Modeling and Prediction of Monthly Total Ozone Concentrations by Use of an Artificial Neural Network Based on Principal Component Analysis

In the work discussed in this paper we considered total ozone time series over Kolkata (22°34′10.92″N, 88°22′10.92″E), an urban area in eastern India. Using cloud cover, average temperature, and rainfall as the predictors, we developed an artificial neural network, in the form of a multilayer perceptron with sigmoid non-linearity, for prediction of monthly total ozone concentrations from values of the predictors in previous months. We also estimated total ozone from values of the predictors in the same month. Before development of the neural network model we removed multicollinearity by means of principal component analysis. On the basis of the variables extracted by principal component analysis, we developed three artificial neural network models. By rigorous statistical assessment it was found that cloud cover and rainfall can act as good predictors for monthly total ozone when they are considered as the set of input variables for the neural network model constructed in the form of a multilayer perceptron. In general, the artificial neural network has good potential for predicting and estimating monthly total ozone on the basis of the meteorological predictors. It was further observed that during pre-monsoon and winter seasons, the proposed models perform better than during and after the monsoon.     

Surface Energy Exchanges during Pre-monsoon Thunderstorm Activity over a Tropical Station Kharagpur

In the present study an attempt has been made to understand the variation of surface energy fluxes such as net radiation, sensible, latent and soil heat during different epochs of thunderstorm activity at Kharagpur. The study also focuses in delineating the difference in the surface energy budget from the days of thunderstorm activity to fair weather days in the pre-monsoon months (April and May) which is locally known as thunderstorm season. For this purpose, experimental data obtained from the Severe Thunderstorms- Observations and Regional Modeling (STORM) programme during pre-monsoon months of 2007, 2009 and 2010 at Kharagpur (22°30′N, 87°20′E), West Bengal, India are used. The present study reveals quick response, in the order of a few days, in the variations of transport of energy fluxes at soil-atmosphere interface to the upper atmosphere vis-à-vis to the occurrence of thunderstorm activity. Rise of surface sensible heat flux to the level of surface latent heat flux a day or two before the occurrence of a thunderstorm has been identified as a precursor signal for the thunderstorm occurrence over Kharagpur. Distinguishable differences are found in the partitioning of the surface energy fluxes to that of net radiation between thunderstorm and non-thunderstorm days. The present study reveals more Bowen’s ratio during thunderstorm days to that of nonthunderstorm days. These results are useful in validating mesoscale model simulations of thunderstorm activity.     

Rain attenuation studies over an earth–space path at a tropical location

The rain rate and rain attenuation measurements have been carried out at Kolkata (22.65°N, 88.45°E), India, a tropical location, since 2004. The measured rain attenuation is compared with the simple attenuation model (SAM) and ITU-R model generated values. The relation between the rain rate and rain attenuation is analyzed for three years data (2005–2007) and a year-to-year variation is noticed. Rain attenuation has been found higher in the pre-monsoon period than in the monsoon months for identical rain rate. Cumulative distributions of rain rate and rain attenuation data along with the respective ITU-R models for three years are also presented.     

The derivation of moist baroclinic Ertel-Rossby invariant in fast manifold and its application to typhoons

Potential vorticity(PV)has been widely applied as a tracer because of its property of conservation in frictionless,dry adiabatic flow.However,PV itself is more effective in describing the slow-manifold flow at large scale.Therefore,we wish to find a materially conserved invariant other than PV to diagnose severe weather such as growing and mature tropical cyclones,whose velocity and dynamic pressure vary rapidly and locally.Starting from the absolute motion equation after elimination of the pressure gradient term by introducing moist entropy and moist enthalpy,the baroclinic Ertel-Rossby invariant(ERI)in moist flow is derived by the Weber transformation.Furthermore,the material conservation property of moist ERI is proven.Besides the traditional moist potential vorticity(MPV)term,the invariant includes the moisture factor that is excluded in dry ERI and the term related to gradients of pressure,kinetic energy and potential energy that reflects the"fast-manifold"property.Therefore,it is more complete to describe the fast motions off the slow manifold for severe weather than is the MPV term.The moist ERI is then applied to diagnose a triple-typhoon system,and is compared with MPV and dry ERI.Contrastive analysis shows that moist ERI is a better tool to diagnose the movements and intensity variations of several coexisting typhoons.The moist ERI can signify the movement and development of a multi-typhoon system.It has wide application prospects for a real moist atmosphere.     

