Climatological Studies Research Articles

EARLINET: 12-year of Aerosol Profiling over Europe

EARLINET has been collecting high quality aerosol optical profiles over Europe since 2000. The comparison with automatic collected dataset of aerosol optical depth (AOD) from AERONET and MODIS demonstrates the effectiveness of EARLINET regular measurement schedule for climatological studies. The analysis of optical properties in the local boundary layer indicates that the general decrease of AOD observed by different platforms over Europe in the last decade could be due to the modification of aerosol properties (towards less absorbing and larger particles) in the lower troposphere.

ISRO’s Geostationary data products archival & dissemination – Retrospect and prospect

Natural extreme weather events have been causing excessive damage to life and property across the globe since time immemorial. Space based techniques and instruments have been improvised and utilised over the years to generate and collect earth observations data. Although a significant amount of research has led to meaningful forecasts of extreme weather events leading to minimising of the loss of life and property, the analytical approaches in this field need to be further studied and explored. Also, since every instance of earth observation is significant in multiple time domains (current as well as past which is required for climatology studies), it needs to be archived and disseminated in an organised and holistic manner. For long time preservation, modern infrastructure and underlying cutting edge technologies need to be adapted. With missions like GISAT, where the volume of data handled per day will be around 200 Mega bytes per second, multi level strategic approach for archival and high speed bandwidth for near real time data dissemination on public networks should be complemented with data broadcast to strategic users, using satellite communications. This paper describes the current infrastructure established for archival and dissemination and archival of ISRO’s Met-Ocean data observations and the future road map in the area of instantaneous data and weather alerts dissemination through an Indian broadcasting system (IMETCAST). This is to ensure timely delivery of satellite data to end users to facilitate near real time analysis of weather events.

Lake ice measurements from soil water content reflectometer sensors

AbstractLake ice depth provides important information about local and regional climate change, weather patterns, and recreational safety, as well as impacting in situ ecology and carbon cycling. However, it is challenging to measure ice depth continuously from a remote location, as existing methods are too large, expensive, and/or time‐intensive. Therefore, we present a novel application that resolves size, cost, and automation issues using commercially‐available soil water content reflectometer sensors from multiple manufactures. Analysis of sensors deployed in an environmental chamber using a scale model of a lake demonstrated accurate measure of the change in ice depth over any time period to within 1 cm, through sensor response of liquid‐to‐solid phase change. A robust correlation exists between volumetric water content in time as a function of environmental temperature and ice growth. This relationship allows us to convert volumetric water content into ice depth. An array of these sensors can be used in lake or river settings to create a temporally high‐resolution ice depth record, which fills in a needed gap for ecological or climatological studies as well as increasing public recreational safety.

Characteristics and Synoptic Environment of Drylines Occurring over the Higher Terrain of Southeastern Wyoming

Abstract Commonly observed over the broadly sloped terrain of the southern Great Plains (SGP), drylines are frequent loci of warm season deep convection and have been the focus of numerous observational, theoretical, and climatological studies over last half century. In this study, a 3-yr (2010–12) analysis of the characteristics and synoptic environment of drylines occurring elsewhere, over the high terrain in southeastern Wyoming just east of the Rocky Mountains, is presented. Observed on ~11% of the days between May and August of the years examined, southeastern Wyoming drylines were often associated with large moisture gradients [~5–10 g kg−1 (100 km)−1], large horizontal virtual potential temperature differences (~2–5 K), and convergent zonal wind flow at the surface. The synoptic conditions leading to their formation and their relationship to thunderstorm activity are also explored in an effort to aid local forecasters in anticipating the development and convective impact of drylines across the region. Similarities exist between these drylines and those found over the SGP, especially with regard to their strength and close relationship to deep convection. However, the frequency at which they occur, some characteristics of their diurnal motion, and the synoptic conditions driving their formation differ noticeably.

Cluster analysis applied to the spatial and temporal variability of monthly rainfall in Mato Grosso do Sul State, Brazil

