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Spatial variability of temperature and wind over heterogeneous surfacesArnold, Klaus, Ziemann, Astrid, Raabe, Armin, Spindler, Gerald 11 January 2017 (has links) (PDF)
Conventional micro-meteorological measuring methods are not particularly suitable for the investigation of the energy exchange under heterogeneous surface conditions. To consider the influence of the different surface properties, area-covered and spatially averaged meteorological measurements in combination with highly resolved simulations are necessary. In this context, the method of acoustic travel time tomography is introduced to provide information about the horizontal temperature and wind field. Within a field experiment (STINHO-1; Melpitz 2001) the tomographic system and conventional
meteorological equipment were utilised inside the investigation area with an extension of several hundred meters (300 x 700 m2), which was arranged over areas with different surface properties: grassland and bare soil. The results of the field experiment show that differences between the measuring systems (insitu and remote sensing) exist and the heterogeneity of the underlying surface is visible in the near surface temperature and wind field at a scale, which can be resolved with highly resolved numerical models. Depending on the incoming solar radiation and the local advection regional distinctions in the air temperature and wind field as well as in the vertical sensible heat fluxes were observed. The investigations demonstrate that the sensitivity of the Acoustic Tomography is sufficient to verify gradients in the meteorological fields even when the horizontal differences are small. / Zur Untersuchung des Energieaustausches über heterogenem Gelände sind konventionelle mikro-meteorologische Messungen und Modellvorstellungen allein nicht ausreichend. Um den Einfluss unterschiedlicher Oberflächen besser berücksichtigen zu können, sind flächendeckende und räumlich mittelnde meteorologische Messungen kombiniert mit hoch aufgelösten numerischen Simulationen notwendig.In diesem Kontext wird die Methode der Akustischen
Laufzeitomographie vorgestellt, mit der horizontale Wind- und Temperaturfelder in geeigneter Weise bereitgestellt werden können.
Im Rahmen eines Feldexperimentes (STINHO-1; Melpitz 2001) wurde das tomographische System zusammen mit konventionellen meteorologischen Geräten in einem Untersuchungsgebiet mit einer Ausdehnung von mehreren hundert Metern (300 x 700 m2) über unterschiedlichen Oberflächen (Wiese und gepflügter Acker) eingesetzt.
Die Ergebnisse des Feldexperimentes zeigen, dass Unterschiede zwischen den einzelnen Messverfahren existierten und die Heterogenität der Unterlage in den oberflächennahen Temperatur- und Windfeldern auf einer Skala sichtbar ist, die mit kleinskaligen numerischen Modellen aufgelöst werden kann. Die vorgestellten Untersuchungen demonstrieren, dass die Sensitivität der Akustischen Tomographie hinreichend ist, um Gradienten meteorologischer Felder auch bei geringeren horizontalen Unterschieden nachzuweisen.
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Acoustic tomography in comparision to in-situ temperature and wind measurementsArnold, Klaus, Ziemann, Astrid, Raabe, Armin 19 December 2016 (has links) (PDF)
Acoustic travel time tomography is presented as an experimental technique for remote monitoring of areally averaged meteorological quantities as the air temperature and the horizontal wind speed. This ground based remote sensing technique uses the nearly horizontal propagation of sound waves in the atmospheric surface layer. Here the acoustic travel time tomography was applied by measuring the travel time at defined propagation paths between several sound sources and
receivers. The resulting sound speed were used to obtain estimates of the meteorological parameters. A measuring campaign was carried out at the test site in Lindenberg (DWD) to compare the acoustically derived data with conventional systems. These observations demonstrated that on one side the accuracy of the acoustic system is comparable with in-situ measurements and on the other side the temperature was particularly significant overestimated by the standard sensors, e.g. due to the radiation influence. / Die Akustische Laufzeittomographie wird als ein experimentelles Verfahren zur Sondierung meteorologischer Parameter, wie z.B. der Lufttemperatur und der horizontalen Windgeschwindigkeit, vorgestellt.
