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1. Overview a. Evapotranspiration, potential evaporation, and pan evaporation Evapotranspiration is the transfer of water from the landscape to the atmosphere, a combination of evaporation from soil and plant transpiration. Evapotranspiration is a critical component of the water cycle in Australia, with over 90% of rainfall returned to the atmosphere through evapotranspiration ( Wang et al. 2001 ). Evapotranspiration is difficult to measure directly, however, and is usually calculated using a
1. Overview a. Evapotranspiration, potential evaporation, and pan evaporation Evapotranspiration is the transfer of water from the landscape to the atmosphere, a combination of evaporation from soil and plant transpiration. Evapotranspiration is a critical component of the water cycle in Australia, with over 90% of rainfall returned to the atmosphere through evapotranspiration ( Wang et al. 2001 ). Evapotranspiration is difficult to measure directly, however, and is usually calculated using a
neglect of subcloud rainfall evaporation leads to an overestimation of rainfall in semiarid climates ( Small et al. 1999 use of RegCM2). Additionally, in a recent paper, Evans et al. (2004) use RegCM3 to study rainfall processes over the Middle East. Their results show an overestimation of rainfall in Saudi Arabia and the Persian Gulf region, which they hypothesize may result from the model’s failure to simulate the effects of evaporation. Recently, Worden et al. (2007) reaffirmed the
neglect of subcloud rainfall evaporation leads to an overestimation of rainfall in semiarid climates ( Small et al. 1999 use of RegCM2). Additionally, in a recent paper, Evans et al. (2004) use RegCM3 to study rainfall processes over the Middle East. Their results show an overestimation of rainfall in Saudi Arabia and the Persian Gulf region, which they hypothesize may result from the model’s failure to simulate the effects of evaporation. Recently, Worden et al. (2007) reaffirmed the
1. Introduction One of the primary roles of a land surface scheme in a global climate model (GCM) is to partition surface available energy into latent and sensible heat fluxes. Determination of latent heat flux, which is directly proportional to total evapotranspiration (ET), is more involved than for sensible heat flux since it is the sum of transpiration ( E T ), soil evaporation ( E S ), and canopy evaporation ( E C ). The relative contribution of each component of ET is calculated within
1. Introduction One of the primary roles of a land surface scheme in a global climate model (GCM) is to partition surface available energy into latent and sensible heat fluxes. Determination of latent heat flux, which is directly proportional to total evapotranspiration (ET), is more involved than for sensible heat flux since it is the sum of transpiration ( E T ), soil evaporation ( E S ), and canopy evaporation ( E C ). The relative contribution of each component of ET is calculated within
1. Introduction Evaporation over bare and partially vegetated soil surfaces is one of the main components of the exchange at the land surface–atmosphere interface (e.g., Lawrence et al. 2007 ). To predict soil evaporation, two distinct approaches can be used—namely, the mechanistic or physical and the simplified or phenomenological approach ( Mahfouf and Noilhan 1991 ). Both are strongly complementary. On one hand, the mechanistic approach (e.g., Chanzy and Bruckler 1993 ; Yamanaka et al
1. Introduction Evaporation over bare and partially vegetated soil surfaces is one of the main components of the exchange at the land surface–atmosphere interface (e.g., Lawrence et al. 2007 ). To predict soil evaporation, two distinct approaches can be used—namely, the mechanistic or physical and the simplified or phenomenological approach ( Mahfouf and Noilhan 1991 ). Both are strongly complementary. On one hand, the mechanistic approach (e.g., Chanzy and Bruckler 1993 ; Yamanaka et al
mechanism by which phase transitions produce infrasound in c-RAMS. We focus on a conceptually simple paradigm—the evaporation of an isolated, homogeneous cloud of water droplets. Analytical expressions are derived for the acoustic emissions in dry and humid environments. Under sufficiently dry conditions, the evaporation may occur in a few seconds or less. Successful comparison of the analytical results to numerical experiments verifies that the practical output of c-RAMS agrees with the theoretical
mechanism by which phase transitions produce infrasound in c-RAMS. We focus on a conceptually simple paradigm—the evaporation of an isolated, homogeneous cloud of water droplets. Analytical expressions are derived for the acoustic emissions in dry and humid environments. Under sufficiently dry conditions, the evaporation may occur in a few seconds or less. Successful comparison of the analytical results to numerical experiments verifies that the practical output of c-RAMS agrees with the theoretical
