Synoptic Analyses Research Articles

Multi-source observations on the effect of atmospheric blocking on air quality in İstanbul: a study case.

Air pollution is affected by the atmospheric dynamics. This study aims to determine that air pollution concentration values in İstanbul increased significantly and reached peak values due to atmospheric blocking between the 30th of December 2022 and the 5th of January 2023. In this study, hourly pollutant data was obtained from 16 air quality monitoring stations (AQMS), the exact reanalysis data was extracted from ERA5 database, and inversion levels and meteorological and synoptic analyses were used to determine the effects of atmospheric blocking on air pollution. Also, cloud base heights and vertical visibility measurements were taken with a ceilometer. Statistical calculations and data visualizations were performed using the R and Grads program. Omega-type blocking, which started in İstanbul on December 30, 2022, had a significant impact on the 1st and 2nd of January 2023, and PM10 and PM2.5 concentration values reached their peak values at 572.8 and 254.20µg/m3, respectively. In addition, it was found that the average concentration values in the examined period in almost all stations were higher than the averages for January and February. As a result, air quality in İstanbul was determined as "poor" between these calendar dates. It was found that the blocking did not affect the ozone (µg/m3) concentration. It was also found that the concentrations of particulate matter (PM) 10µm or less in diameter (PM10) and PM 2.5µm or less in diameter (PM2.5) were increased by the blocking effect in the İstanbul area. Finally, according to the data obtained using the ceilometer, cloud base heights decreased to 30m and vertical visibility to 10m.

A Climatology of Dryline‐Related Convection on the Western Plateau of Subtropical Southern Africa

AbstractDrylines occur regularly during summer over the interior of sub‐tropical southern Africa. The highest frequency of drylines is over the western interior where it is also climatologically much drier than the eastern parts. An existing drylines data set is compared with lightning data between 2010 and 2021, to determine how often drylines were associated with convective storms. A minimum stroke threshold is applied to eliminate instances of weak convection. Seventy‐six percent of drylines during austral summer (October–March) were associated with significant convection with a standard deviation of 8.6. There is a peak frequency of 12 convective dryline days during December. Composite synoptic analyses were conducted for 591 convective and 186 non‐convective dryline days to determine the ideal formation environment for convective drylines. Composites were also created for the days leading up to convective and non‐convective drylines, showing the importance of moisture advection from the southwest Indian Ocean, through the Zambezi and Limpopo River Valleys. Early summers tend to be drier than late summers over the southern African interior and colder in the mid‐levels. These differences affect the formation environment of convective drylines. Composites show that dryline‐related convection during early summer tends to occur on days with a deep surface trough and a trough at 500 hPa further west. Convection during late summer is associated with increased surface moisture, higher instability, and a weaker trough at 500 hPa than during early summer.

Contribution of PDO to Decadal Variations of Glaze Dipole Pattern in China

Abstract Based on the in situ observations, reanalysis, and model simulation, the variations in glaze dipole pattern in China and its underlying physical mechanism have been explored. The glaze dipole pattern features an out-of-phase relationship between winter glaze in the south of the Yangtze River valley (YRV) and northern China, accompanied by pronounced interdecadal variation around the late 1970s. The results from synoptic analyses suggest that cold air brought by the northerly winds and warm moist air by the southwesterly winds, as well as the occurrence of inversion layer are vital to the glaze weather in the south of YRV. Further analyses indicate that the interdecadal shift of the Pacific decadal oscillation (PDO) contributes largely to variations in glaze dipole pattern. Specifically, the warm PDO provides a beneficial environment for the occurrence of glaze dipole pattern by stimulating the tropical–extratropical circulation configuration with the deepened East Asian trough, strengthened East Asian westerly jet, anomalous anticyclone over the tropical western Pacific Ocean, and cyclone over the southern Tibetan Plateau at the decadal time scale. Consequently, the enhanced moisture transport brought by southwesterly and cold air intrusion induced by the deepened East Asian trough benefit the glaze weather in the south of YRV, while the decreased precipitation and a much lower temperature in northern China depress the generation of glaze. Moreover, the results from the CAM4 model simulation indicate the atmospheric circulation anomalies forced by PDO-like SST can roughly reproduce the extratropical configuration related to the glaze, but it has difficulties in capturing the tropical circulation anomalies. Significance Statement The purpose of this study is to better understand how the glaze dipole pattern in China responds to climate anomalies, which focuses on the spatial–temporal evolution of glaze days and its underlying physical mechanism. This study highlights the important role of Pacific Ocean sea surface temperature anomalies in the interdecadal variations in glaze dipole pattern, and it gives a clear clarification to demonstrate the impacts of Pacific decadal oscillation on the climatological background for the occurrence of glaze. Our results provide a guide on what drives the interdecadal variation in the glaze dipole pattern and help to understand the climate dynamic mechanism of variations in freezing events in China.