Evaluation of temperature trends over India / Evaluation de tendances de température en Inde

Abstract

Abstract The impact of climate change is projected to have different effects within and between countries. Information about such change is required at global, regional and basin scales for a variety of purposes. An investigation was carried out to identify trends in temperature time series of 125 stations distributed over the whole of India. The non-parametric Mann-Kendall test was applied to detect monotonic trends in annual average and seasonal temperatures. Three variables related to temperature, viz. mean, mean maximum and mean minimum, were considered for analysis on both an annual and a seasonal basis. Each year was divided into four principal seasons, viz. winter, pre-monsoon, monsoon and post-monsoon. The percentages of significant trends obtained for each parameter in the different seasons are presented. Temperature anomalies are plotted, and it is observed that annual mean temperature, mean maximum temperature and mean minimum temperature have increased at the rate of 0.42, 0.92 and 0.09°C (100 year)^-1, respectively. On a regional basis, stations of southern and western India show a rising trend of 1.06 and 0.36°C (100 year)^-1, respectively, while stations of the north Indian plains show a falling trend of –0.38°C (100 year)^-1. The seasonal mean temperature has increased by 0.94°C (100 year)^-1 for the post-monsoon season and by 1.1°C (100 year)^-1 for the winter season.     

The Effects of Solar Eclipse of August 1, 2008 on Earth’s Atmospheric Parameters

Several experiments were undertaken at Kolkata (latitude: 22°34′N, longitude: 88°30′E) on the solar eclipse day of August 1, 2008 to observe the effects of the solar eclipse on Fair Weather Field (FWF) and VLF amplitude and phase. The experimental results presented here show significant deviations of the observed parameters from their normal values, as they are determined by the average of the records obtained on 5 days adjacent to the day of the solar eclipse.     

非均匀饱和大气中的广义位温

从热力学第一定律出发证明了广义位温的物理基础及其守恒性,完善了Gao等在2004年提出的非均匀饱和大气动力学的理论基础.探讨了广义湿位涡理论及其倾向方程在地面气旋追踪、雾区预报等方面的可应用性,为湿空气动力学的理论研究和业务应用提供了新思路.结果表明,非均匀饱和大气中的广义位温和位温、相当位温一样,具有守恒性;但由于其体现了实际大气的非均匀饱和特性,比位温、相当位温具有更广泛的应用前景.     

湿饱和流中的Richardson数和不稳定的研究

本文推导了干、湿饱和流中的Ri数方程.选取华北的一次降水过程,利用模式输出资料计算并对比分析干空气、湿饱和流中Ri方程中的各项,发现干过程中水平风速的垂直切变对干Ri数的变化和不稳定的影响占主导地位,而在湿过程中,湿饱和Ri的分子(Brunt_Vaisala frequency, 简称BVF)对Ri数的变化及不稳定的影响可达到与分母相当的量级. 既然BVF在湿过程中对不稳定有非常重要的影响,我们寻找了更符合湿过程中实际情况的BVF表达式,以对Ri进行修正,从而更好地判断湿过程的不稳定.研究发现,由于考虑了气块的虚温效应和总的水物质混合比的变化,即考虑降水过程中部分液态水脱离气块,有效地减小了雨区的稳定性,使得修正后的湿Ri公式可能更适合于诊断雨区的不稳定.     

