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- Author or Editor: Norman J. Rosenberg x
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During nearly five weeks in China (May–June 1981), the author visited scientific institutions and experiment stations engaged in agricultural meteorology and climatology research and teaching. The facilities, studies, and research programs at each institution are described and the scientific work in these fields is evaluated. Agricultural meteorology and climatology are faced with some unique problems and opportunities in China and progress in these fields may be of critical importance to that nation in coming years. The author includes culinary notes and comments on protocol in China.
During nearly five weeks in China (May–June 1981), the author visited scientific institutions and experiment stations engaged in agricultural meteorology and climatology research and teaching. The facilities, studies, and research programs at each institution are described and the scientific work in these fields is evaluated. Agricultural meteorology and climatology are faced with some unique problems and opportunities in China and progress in these fields may be of critical importance to that nation in coming years. The author includes culinary notes and comments on protocol in China.
Abstract
The rate of evapotranspiration by irrigated alfalfa at Mead, NE (41°09′N; 96°30′W, elevation 354 m) reached record levels in 1976. Evapotranspiration was measured with precision weighing lysimeters in a field 1.9 ha in size. Evapotranspiration ranged during the growing season from 4.75 to 14.22 mm day−1 and exceeded 10 mm day−1 on one-third of the days studied. On each day of study the ratio of latent heat flux density (LE) to the sum of the net radiation and soil heat flux densities (Rn + S) was such that LE/(Rn + S) > 1, indicating the occurrence of significant sensible heat advection. On clear days during mid-summer the net radiation provides energy sufficient for evaporation of no more than 7 mm day−1. Sensible heat advection provided the remaining energy consumed in evapotranspiration. The unusually strong sensible heat advection likely was due to the generally dry condition of surrounding regions during the drought of 1976.
Abstract
The rate of evapotranspiration by irrigated alfalfa at Mead, NE (41°09′N; 96°30′W, elevation 354 m) reached record levels in 1976. Evapotranspiration was measured with precision weighing lysimeters in a field 1.9 ha in size. Evapotranspiration ranged during the growing season from 4.75 to 14.22 mm day−1 and exceeded 10 mm day−1 on one-third of the days studied. On each day of study the ratio of latent heat flux density (LE) to the sum of the net radiation and soil heat flux densities (Rn + S) was such that LE/(Rn + S) > 1, indicating the occurrence of significant sensible heat advection. On clear days during mid-summer the net radiation provides energy sufficient for evaporation of no more than 7 mm day−1. Sensible heat advection provided the remaining energy consumed in evapotranspiration. The unusually strong sensible heat advection likely was due to the generally dry condition of surrounding regions during the drought of 1976.
Abstract
Historical frost events (minimum shelter temperature ≤32° F.) were studied at 10 locations within and adjacent to the Platte Valley of Nebraska and the cause of these frosts was determined with the aid of synoptic maps. Frost series based upon last spring or first fall advection or radiation are defined and found to be random and normally distributed. The “potential growing season”, defined as the interval between last spring and first fall advection frosts, is found to be from 15 to 32 days longer than the “growing season” defined by the interval from last spring to first fall occurrences of minimum shelter temperature of 32° F. or below. The numbers of annual spring and fall radiation frosts and the number of days between last two spring and first two fall radiation frosts are presented to permit estimates of the practicality of frost protection for specialized crops in the area of study.
Abstract
Historical frost events (minimum shelter temperature ≤32° F.) were studied at 10 locations within and adjacent to the Platte Valley of Nebraska and the cause of these frosts was determined with the aid of synoptic maps. Frost series based upon last spring or first fall advection or radiation are defined and found to be random and normally distributed. The “potential growing season”, defined as the interval between last spring and first fall advection frosts, is found to be from 15 to 32 days longer than the “growing season” defined by the interval from last spring to first fall occurrences of minimum shelter temperature of 32° F. or below. The numbers of annual spring and fall radiation frosts and the number of days between last two spring and first two fall radiation frosts are presented to permit estimates of the practicality of frost protection for specialized crops in the area of study.
Abstract
Most reports show good agreement between evapotranspiration (ET) rates estimated by the Bowen Ratio-Energy Balance (BREB) method and rates measured with lysimeters, although underestimation by the BREB model has occasionally been reported. This study was conducted to evaluate the performance of the BREB technique in the climatic conditions characteristic of the central Great Plains, a region where a significant proportion of the energy consumed by evapotranspiration is supplied from advected sensible heat.