Dieses bodengebundene Fernerkundungsverfahren nutzt die horizontale Ausbreitung von Schallwellen in der atmosphärischen Grenzschicht. Hier wird das Verfahren der Laufzeittomographie angewendet, d.h. bei bekannter Weglänge wird die Ausbreitungszeit von ausgesendeten Schallsignalen zwischen mehreren Schallquellen und Empfängern gemessen. Die resultierenden Schallgeschwindigkeitsinformationen werden genutzt, um daraus die entsprechenden meteorologischen Parameter abzuleiten. Auf dem Gelände des Meteorologischen Observatoriums Lindenberg (DWD) wurde eine Messkampagne durchgeführt, um die akustischen Sondierungen mit konventionellen Systemen zu vergleichen. Die Auswertungen zeigen, dass einerseits die Genauigkeit der Akustischen
Tomographie vergleichbar mit den konventionellen in-situ Messungen ist und andererseits, dass die Lufttemperatur aufgrund des Strahlungseinflusses bei Messungen mit den üblichen Sensoren zum Teil erheblich überschätzt wird.
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Messung der Lufttemperatur und Luftfeuchte unter Berücksichtigung des Strahlungsfehlers auf einem VersuchsgeländeSchienbein, Sigurd, Arnold, Klaus 19 December 2016 (has links) (PDF)
Zur Validierung des Verfahrens der akustischen Tomographie, das als Fernerkundungssverfahren trägheits- und berührungslos arbeitet, werden Vergleichsmessungen mit herkömmlichen Sensoren für die Lufttemperatur und Luftfeuchte durchgeführt. Dabei zeigen sich die Grenzen der Erfassung dieser Größen in Bezug auf Strahlungseinfluss und Trägheit der Messgeräte. Hier werden einige Probleme bei der Verwendung konventioneller Hütten und Lösungsvorschläge aufgezeigt. / In order to validate measurements with the acoustic tomography, which operates as an remote sensing system lagless and contactless, comparison measurements were performed with conventional sensors for the air temperature and humidity. The accuracy of these quantities is limited by the radiation influence and the lag of the instruments. Here some difficulties are pointed out by using conventional shelters and solutions are demonstrated.
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Akustische Tomographie und optische Scintillometertechnik zur Sondierung der atmosphärischen GrenzschichtTeichmann, Ulrich, Ziemann, Astrid, Arnold, Klaus, Raabe, Armin 24 November 2016 (has links) (PDF)
Während eines Experimentes an der Forschungsstation Melpitz des IfT (Institut für Tropossphärenforschung) im September 1997 wurden erstmalig zwei verschiedene Meßmethoden gleichzeitig eingesetzt, die flächengemittelte Lufttemperaturen (Akustische Tomographie - Leipziger Institut für Meteorologie (LIM)) sowie liniengemittelte fühlbare Wärmeflüsse (Scintillometertechnik - IfT) lieferten. Es konnte gezeigt werden, daß teilweise erhebliche Temperaturdifferenzen an einem Strahlungstag auf dieser oberflächlich betrachteten horizontal homogenen Wiese existieren. Die geringe Datenbasis, größtenteils bedingt durch die ungünstige Anströmrichtung während dieses Zeitraums, läßt noch keinen sicheren Schluß zu, ob diese horizontalen Temperaturdifferenzen für die ebenfalls beobachteten horizontalen Unterschiede der vertikalen fühlbaren Wärmeflüsse und damit für die manchmal in Melpitz beobachtete Nicht-Schließung der Energiebilanz verantwortlich sind. / During an experiment at the Iff field research station Melpitz in September 1997 for the first time two different techniques were used to determine simultaneously area averaged air temperatures (Acoustic Tomography -LIM) and line averaged sensible heat fluxes (Scintillation
technique - IfT). lt could be shown that on a \'golden\' day appreciably large temperature differences occurred on this superficially considered horizontal homogeneous meadow. Because of the weak data base mostly due to difficult fetch conditions it could not be proven that these
temperature differences led to the horizontal differences of vertical sensible heat fluxes and therefore to the sometimes observed non-closure of the energy balance in Melpitz.