Synoptic analysis of the January 2004 snowstorm: Example of Çanakkale

Many natural disasters have occurred on the Earth we live in. Humans have always been in a struggle with these natural phenomena. Today, people are still struggling with atmospheric extreme events. One of the most important disasters like this is snowstorms that occur suddenly in winter. Especially countries in the middle belt (30-60 latitudes in the Northern Hemisphere) are constantly affected by snowstorms. Turkey, located in the Middle Belt, is also exposed to these storms during the winter season. From this perspective, the analysis of synoptic conditions and weather forecast is an important factor for risk analysis and take precautions for winter storms. Thus, the predictions made with the tracking of air masses and synoptic analysis make it easier to understand how the storm occurred. For this purpose, synoptic analyses were conducted to understand the development of the snowstorm that occurred in the high atmosphere in Çanakkale on January 20-30, 2004. This study examined how weather conditions change. Radiosonde data, surface maps, and daily bulletins provided from the Turkish State Meteorological Service were used in the study. Archival data were used to track air mass orbits using the Hysplit trajectory method. Stability and instability assessments of air masses were evaluated using the data from radiosonde stations using the K Index. Spatial analysis software was used to analyze the data and show the thematic distribution of topography. According to the findings, during the passage of a cold front of air masses coming from the north to Çanakkale on January 22, gusty winds began, suddenly dropped the temperatures, and began heavy snow events. Later, it turned into a blizzard and formed a type of snow.

Mechanisms governing the evolution of a long-lived northwest vortex that caused a series of disasters in Northwest China

The northwest vortex (NWV) is a type of mesoscale vortex that appears with a relatively high frequency in Northwest China. To further the understanding of the NWV's evolution, in this study, the moisture and circulation budgets of a long-lived NWV (∼132 h) that appeared in early August 2019 were calculated. This vortex induced a series of torrential rainfall events in Northwest China and Mongolia, which caused severe transmission line faults and urban waterlogging. Synoptic analyses indicate that the NWV was generated in a favorable background environment characterized by notable upper-level divergence and strong mid-level warm advection. The moisture budget shows that the East China Sea and Bohai Sea acted as the main moisture sources for the NWV-associated precipitation, and the water vapor was transported into the rainfall regions mainly by easterly and southeasterly winds. The circulation budget indicates that, during the developing stage, convergence-related vertical stretching was a dominant factor for the NWV's development; whereas, the vortex's displacement from regions with stronger cyclonic vorticity to those with weaker cyclonic vorticity mainly decelerated its development. In the decaying stage, divergence-related vertical shrinking and the net export of cyclonic vorticity due to the eddy flow's transport resulted in the NWV's dissipation.摘要西北涡是我国西北地区一类发生频率较高的中尺度涡旋, 其所引发灾害的强度与西南低涡, 高原涡相当, 但相关研究却远远少于前两种涡旋.为了深化对西北涡的认识, 本文利用水汽与环流收支对一次长生命史西北涡 (其在西北地区引发了一系列暴雨过程, 导致了严重的输电线路故障与城市内涝) 进行了研究, 发现, 东海与渤海是此西北涡引发暴雨的主要水汽来源, 东风与东南风则是主要的输送气流. 辐合所引起的垂直伸展是西北涡发展的主导因子, 而涡旋由较强背景涡度区向较弱背景涡度区的移动则一定程度上延缓了涡旋的发展.