Agreement between the BREB method and lysimetric measurements of ET is good during non-advective periods but during advective periods the BREB model underestimates ET by about 20%. Data collected in this study suggest that the difference is due primarily to an inequality of the exchange coefficients for beat (K h ) and water vapor (K w ). In the development of the BREB method these coefficients are assumed to be identical but our results indicate that the ratio K h /K w is greater than 1 for the stable conditions associated with the downward transport of sensible heat.
Abstract
Most reports show good agreement between evapotranspiration (ET) rates estimated by the Bowen Ratio-Energy Balance (BREB) method and rates measured with lysimeters, although underestimation by the BREB model has occasionally been reported. This study was conducted to evaluate the performance of the BREB technique in the climatic conditions characteristic of the central Great Plains, a region where a significant proportion of the energy consumed by evapotranspiration is supplied from advected sensible heat.
Agreement between the BREB method and lysimetric measurements of ET is good during non-advective periods but during advective periods the BREB model underestimates ET by about 20%. Data collected in this study suggest that the difference is due primarily to an inequality of the exchange coefficients for beat (K h ) and water vapor (K w ). In the development of the BREB method these coefficients are assumed to be identical but our results indicate that the ratio K h /K w is greater than 1 for the stable conditions associated with the downward transport of sensible heat.
Abstract
The concentration of CO2 in air sampled above a sugar beet crop was measured during July, August, and early September 1966 at Scottsbluff, Nebr. During July the mean daytime concentration decreased from 310 ppm to 283 ppm as the leaf area index increased from 0.8 to 4.0. Only small deviations from the mean daytime concentration of 283 ppm occurred during the remainder of the season. The mean nocturnal concentration during this period was 320 ppm and was more variable than the daytime concentration. The daily amplitude of concentration averaged 70 ppm and was as great at times as 100 ppm.
Regression analysis revealed strong negative correlation between CO2 concentration and mean wind speed during the night. Mean concentration was independent of mean temperature, mean incident radiation, and predominant wind direction.
During each day the concentration remained constant between 1½ hr after sunrise and 1 hr before sunset except for a few cases. These were associated with incident radiation below 0.2 cal cm–2 min–1 and/or wind speeds at 25 cm above the crop of less than 0.3 m sec–1 or more than 3 m sec–1.
Evidence is presented that the concentrations reported here are at least partially dependent on the flux to and from the sugar beet crop.
Abstract
The concentration of CO2 in air sampled above a sugar beet crop was measured during July, August, and early September 1966 at Scottsbluff, Nebr. During July the mean daytime concentration decreased from 310 ppm to 283 ppm as the leaf area index increased from 0.8 to 4.0. Only small deviations from the mean daytime concentration of 283 ppm occurred during the remainder of the season. The mean nocturnal concentration during this period was 320 ppm and was more variable than the daytime concentration. The daily amplitude of concentration averaged 70 ppm and was as great at times as 100 ppm.
Regression analysis revealed strong negative correlation between CO2 concentration and mean wind speed during the night. Mean concentration was independent of mean temperature, mean incident radiation, and predominant wind direction.
During each day the concentration remained constant between 1½ hr after sunrise and 1 hr before sunset except for a few cases. These were associated with incident radiation below 0.2 cal cm–2 min–1 and/or wind speeds at 25 cm above the crop of less than 0.3 m sec–1 or more than 3 m sec–1.
Evidence is presented that the concentrations reported here are at least partially dependent on the flux to and from the sugar beet crop.
Abstract
Severe and widespread drought occurred over a large portion of the United States between 1974 and 1977. Impacts on agriculture and other industries, as well as local water supplies, were substantial. The federal government responded with forty assistance programs administered by sixteen federal agencies. Assistance was provided primarily in the form of loans and grants to people, businesses and governments experiencing hardship caused by drought. The total cost of the program is estimated at $7–8 billion.
Federal response to the mid-1970s drought was largely untimely, ineffective and poorly coordinated. Four recommendations are offered that, if implemented, would improve future drought assessment and response efforts: 1) reliable and timely informational products and dissemination plans; 2) improved impact assessment techniques, especially in the agricultural sector, for use by government to identify periods of enhanced risk and to trigger assistance measures; 3) administratively centralized drought declaration procedures that are well publicized and consistently applied; and 4) standby assistance measures that encourage appropriate levels of risk management by producers and that are equitable, consistent and predictable. The development of a national drought plan that incorporates these four items is recommended. Atmospheric scientists have an important role to play in the collection and interpretation of near-real time weather data for use by government decision makers.