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Incertezas associadas à temperatura do ar no contexto das mudanças climáticas: determinação das causas e efeitos de heterogeneidades e discussão das implicações práticas / Uncertainties associated with the air temperature in the context of climate change: determination of the causes and effects of heterogeneities and discussion of the practical implicationsOliveira, Marcos José de 08 October 2010 (has links)
O registro da temperatura terrestre é um indicador fundamental nas análises de mudanças do clima global. A presente investigação tratou da verificação e quantificação dos efeitos de heterogeneidades (erros) em séries da temperatura do ar obtidas em estação climatológica localizada em Itirapina, SP, Brasil. As principais causas de heterogeneidades estudadas foram: mudanças dos horários de observação e cálculos da temperatura média diária; mudanças dos tipos de instrumentos utilizados (convencionais e automáticos) e mudanças nos abrigos meteorológicos. A metodologia aplicada consistiu em comparar, em diferentes escalas temporais, várias séries de temperatura do ar em relação a uma série de referência, assumida como mais confiável. As diferenças obtidas, em termos de desvios, resultaram em valores nas seguintes ordens de grandeza, de acordo com cada escala: 10,0ºC na escala das medições horárias; 5,0ºC na escala das médias diárias; 2,0ºC, na escala mensal; 1,0ºC na escala anual; e 1,5ºC na escala de normal climatológica (30 anos) de exibição dos valores médios da temperatura do ar. Conclui-se que em escalas reduzidas (horárias e diárias) existem erros de alta magnitude de variação, porém de baixa frequência de ocorrência. Com o aumento da escala, a magnitude dos desvios diminui. As causas de heterogeneidades, de acordo com os desvios observados, ficam classificadas, na ordem de menor para a maior intensidade de influência: mudanças dos abrigos; mudanças dos cálculos das médias diárias; e mudanças dos instrumentos. No contexto da discussão do aquecimento global, na ordem de 0,6ºC no último século, a ocorrência de erros e incertezas de mesma ou maior magnitude pode comprometer o uso da temperatura do ar como uma evidência confiável de mudanças do clima, uma vez que mudanças não-climáticas interferem significativamente nas medições. O uso da evidência é discutido no contexto da interação entre a Ciência, Política, Mídia e Economia. Foi identificado que, neste âmbito externo ao meio científico, as incertezas são diminuídas e ignoradas, tanto devido ao processo de simplificação da informação para sua difusão, quanto devido a interesses que norteiam a manipulação intencional e tendenciosa do tema. Devido à disputa de diferentes interesses, foi feita uma breve discussão de alguns aspectos controversos, permeando a atuação de cientistas céticos à crença da contribuição humana significativa nas mudanças climáticas. / The instrumental temperature record is a key indicator in the analysis of global climate change. This research dealt with the verification and quantification of the effects of heterogeneities (errors) in air temperature series obtained from a climatological station located in Itirapina, SP, Brazil. The main causes of heterogeneity studied were: changes on the times of observation and on the daily mean air temperature calculation; changes on the types of instruments (conventional and automatic); and changes in thermometer screens. The methodology consisted of comparing, at different time scales, several series of air temperature series in relation to a reference series, assumed to be more reliable. The differences obtained, in terms of deviations, resulted in the following orders of magnitude, according to each scale: 10.0ºC in the range of hourly measurements, 5.0ºC in the range of daily mean, 2.0°C in monthly scale, 1.0°C in the annual scale and 1.5°C in the climatological normal scale (30 years). It follows that at small scales (hourly and daily) exist errors of high magnitude of change, but low frequency of occurrence. With increasing scale, the magnitude of the deviations decreases. The causes of heterogeneity, according to the observed deviations, are ranked in order of lowest to highest extent of influence: changes on screens, changes on daily mean air temperature calculation, and changes of the instruments. In the context of the discussion of global warming, on the order of 0.6ºC over the last century, the occurrence of errors and uncertainties in same or greater magnitude can compromise the use of air temperature as a reliable evidence of climate changes, since non-climatic changes significantly interfere the measurements. The use of evidence is discussed in the context of the interaction between Science, Politics, Media and Economics. It was identified that, outside the scientific environment context, the uncertainties are reduced and neglected, both due to the simplification process for the information dissemination, as due to concerns that guide the intentional and biased manipulation on the subject. Due to the competition of different interests, there was held a brief discussion of some controversial aspects, permeating the work of skeptical scientists on the belief of the significant human contribution to the climate change.
