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Lieut. J. B. ANDERSON

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Lieut. J. B. Anderson
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Lloyd J. Anderson

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.

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R. J. Anderson

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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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J. B. Anderson
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L. J. Anderson

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.

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Lloyd J. Anderson

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.

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B. J. Anderson and J. Hallett

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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.

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F. Vitart and J. L. Anderson

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A significant reduction (increase) of tropical storm activity over the Atlantic basin is observed during El Niño (La Niña) events. Furthermore, the number of Atlantic tropical storms displays an interdecadal variability with more storms in the 1950s and 1960s than in the 1970s and 1980s. Ensembles of simulations with an atmospheric general circulation model (AGCM) are used to explore the mechanisms responsible for this observed variability.

The interannual variability is investigated using a 10-member ensemble of AGCM simulations forced by climatological SSTs of the 1980s everywhere except over the tropical Pacific and Indian Oceans. Significantly fewer tropical storms are simulated with El Niño SSTs imposed over the tropical Pacific and Indian Oceans than with La Niña conditions. Increased simulated vertical wind shear over the Atlantic is the most likely explanation for the reduction of simulated tropical storms during El Niño years. SST forcing from different El Niño events has distinct impacts on Atlantic tropical storms in the simulation: simulated tropical storms are significantly less numerous with 1982 SSTs imposed over the tropical Pacific and Indian Oceans than with 1986 SSTs.

The interdecadal variability of tropical storm activity seems to coincide with an interdecadal variability of the North Atlantic SSTs with colder SSTs in the 1970s than in the 1950s. Ensembles of AGCM simulations produce significantly more tropical storms when forced by observed SSTs of the 1950s than when forced by SSTs of the 1970s. This supports the theory that the interdecadal variability of SSTs has a significant impact on the expected number of Atlantic tropical storms and suggests that Atlantic tropical storms may be more numerous in coming years if North Atlantic SSTs are getting warmer. A significant increase of vertical wind shear and a significant decrease in the convective available potential energy over the tropical Atlantic in the 1970s may explain the simulated interdecadal variability of Atlantic tropical storms.

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B. J. Anderson, J. D. Sutkoff, and J. Hallett

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Ice crystals grow from the vapor in the presence of Eastman9 10 cement (containing methyl 2-cyanoacrylate monomer) in the form of fine fibres a few microns in diameter, in the c axis direction of the nucleating crystal. A previous suggestion that similar fibers observed using this material for the replication process occur undernatural conditions and are a source of atmospheric ice crystals appears unlikely.

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