Abstract
Severe and widespread drought occurred over a large portion of the United States between 1974 and 1977. Impacts on agriculture and other industries, as well as local water supplies, were substantial. The federal government responded with forty assistance programs administered by sixteen federal agencies. Assistance was provided primarily in the form of loans and grants to people, businesses and governments experiencing hardship caused by drought. The total cost of the program is estimated at $7–8 billion.
Federal response to the mid-1970s drought was largely untimely, ineffective and poorly coordinated. Four recommendations are offered that, if implemented, would improve future drought assessment and response efforts: 1) reliable and timely informational products and dissemination plans; 2) improved impact assessment techniques, especially in the agricultural sector, for use by government to identify periods of enhanced risk and to trigger assistance measures; 3) administratively centralized drought declaration procedures that are well publicized and consistently applied; and 4) standby assistance measures that encourage appropriate levels of risk management by producers and that are equitable, consistent and predictable. The development of a national drought plan that incorporates these four items is recommended. Atmospheric scientists have an important role to play in the collection and interpretation of near-real time weather data for use by government decision makers.
Abstract
Spectra of vertical and horizontal velocity, air temperature and humidity fluctuations were analyzed from measurements made over a well-watered alfalfa crop under conditions of sensible heat advection. Vertical velocity and air temperature spectra as well as cospectra of momentum, sensible heat and water vapor were found to be dependent on atmospheric thermal stratification. These spectra and cospectra were shifted toward higher frequencies under advective as compared to lapse conditions. These results indicate that the predominant eddy sizes are relatively smaller under advective conditions. Humidity spectra, on the other hand, were independent of daytime thermal stratification conditions but were influenced by conditions of the crop. The humidity spectra over a transpiring crop were shifted toward lower frequencies as compared to those over a less well-developed crop canopy.
Abstract
Spectra of vertical and horizontal velocity, air temperature and humidity fluctuations were analyzed from measurements made over a well-watered alfalfa crop under conditions of sensible heat advection. Vertical velocity and air temperature spectra as well as cospectra of momentum, sensible heat and water vapor were found to be dependent on atmospheric thermal stratification. These spectra and cospectra were shifted toward higher frequencies under advective as compared to lapse conditions. These results indicate that the predominant eddy sizes are relatively smaller under advective conditions. Humidity spectra, on the other hand, were independent of daytime thermal stratification conditions but were influenced by conditions of the crop. The humidity spectra over a transpiring crop were shifted toward lower frequencies as compared to those over a less well-developed crop canopy.
Abstract
Simultaneous measurements of humidity fluctuations over a crop made with a specially modified Lyman-alpha hygrometer and a fine-wire thermocouple psychrometer are compared. Standard deviations of the two sets of data are comparable except occasionally when wind speeds were low. The psychrometer appears to underestimate the vertical flux of water vapor due to its slow response. Analysis of humidity spectra and moisture flux cospectra shows that the Lyman-alpha hygrometer is superior to the psychrometer in response at high frequencies and low wind speeds.
Abstract
Simultaneous measurements of humidity fluctuations over a crop made with a specially modified Lyman-alpha hygrometer and a fine-wire thermocouple psychrometer are compared. Standard deviations of the two sets of data are comparable except occasionally when wind speeds were low. The psychrometer appears to underestimate the vertical flux of water vapor due to its slow response. Analysis of humidity spectra and moisture flux cospectra shows that the Lyman-alpha hygrometer is superior to the psychrometer in response at high frequencies and low wind speeds.
Abstract
Turbulent fluctuations of vertical wind and fluxes of momentum, sensible heat and latent heat measured with a drag anemometer are compared to like data measured with other instruments. Means of the measured parameters agreed well with energy balance computations of the heat fluxes and profile measurements of the momentum flux. Drag anemometer measurements of turbulent fluxes generally exceeded those obtained with a propeller anemometer, run concurrently. Spectral analysis indicates that the propeller anemometer did not respond well at high frequencies, causing an underestimation of the fluxes and vertical wind fluctuations. The drag anemometer appears to respond well up to 5 Hz.
Abstract
Turbulent fluctuations of vertical wind and fluxes of momentum, sensible heat and latent heat measured with a drag anemometer are compared to like data measured with other instruments. Means of the measured parameters agreed well with energy balance computations of the heat fluxes and profile measurements of the momentum flux. Drag anemometer measurements of turbulent fluxes generally exceeded those obtained with a propeller anemometer, run concurrently. Spectral analysis indicates that the propeller anemometer did not respond well at high frequencies, causing an underestimation of the fluxes and vertical wind fluctuations. The drag anemometer appears to respond well up to 5 Hz.
