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- Author or Editor: R. L. Grossman x
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Abstract
A method for determining bias errors in winds derived from airborne Doppler radar and inertial navigation wind-finding systems is presented and tested on samples of field quality data from the GARP Atlantic Tropical Experiment (GATE). The method requires only the measured wind components and true heading of the aircraft before and after a reasonable change in true heading.
Abstract
A method for determining bias errors in winds derived from airborne Doppler radar and inertial navigation wind-finding systems is presented and tested on samples of field quality data from the GARP Atlantic Tropical Experiment (GATE). The method requires only the measured wind components and true heading of the aircraft before and after a reasonable change in true heading.
Abstract
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Abstract
Seven-year averaged values of percent frequency of occurrence of highly reflective cloud for the months June, July, and August indicate that offshore convection is a major component of the cloudiness of the southwest monsoon. Principal areas of convection occur off of the western coats of India, Burma, Thailand, and the Philippines. This study concentrates on the area upstream of the Western Ghats Mountains of India. Analysis of a special boundary layer mission flown during the WMO/ICSU Summer Monsoon Experiment leads us to believe that partial deceleration of the monsoon flow by upstream blocking effects of the mountains initiates and maintains a vertical and horizontal motion field that could support the observed convection. Data obtained on this mission allow a large-scale momentum budget computation for the subcloud layer, which shows pressure deceleration to be significant. The budget, dominated by advection, predicts an increase of average wind speed which is observed. The pressure deceleration result is further explored by applying an idealized monsoon flow to an analytical, nonliner, two-dimensional mountain-flow interaction model using a smoothed profile of the Western Ghats Mountains. The model qualitatively agrees with aircraft observations taken in the subcloud layer, and predicts large vertical wind shears over the coastal area and mountain crest which would inhibit deep convection. These shears are confirmed by earlier observations.
When the lifting predicted by the model is applied to mean dropwindsonde soundings, well upstream of the coast, for days with and without offshore convection, deep convection is predicted for the mean sounding associated with offshore convection. The mean sounding for days without deep convection shows more offshore lifting is needed to produce convection; even if the lifting were applied, the convection would not be very deep due to a cooler surface layer and a dry layer above the boundary layer which may have originated from the desert areas to the west and/or upper tropospheric downward motion. We conclude that the mountains, though not very high, play an important role in overall monsoon convection for India. It is suggested that, given the climatic character of offshore monsoon convection, interaction of the low-level flow with the western coastal mountains of India, Burma, Thailand, and the Philippines should be considered a factor in monsoon climatology.
Abstract
Seven-year averaged values of percent frequency of occurrence of highly reflective cloud for the months June, July, and August indicate that offshore convection is a major component of the cloudiness of the southwest monsoon. Principal areas of convection occur off of the western coats of India, Burma, Thailand, and the Philippines. This study concentrates on the area upstream of the Western Ghats Mountains of India. Analysis of a special boundary layer mission flown during the WMO/ICSU Summer Monsoon Experiment leads us to believe that partial deceleration of the monsoon flow by upstream blocking effects of the mountains initiates and maintains a vertical and horizontal motion field that could support the observed convection. Data obtained on this mission allow a large-scale momentum budget computation for the subcloud layer, which shows pressure deceleration to be significant. The budget, dominated by advection, predicts an increase of average wind speed which is observed. The pressure deceleration result is further explored by applying an idealized monsoon flow to an analytical, nonliner, two-dimensional mountain-flow interaction model using a smoothed profile of the Western Ghats Mountains. The model qualitatively agrees with aircraft observations taken in the subcloud layer, and predicts large vertical wind shears over the coastal area and mountain crest which would inhibit deep convection. These shears are confirmed by earlier observations.
When the lifting predicted by the model is applied to mean dropwindsonde soundings, well upstream of the coast, for days with and without offshore convection, deep convection is predicted for the mean sounding associated with offshore convection. The mean sounding for days without deep convection shows more offshore lifting is needed to produce convection; even if the lifting were applied, the convection would not be very deep due to a cooler surface layer and a dry layer above the boundary layer which may have originated from the desert areas to the west and/or upper tropospheric downward motion. We conclude that the mountains, though not very high, play an important role in overall monsoon convection for India. It is suggested that, given the climatic character of offshore monsoon convection, interaction of the low-level flow with the western coastal mountains of India, Burma, Thailand, and the Philippines should be considered a factor in monsoon climatology.