The State of Mato Grosso do Sul (MS) located in Brazil Midwest is devoid of climatological studies, mainly in the characterization of rainfall regime and producers’ meteorological systems and rain inhibitors. This state has different soil and climatic characteristics distributed among three biomes: Cerrado, Atlantic Forest and Pantanal. This study aimed to apply the cluster analysis using Ward’s algorithm and identify those meteorological systems that affect the rainfall regime in the biomes. The rainfall data of 32 stations (sites) of the MS State were obtained from the Agencia Nacional de Aguas (ANA) database, collected from 1954 to 2013. In each of the 384 monthly rainfall temporal series was calculated the average and applied the Ward’s algorithm to identify spatial and temporal variability of rainfall. Bartlett’s test revealed only in January homogeneous variance at all sites. Run test showed that there was no increase or decrease in trend of monthly rainfall. Cluster analysis identified five rainfall homogeneous regions in the MS State, followed by three seasons (rainy, transitional and dry). The rainy season occurs during the months of November, December, January, February and March. The transitional season ranges between the months of April and May, September and October. The dry season occurs in June, July and August. The groups G1, G4 and G5 are influenced by South Atlantic Subtropical Anticyclone (SASA), Chaco’s Low (CL), Bolivia’s High (BH), Low Levels Jet (LLJ) and South Atlantic Convergence Zone (SACZ) and Maden-Julian Oscillation (MJO). Group G2 is influenced by Upper Tropospheric Cyclonic Vortex (UTCV) and Front Systems (FS). The group G3 is affected by UTCV, FS and SACZ. The meteorological systems’ interaction that operates in each biome and the altitude causes the rainfall spatial and temporal diversity in MS State.

Analysis of Relationship between Land Surface Temperature and Land Use in Colombo Municipal Area in Sri Lanka, Using Geographical Information System and Remote Sensing

The recent climatological studies try to find out the relationship between land surface temperature and land use type. Specially urban and industrial area was selected for that study, as well as this study was done in Colombo Municipal Council (CMC). The CMC area was central industrial and economical area in Sri Lanka. The majority of people travel to the Colombo Metropolitan area daily for their needs. In the present, both developed and developing countries face to global warming. As the developing country in Sri Lanka, industrial and vehicle usage was very high in the city center in Colombo. In that case land surface temperature (LST) increased day by day. The main objective of this study to analyse the LST using Landsat TM, ETM+ and Landsat 8 images. In addition find out the relationship between LST and land use in CMC area. Arc GIS 10.1 and ERDAS 2014 software were used for this study. It was found out the LST range from 22° C to 33° C. Some of the high temperature zones are shown in Fort and Maradana. Generally there was a high building density (commercial and industrial) and traffic density in while the day. In 1987 high temperature was also recorded close to the Fort and Maradana. However, it has gradually increased to the other areas. It was seen that the impact of that LST distributes to the southern part of the CMC. In addition, all the LST of all areas of CMC passed minimum 30° C during the day time. Keywords: Land surface temperature, Remote sensing, Land use, Colombo

Observational investigation of relationships between moisture surges and mesoscale‐ to large‐scale convection during the North American monsoon

ABSTRACTThis article consists of a comprehensive climatological study of moisture surges (MSs) in the North American monsoon (NAM) core region using a multiyear (1990–2006) set of surges, surface and upper air data, satellite‐estimated mesoscale convective systems (MCSs), and North American Regional Reanalysis (NARR) products. Composites of surges are created with respect to MCSs occurrence in the NAM core region. MSs are further stratified based on co‐occurrence with tropical easterly waves and tropical storms/tropical cyclones. These results provide new insights into the nature of the Gulf of California (GoC) moisture flux variability and describe the influence of these multi‐scale processes on the occurrence and intensity of surges and the GoC diurnal circulations – especially the Gulf of California low‐level jet (GCLLJ). Results show that over the GoC Coastal Plain, MCSs modulate the diurnal cycle of the GoC low‐level circulation during ‘major surge’, ‘minor surge’, and ‘non‐surge’ environments. We found that MCS activity enhances the offshore flow along the eastern GoC coast, which then enhances the GCLLJ. On the other hand, immediately before major surges onset, the occurrence of MCSs over the southern GoC produces more intense surges. It is also shown that this relationship holds regardless of the intensity and type of tropical synoptic‐scale disturbance forcing the surge.

Propagation of Strong Rainfall Events from Southeastern South America to the Central Andes

Abstract Based on high-spatiotemporal-resolution data, the authors perform a climatological study of strong rainfall events propagating from southeastern South America to the eastern slopes of the central Andes during the monsoon season. These events account for up to 70% of total seasonal rainfall in these areas. They are of societal relevance because of associated natural hazards in the form of floods and landslides, and they form an intriguing climatic phenomenon, because they propagate against the direction of the low-level moisture flow from the tropics. The responsible synoptic mechanism is analyzed using suitable composites of the relevant atmospheric variables with high temporal resolution. The results suggest that the low-level inflow from the tropics, while important for maintaining sufficient moisture in the area of rainfall, does not initiate the formation of rainfall clusters. Instead, alternating low and high pressure anomalies in midlatitudes, which are associated with an eastward-moving Rossby wave train, in combination with the northwestern Argentinean low, create favorable pressure and wind conditions for frontogenesis and subsequent precipitation events propagating from southeastern South America toward the Bolivian Andes.