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Análise das características socioambientais na cidade de Belém/PA: um estudo da vegetação e clima urbano / Environmental and social analysis of characteristics in Belém city, Pará: a study of vegetation and urban climateRodrigues, José Edilson Cardoso [UNESP] 24 January 2017 (has links)
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Previous issue date: 2017-01-24 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Nas últimas décadas, o rápido crescimento das cidades ocasionou modificações substanciais na paisagem urbana, fazendo com que passassem a gerar suas próprias condições ambientais, as quais, nem sempre, são favoráveis à população. Uma das modificações observadas é a geração do clima urbano, pois a cidade altera o clima principalmente na micro e meso escala, por meio das transformações da superfície, ocasionando o aumento de temperatura, variação da precipitação, modificação do fluxo dos ventos e da umidade do ar. Outra grande modificação observada na paisagem urbana é a redução da Cobertura Vegetal, que exerce diversas funções no âmbito social, estético e climático, amenizando a temperatura e umidificando o ambiente urbano. O interesse pelo estudo da interação entre cobertura vegetal e clima urbano da cidade de Belém-PA ocorreu a partir de observação da redução que a vegetação sofreu, o que pode ter impactado significativamente na temperatura intraurbana, com o consequente registro de aumento nas últimas décadas. O principal objetivo da pesquisa foi realizar um estudo relacionando à redução da cobertura vegetal e a mudança nos padrões de temperatura na área que consiste a Primeira Légua Patrimonial da cidade de Belém-PA. A metodologia adotada por nós abarcou uma análise teórica conceitual, tendo como método de análise o hipotético-dedutivo, adotando como referencial teórico o Sistema Clima Urbano, proposto por Monteiro (1976), com ênfase no subsistema termodinâmico. Nos procedimentos realizou-se levantamento cartográfico, uso de imagens termais, mapeamento da Cobertura Vegetal, para levantamento de Índice de Cobertura Vegetal (ICV), Índice de Cobertura Vegetal por habitante (ICV/hab.), mapeamento do uso do solo, levantamento das temperaturas, espacial e temporal, com base nos dados do INMET, de miniestações fixas, transectos e trabalho de campo para registros e observações. Assim, o que se constatou é que a perda da Cobertura Vegetal em Belém é considerada um processo histórico em função do processo de ocupação da cidade. Analisando o ICV por Distrito, o DABEL (9,41%) apresentou o melhor índice, seguido pelo DASAC (5,66%) e DAGUA (3,37%). A análise temporal da temperatura revelou uma tendência de crescimento considerável, ao longo das décadas. A partir das imagens termais, as temperaturas dos alvos sofreram oscilações, principalmente em alguns bairros localizados mais ao norte e ao sul da Légua. Bairros com pouca vegetação apresentaram temperaturas mais elevadas em relação a bairros com arborização considerável. Portanto a perda da cobertura vegetal na área da Primeira Légua, associada às elevadas temperaturas, revelou um quadro ambiental preocupante, sobretudo em bairros que apresentaram ICV baixo e alta densidade de construções, o que refletiu diretamente no aumento da temperatura nesses bairros. / In recent decades the rapid growth of cities has caused substantial changes in the urban landscape, making start to generate their own environmental conditions and which are not always favorable to the population. One of the changes observed is the urban climate generation, because the city changes the climate mainly in micro and meso scale, through the surface changes causing the temperature rise, precipitation change, the winds flow modification and humidity. Another major change observed in the urban landscape is the reduction of vegetation cover, which performs various functions in the social, aesthetic and climatic context softening temperature and humidifying the in the urban environment and other. Interest in the study of the interaction between vegetation and urban climate of the city of Belém-PA, due to the reduction that vegetation has suffered and may have a significant impact on intra-urban temperature that has seen an increase in recent decades. Thus, the main objective was to conduct a study relating to the reduction of the vegetation cover and the change in temperature patterns in the area that is the First League Balance of Belém-PA. The methodology embraced a conceptual theoretical analysis, with the method of the hypothetical-deductive analysis, adopting as a theoretical reference the urban climate system proposed by Monteiro (1976), emphasizing the thermodynamic subsystem. In proceedings conducted cartographical survey, use of thermal images, mapping of vegetation cover for lifting Vegetation Cover Index (VCI) and Vegetation Cover Index by Inhabitant (VCI / I), land use mapping, survey of temperature, time and space from INMET data, fixed mini-stations, transects and field work for records and observations. Thus, it was found that the loss of plant cover in Belém has been considered a historical process due to the city occupation process. Looking for VCI District, the DABEL (9.41%) had the highest rate, followed by DASAC (5.66%) and DAGUA (3.37%). The time temperature analysis showed a considerable growth trend over the decades and from thermal images the temperature of targets experienced fluctuations, especially in some neighborhoods located further north and south of League. Neighborhoods with little vegetation had higher temperatures compared to neighborhoods with large trees. Therefore, the loss of plant cover in the First League area associated with high temperatures has revealed a worrying environmental framework, particularly in neighborhoods that had VCI low and high density buildings which is directly reflected in the increase in temperature in these neighborhoods.