Variability of GPS derived water vapor and comparison with MODIS data over the Indo-Gangetic plains

The water vapor is one of the important constituents of the atmosphere that affects the thermodynamics of the atmosphere and has direct impact on the weather conditions. The total column atmospheric water vapor, obtained from Global Positioning System (GPS) and Moderate Resolution Imaging Spectroradiometer (MODIS), is found to be very dynamic over the Indo-Gangetic (IG) plains. In this paper, we present an analysis of GPS data recently deployed (as of May 2007) on the campus of Banaras Hindu University, Varanasi (latitude 25°15′N, longitude 82°59′E). Further, we have compared the variability of water vapor from Kanpur GPS, AERONET and MODIS water vapor data for the year 2007. The monthly variability of water vapor shows characteristic features and dynamics of water vapor between two closely spaced GPS stations, found to be controlled by monsoon dynamics and wind pattern.     

Analyses of hot and humid weather in Beijing city in summer and its dynamical identification

The circulation, hygrothermal property and moisture transport character of typical hot and humid weather were analyzed in Beijing areas from July 30 to August 4, 2002. It was pointed out that, under the control of subtropical anticyclone which stretches to the west and north, downdraft suppresses the lifting of lower-troposphere moisture, which makes moisture keep in the lower troposphere. That is the direct reason causing hot and humid weather. Considering the non-uniformity saturated character in real atmosphere, generalized moist potential vorticity (GMPV) equation is derived by the introduction of generalized moist potential temperature concept. The analysis of GMPV shows that negative GMPV anomaly occurs in the lower troposphere. It has indicative sense to hot and humid weather. Thus, the GMPV anomaly can be utilized to identify this kind of weather and to make a short-term prediction.     

The effects of climate change on potential groundwater recharge in Great Britain

The predicted increase in mean global temperature due to climate change is expected to affect water availability and, in turn, cause both environmental and societal impacts. To understand the potential impact of climate change on future sustainable water resources, this paper outlines a methodology to quantify the effects of climate change on potential groundwater recharge (or hydrological excess water) for three locations in the north and south of Great Britain. Using results from a stochastic weather generator, actual evapotranspiration and potential groundwater recharge time‐series for the historic baseline 1961–1990 and for a future ‘high’ greenhouse gas emissions scenario for the 2020s, 2050s and 2080s time periods were simulated for Coltishall in East Anglia, Gatwick in southeast England and Paisley in west Scotland. Under the ‘high’ gas emissions scenario, results showed a decrease of 20% in potential groundwater recharge for Coltishall, 40% for Gatwick and 7% for Paisley by the end of this century. The persistence of dry periods is shown to increase for the three sites during the 2050s and 2080s. Gatwick presents the driest conditions, Coltishall the largest variability of wet and dry periods and Paisley little variability. For Paisley, the main effect of climate change is evident during the dry season (April–September), when the potential amount of hydrological excess water decreases by 88% during the 2080s. Overall, it is concluded that future climate may present a decrease in potential groundwater recharge that will increase stress on local and regional groundwater resources that are already under ecosystem and water supply pressures. Copyright © 2007 John Wiley & Sons, Ltd.     

Site-Specific Modeling of SH and P-SV Waves for Microzonation Study of Kolkata Metropolitan City, India