Climatic changes and their impact on socio-economic sectors in the Bhutan Himalayas: an implementation strategy

This paper contributes to an enhanced understanding of present climatic conditions, observed climate trends and regional climate vulnerability of the Bhutan Himalayas. Bhutan’s complex, often high-altitude terrain and the severe impact of the Indian summer monsoon leads to a strong exposure of the countries’ key economic sectors (agriculture, forestry, hydropower generation and tourism) to climatic changes. Climate change also threatens Bhutan’s vast biodiversity and increases the likelihood of natural hazards (e.g. glacier lake outburst floods, flash floods, droughts and forest fires). A better understanding of Bhutan’s climate and its variability, as well as observed and possible climate impacts, will help in improving the handling of regional social, economic and ecologic challenges not limited to the Himalayas. Only a few climatological studies exist for the eastern Himalayas. They mainly focus on adaptation to immediate threats by glacier lake outbursts. In contrast, this paper (1) investigates the average spatial and inner-annual diversity of the air temperature regime of Bhutan, based on local meteorological observations, (2) discusses past temperature variability, based on global datasets, and (3) relates effects of observed warming to water availability, hydropower development, natural hazards, forests, biodiversity, agriculture, human health and tourism in the Bhutan Himalayas. Results indicate a large spatial and temporal temperature variability within Bhutan and considerably increasing temperatures especially over recent decades. Implications of regional climatic changes on various socio-economic sectors and possible adaptation efforts are discussed.

Statistical analysis of the ionospheric response during geomagnetic storm conditions over South Africa using ionosonde and GPS data

AbstractThis paper presents a statistical analysis of ionospheric response over ionosonde stations Grahamstown (33.3°S, 26.5°E, geographic) and Madimbo (22.4°S, 30.9°E, geographic), South Africa, during geomagnetic storm conditions which occurred during the period 1996–2011. Such a climatological study is important in establishing local ionospheric behavior trend which later forms a basis for accurate modeling and forecasting electron density and critical frequency of the F2 layer (foF2) useful for high‐frequency communication. The analysis was done using foF2 and total electron content (TEC), and to identify the geomagnetically disturbed conditions, the Dst index with a storm criterion of Dst ≤−50 nT was used. Results show a strong solar cycle dependence with negative ionospheric storm effects following the solar cycle and positive ionospheric storm effects occurring most frequently during solar minimum. Seasonally, negative and positive ionospheric storm effects occurred most in summer (63.24%) and in winter (53.62%), respectively. An important finding is that only negative ionospheric storms were observed during great geomagnetic storm activity (Dst ≤−350 nT). For periods when both foF2 and TEC data (from colocated ionosonde and GPS receiver stations) were available, a similar response in terms of variational trend was observed. Hence, GPS data can be used to effectively identify the ionospheric response in the absence of ionosonde data.

An Evaluation of Thunderstorm Observations in Southern Ontario Using Automated Lightning Detection Data

AbstractHigh-impact weather events, such as thunderstorms and their associated hazards, are aspects of a changing climate that are likely to have an adverse effect on society. Southern Ontario is Canada’s most populated region as well as the region of Canada that receives the most thunderstorms. Before completing climatological studies of thunderstorms in southern Ontario, it is important to determine whether historical thunderstorm data are reliable. Archived thunderstorm data are available from eight 24-h-staffed weather stations across southern Ontario. The data may be subject to observer bias. This study compared the manual observations of thunderstorms with automated data from the Canadian Lightning Detection Network. It was found that the data that are based on the manual observations are reliable enough that any significant trends in thunderstorm occurrence over time should be apparent. Because of the small-scale nature of thunderstorms, however, the data may only be valid for small distances (up to 10 km) around each weather station. A diurnal bias was also discovered, with manual thunderstorm observations being slightly better at night.