A Synoptic Climatology of Spring Dryline Convection in the Southern Great Plains

AbstractA dataset of drylines within a region of the southern Great Plains was constructed to investigate the large-scale environments associated with the initiation of deep moist convection. Drylines were identified using NOAA/NWS Weather Prediction Center surface analyses for all April, May, and June days 2006–15. Doppler radar and visible and infrared satellite imagery were used to identify convective drylines, where deep, moist convection was deemed to have been associated with the dryline circulation. Approximately 60% of drylines were convective, with initiation most frequently occurring between 2000 and 2100 UTC. Composite synoptic analyses were created of 179 convective and 104 nonconvective dryline days. The composites featured an upper-level long-wave trough to the west of the Rockies and a ridge extending across the northern and eastern United States. At the surface, the composites featured a broad surface cyclone over western Texas and southerly flow over the south-central states. Convective drylines featured more amplified upper-level flow, associated with a deeper trough in the western United States and a stronger downstream ridge than nonconvective drylines up to 5 days preceding a dryline event. By the day of a dryline event, the convective composite features greater low-level specific humidity and higher CAPE than the nonconvective composite. These results demonstrate that synoptic-scale processes over several days help create conditions conducive to deep, moist convection along the dryline.

Extreme Daily Rainfall in Central-Southern Chile and Its Relationship with Low-Level Horizontal Water Vapor Fluxes

AbstractExtreme rainfall events are thought to be one of the major threats of climate change given an increase of water vapor available in the atmosphere. However, before projecting future changes in extreme rainfall events, it is mandatory to know current patterns. In this study we explore extreme daily rainfall events along central-southern Chile with emphasis in their spatial distribution and concurrent synoptic-scale circulation. Surface rain gauges and reanalysis products from the Climate Forecast System Reanalysis are employed to unravel the dependency between extreme rainfall and horizontal water vapor fluxes. Results indicate that extreme rainfall events can occur everywhere, from the subtropical to extratropical latitudes, but their frequency increases where terrain has higher altitude, especially over the Andes Mountains. The majority of these events concentrate in austral winter, last a single day, and encompass a north–south band of about 200 km in length. Composited synoptic analyses identified extreme rainfall cases dominated by northwesterly (NW) and westerly (W) moisture fluxes. Some features of the NW group include a 300-hPa trough projecting from the extratropics to subtropics, a surface-level depression, and cyclonic winds at 850 hPa along the coast associated with integrated water vapor (IWV) > 30 mm. Conversely, features in the W group include both a very weak 300-hPa trough and surface depression, as well as coastal westerly winds associated with IWV > 30 mm. About half of extreme daily rainfall is associated with an atmospheric river. Extreme rainfall observed in W (NW) cases has a strong orographic (synoptic) forcing. In addition, W cases are, on average, warmer than NW cases, leading to an amplified hydrological response.