Kolkata, one of the oldest cities of India, is situated over the thick alluvium of the Bengal Basin, where it lies at the boundary of the zone III and zone IV of the seismic zonation map of India. An example of the study of site effects of the metropolitan Kolkata is presented based on theoretical modeling. Full synthetic strong motion waveforms have been computed using a hybrid method that combines the modal summation and finite difference techniques. The 1964 Calcutta earthquake, which was located at the southern part of Kolkata, is taken as the source region, with the focal mechanism parameters of dip?=?32°, strike?=?232° and rake?=?56°. Four profiles are considered for the computation of the synthetic seismograms from which the maximum ground acceleration (A _MAX) is obtained. Response spectra ratios (RSR) are then computed using a bedrock reference model to estimate local amplifications effects. The A _MAX varies from 0.05 to 0.17?g and the comparison of the A _MAX with the different intensity scales (MM, MSK, RF and MCS) shows that the expected intensity is in the range from VII to X (MCS) for an earthquake of magnitude 6.5 at an epicentral distance of about 100?km. This theoretical result matches with the empirical (historical and recent) intensity observations in Kolkata. The RSR, as a function of frequency, reaches the largest values (largest amplification) in the frequency range from 1.0 to 2.0?Hz. The largest site amplification is observed at the top of loose soil.     

Laboratory simulation of the salt weathering of schist: 1. Weathering of schist blocks in a seasonally wet tropical environment

Data describing sediment generation focusing on the temporal evolution of size gradation are required for the prediction of long‐term landform evolution. This paper presents such data for the salt weathering of a quartz‐chlorite schist obtained from the Ranger Uranium Mine in northern Australia. Rock fragment samples are subjected to three different climate regimes: (1) a dry season climate; (2) a wet season climate (both based on observations at the Ranger site); and (3) an oven‐drying sequence designed to test the sensitivity of the weathering process by exposing the rocks to more extreme temperatures. Two MgSO₄ salt solutions are applied, one being typical of wet season runoff and the other a more concentrated solution. Salt solution is applied daily in the wet season experiments and once only at the beginning of the dry season experiments. Results of the experiments reveal four stages of weathering. The kinetics of each stage are described and related to the formation of sediment of different sizes. Wet season climate conditions are shown to produce greater moisture variability and lead to faster weathering rates. However, salt concentrations in the wet season are typically lower and so when climate is combined with observed salt concentrations, the dry and wet season experiments weather at approximately equal rates. Finally, small variations in rock properties were shown to have a large impact on weathering rates, leading to the conclusion that rock weathering experiments need to be carefully designed if results are to be used to help predict weathering behaviour at the landscape scale. Copyright © 2006 John Wiley & Sons, Ltd.     

Spatial and Temporal Variations in Indian Summer Monsoon Rainfall and Temperature: An Analysis Based on RegCM3 Simulations

Regional climate models are important tools to examine the spatial and temporal characteristics of rainfall and temperature at high resolutions. Such information has potential applications in sectors like agriculture and health. In this study, the Regional Climate Model Version 3 (RegCM3) has been integrated in the ensemble mode at 55 km resolution over India for the summer monsoon season during the years 1982–2009. Emphasis has been given on the validation of the model simulation at the regional level. In Central India, both rainfall and temperature show the best correlations with respective observed values. The model gives rise to large wet biases over Northwest and Peninsular India. RegCM3 slightly underestimates the summer monsoon precipitation over the Central and Northeast India. Nevertheless, over these regions, RegCM3 simulated rainfall is closer to the observations when compared to the other regions where rainfall is overestimated. The position of the monsoon trough simulated by the model lies to the north of its original observed position. This is similar to the usual monsoon break conditions leading to less rainfall over Central India. RegCM3 simulated surface maximum temperature shows a large negative bias over the country while the surface minimum temperature is close to the observation. Nevertheless, there is a strong correlation between the all India weighted average surface temperature simulated by RegCM3 and IMD observed values. While examining the extreme weather conditions in Central India, it is found that RegCM3 simulated frequencies of occurrence of very wet days, extremely wet days, warm days and warm nights more often as compared to those in IMD observed values. However, these are systematic biases. The model biases in the frequencies of distribution of rainfall extremes explain the wet and dry biases in different regions in the country. Overall, the inter-annual characteristics of both the rainfall and temperature extremes simulated by RegCM3 in Central India are well in phase with those found in the observed data.     