Abstract
The initial analysis of the water vapor flux measurements taken onboard a NOAA DC-6 during the Barbados Oceanographic and Meteorological Experiment (BOMEX) is presented. The flux of water vapor seems to be constant in the lower subcloud layer. Day-to-day variations, as well as variations within a day are apparent in the evaporation data. Spatial variations of evaporation also seem to be present. The average value of water vapor flux for the experimental period is ∼0.5 cm day−1. Spectra of the instantaneous flux reveal significant alongwind-crosswind differences. Height variation of the wavelength of maximum spectral density for crosswind runs is confirmed. The instantaneous flux is intermittent in nature. Consideration of the cross spectra and time series signatures allows some speculation upon models which may be responsible for a major portion of the water vapor transport in the lower subcloud layer during BOMEX.
Abstract
The initial analysis of the water vapor flux measurements taken onboard a NOAA DC-6 during the Barbados Oceanographic and Meteorological Experiment (BOMEX) is presented. The flux of water vapor seems to be constant in the lower subcloud layer. Day-to-day variations, as well as variations within a day are apparent in the evaporation data. Spatial variations of evaporation also seem to be present. The average value of water vapor flux for the experimental period is ∼0.5 cm day−1. Spectra of the instantaneous flux reveal significant alongwind-crosswind differences. Height variation of the wavelength of maximum spectral density for crosswind runs is confirmed. The instantaneous flux is intermittent in nature. Consideration of the cross spectra and time series signatures allows some speculation upon models which may be responsible for a major portion of the water vapor transport in the lower subcloud layer during BOMEX.
Abstract
An improved calibration technique for an airborne Lyman-alpha hygrometer is presented. Like previous methods, it relies upon simultaneous measurement of absolute humidity determined from a slower response hygrometer. We show that a substantial improvement in the Lyman-alpha calibration is obtained by accounting for the time lag of the slower instrument.
To show our technique we use data from Lyman-alpha and thermoelectric devices on the NCAR Electra during an investigation of the nearly neutral boundary layer over the Arabian Sea as part of the WMO/ICSU Summer Monsoon Experiment. We also show that for near-neutral conditions the eddy-correlation water vapor flux can be adequately estimated using the fast response vertical velocity data from a gust probe and slower response data from the thermoelectric device, which has been properly advanced to account for the time lag.
Abstract
An improved calibration technique for an airborne Lyman-alpha hygrometer is presented. Like previous methods, it relies upon simultaneous measurement of absolute humidity determined from a slower response hygrometer. We show that a substantial improvement in the Lyman-alpha calibration is obtained by accounting for the time lag of the slower instrument.
To show our technique we use data from Lyman-alpha and thermoelectric devices on the NCAR Electra during an investigation of the nearly neutral boundary layer over the Arabian Sea as part of the WMO/ICSU Summer Monsoon Experiment. We also show that for near-neutral conditions the eddy-correlation water vapor flux can be adequately estimated using the fast response vertical velocity data from a gust probe and slower response data from the thermoelectric device, which has been properly advanced to account for the time lag.
Abstract
The second part of the parameterization of subgrid-scale surface fluxes model (PASS2) has been developed to estimate long-term evapotranspiration rates over extended areas at a high spatial resolution by using satellite remote sensing data and limited, but continuous, surface meteorological measurements. Other required inputs include data on initial root-zone available moisture (RAM) content computed by PASS1 for each pixel at the time of clear-sky satellite overpasses, normalized difference vegetation index (NDVI) from the overpasses, and databases on available water capacity and land-use classes. Site-specific PASS2 parameterizations evaluate surface albedo, roughness length, and ground heat flux for each pixel, and special functions distribute areally representative observations of wind speed, temperature, and water vapor pressure to individual pixels. The surface temperature for each pixel and each time increment is computed with an approximation involving the surface energy budget, and the evapotranspiration rates are computed via a bulk aerodynamic formulation. Results from PASS2 were compared with observations made during the 1997 Cooperative Atmosphere–Surface Exchange Study field campaign in Kansas. The modeled diurnal variation of RAM content, latent heat flux, and daily evapotranspiration rate were realistic in comparison to measurements at eight surface sites. With the limited resolution of the NDVI data, however, model results deviated from the observations at locations where the measurement sites were in fields with surface vegetative conditions notably different than surrounding fields. Comparisons with aircraft-based flux measurements suggested that the evapotranspiration rates over distances of tens of kilometers were modeled without significant bias.