Statistical and synoptic analyses of offshore wind variations

In this study, variations of offshore wind speed in the northern and central coasts of British Columbia are examined using wind observations from nine buoys distributed in the region. Wind speeds from all buoys are extrapolated to the standard (10 m) wind measurement height as well as to the wind turbine hub height (100 m) using Monin–Obukhov similarity theory. Sustained winds above several thresholds are analysed and values of 50 and 100‐year return extreme wind speed levels are calculated for all locations. The percentage of sustained winds between the wind turbine cut‐in and cut‐out wind speed thresholds at 100 m indicates short periods without power generation. The highest 50 and 100‐year return level values are found at locations west of Haida Gwaii, while the lowest values are calculated at the most southern and eastern locations. Spatial coherency analysis of high wind speeds between all locations shows high same‐day coherency ratios between all buoys located offshore of the mainland coast, which emphasizes the importance of the atmospheric circulation at the synoptic‐scale as the main driver of intense wind events; consequently, a synoptic‐scale circulation analysis is carried out by applying principal components analysis and k‐means clustering, and then relating the calculated synoptic patterns to some of the previously classified wind categories. The synoptic‐scale circulation analysis reveals that high wind speed events are mainly associated with a system of low pressure located west or northwest of the study region, which induces intense southerly to southeasterly winds. Low wind speeds are often associated with a high‐pressure system (Pacific High) originating southwest of the region that mainly predominates during the summer.

Extreme Rainfall Events in the Southwest of Rio Grande do Sul (Brazil) and Its Association with the Sandization Process

Part of the sandization process in southwestern Rio Grande do Sul (Brazil) originates from daily torrential rains. However, it is believed that climate changes have been provoking more frequent and more intense rains in the region, a phenomenon which can change the dynamic of erosion/transport/sedimentation natural processes. The objective of this work is to identify the behavior of daily rainfall extreme events (in terms of their frequency, return time, tendency and genesis), relating them to both climatic change issue and enhancement of erosive processes. We have used daily rainfall data from meteorology stations of Brazilian National Water Agency (ANA) for the period between 1928 and 2017 and the percentile 99 was used to identify daily rainfall extreme value (71.5 mm). The upper values were categorized and their absolute and relative frequencies as well as their return time were identified. The temporal tendency of these events was evaluated by the Mann-Kendall test, considering the 90 years of the series. The results showed that there was a significant increase in heavy rainfall events in November and December in the last two decades and that the return time for these events decreased throughout the time. Synoptic analyses from GOES 13 satellite infrared imagery and from ECMWF/ERA/Interim reanalysis data allowed concluding that such intense rainfall events originated themselves from the transport of moisture from the Amazon by Low-Level Jets, which promoted the formation of Mesoscale Convective Complex, with large volumes of rain in the study region. Thus, the recurrence of these events in the southwest of Rio Grande do Sul may intensify these sandization processes, since they arise from the association between natural morphoscultural dynamics and agricultural practices, generating environmental problems for the region.

Influence of the Northeast Cold Vortex on Flooding in Northeast China in Summer 2013

Severe flooding occurred in Northeast China (NEC) in summer 2013. Compared with the rainfall climatology of the region, the rainy season began earlier in 2013 and two main rainy periods occurred from late June to early July and from mid July to early August, respectively. During the summer season of 2013, the western Pacific subtropical high (WPSH) was located farther westward, which strengthened the southerly winds on its west side in the lower troposphere. Under this circulation pattern, more water vapor was transported to North China and NEC. Another moisture transport pathway to NEC was traced to the cross-equatorial flow over the Bay of Bengal. In mid–high latitudes in summer 2013, the Northeast Cold Vortex (NECV) was much stronger and remained stable over NEC. Thus, the cold air flow from its northwest side frequently met with the warm and wet air from the south to form stronger moisture convergence at lower levels in the troposphere, resulting in increased precipitation over the region. Correlation analysis indicated that the NECV played a more direct role than the WPSH. Synoptic analyses of the two heaviest flood cases on 2 and 16 July confirmed this conclusion. The four wettest summers in NEC before 2000 were also analyzed and the results were consistent with the conclusion that both the WPSH and the NECV led to the intense rainfall in NEC, but the NECV had a more direct role.