Land Surface Layer Characteristics During Monsoon at a Tropical Station

—The atmospheric surface layer over land may behave differently in the tropics, particu larly during the monsoon. A preliminary attempt is made to observe the behavior of surface layer characteristics such as fluxes of momentum, sensible heat and latent heat, friction velocity, friction temperature, M-O length scale, Richardson number and Bowen’s ratio over Kharagpur (22°20′N, 87°18′E), a typical moist tropical station. The diurnal and day-to-day variations have been studied. It is observed that during the active phase of the monsoon the sensible heat flux and Bowen’s ratio are low. The diurnal variation is apparent for most parameters. Mostly near neutral conditions are observed.     

Thermodynamical Structure of Atmosphere during Pre-monsoon Thunderstorm Season over Kharagpur as Revealed by STORM Data

Variation of atmospheric thermodynamical structure parameters between days of thunderstorm occurrence and non-occurrence is presented based on data sets obtained during Severe Thunderstorm-Observations and Regional Modeling (STORM) experiments conducted over Kharagpur (22.3°N, 87.2°E) in pre-monsoon season of 2009 and 2010. Potential instability (stable to neutral) is noticed in the lower layers and enhanced (suppressed) convection in the middle troposphere during thunderstorm (non-thunderstorm) days. Low-level jets are observed during all days of the experimental period but with higher intensity on thunderstorm days. Convective available potential energy (CAPE) builds up until thunderstorm occurrence and becomes dissipated soon after, whereas convective inhibition (CIN) is greatly decreased prior to the event on thunderstorm days. In contrast, higher CAPE and CIN are noticed on non-thunderstorm days. Analysis of thermodynamic indices showed that indices including moisture [humidity index (HI) and dew point temperature at 850 hPa (DPT850)] are useful in differentiating thunderstorm from non-thunderstorm days. The present study reveals that significant moisture availability in the lower troposphere in the presence of convective instability conditions results in thunderstorm occurrence at Kharagpur.     

A Study of Mean Winter Circulation Characteristics and Energetics over Southeastern Asia

A mean climatology is studied to examine atmospheric circulation characteristics to assess the wintertime (December, January, February and March - DJFM) synoptic weather system affecting northern India. The main objective is to study the mean circulation and mean energetics distribution pertaining to the winter season, which are embedded with an eastward moving synoptic weather system in westerlies, called Western Disturbances (WDs). Forty years (1958–1997) of uninitialized daily re-analysis data of the National Center for Environmental Prediction - National Center for Atmospheric Research (NCEP- NCAR, henceafter NCEP), U.S. has been considered for this study. Winter circulations are considered over the domain 15°S–45°N and 30°E–120°E. This domain is considered particularly to illustrate the impact of wintertime synoptic weather system Western Disturbances (WDs), which travel towards the east over the western Himalayas during winter and yield an enormous amount of precipitation in the form of snow. Large-scale balances of kinetic energy, vorticity, angular momentum, heat and moisture budget terms are analyzed. The main findings of the study show that strong rising motion in the extratropical region brings a significant amount of precipitation over the region of study. Also, horizontal flux of kinetic energy converges in the tropical region and diverges over the extratropical region. It is seen that both the zonal and meridional component of kinetic energy contributes to the production of kinetic energy in the upper troposphere. Vorticity budget shows that wintertime circulation over the western Himalayas is characterized by a negative generation of vorticity. The relative and planetary vorticity advection contributes to the horizontal transport of vorticity. The moisture flux transported into the region shows that in the middle tropospheric levels moisture undergoes phase transformation due to turbulent exchange and hence releases latent heat.     

