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A simple instrument is described for measuring or recording wind speed, using a 1-in. length of heated platinum wire as the sensing element. As a practical laboratory and field device, its main virtues are its excellent response at low wind speeds and its utility in confined spaces. Calibration techniques are described, and the circuit diagram is included for a three-range instrument.
A simple instrument is described for measuring or recording wind speed, using a 1-in. length of heated platinum wire as the sensing element. As a practical laboratory and field device, its main virtues are its excellent response at low wind speeds and its utility in confined spaces. Calibration techniques are described, and the circuit diagram is included for a three-range instrument.
Measurements on rainfall near Hilo, Hawaii are described. Quartile deviations of drop-size distributions are plotted versus rainfall intensity. Comparison is made with similar data of Laws and Parsons, and certain similarities and differences are pointed out.
Measurements on rainfall near Hilo, Hawaii are described. Quartile deviations of drop-size distributions are plotted versus rainfall intensity. Comparison is made with similar data of Laws and Parsons, and certain similarities and differences are pointed out.
Meteorological equipment for taking detailed temperature and humidity soundings to 3000 ft. altitude is discussed. It consists of a captive balloon wired-sonde system using a ceramic temperature element and an electrolytic hygrometer strip. Similar equipment is also adapted for use in airplane soundings. Calibration techniques and results are discussed, together with a method for correcting the humidity strip to ± 1% R.H. Temperature accuracy is ± 0.1°C. The limitations of the balloon and airplane equipment are discussed and the two are found to be complementary.
Meteorological equipment for taking detailed temperature and humidity soundings to 3000 ft. altitude is discussed. It consists of a captive balloon wired-sonde system using a ceramic temperature element and an electrolytic hygrometer strip. Similar equipment is also adapted for use in airplane soundings. Calibration techniques and results are discussed, together with a method for correcting the humidity strip to ± 1% R.H. Temperature accuracy is ± 0.1°C. The limitations of the balloon and airplane equipment are discussed and the two are found to be complementary.
Abstract
A bow-mounted propeller anemometer and fast-response temperature sensors were operated during several cruises of CSS Dawson. Spectra of wind speed and temperature fluctuations were measured over the open ocean for a wind speed range of 6 to 21 m s−1 and a sea-air temperature difference range of ±6°C. Wind stress on the sea surface and sensible heat fluxes were determined by the inertial-dissipation method over a wide range of wind speeds for both stable and unstable atmospheric conditions. Neutral drag and sensible beat flux coefficients as functions of the wind speed at a 10-m reference height are in excellent agreement with the only existing eddy fluxes measured over the ocean from a stable platform and also with open sea inertial-dissipation measurements from a ship.
Abstract
A bow-mounted propeller anemometer and fast-response temperature sensors were operated during several cruises of CSS Dawson. Spectra of wind speed and temperature fluctuations were measured over the open ocean for a wind speed range of 6 to 21 m s−1 and a sea-air temperature difference range of ±6°C. Wind stress on the sea surface and sensible heat fluxes were determined by the inertial-dissipation method over a wide range of wind speeds for both stable and unstable atmospheric conditions. Neutral drag and sensible beat flux coefficients as functions of the wind speed at a 10-m reference height are in excellent agreement with the only existing eddy fluxes measured over the ocean from a stable platform and also with open sea inertial-dissipation measurements from a ship.
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No Abstract Available.
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No Abstract Available.
Abstract
Nucleation of individual ice crystals on large (3.0 mm) cleaved crystals of solution-grown silver iodide and covellite is investigated by microscopy. The environmental vapor pressure is controlled by saturating two air streams by passage through ice labyrinths at different temperatures and mixing them in known proportion. This enables the vapor pressure to be changed over a period of about 10 s.
Ice crystals do not usually appear immediately when a supersaturation is imposed. Nucleation, defined as the appearance of crystals of 1 µm radius, is delayed between zero and 70 s near water saturation and between 20 and 400 s at a few percent ice supersaturation, the longer times occurring at higher temperature. This time decreases only marginally when the crystal is exposed to a period of higher supersaturation which ends a few seconds prior to the time crystals would appear at this higher value. The number of crystals per unit area increases with ice supersaturation at a given temperature; for CuS at −16°C, it increases by a factor of 3 between 3% and water saturation. Number concentrations on silver iodide are comparable, but increase with time when the surface is exposed to light. The absolute crystal concentration varies over the substrate surface. Large areas fail to nucleate at all; some areas give high concentrations, 500 mm−2. Crystals form at specific nucleation sites. Each requires a different critical ice supersaturation for nucleation which remains unchanged in sequential tests. This property disappears for AgI after exposure to light; then nucleation sites do not repeat. Nucleation events per unit area are fewer than on particulates which are inferred to contain a proportionately greater surface concentration
of nucleation sites.
Results are applied to crystal nucleation in the atmosphere and the characterization of ice nuclei in laboratory instruments.
Abstract
Nucleation of individual ice crystals on large (3.0 mm) cleaved crystals of solution-grown silver iodide and covellite is investigated by microscopy. The environmental vapor pressure is controlled by saturating two air streams by passage through ice labyrinths at different temperatures and mixing them in known proportion. This enables the vapor pressure to be changed over a period of about 10 s.