Synoptic estimates of diffuse groundwater seepage to a spring-fed karst river at high spatial resolution using an automated radon measurement technique

Groundwater (GW) seepage can provide a major source of water, solutes, and contaminants to rivers, but identifying magnitudes, directions and locations of seepage is complicated by its diffuse and heterogeneous distributions. However, such information is necessary to develop programs and policies for protecting ecosystems and managing water resources. Here, we assess GW seepage to the Ichetucknee River, a spring-fed, low gradient, gaining stream in north-central Florida, through automated longitudinal surveys of radon (222Rn) activities at three different flow conditions. A 222Rn mass balance model, which integrates groundwater and spring water end member 222Rn activities and longitudinal 222Rn distributions in river water, shows that diffuse groundwater seepage represents about 16% of the total river baseflow, consistent with previous results obtained from ion (Ca2+, Cl−, SRP and Fe) mass balances and dye tracer methods. During high river stage, the contribution from seepage increases to 18–23% of the river flow. The spatial distribution of GW seepage is more variable in the upper 2.2-km reach of the river than the lower 2.8-km reach, regardless of river flow conditions. The upper reach has a narrower flood plain than the lower reach, which limits evapotranspiration and increases hydraulic gradients toward the river following storm events. Seepage in the lower reach is also limited by hydrologic damming by the receiving river, which inundates the floodplain during high flow conditions, and reduces the hydraulic head gradient. These results demonstrate the variable nature of seepage to a gaining river in both time and space and indicate that multiple synoptic analyses of GW seepage are required to assess seepage rates, determine time-averaged solute fluxes, and develop optimal management policies for riverine ecosystems.

Analysis of GNSS-R Altimetry for Mapping Ocean Mesoscale Sea Surface Heights Using High-Resolution Model Simulations

The capability of global navigation satellite system reflectometry (GNSS-R) altimetry to map mesoscale sea surface height (SSH) fields is analyzed using synthetic measurements derived from a high-resolution (1/10°) numerical model of the North Pacific. As an example, we consider the GPS and GLONASS constellation transmitters and assume six reflection-capable receivers onboard the Constellation Observing System for Meteorology, Ionosphere, and Climate satellites in high-inclination (720 km, 72°) orbits. An individual GNSS-R measurement has a ∼10-km footprint. The SSH measurement error is simulated as a function of the incidence angle and the error in the delay measurement between the transmitter and receiver. The delay measurement error is assumed to have Gaussian white noise distribution with a root-mean-square error (RMSE) of 1.0 or 2.0 m. Two days of synthetic measurements are used to reconstruct SSH fields using a two-dimensional variational algorithm. For the 1.0-m delay error, the basin-wide RMSE of the mapped field is 2.3 cm and the spatial correlation between the mapped and true mesoscale fields is larger than 0.9. For the 2.0-m delay error, the basin-wide RMSE is 3.8 cm and the spatial correlation is larger than 0.8. Spectral and synoptic analyses suggest that two days of measurements can reproduce mesoscale features down to 100 km. The result demonstrates the ability of GNSS-R altimetry to suppress large measurement errors due to the high density of measurements and the potential to constrain mesoscale features down to scales beyond what the constellation of existing nadir-altimeters allows.

Precipitation regime and stable isotopes at Dome Fuji, East Antarctica

Abstract. A unique set of 1-year precipitation and stable water isotope measurements from the Japanese Antarctic station, Dome Fuji, has been used to study the impact of the synoptic situation and the precipitation origin on the isotopic composition of precipitation on the Antarctic Plateau. The Antarctic Mesoscale Prediction System (AMPS) archive data are used to analyse the synoptic situations that cause precipitation. These situations are investigated and divided into five categories. The most common weather situation during a precipitation event is an upper-level ridge that extends onto the Antarctic Plateau and causes strong northerly advection from the ocean. Most precipitation events are associated with an increase in temperature and wind speed, and a local maximum of δ18O. During the measurement period, 21 synoptically caused precipitation events caused 60 % of the total annual precipitation, whereas the remaining 40 % were predominantly attributed to diamond dust. By combining the synoptic analyses with 5-day back-trajectories, the moisture source regions for precipitation events were estimated. An average source region around a latitude of 55° S was found. The atmospheric conditions in the source region were used as initial conditions for running a Rayleigh-type isotopic model in order to reproduce the measured isotopic composition of fresh snow and to investigate the influence of the precipitation source region on the isotope ratios. The model represents the measured annual cycle of δ18O and the second-order isotopic parameter deuterium excess reasonably well, but yields on average too little fractionation along the transport/cooling path. While simulations with an isotopic general circulation model (GCM) (ECHAM5-wiso) for Dome Fuji are on average closer to the observations, this model cannot reproduce the annual cycle of deuterium excess. In the event-based analysis, no evidence of a correlation of the measured deuterium excess with the latitude of the moisture source region or the corresponding conditions was identified. Contrary to the assumption used for decades in ice core studies, a more northerly moisture source does not necessarily mean a larger temperature difference between source area and deposition site, thus a more depleted precipitation in heavy isotopes with a higher deuterium excess.