Hydro-climatic trends in the Abay/Upper Blue Nile basin,Ethiopia

Trends of the three hydro-meteorological variables precipitation, temperature and stream flow, represented by 13, 12, and 9 gauging stations, respectively, within the Abay/Upper Blue Nile basin have been studied to support water management in the region. The Trends were evaluated over different time periods depending on data availability at the stations. The statistical Mann–Kendall and Pettitt tests have been used to assess trends and change points respectively. The tests have been applied to mean annual, monthly, seasonal, 1- and 7-days annual minimum and maximum values for streamflow, while mean annual, monthly and seasonal timescales were applied to meteorological variables. The results are heterogeneous and depict statistically significant increasing/decreasing trends. Besides, it showed significant abrupt change of point upward/downward shift for streamflow and temperature time series. However, precipitation time series did not show any statistically significant trends in mean annual and seasonal scales across the examined stations.Increasing trends in temperature at different weather stations for the mean annual, rainy, dry and small rainy seasons are apparent. The mean temperature at Bahir Dar – typical station in the Lake Tana sub basin, has been increasing at the rate of about 0.5 °C/decade, 0.3 °C/decade in rainy season (June–September), 0.6 °C/decade in small rainy season (March–May), and 0.6 °C/decade in dry season (October–February). Other stations in the Abay/Upper Blue Nile show comparable results. Overall it is found that trends and change point times varied considerably across the stations and catchment to catchment. Identified significant trends can help to make better planning decisions for water management. However, the cause attributes to the observed changes in hydro-meteorological variables need further research. In particular the combined effects of land use/land cover change and climate variability on streamflow of Abay/Blue Nile basin and its tributaries needs to be understood better.     

Radon volumetric activity and ion production in the undisturbed lower atmosphere: Ground-based observations and numerical modeling

The results of in situ ground-based observations of radon volumetric activity carried out at the Borok Geophysical Observatory of Schmidt Institute of Physics of the Earth of the Russian Academy of Sciences (58°04′ N; 38°14′ E) are presented. Modeling the characteristic diurnal variation in the ion production rate in the undisturbed midlatitude lower atmosphere above land is carried out. The Lagrangian stochastic model of turbulent transport is developed in application to determining the vertical profiles of radon activity for 222Rn and 220Rn isotopes and their radioactive decay products. The results calculated by the Lagrangian stochastic model are matched with the analytical solution for the free atmosphere. Based on the model, the estimate is obtained for the rate of radon outflow from the convective boundary layer to the free clear sky atmosphere. The implications of temperature stratification of the atmosphere for the vertical distribution of the ion production rate at the different radon emission rate are explored.     

Modeling studies of the upper ocean response to a tropical cyclone

A coupled ocean and boundary layer flux numerical modeling system is used to study the upper ocean response to surface heat and momentum fluxes associated with a major hurricane, namely, Hurricane Dennis (July 2005) in the Gulf of Mexico. A suite of experiments is run using this modeling system, constructed by coupling a Navy Coastal Ocean Model simulation of the Gulf of Mexico to an atmospheric flux model. The modeling system is forced by wind fields produced from satellite scatterometer and atmospheric model wind data, and by numerical weather prediction air temperature data. The experiments are initialized from a data assimilative hindcast model run and then forced by surface fluxes with no assimilation for the time during which Hurricane Dennis impacted the region. Four experiments are run to aid in the analysis: one is forced by heat and momentum fluxes, one by only momentum fluxes, one by only heat fluxes, and one with no surface forcing. An equation describing the change in the upper ocean hurricane heat potential due to the storm is developed. Analysis of the model results show that surface heat fluxes are primarily responsible for widespread reduction (0.5°–1.5°C) of sea surface temperature over the inner West Florida Shelf 100–300 km away from the storm center. Momentum fluxes are responsible for stronger surface cooling (2°C) near the center of the storm. The upper ocean heat loss near the storm center of more than 200 MJ/m² is primarily due to the vertical flux of thermal energy between the surface layer and deep ocean. Heat loss to the atmosphere during the storm’s passage is approximately 100–150 MJ/m². The upper ocean cooling is enhanced where the preexisting mixed layer is shallow, e.g., within a cyclonic circulation feature, although the heat flux to the atmosphere in these locations is markedly reduced.