars and policy makers. Besides, the altered hydrological circulation and associated seasonal transition of precipitation drive us to face new challenges in terms of conservations of wetlands and ecological environment under the changing climate. Copyright © 2010 John Wiley & Sons, Ltd.     

A continental shelf scale examination of the Leeuwin Current off Western Australia during the austral autumn-winter

A continental shelf scale survey from 22°S to 34°S along the Western Australia coast provides the first detailed synoptic examination of the structure, circulation and modification of the southward flowing Leeuwin Current (LC) during the late austral autumn-early winter (May-June 2007). At lower latitudes (22°S-25°S), the LC was masked within a broad expanse of warm ambient surface water, which extended across the shelf and offshore before becoming constrained at the shelf break and attaining its maximum velocity of ∼1.0 m s⁻¹ at 28°S. The temperature and salinity signature of the LC experienced substantial modification as it flowed poleward; surface temperature of the LC decreased by ∼5.25 °C while surface salinity increased by ∼0.72, consistent with climatology estimates and smaller (larger) for temperature (salinity) than those found during summer. Subsequently, LC water was denser by ∼2σ_T in the south compared to the north, and the surface mixed layer of the LC revealed only a small deepening trend along its poleward trajectory. Modification of the LC resulted from a combination of mixing due to geostrophic inflow and entrainment of cooler, more saline surrounding subtropical waters, and convective mixing driven by large heat loss to the atmosphere. Air-sea heat fluxes accounted for 50% of the heat lost from the LC in the south, whilst only accounting for 25% in the north, where large geostrophic inflow occurred and the LC displayed its maximum flow. The onshore transport was characterised by distinct jet-like structures, enhanced in the upper 200 m of the water column, and the presence of eddies in the vicinity of the shelf break generated offshore transport.