Arctic sea ice and warm season North American extreme surface air temperatures

CR Climate Research Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials CR 67:15-29 (2016) - DOI: https://doi.org/10.3354/cr01349 Arctic sea ice and warm season North American extreme surface air temperatures Dagmar Budikova1,*, Leonardo Chechi2 1Department of Geography-Geology, Illinois State University, Normal, IL 61790-4400, USA 2Agronomy, Universidade federal da Fronteira Sul (Federal University of South Border), Erechim, RS 99700-000, Brazil *Corresponding author: dbudiko@ilstu.edu ABSTRACT: A growing amount of evidence points to a notable linkage between the changing Arctic cryosphere and weather in the middle latitudes of the Northern Hemisphere. Recent studies propose a series of mechanisms that make plausible the connection between Arctic amplification/sea ice decline and extreme weather. Using composite analyses, this study examines associations between the frequency of occurrence of boreal summer daily extreme surface air temperatures across North America and simultaneous mean Arctic sea ice concentration (SIC) conditions during the period 1979-2013. Four distinct regions show coherent relationships including large sections of the eastern USA, Canada and the Canadian Arctic, central North America, southeast USA, and the west coast from southern Canada to Alaska. Across the eastern USA and Canada, as well as in western North America, the connections are principally shaped by low ice conditions with an expected decline in the incidence of cool nights/days and an increase in the incidence of warm nights/days. The ice-temperature relationships observed in the other regions are mostly shaped by high ice conditions. Synoptic analyses indicate the associations to be reflected in mean summer surface air temperature (SAT) and surface anomaly flows, as well as in the 500 and 200 hPa geopotential height flow and mean zonal wind anomaly patterns. Areas with the greatest atmospheric flow modifications have been generally associated with regions that display most notable extreme temperature frequency modifications. KEY WORDS: Arctic ice · Summer extreme temperature · North America Full text in pdf format PreviousNextCite this article as: Budikova D, Chechi L (2016) Arctic sea ice and warm season North American extreme surface air temperatures. Clim Res 67:15-29. https://doi.org/10.3354/cr01349 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in CR Vol. 67, No. 1. Online publication date: January 12, 2016 Print ISSN: 0936-577X; Online ISSN: 1616-1572 Copyright © 2016 Inter-Research.

A collection of sub-daily pressure and temperature observations for the early instrumental period with a focus on the "year without a summer" 1816

Abstract. The eruption of Mount Tambora (Indonesia) in April 1815 is the largest documented volcanic eruption in history. It is associated with a large global cooling during the following year, felt particularly in parts of Europe and North America, where the year 1816 became known as the "year without a summer". This paper describes an effort made to collect surface meteorological observations from the early instrumental period, with a focus on the years of and immediately following the eruption (1815–1817). Although the collection aimed in particular at pressure observations, correspondent temperature observations were also recovered. Some of the series had already been described in the literature, but a large part of the data, recently digitised from original weather diaries and contemporary magazines and newspapers, is presented here for the first time. The collection puts together more than 50 sub-daily series from land observatories in Europe and North America and from ships in the tropics. The pressure observations have been corrected for temperature and gravity and reduced to mean sea level. Moreover, an additional statistical correction was applied to take into account common error sources in mercury barometers. To assess the reliability of the corrected data set, the variance in the pressure observations is compared with modern climatologies, and single observations are used for synoptic analyses of three case studies in Europe. All raw observations will be made available to the scientific community in the International Surface Pressure Databank.