Abstract
The second part of the parameterization of subgrid-scale surface fluxes model (PASS2) has been developed to estimate long-term evapotranspiration rates over extended areas at a high spatial resolution by using satellite remote sensing data and limited, but continuous, surface meteorological measurements. Other required inputs include data on initial root-zone available moisture (RAM) content computed by PASS1 for each pixel at the time of clear-sky satellite overpasses, normalized difference vegetation index (NDVI) from the overpasses, and databases on available water capacity and land-use classes. Site-specific PASS2 parameterizations evaluate surface albedo, roughness length, and ground heat flux for each pixel, and special functions distribute areally representative observations of wind speed, temperature, and water vapor pressure to individual pixels. The surface temperature for each pixel and each time increment is computed with an approximation involving the surface energy budget, and the evapotranspiration rates are computed via a bulk aerodynamic formulation. Results from PASS2 were compared with observations made during the 1997 Cooperative Atmosphere–Surface Exchange Study field campaign in Kansas. The modeled diurnal variation of RAM content, latent heat flux, and daily evapotranspiration rate were realistic in comparison to measurements at eight surface sites. With the limited resolution of the NDVI data, however, model results deviated from the observations at locations where the measurement sites were in fields with surface vegetative conditions notably different than surrounding fields. Comparisons with aircraft-based flux measurements suggested that the evapotranspiration rates over distances of tens of kilometers were modeled without significant bias.
The authors have developed a new extended-range flood forecasting system for large river basins that uses satellite data and statistically rendered probabilistic weather and climate predictions to initialize basin-scale hydrological models. The forecasting system overcomes the absence of upstreamflow data, a problem that is prevalent in the developing world. Forecasts of the Ganges and Brahmaputra discharge into Bangladesh were made in real time on 1–10-day time horizons for the period 2003–08. Serious flooding of the Brahmaputra occurred in 2004, 2007, and 2008. Detailed forecasts of the flood onset and withdrawal were made 10 days in advance for each of the flooding events with correlations at 10 days ≥0.8 and Brier scores <0.05. Extensions to 15 days show useable skill. Based on the 1–10-day forecasts of the 2007 and 2008 floods, emergency managers in Bangladesh were able to act preemptively, arrange the evacuation of populations in peril along the Brahmaputra, and minimize financial loss. The particular application of this forecast scheme in Bangladesh represents a “world is f lat” approach to emergency management through the collaboration of scientists in Europe (generating global ensemble meteorological and climate forecasts), the United States (developing and producing the integrated flood forecasts), and the developing world (integrating the flood forecasts into their disaster management decision-making protocol), all enabled by high-speed Internet connections. We also make suggestions of how scientific and technical collaborations between more developed and developing nations can be improved to increase their prospects for sustaining the technology adoption and transfer.
The authors have developed a new extended-range flood forecasting system for large river basins that uses satellite data and statistically rendered probabilistic weather and climate predictions to initialize basin-scale hydrological models. The forecasting system overcomes the absence of upstreamflow data, a problem that is prevalent in the developing world. Forecasts of the Ganges and Brahmaputra discharge into Bangladesh were made in real time on 1–10-day time horizons for the period 2003–08. Serious flooding of the Brahmaputra occurred in 2004, 2007, and 2008. Detailed forecasts of the flood onset and withdrawal were made 10 days in advance for each of the flooding events with correlations at 10 days ≥0.8 and Brier scores <0.05. Extensions to 15 days show useable skill. Based on the 1–10-day forecasts of the 2007 and 2008 floods, emergency managers in Bangladesh were able to act preemptively, arrange the evacuation of populations in peril along the Brahmaputra, and minimize financial loss. The particular application of this forecast scheme in Bangladesh represents a “world is f lat” approach to emergency management through the collaboration of scientists in Europe (generating global ensemble meteorological and climate forecasts), the United States (developing and producing the integrated flood forecasts), and the developing world (integrating the flood forecasts into their disaster management decision-making protocol), all enabled by high-speed Internet connections. We also make suggestions of how scientific and technical collaborations between more developed and developing nations can be improved to increase their prospects for sustaining the technology adoption and transfer.