Recent trend analysis of mean air temperature in Greece based on homogenized data

Numerous studies analyze the temperature variations in the Mediterranean area due to the anticipated impact of climate change in this part of the world. A number of studies examined the temperature climate in Greece, but few are based on a large number of synoptic stations covering all regions and climatic zones and even fewer are based on homogenized data set series, despite the fact that climatological studies must use high-quality homogeneous data series. The present work reviews previous studies dealing with climatic changes in Greece and addresses changes of mean air temperature, based on a large set of homogenized data from 52 synoptic stations. A statistically significant negative trend during 1960–1976 and a positive one during 1977–2004 were revealed. During 1960–1976, the lowest negative annual temperature trend is observed in Crete. During 1977–2004, the northern region of Greece was characterized by prominent annual warming, whereas the north and central Aegean Sea and the semi-mountainous area were characterized by the lowest warming. All stations are characterized by high seasonal trends in summer; the most extreme trends are observed in the northern and eastern regions and in the Attica area. Positive temperature trends occur from May to October, while negative trends dominate from November to February. The most pronounced warming is recorded in June and July, and the most strongly decreasing trend occurs in November. Annual temperature trends in northern Greece follow the hemispheric pattern, and the overall summer warming in Greece is greater than the hemisphere’s.

Evaluating changes in season length, onset, and end dates across the United States (1948–2012)

ABSTRACTDiscussed in a global context, the issue of scale is important to consider as it relates to climate change. As climatological studies utilize temporally and spatially static definitions of seasonal definitions, the understanding of seasonal change may be limited by the way in which seasons are defined. This research serves as a challenge to this perspective by examining the changes in seasons by incorporating variability into the way in which seasons are defined. Temporally and spatially variable seasons were defined based on thresholds of apparent temperature and upper‐level circulation patterns for the period 1948–2012. Using 60 US surface stations, two apparent air temperature metrics were used to define seasons that vary spatially and temporally. Stations represented major cities found in the contiguous United States. A large‐scale circulation approach utilized synoptic categorizations based on 250‐mb geopotential heights from the NCEP‐NCAR reanalysis (NNR) as a metric of seasonal delineation. In this method, seasons varied temporally but not spatially. Despite the different methodological approaches, consistent trends were found. Since 1948, late starts of autumn and winter have been observed while earlier onsets of spring and summer have taken place. For the individual stations, the largest shifts occurred along coasts and in larger, more urbanized environments. Individual locations also showed increased variability in start date, and significant changes were found for all four seasons in the circulation approach. Seasons have been shown to be important for a variety of processes including phenological responses and human adaptation to extreme temperature environments; therefore, the consideration of season variability may be appropriate for future climatological research.

A climatological study of the effect of sea-surface temperature on North Atlantic hurricane intensification

The climatic influence of sea-surface temperature (SST) on intensification is examined for North Atlantic hurricanes by averaging hourly intensity increases from best-track data over the period 1986–2013 in 4° by 4° latitude–longitude grid cells. Independent monthly SST data over the same period are averaged in the same cells. After removing cells with cold water or fast moving hurricanes, the SST effect on intensification, at the climate scale, is quantified by regressing intensification onto SST while controlling for average intensity. The regression is performed using a generalized linear model from a gamma family and a logarithmic link function. The model shows a statistically significant relationship, with higher intensification values associated with higher SST values. On average, mean intensification increases by 16% [(9, 20)% uncertainty interval] for every 1 °C increase in mean SST. A clustered region where the model underpredicts intensification is noted over the southeastern Caribbean Sea, perhaps related to the fresh water plume from the Orinoco River.

Polar low climatology over the Nordic and Barents seas based on satellite passive microwave data

AbstractA new climatology of polar lows over the Nordic and Barents seas for 14 seasons (1995/1996–2008/2009) is presented. For the first time in climatological studies of polar lows an approach based on satellite passive microwave data was adopted for polar low identification. A total of 637 polar lows were found in 14 extended winter seasons by combining total atmospheric water vapor content and sea surface wind speed fields retrieved from Special Sensor Microwave/Imager data. As derived, the polar low activity in the Norwegian and Barents Seas is found to be almost equal, and the main polar low genesis area is located northeastward of the North Cape. For the Barents Sea, a significant correlation is found between the number of polar lows and mean sea ice extent. Individual indicative polar low characteristics (i.e., diameter, lifetime, distance traveled, translation speed, and maximum wind speed) are also presented.

Diagnostics of atmospheric water vapor content according to GPS measurements

A continuously operating GPS network, comprising seven permanent observation sites, is created to study the geodynamic processes in the Baikal region. Processing of the initial GPS data provides continuous atmospheric data in the form of total zenith tropospheric delay, which can be used for meteorological and climatological studies. The total delay is the sum of “dry”, or hydrostatic, and “wet” components. The wet component determines the total water vapor amount and amount of precipitable water over the measurement site. Thus, GPS measurements make it possible to obtain initial data for creating new numerical models of zenith tropospheric delay and total precipitable water vapor for meteorological applications.

