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R. J. Anderson

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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R. C. Anderson and J. G. Pipes

Abstract

A simplified model of Jovian clouds was used to fit the shape of the geometric albedo curve between 1800 and 1950 Å. Absorption by uniform layers of gaseous and solid cubic ammonia over a gray surface resulted in a curve that was in good agreement with reported experimental measurements.

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F. R. Bellaire and L. J. Anderson

A new thermocouple psychrometer, designed to indicate true air temperature and humidity in remote locations, is described. In order to minimize maintenance, it utilizes natural ventilation, but provides adequate shielding of sensing elements against radiation. Wet and dry bulb temperature errors of less than + 0.1C° are obtained in winds above 1 mph.

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L. R. Wyatt, L. J. Ledgard, and C. W. Anderson

Abstract

The maximum-likelihood method is used to extract parameters of two-parameter models of the directional spreading of short wind waves from the power spectrum of high-frequency (HF) radar backscatter. The wind waves have a wavelength of half the radio wavelength that, for the data presented here, is at a frequency of 0.53 Hz. The parameters are short-wave direction, which at this frequency can be identified with wind direction, and the directional spread angle, the parameterization of which is model dependent. For the data presented here, the results suggest that the Donelan directional spreading model provides a better description of directional spreading than the coss model. The HF radar and wave buoy measurements are compared and show good agreement. Measurements are presented that show the temporal and spatial structure of the short-wave field responding to the passage of a frontal system.

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V. J. OLIVER, R. K. ANDERSON, and E. W. FERGUSON

Abstract

TIROS photographs of cloud patterns in the vicinity of the jet stream are examined and compared with surface, upper air, and pilot-report data. It is found that with certain conditions of lighting and satellite attitude the northern edge of the cirrus cloud shield, which lies immediately south of the jet, can be easily identified by a shadow cast by the higher cloud deck on the lower underlying surface. This shadow identifies the cloud structure associated with the jet stream. Differences in texture and pattern also help to identify the northern limits of the high-level cirrus and thus aid in positioning the jet stream.

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S. H. Suck, J. L. Kassner Jr., R. E. Thurman, P. C. Yue, and R. A. Anderson

Abstract

The clustering of water vapor about ions is important because of its relevance to atmospheric electrical processes. For this reason we have placed our emphasis particularly on the description of the size distribution (concentrations) and mobilities of the small ion clusters at various humidities. From our present theoretical study, we find that most of the hydronium ions H3O+ tend to associate with a small number of water molecules to form a hydrated ion cluster even at extremely low humidities in the range of 5 × 10−3 to 1%. At atmospherically more realistic humidities and at the room temperature, our computed number of water molecules in the hydrated ion clusters is predicted to be relatively small. It is then conjectured that ion-induced nucleation process (if it occurs) starts rather from the small hydrated ion clusters which initially existed even at extremely low humidities in the atmosphere. In addition, we also find that, in general, the hydrated ion clusters of small sizes corresponding to the mass range of 2–5 water molecules are responsible for the ion mobility range of 2–2.5 cm−2 (V s)−1. For reduced mobility below 2.0 cm2 (V s)−1, the mass of the hydrated ion cluster is predicted to be greater than that of approximately five water molecules. The simultaneous estimation of size distribution and mobility aids us in better understanding observed mobility spectra and the nature of atmospherically important prenucleation clusters, including the information of their electric conductivities in the atmosphere.

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R. J. Breeding, P. L. Haagenson, J. A. Anderson, J. P. Lodge Jr., and J. F. Stampfer Jr.

Abstract

The records from pollutant sensors abroad two aircraft are compared. The aircraft flew along arcs of either 80 or 120 km radius from the Gateway Arch in St. Louis. One aircraft contained a light-scattering instrument which determined the concentrations of particles with radii between 0.15 and 0.30 μm and between 0.30 and 1.3 μm. The other airplane contained an integrating nephelometer, a condensation nucleus counter, and an ozone monitor. It appears that neither the concentration of the condensation nuclei nor the ozone concentration are as reliable indicators of the location of the St. Louis plume at these distances as are data from the light-scattering particle counter or the nephelometer.

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David J. Lorenz, Jason A. Otkin, Mark Svoboda, Christopher R. Hain, Martha C. Anderson, and Yafang Zhong

Abstract

The U.S. Drought Monitor (USDM) classifies drought into five discrete dryness/drought categories based on expert synthesis of numerous data sources. In this study, an empirical methodology is presented for creating a nondiscrete USDM index that simultaneously 1) represents the dryness/wetness value on a continuum and 2) is most consistent with the time scales and processes of the actual USDM. A continuous USDM representation will facilitate USDM forecasting methods, which will benefit from knowledge of where, within a discrete drought class, the current drought state most probably lies. The continuous USDM is developed such that the actual discrete USDM can be reconstructed by discretizing the continuous USDM based on the 30th, 20th, 10th, 5th, and 2nd percentiles—corresponding with USDM definitions for the D4–D0 drought classes. Anomalies in precipitation, soil moisture, and evapotranspiration over a range of different time scales are used as predictors to estimate the continuous USDM. The methodology is fundamentally probabilistic, meaning that the probability density function (PDF) of the continuous USDM is estimated and therefore the degree of uncertainty in the fit is properly characterized. Goodness-of-fit metrics and direct comparisons between the actual and predicted USDM analyses during different seasons and years indicate that this objective drought classification method is well correlated with the current USDM analyses. In Part II, this continuous USDM index will be used to improve intraseasonal USDM intensification forecasts because it is capable of distinguishing between USDM states that are either far from or near to the next-higher drought category.

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M. Segal, R. W. Arritt, J. Shen, C. Anderson, and M. Leuthold

Abstract

In this note the forcing of cumulus cloud clearing over and downwind from lakes during the warm season is evaluated conceptually by modeling and observational approaches. It is suggested that drying by dynamically induced subsidence and suppression of the CBL over the lake mutually contribute to the cloud clearing. The effect of background flow speed and the extent of potential clearing area is illustrated. Various implications of the cloud clearing are discussed.

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R. C. Anderson, J. G. Pipes, A. L. Broadfoot, and L. Wallace

Abstract

The results of two Aerobee rocket flights are reported. One obtained spectra of Venus from 3200 to 1900 Å at 16.5 Å resolution and the other spectra of Jupiter from 32M to 1800 Å at 28 Å resolution. The spectra of both planets are of much higher statistical accuracy than those that have been obtained previously. The peculiarities indicated by the previous observations are not confirmed. In particular, there does not appear to be an absorption feature in the Jupiter spectrum at 2600 Å or an ozone absorption in the Venus spectrum.

Two extreme models are used to interpret the data: the reflecting layer model and the cloud model. We find that the CO2 abundances for Venus and the H2 abundances for Jupiter, deduced with the reflecting layer model from observations in the red and IR parts of the spectrum, are much ton large to be compatible with the UV albedos. In terms of the cloud model, the albedos of both planets down to 2200 Å are the result of the decreasing single scattering albedo of the cloud particles and the increasing Rayleigh scattering. These two effects produce an almost constant geometric albedo from 2800 to 2200 Å. Below 2200 Å, the Venus albedo drops sharply due to CO2, absorption; the Jupiter albedo drops off by a factor of 4 due to NH3 absorption, an unidentified absorber, a decrease in the cloud particle albedo, or Borne combination of these effects.

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