22,204 research outputs found

    A Workshop on Using NASA AIRS Data to Monitor Drought for the U.S. Drought Monitor

    Get PDF
    Recent studies indicate that drought indicators based on near-surface air relative humidity (RH), air temperature (T), and air vapor pressure deficit (VPD), derived from the Atmospheric Infrared Sounder (AIRS) instrument aboard NASA’s Aqua satellite can detect the onset of drought earlier than other drought indicators, specifically standardized precipitation index (SPI), which is widely used for drought onset detection. A recent study showed that standardized relative humidity index (SRHI) can detect drought signals earlier than SPI (Farahmand et al. 2015). Relative humidity is a climate variable defined as the ratio of air vapor pressure to saturated vapor pressure. Precipitation and relative humidity are related to each other in the sense that significant precipitation is not expected at low relative humidity. SRHI detected drought onset earlier or at the same time as SPI with a global average of approximately 0.6 (i.e., 60% of all events) and the mean lead time of 1.9 months. Also, SRHI successfully detected the early signs of the 2012 Midwestern drought, the 2011 Texas drought, and the 2010 Russian drought (Farahmand et al. 2015). In another study, standardized vapor pressure deficit (SVPD) and standardized temperature (ST) indicators from the AIRS mission have been shown to detect drought earlier or at the same time as SPI with an average lead time of 1.5 months and in 60% of events in the CONUS (Behrangi et al. 2016). VPD is an important climate variable, incorporating elements of both temperature and relative humidity. VPD is also a major controlling factor of evapotranspiration demand. With increasing air aridity, VPD increases which in turn indicates greater evaporation stress. Studies show that VPD reported increases during the formation and rapid intensification of drought conditions during the 2011 and 2012 drought events, suggesting that remotely sensed VPD holds considerable potential for drought early warning and assessment (Behrangi et al. 2015; Farahmand et al. 2021)

    Automatic control of the droplet spectrum of a hydropneumatic sprayer according to the vapor pressure deficit in the air

    Get PDF
    The principle of fractionation and droplets size are crucial for the success of pest control. This study aimed at developing and evaluating an automated system to control the spraying droplet spectrum according to the vapor pressure deficit in the air. The automatic control system consisted of a temperature and relative humidity sensor, a microcontroller, a servomotor and a hydropneumatic sprayer. Spraying was performed on water sensitive paper labels arranged on wooden supports for different vapor pressure deficits in the air. After scanning and analysing the paper labels, three working pressures were selected (633 kPa, 844 kPa and 1,055 kPa) for use in the automated system. The results indicated that the controller efficiently maintained the droplets spectrum when spraying pesticides. Automation enabled the maintenance of the spray volume by altering the working pressure, according to the vapor pressure deficit in the air. Spraying with the automated system presented a droplet spectrum quality superior to the one obtained by using the manual system at the pressure of 633 kPa

    Gas exchange of four Viburnum species

    Get PDF
    In the natural environment, a plant\u27s gas exchange and water use efficiency characteristics in response to environmental stresses such as vapor pressure deficit, temperature, light intensity, and water potential may vary according to physiological and morphological species differences, leaf types (deciduous or evergreen), and habitat types (northern and southern). In the field, laboratory, and growth chamber, the effect of vapor pressure deficit, temperature, and light intensity on gas exchange characteristics was investigated for four woody shrub species from the genus Viburnum. The species under investigation include: y. rhytidophyllum (northern evergreen), y. awabuki (southern evergreen), y. dentatum (northern deciduous), and y. integrifolium (southern deciduous). Previous scanning electron microscopy studies showed that y. awabuki had a distinctive leaf anatomy, while the other three species were similar to each other. Field studies were conducted on sunny days in August and September, 1989, using a closed, steady state gas exchange system. Gas exchange measurements were recorded for three leaves per species at ambient conditions from 0600 to 1800 hours, and leaf water potential was determined with a pressure chamber at each sampling time. In the laboratory, gas exchange parameters were measured for three leaves per species using well watered greenhouse grown plants as light intensity, leaf-to-air vapor pressure deficit, or leaf temperature was varied. Growth chamber studies were conducted using greenhouse grown plants, and stomatal conductance was measured for six leaves per species using a steady state porometer at four water potential ranges at high and low vapor pressure deficits. Under drought conditions in the field and well watered conditions in the laboratory, the evergreen species, especially y. awabuki, typically showed lower conductance, net photosynthesis, and intercellular CO2 than did the deciduous species, but not to the degree expected. Growth chamber studies showed that vapor pressure deficit and water potential were both important in effecting declines in conductance for all species. Water use efficiency varied little between species in the field or in the laboratory. Gas exchange responses of the plants to environmental variables were associated with deciduous or evergreen leaf types, but more strongly with leaf anatomy