1. Introduction Evaporation is an important component of the land surface water balance ( Zhang and Wang 2007 ) and also the main process removing surface water. Its temporal and spatial variation affects the availability of water resources and its utilization by vegetation for growth and crop yield. There are two critical processes that are linked through evaporation: surface liquid water is vaporized consuming heat energy, and moisture is transported to the atmosphere by air movement, a
1. Introduction Evaporation is an important component of the land surface water balance ( Zhang and Wang 2007 ) and also the main process removing surface water. Its temporal and spatial variation affects the availability of water resources and its utilization by vegetation for growth and crop yield. There are two critical processes that are linked through evaporation: surface liquid water is vaporized consuming heat energy, and moisture is transported to the atmosphere by air movement, a
variability of the regional water budget, it is important to resolve all components of that budget as well as the variability of the atmospheric processes that affect those components. In the Mediterranean region, freshwater fluxes at the sea surface [i.e., the difference between evaporation and precipitation ( E − P ) provide the major source of water to the atmospheric hydrologic cycle ( Mariotti et al. 2002 ). Long-term variability of E − P over the Mediterranean Sea will determine to a large
variability of the regional water budget, it is important to resolve all components of that budget as well as the variability of the atmospheric processes that affect those components. In the Mediterranean region, freshwater fluxes at the sea surface [i.e., the difference between evaporation and precipitation ( E − P ) provide the major source of water to the atmospheric hydrologic cycle ( Mariotti et al. 2002 ). Long-term variability of E − P over the Mediterranean Sea will determine to a large
probes are used on aircraft, radiometric, and immersion thermometers. The latter type uses a sensor immersed in the airstream, for instance the commonly used Rosemount thermometer. The exposure of the sensing element, usually a platinum wire, to a stream of water droplets yields an anomalously low temperature in cloud and mainly as the aircraft exits the cloud ( Heymsfield et al. 1979 ; LeMone 1980 ). Rain below cloud base may also cause instrument wetting and thus evaporative cooling below the air
probes are used on aircraft, radiometric, and immersion thermometers. The latter type uses a sensor immersed in the airstream, for instance the commonly used Rosemount thermometer. The exposure of the sensing element, usually a platinum wire, to a stream of water droplets yields an anomalously low temperature in cloud and mainly as the aircraft exits the cloud ( Heymsfield et al. 1979 ; LeMone 1980 ). Rain below cloud base may also cause instrument wetting and thus evaporative cooling below the air
1. Introduction Coupled heat and water processes occurring in shallow surface soil have inordinate impacts on terrestrial life, in particular soil-water evaporation and storage exert critical influences on land–atmosphere exchange of water and energy ( Brubaker and Entekhabi 1996 ; D’Odorico et al. 2004 ). Early field experiments provided the first opportunity to observe temporal patterns in near-surface soil moisture and temperature (e.g., Jackson 1978 ). Since then, soil’s role in land
1. Introduction Coupled heat and water processes occurring in shallow surface soil have inordinate impacts on terrestrial life, in particular soil-water evaporation and storage exert critical influences on land–atmosphere exchange of water and energy ( Brubaker and Entekhabi 1996 ; D’Odorico et al. 2004 ). Early field experiments provided the first opportunity to observe temporal patterns in near-surface soil moisture and temperature (e.g., Jackson 1978 ). Since then, soil’s role in land
1. Introduction In stationary conditions at a level sea surface, the vertical velocity ( w ) that is induced by evaporation ( E ) and precipitation ( P ) is nearly ( E − P ). In recognition that the mass flux into (or out of) the atmosphere is of freshwater alone, attempts have been made to improve the representation: w = ( E − P )/(1 − S ), where S is the mass-fraction salinity, at the sea surface (e.g., Schmitt et al. 1989 ); or w = ρ F ( E − P )/[ ρ (1 − S )], where ρ is
1. Introduction In stationary conditions at a level sea surface, the vertical velocity ( w ) that is induced by evaporation ( E ) and precipitation ( P ) is nearly ( E − P ). In recognition that the mass flux into (or out of) the atmosphere is of freshwater alone, attempts have been made to improve the representation: w = ( E − P )/(1 − S ), where S is the mass-fraction salinity, at the sea surface (e.g., Schmitt et al. 1989 ); or w = ρ F ( E − P )/[ ρ (1 − S )], where ρ is