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Long-Term Patterns of Dissolved Organic Carbon in Boreal LakesZhang, Jan 24 October 2008
I analyzed the 21 year dynamics of dissolved organic carbon (DOC) in 55 lakes in five sites across Eastern Canada in relation to regional and global variables. Regional variables included total solar radiation (TSR), precipitation (PPTN), air temperature (T) and sulfate deposition (SO4). Global variables included the Southern Oscillation Index (SOI), North Atlantic Oscillation (NAO) and Pacific Decadal Oscillation (PDO). A synchronous pattern in DOC was found among lakes within each region; however, a synchronous pattern in DOC was not found between sites, except for Kejimkujik and Yarmouth which were only 80 km apart from each other. This suggested that the variation of the long-term DOC pattern was in response to the temporal pattern of regional variables, and it supports the recent understanding that regional factors have a strong influence on many lake properties. Significant long-term trends in DOC were not evident except at the Experimental Lakes Area (ELA), where an increase in DOC was observed together with a decrease in summer TSR and an increase in summer precipitation. Annual mean air temperature has increased at the Nova Scotia and Turkey lakes sites over the study period.
The relationship between the long-term pattern in DOC with the regional and global variables was analyzed for each study site to determine the key variables that could best explain the variation in the long-term pattern in DOC. TSR and PPTN were important independent variables across all sites, except for the Turkey Lakes Watershed site (TLW). Summer TSR (annual TSR for Kejimkujik and Yarmouth) had a negative relationship, while summer precipitation had a positive relationship with the long-term DOC pattern for all sites except TLW. TSR and PPTN explained 78%, 49% and 84% of the variation in the long-term DOC pattern at Dorset, ELA, and Nova Scotia (NS) sites, respectively. In contrast, the long-term pattern in DOC at TLW only had a weak relationship with the regional and global variables considered.
A General model was developed to compare the strength of the response of DOC to the regional variables among sites. Therefore, only the variables which had a significant linear correlation with DOC across sites were selected. If a site had no variables in common with other sites, it was excluded from the general model. This resulted in TLW being excluded from the general model because the long-term DOC pattern at TLW was not significantly correlated with any regional variables.
The best general model included TSR from Dorset, ELA and NS sites and precipitation from only the NS site. The strengths of the response of DOC to precipitation were weak at Dorset and ELA compared to NS, therefore, they were excluded. The general model explained 91% of the site-to-site variation of DOC among sites. Among them, TSR was an important negative variable which contributed 56% of the explanation to the general model. Precipitation at NS was an important positive variable for the general model. It contributed 34% of the explanation to the model. As the response of the long-term DOC pattern to the changes of environmental variables (TSR and PPTN) was very strong at NS, the NS site dominated the general model, and its temporal (year-to-year) variation in the long-term DOC pattern explained 60% of the site-to-site variation of DOC in Eastern Canada. The other two sites, Dorset and ELA, had weak contributions (20% and 11%, respectively) to the general model.
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Long-Term Patterns of Dissolved Organic Carbon in Boreal LakesZhang, Jan 24 October 2008 (has links)
I analyzed the 21 year dynamics of dissolved organic carbon (DOC) in 55 lakes in five sites across Eastern Canada in relation to regional and global variables. Regional variables included total solar radiation (TSR), precipitation (PPTN), air temperature (T) and sulfate deposition (SO4). Global variables included the Southern Oscillation Index (SOI), North Atlantic Oscillation (NAO) and Pacific Decadal Oscillation (PDO). A synchronous pattern in DOC was found among lakes within each region; however, a synchronous pattern in DOC was not found between sites, except for Kejimkujik and Yarmouth which were only 80 km apart from each other. This suggested that the variation of the long-term DOC pattern was in response to the temporal pattern of regional variables, and it supports the recent understanding that regional factors have a strong influence on many lake properties. Significant long-term trends in DOC were not evident except at the Experimental Lakes Area (ELA), where an increase in DOC was observed together with a decrease in summer TSR and an increase in summer precipitation. Annual mean air temperature has increased at the Nova Scotia and Turkey lakes sites over the study period.