The influence of the polar front jet stream on the formation of dust events in the southwest of Iran

Dust events are among the climatic hazards which may occur the year over in the southwest of Iran. The goal of this research was to investigate the role of the polar front jet stream (PFJ) as one of the most important synoptic patterns affecting the formation of dust events in the southwest of Iran during a statistical period (1998–2012). The research method was a combination of statistical–synoptic and remote-sensing analyses. The frequency of occurrence, duration, and intensity of dust events were studied by using hourly data of five synoptic weather stations. Also, climatic stability condition considering climatic conditions of ground level and 500-hpa level was investigated by using networked data obtained from the NCEP. Dust detection was done by using the data of Meteosat-7 satellite and MODIS sensor of Aqua satellite. In addition, weather conditions were analyzed simultaneously with dust events using dust measurement indices such as aerosol absorption index (AAI) of TOMS sensor and aerosol optical depth (AOD), and concentration rate of dust and visibility extracted from the output data of the numerical simulation model (COAMPS). Statistical results showed that the main factor of more than 20 % of total dust events in the southwest of Iran was the synoptic pattern of the PFJ, leading to the formation of dust events in the cold period of the year. Finally, synoptic analysis of weather maps and satellite images clearly indicated the effective role of PFJ in the formation of dust events of cold periods in the southwest of Iran.

Geospatial Assessment and Monitoring of the Dynamics of Urban Expansion of Ogbomoso, South-Western Nigeria

This study focuses on the dynamics of urban expansion along with the Landuse/Landcover changes in Ogbomoso North and South LGAs, Oyo State, Nigeria, using Remote Sensing and Geographic Information Systems Technology. Ogbomoso has witnessed remarkable expansion, growth and development of large infrastructural facilities such as highway/expressway, power stations as well as the Ladoke Akintola University of Technology, the University Teaching Hospital Complex, modern markets, very many schools, a number of low cost housing estates, local authority offices, etc. This has therefore, resulted in loss of agricultural land, modification and alterations in the land use/land cover over time without any detailed and comprehensive evaluation of the changes. There is therefore, need for synoptic analyses of patterning, change and expansion at regional scales over time in the environment. LandSat imageries of 1990, 2000 and NigeriaSat-1 imagery of 2007 of the environment were subjected to supervised image classification using IDRISI Selva 17.0 software. Results obtained from classifications were cross- tabulated for change detection. The results reveal that water body appreciated from 1.2% (1990), 3.1% (2000) to 3.7% (2007). Built-up area appreciated from 6.4 to 20.3% (1990-2007). Arable land remained the largest land cover, with the value of 57.8% in 1990, 47.8% in 2000 and 62% in 2007. Compound Interest formula was used to determine the rate of urban expansion of Ogbomoso town and the expansion of the town was projected for the year 2020 and 2025. The average rate of urban expansion of Ogbomoso was found to be significantly high with a value of 8.92%.