    Simulating sunflower canopy temperatures to infer root-zone soil water potential

    Get PDF
    A soil-plant-atmosphere model for sunflower (Helianthus annuus L.), together with clear sky weather data for several days, is used to study the relationship between canopy temperature and root-zone soil water potential. Considering the empirical dependence of stomatal resistance on insolation, air temperature and leaf water potential, a continuity equation for water flux in the soil-plant-atmosphere system is solved for the leaf water potential. The transpirational flux is calculated using Monteith's combination equation, while the canopy temperature is calculated from the energy balance equation. The simulation shows that, at high soil water potentials, canopy temperature is determined primarily by air and dew point temperatures. These results agree with an empirically derived linear regression equation relating canopy-air temperature differential to air vapor pressure deficit. The model predictions of leaf water potential are also in agreement with observations, indicating that measurements of canopy temperature together with a knowledge of air and dew point temperatures can provide a reliable estimate of the root-zone soil water potential

    Simulating soybean canopy temperature as affected by weather variables and soil water potential

    Get PDF
    Hourly weather data for several clear sky days during summer at Phoenix and Baltimore which covered a wide range of variables were used with a plant atmosphere model to simulate soybean (Glycine max L.) leaf water potential, stomatal resistance and canopy temperature at various soil water potentials. The air and dew point temperatures were found to be the significant weather variables affecting the canopy temperatures. Under identical weather conditions, the model gives a lower canopy temperature for a soybean crop with a higher rooting density. A knowledge of crop rooting density, in addition to air and dew point temperatures is needed in interpreting infrared radiometric observations for soil water status. The observed dependence of stomatal resistance on the vapor pressure deficit and soil water potential is fairly well represented. Analysis of the simulated leaf water potentials indicates overestimation, possibly due to differences in the cultivars

    Satellite Microwave Remote Sensing of Boreal-Arctic Land Surface State and Meteorology from AMSR-E

    Get PDF
    High latitude regions are undergoing significant climate-related change and represent an integral component of the Earth’s climate system. Near-surface vapor pressure deficit, soil temperature, and soil moisture are essential state variables for monitoring high latitude climate and estimating the response of terrestrial ecosystems to climate change. Methods are developed and evaluated to retrieve surface soil temperature, daily maximum/minimum air temperature, and land surface wetness information from the EOS Advanced Microwave Scanning Radiometer (AMSR-E) on the Aqua satellite for eight Boreal forest and Arctic tundra biophysical monitoring sites across Alaska and northern Canada. Daily vapor pressure deficit is determined by employing AMSR-E daily maximum/minimum air temperature retrievals. The seasonal pattern of microwave emission and relative accuracy of the estimated land surface state are influenced strongly by landscape properties including the presence of open water, vegetation type and seasonal phenology, snow cover and freeze-thaw transitions. Daily maximum/minimum air temperature is retrieved with RMSEs of 2.88 K and 2.31 K, respectively. Soil temperature is retrieved with RMSE of 3.1 K. Vapor pressure deficit (VPD) is retrieved to within 427.9 Pa using thermal information from AMSR-E. AMSR-E thermal information imparted 27% of the overall error in VPD estimation with the remaining error attributable to underlying algorithm assumptions. Land surface wetness information derived from AMSR-E corresponded with soil moisture observations and simple soil moisture models at locations with tundra, grassland, and mixed -forest/cropland land covers (r = 0.49 to r = 0.76). AMSR-E 6.9 GHz land surface wetness showed little correspondence to soil moisture observation or model estimates at locations with \u3e 20% open water and \u3e 5 m2 m-2 Leaf Area Index, despite efforts to remove the impact of open water and vegetation biomass. Additional information on open water fraction and vegetation phenology derived from AMSR-E 6.9 GHz corresponds well with independent satellite observations from MODIS, Sea-Winds, and JERS-1. The techniques and interpretations of high-latitude terrestrial brightness temperature signatures presented in this investigation will likely prove useful for future passive microwave missions and ecosystem modeling

    CONTROLLING FACTORS OF POTENTIAL EVAPOTRANSPIRATION ABOVE GRASSLAND IN HUMID AND ARID AREA

    Get PDF
    Potential evapotranspiration (PET) is an importance process in water balance studies controlled by a number of meteorological factors such as temperature, wind speed, atmospheric pressure, solar radiation, vapor pressure gradient, relative humidity and biological factors such as vegetation type, canopy height and plant density that varied in time-scale and in spatial scale. Of all those variables, determining the most controlling factors of evapotranspiration in humid and arid area is of interest of this paper. Two sites representing humid and arid area i.e. Fermi Prairie site in Illinois and Audubon Research Ranch in Arizona respectively were investigated in this study.  The flux data employed in this study was acquired from Ameriflux Netwotk. Penmann-Monteith formula is employed in to estimate evapotranspiration rate in both sites. The result shows that the PET is in dependence on the considered meteorological factor such as shortwave radiation, vapor pressure, air temperature, wind speed, net radiation and vapor pressure deficit. It is also can be inferred from the analysis that PET is also strongly controlled by vegetation factors represented as stomatal resistance. Keywords: Potential evapotranspiration, Penmann-Monteith, humid, arid
    • …
    corecore