The relationship between the long-term pattern in DOC with the regional and global variables was analyzed for each study site to determine the key variables that could best explain the variation in the long-term pattern in DOC. TSR and PPTN were important independent variables across all sites, except for the Turkey Lakes Watershed site (TLW). Summer TSR (annual TSR for Kejimkujik and Yarmouth) had a negative relationship, while summer precipitation had a positive relationship with the long-term DOC pattern for all sites except TLW. TSR and PPTN explained 78%, 49% and 84% of the variation in the long-term DOC pattern at Dorset, ELA, and Nova Scotia (NS) sites, respectively. In contrast, the long-term pattern in DOC at TLW only had a weak relationship with the regional and global variables considered.
A General model was developed to compare the strength of the response of DOC to the regional variables among sites. Therefore, only the variables which had a significant linear correlation with DOC across sites were selected. If a site had no variables in common with other sites, it was excluded from the general model. This resulted in TLW being excluded from the general model because the long-term DOC pattern at TLW was not significantly correlated with any regional variables.
The best general model included TSR from Dorset, ELA and NS sites and precipitation from only the NS site. The strengths of the response of DOC to precipitation were weak at Dorset and ELA compared to NS, therefore, they were excluded. The general model explained 91% of the site-to-site variation of DOC among sites. Among them, TSR was an important negative variable which contributed 56% of the explanation to the general model. Precipitation at NS was an important positive variable for the general model. It contributed 34% of the explanation to the model. As the response of the long-term DOC pattern to the changes of environmental variables (TSR and PPTN) was very strong at NS, the NS site dominated the general model, and its temporal (year-to-year) variation in the long-term DOC pattern explained 60% of the site-to-site variation of DOC in Eastern Canada. The other two sites, Dorset and ELA, had weak contributions (20% and 11%, respectively) to the general model.
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Klimato kaitos įtaka pušų spyglius graužiantiems kenkėjams / Climate change impact on pine needle-eating pestsAndriuškevičienė, Irina 21 June 2013 (has links)
Tarpvyriausybinė klimato kaitos komisija pažymi, kad nuo XX a. pradžios planetos oro temperatūra pakilo 0,7oC, Europoje – 1oC. Per XXI a. ji gali padidėti dar 1,5–5,5oC. Didžiausią neigiamą poveikį papr. pušiniam pjūkleliui daro aukšta ( + 27 - + 31 0C) oro temperatūra ir padidėjęs kritulių kiekis. Didžiausią poveikį pušinio pelėdgalvio sunykimui turėjo šalnos bei krituliai (liūtis, kruša). Didelę žalą pušinio verpiko populiacijos gausumui turėjo stichinė-ekstremali aktyvios augalų vegetacijos laikotarpio šalna. Verpiko vienuolio populiacijos gausumui turėjo įtakos 1982 m. vietinė stichinė sausra. O 1996 m. populiacijos mažėjimą galima sieti su dideliu miško gaisringumu, metų pradžioje užfiksuotu speigu (-33 0C), bei rudens šalnomis rugsėjo viduryje (-6 0C). / The IPCC notes that the twentieth century. the beginning of the planet's surface temperature has increased by 0,7 ° C in Europe - 1 º C.. In the twenty-first century. It may be increased by 1,5 to 5,5 °. The greatest negative impact on compressor. for half saw blade makes the high (+ 27 - + 31 0C) temperatures and increased rainfall. The greatest impact can withstand destruction had frost and precipitation (rain, hail). Significant damage to the pine lappet population abundance had extreme natural-active vegetation period of frost. In the population significantly reduced the use of sanitary protection. Nun Moth in the population affected in 1982 local drought. And in 1996 population decline may be associated with a large forest fire, ice, beginning of the year (-33 0C), and autumn frosts in mid-September (-6 0C.).