Synoptic Analysis of Storms and Severe Storms of Zahedan City with an Emphasis on Predicting the Probability of Their Incidence

Hurricane is one of the climate risks that are always led to life and financial losses. The purpose of this study is to predict the incidence of hurricanes at Zahedan city based on statistical analysis and synoptic analyses of this phenomenon. For this reason, the data related to wind survey of synoptic stations of Zahedan in 1983-2011 were collected. First, the accuracy and homogeneity of data were conducted using Run Test. Then, the hurricanes that their average annual incidence was between 3-5 times per year were selected based on partial series analysis model and the basic wind speed was determined 22 m/sec. After creating data matrix in Mat lab, the number of severe winds identified during the statistical period was 79 storms which their frequency has been increased in recent years. Results have shown that the storms with a speed of more than 26.4 m/s in 2-year period with a 50% probability and the storms with a speed of more than 36.52 m/s in a hundred-year return period can be occurred. Although the strongest winds occur in spring, January is the most incidence of occurring storms. Also the cyclone shows 80% of hurricanes northward. For example, the synoptic pattern of the storms occurred in 4 April 2002 and 2 April 2002 using maps of mean daily pressure, temperature, Zonal and Meridional winds at two sea levels and 850 hPa. The patterns indicate establishing low-pressure nuclear and locating 1000 hPa tabs on the region. Creating two high pressures, one on Zagros and the other Asian high pressure makes possible the conditions to intensify pressure gradient, making steep and severe pressures in the region, conditions are occurred by the winds exceeds more than 40 m/s. in this condition, Zahedan region is the maximum temperature of the surrounding in which severe temperature conflicts predominated on the region.

Plato's Political Puzzle

Mark Blitz begins his book Plato’s Political Philosophy by making a strong case for Plato’s continuing relevance to us. The book’s three parts are centered on three dialogues of special importance to Blitz’s topic: the Laws, the Republic, and the Statesman. Blitz also pulls into his discussion other dialogues that illuminate the teachings of these three central ones. Blitz’s analyses of the dialogues are illuminating. He lays out the dialogues’ intellectual pathways and gives us an important sense of their meaning. In addition to his examination of particular dialogues, Blitz also gives us rich discussions of four key concepts that underlie and are found throughout Plato’s works: nature, wonder, perplexity, and laughter. The book lacks a deeper discussion of the view that we should be guided by nature in determining our ends. Also missing is a better appreciation of both the challenge posed to philosophy by piety, and the attraction of institutions of modern republics. And we could have a better understanding of the limits of a rational politics in the Statesman. Plato has difficulty finding a place for the philosopher in the city, and this could come through more clearly in Blitz’s account. But these shortcomings are minor when set against the book’s strengths. Its synoptic analyses can help guide those new to Plato. But there is also much here for mature scholars in Blitz’s detailed and careful exploration of Plato’s more important concepts and arguments.

A Comparative Study and Evaluation of Mixing-Height Estimation Based on Sodar-RASS, Ceilometer Data and Numerical Model Simulations

A comparative study and evaluation of mixing-layer height estimation was conducted, using data from remote sensing and in-situ instrumentation, radiosondes, synoptic analyses and model simulations. The data were collected during an experimental campaign conducted at the Athens International Airport, Greece, from 15 to 26 September 2007. Mixing-layer height from the sodar dataset was estimated taking into account the backscatter signal, temperature, Richardson number profiles and surface-based measurements, while for the ceilometer data, the optical attenuated aerosol backscatter intensity first derivative was utilized. Numerical simulations using the Penn State/NCAR MM5 numerical mesoscale model and the Weather Research and Forecast numerical model were also performed. Comparative results under different meteorological conditions (local flows, moderate to strong background flows) are presented and discussed. According to our results under moderate to strong winds the existing mechanical turbulence creates good signal conditions for the two remote systems leading to a good overall agreement between the two methodologies, while both models give reliable estimations of the mixing height. The sodar-RASS system is more suitable under low to moderate winds or when local flows are developed with weak stability, while the ceilometer system is more suitable for moderate to strong winds, which is associated with a homogeneous atmosphere and weaker low-level temperature inversions. In the models, the existing approach for atmospheric boundary-layer depth simulation usually provides higher compared to remote sensing values, especially during local flow events. An alternative approach for the estimation of mixing height by the models, the estimation and use of the diffusion coefficient profiles, is a promising methodology regarding the comparison with the sodar-RASS mixing-height estimations.