Capturing Cold-Air Flow Using Thermal Imaging

We present a thermal imaging field design for climatological studies with an application to microscale cold-air flow analysis. Measurements of microclimatic processes are often limited by a lack of spatial coherence and consequently incomplete information on spatial and temporal patterns in the airflow. We introduce and evaluate an approach for investigating cold-air flow using an infrared camera pointed at a custom-built projection screen. A statistical analysis of a cold-air-flow case study is presented that explores the potential and limitations of the proposed technique. Results indicate good compatibility with traditional methods, while spatial coherence in measurements is achieved. A few examples of additional information obtained from the thermal camera analysis are presented, including analyses of cold-air-flow characteristics.

Radial frequency diagram (sunflower) for the analysis of diurnal cycle parameters: Solar energy application

Abstract Many meteorological parameters present a natural diurnal cycle because they are directly or indirectly dependent on sunshine exposure. The solar radiation diurnal pattern is important to energy production, agriculture, prognostic models, health and general climatology. This article aims at introducing a new type of radial frequency diagram – hereafter called sunflower – for the analysis of solar radiation data in connection with energy production and also for climatological studies. The diagram is based on two-dimensional data sorting. Firstly data are sorted into classes representing hours in a day. Then the data in each hourly class is sorted into classes of the observed variable values. The relative frequencies of the value classes are shown as sections on each hour’s segment in a radial diagram. The radial diagram forms a unique pattern for each analysed dataset. Therefore it enables the quick detection of features and the comparison of several such patterns belonging to the different datasets being analysed. The sunflower diagram enables a quick and comprehensive understanding of the information about diurnal cycle of the solar radiation data. It enables in a graphical form, quick screening and long-term statistics of huge data quantities when searching for their diurnal features and finding the differences between the data for several locations. The results of the data analysis using the sunflower diagram show how daily or monthly-based patterns are identified within small or huge data sets. The paper demonstrates the sunflower diagram usefulness over a wide range of applications from green energy production to weather analysis.

Atmospheric brown clouds reach the Tibetan Plateau by crossing the Himalayas

Abstract. The Himalayas and the Tibetan Plateau region (HTP), despite being a remote and sparsely populated area, is regularly exposed to polluted air masses with significant amounts of aerosols including black carbon. These dark, light-absorbing particles are known to exert a great melting potential on mountain cryospheric reservoirs through albedo reduction and radiative forcing. This study combines ground-based and satellite remote sensing data to identify a severe aerosol pollution episode observed simultaneously in central Tibet and on the southern side of the Himalayas during 13–19 March 2009 (pre-monsoon). Trajectory calculations based on the high-resolution numerical weather prediction model COSMO are used to locate the source regions and study the mechanisms of pollution transport in the complex topography of the HTP. We detail how polluted air masses from an atmospheric brown cloud (ABC) over South Asia reach the Tibetan Plateau within a few days. Lifting and advection of polluted air masses over the great mountain range is enabled by a combination of synoptic-scale and local meteorological processes. During the days prior to the event, winds over the Indo-Gangetic Plain (IGP) are generally weak at lower levels, allowing for accumulation of pollutants and thus the formation of ABCs. The subsequent passing of synoptic-scale troughs leads to southwesterly flow in the middle troposphere over northern and central India, carrying the polluted air masses across the Himalayas. As the IGP is known to be a hotspot of ABCs, the cross-Himalayan transport of polluted air masses may have serious implications for the cryosphere in the HTP and impact climate on regional to global scales. Since the current study focuses on one particularly strong pollution episode, quantifying the frequency and magnitude of similar events in a climatological study is required to assess the total impact.

Estimation of annual variation of water vapor in the Arctic Ocean between 80°–87°N using shipborne GPS data based on kinematic precise point positioning

The measurement of atmospheric water vapor (WV) content and variability is important for meteorological and climatological research. A technique for the remote sensing of atmospheric WV content using ground-based Global Positioning System (GPS) has become available, which can routinely achieve accuracies for integrated WV content of 1–2 kg/m2. Some experimental work has shown that the accuracy of WV measurements from a moving platform is comparable to that of (static) land-based receivers. Extending this technique into the marine environment on a moving platform would be greatly beneficial for many aspects of meteorological research, such as the calibration of satellite data, investigation of the air-sea interface, as well as forecasting and climatological studies. In this study, kinematic precise point positioning has been developed to investigate WV in the Arctic Ocean (80°–87°N) and annual variations are obtained for 2008 and 2012 that are identical to those related to the enhanced greenhouse effect.