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Estimation of the near-surface air temperature and soil moisture from satellites and numerical modelling in New ZealandSohrabinia, Mohammad January 2013 (has links)
Satellite observations provide information on land surface processes over a large spatial extent with a frequency dependent on the satellite revisit time. These observations are not subject to the spatial limitations of the traditional point measurements and are usually collected in a global scale. With a reasonable spatial resolution and temporal frequency, the Moderate Resolution Imaging Spectroradiometer (MODIS) is one of these satellite sensors which enables the study of land-atmospheric interactions and estimation of climate variables for over a decade from remotely sensed data.
This research investigated the potential of remotely sensed land surface temperature
(LST) data from MODIS for air temperature (Ta) and soil moisture (SM) estimation in New Zealand and how the satellite derived parameters relate to the numerical model simulations and the in-situ ground measurements. Additionally, passive microwave SM product from the Advanced Microwave Scanning Radiometer for the Earth Observing System (AMSR-E) was applied in this research.
As the first step, the MODIS LST product was validated using ground measurements at two test-sites as reference. Quality of the MODIS LST product was compared with the numerical simulations from the Weather Research and Forecasting (WRF) model. Results from the first validation site, which was located in the alpine areas of the South Island, showed that the MODIS LST has less agreement with the in-situ measurements than the WRF model simulations. It turned out that the MODIS LST is subject to sources of error, such as the effects of topography and variability in atmospheric effects over alpine areas and needs a careful pre-processing for cloud effects and outliers. On the other hand, results from the second validation site, which was located on the flat lands of the Canterbury Plains, showed significantly higher agreement with the ground truth data. Therefore, ground measurements at this site were used as the main reference data for the accuracy assessment of Ta and SM estimates.
Using the MODIS LST product, Ta was estimated over a period of 10 years at several sites across New Zealand. The main question in this part of the thesis was whether to use LST series from a single MODIS pixel or the series of a spatially averaged value from multiple pixels for Ta estimation. It was found that the LST series from a single pixel can be used to model Ta with an accuracy of about ±1 ºC. The modelled
Ta in this way showed r ≈ 0.80 correlation with the in-situ measurements. The Ta estimation accuracy improved to about ±0.5 ºC and the correlation to r ≈ 0.85 when LST series from spatially averaged values over a window of 9x9 to 25x25 pixels were applied. It was discussed that these improvements are due to noise reduction in the spatially averaged LST series. By comparison of LST diurnal trends from MODIS with Ta diurnal trends from hourly measurements in a weather station, it was shown that the MODIS LST has a better agreement with Ta measurements at certain times of the day with changes over day and night.
After estimation of Ta, the MODIS LST was applied to derive the near-surface SM using two Apparent Thermal Inertia (ATI) functions. The objective was to find out if more daily LST observations can provide a better SM derivation. It was also aimed to identify the potential of a land-atmospheric coupled model for filling the gaps in derived SM, which were due to cloud cover. The in-situ SM measurements and rainfall data from six stations were used for validation of SM derived from the two ATI functions and simulated by the WRF model. It was shown that the ATI function based on four LST observations has a better ability to derive SM temporal profiles and is better able to detect rainfall effects.
Finally, the MODIS LST was applied for spatial and temporal adjustment of the near-surface SM product from AMSR-E passive microwave observations over the South Island of New Zealand. It was shown that the adjustment technique improves AMSR-E seasonal trends and leads to a better matching with rainfall events. Additionally, a clear seasonal variability was observed in the adjusted AMSR-E SM in the spatial domain.
Findings of this thesis showed that the satellite observed LST has the potential for the estimation of the land surface variables, such as the near-surface Ta and SM. This potential is greatly important on remote and alpine areas where regular measurements from weather stations are not often available. According to the results from the first validation site, however, the MODIS LST needs a careful pre-processing on those areas. The concluding chapter included a discussion of the limitations of remotely sensed data due to cloud cover, dense vegetation and rugged topography. It was concluded that the satellite observed LST has the potential for SM and Ta estimations in New Zealand. It was also found that a land-atmospheric model (such as the WRF coupled with the
Noah and surface model) can be applied for filling the gaps due to cloud cover in
remotely sensed variables.
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