Ice crystals do not usually appear immediately when a supersaturation is imposed. Nucleation, defined as the appearance of crystals of 1 µm radius, is delayed between zero and 70 s near water saturation and between 20 and 400 s at a few percent ice supersaturation, the longer times occurring at higher temperature. This time decreases only marginally when the crystal is exposed to a period of higher supersaturation which ends a few seconds prior to the time crystals would appear at this higher value. The number of crystals per unit area increases with ice supersaturation at a given temperature; for CuS at −16°C, it increases by a factor of 3 between 3% and water saturation. Number concentrations on silver iodide are comparable, but increase with time when the surface is exposed to light. The absolute crystal concentration varies over the substrate surface. Large areas fail to nucleate at all; some areas give high concentrations, 500 mm−2. Crystals form at specific nucleation sites. Each requires a different critical ice supersaturation for nucleation which remains unchanged in sequential tests. This property disappears for AgI after exposure to light; then nucleation sites do not repeat. Nucleation events per unit area are fewer than on particulates which are inferred to contain a proportionately greater surface concentration
of nucleation sites.
Results are applied to crystal nucleation in the atmosphere and the characterization of ice nuclei in laboratory instruments.
Abstract
Large, long-lived convective systems over the United States in 1992 and 1993 have been classified according to physical characteristics observed in satellite imagery as quasi-circular [mesoscale convective complex (MCC)] or elongated [persistent elongated convective system (PECS)] and cataloged. The catalog includes the time of initiation, maximum extent, termination, duration, area of the −52°C cloud shield at the time of maximum extent, significant weather associated with each occurrence, and tracks of the −52°C cloud-shield centroid.
Both MCC and PECS favored nocturnal development and on average lasted about 12 h. In both 1992 and 1993, PECS produced −52°C cloud-shield areas of greater extent and occurred more frequently compared with MCCs. The mean position of initiation for PECS in 1992 and 1993 followed a seasonal shift similar to the climatological seasonal shift for MCC occurrences but was displaced eastward of the mean position of MCC initiation in 1992 and 1993. The spatial distribution of MCC and PECS occurrences contain a period of persistent development near 40°N in July 1992 and July 1993 that contributed to the extreme wetness experienced in the Midwest during these two months.
Both MCC and PECS initiated in environments characterized by deep, synoptic-scale ascent associated with continental-scale baroclinic waves. PECS occurrences initiated more often as vigorous waves exited the intermountain region, whereas MCCs initiated more often within a high-amplitude wave with a trough positioned over the northwestern United States and a ridge positioned over the Great Plains. The low-level jet transported moisture into the region of initiation for both MCC and PECS occurrences. The areal extent of convective initiation was limited by the orientation of low-level features for MCC occurrences.
Abstract
Large, long-lived convective systems over the United States in 1992 and 1993 have been classified according to physical characteristics observed in satellite imagery as quasi-circular [mesoscale convective complex (MCC)] or elongated [persistent elongated convective system (PECS)] and cataloged. The catalog includes the time of initiation, maximum extent, termination, duration, area of the −52°C cloud shield at the time of maximum extent, significant weather associated with each occurrence, and tracks of the −52°C cloud-shield centroid.
Both MCC and PECS favored nocturnal development and on average lasted about 12 h. In both 1992 and 1993, PECS produced −52°C cloud-shield areas of greater extent and occurred more frequently compared with MCCs. The mean position of initiation for PECS in 1992 and 1993 followed a seasonal shift similar to the climatological seasonal shift for MCC occurrences but was displaced eastward of the mean position of MCC initiation in 1992 and 1993. The spatial distribution of MCC and PECS occurrences contain a period of persistent development near 40°N in July 1992 and July 1993 that contributed to the extreme wetness experienced in the Midwest during these two months.
Both MCC and PECS initiated in environments characterized by deep, synoptic-scale ascent associated with continental-scale baroclinic waves. PECS occurrences initiated more often as vigorous waves exited the intermountain region, whereas MCCs initiated more often within a high-amplitude wave with a trough positioned over the northwestern United States and a ridge positioned over the Great Plains. The low-level jet transported moisture into the region of initiation for both MCC and PECS occurrences. The areal extent of convective initiation was limited by the orientation of low-level features for MCC occurrences.
Abstract
Large, long-lived mesoscale convective systems (MCSs) over the United States during the 1997–98 El Niño are documented. Two periods of abnormal MCS activity are identified in 1998: from March to mid-April an unusually large number of quasi-linear MCSs were observed in the Midwest; while quasi-circular MCSs in June–August of 1998 were concentrated near 37°N rather than following a seasonal shift similar to that observed in the climatological distribution. Episodic surges of northerly low-level flow were infrequent in March 1998, thereby leading to an unusually high incidence of quasi-linear MCSs and to precipitation anomalies in the central United States.
Abstract
Large, long-lived mesoscale convective systems (MCSs) over the United States during the 1997–98 El Niño are documented. Two periods of abnormal MCS activity are identified in 1998: from March to mid-April an unusually large number of quasi-linear MCSs were observed in the Midwest; while quasi-circular MCSs in June–August of 1998 were concentrated near 37°N rather than following a seasonal shift similar to that observed in the climatological distribution. Episodic surges of northerly low-level flow were infrequent in March 1998, thereby leading to an unusually high incidence of quasi-linear MCSs and to precipitation anomalies in the central United States.
Abstract
No abstract available.
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No abstract available.
