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Margaret C. Anderson

Abstract

The overall heat transfer coefficient of three types of thermopile solarimeters were determined from the rate of change of emf after an instantaneous change in the level of incident radiation. Conductive and radiative transfer coefficients were calculated from instrument dimensions, but experiments with Moll-Gorczynski solarimeters filled with different gases provided indirect proof of their accuracy. The empirical relation between Nusselt and Rayleigh numbers agreed reasonably with previous estimates for comparable systems. Increasing the overall heat transfer coefficient for a given type of thermopile element, by altering the gaseous content or the casing dimensions, will decrease sensitivity and linearity of response, increase the temperature coefficient and decrease the response time. Decreasing the thermal capacity of the element will decrease response time and increase sensitivity. A unique determination of sensitivity, linearity, temperature coefficient and response time of any instrument cannot be given, since all of these characteristics are functions of the incident radiation flux density.

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M. Balser, C. A. McNary, and D. Anderson

Abstract

A Doppler acoustic system was installed on the approach to the Los Angeles International Airport in a demonstration of its capability of remotely measuring wind and wind shear in a real airport environment. The instrument continued to read valid 1 min averages of wind even when aircraft passed overhead directly through the receiver beams. An example is shown in which the observed wind was highly variable in altitude and time, and would at times have constituted a dangerous wind shear.

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R. C. Anderson and D. R. Keefer

Abstract

Atmospheric pressure, temperature and wind speed were measured at the ground in Chinguetti, Mauritania, during the 1973 solar eclipse. The pressure measurements were intended to determine if barometric pressure changes were caused by the eclipse, but they produced a null result because of local weather conditions. Eclipse-induced temperature changes were measured continuously at altitudes of 0.3, 6.75 and 13.5 m. The maximum temperature changes were 3.5°C at the lowest level and 2.5°C at the two upper levels. The wind decreased by approximately 4.5 m s−1.

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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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S. J. Birstein and C. E. Anderson

Abstract

A careful study has been made of the nucleating ability of various chemicals. The nuclei were prepared in a nitrogen atmosphere, rather than air, to prevent a reaction at the hot filament with atmospheric oxygen. With use of these carefully controlled conditions, numerous materials previously reported as effective were found to be poor nucleating agents. The discrepancies among the various sets of data were found to be due to reaction at the filament of the solid material and oxygen in previous investigations. The results are examined to determine how they support prevailing theories on ice-crystal formation.

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F. G. FINGER, H. M. WOOLF, and C. E. ANDERSON

Abstract

A method of numerical objective analysis has been developed for application to stratospheric constant-pressure data at the 100-, 50-, 30-, and 10-mb. levels (approximately 16, 20, 24, and 31 km., respectively). This system evolved from successive modifications of the programs employed for operational objective analysis of lower-level charts at the National Meteorological Center. For use with stratospheric data, the Automatic Data Processing portion of these programs was expanded to correct for the errors in high-level rawinsonde temperatures and heights caused by short and long-wave radiational effects on the temperature sensor. In addition, procedures for vertical extrapolation of rawinsonde reports and merging of off-time data were incorporated to compensate for the scarcity of reports at a given observation time.

General degradation of stratospheric data with increasing height necessitated more stringent data rejection criteria within the entire system. It was also essential that increased emphasis be placed on wind observations as an analysis parameter. The resulting charts have shown that the objective system employed produces analyses of acceptable quality. Improvements are continually being developed and incorporated to increase the efficacy and objectivity of the procedures and the quality and usefulness of the product.

The main purposes of the computerized system are to provide good quality stratospheric analyses for anticipated operational requirements and to satisfy the needs of research. Daily analysis of Northern Hemisphere charts is being performed during the IQSY and is expected to continue after the end of the period. These maps are recorded for distribution on microfilm and also on punched-card decks containing grid-point data.

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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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Yafang Zhong, Jason A. Otkin, Martha C. Anderson, and Christopher Hain

Abstract

Despite the key importance of soil moisture–evapotranspiration (ET) coupling in the climate system, limited availability of soil moisture and ET observations poses a major impediment for investigation of this coupling regarding spatiotemporal characteristics and potential modifications under climate change. To better understand and quantify soil moisture–ET coupling and relevant processes, this study takes advantage of in situ soil moisture observations from the U.S. Climate Reference Network (USCRN) for the time period of 2010–17 and a satellite-derived version of the evapotranspiration stress index (ESI), which represents anomalies in a normalized ratio of actual to reference ET. The analyses reveal strong seasonality and regional characteristics of the ESI–land surface interactions across the United States, with the strongest control of soil moisture on the ESI found in the southern Great Plains during spring, and in the north-central United States, the northern Great Plains, and the Pacific Northwest during summer. In drier climate regions such as the northern Great Plains and north-central United States, soil moisture control on the ESI is confined to surface soil layers, with subsurface soil moisture passively responding to changes in the ESI. The soil moisture–ESI interaction is more uniform between surface and subsurface soils in wetter regions with higher vegetation cover. These results provide a benchmark for simulation of soil moisture–ET coupling and are useful for projection of associated climate processes in the future.

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Jason A. Otkin, Martha C. Anderson, Christopher Hain, and Mark Svoboda

Abstract

In this study, the potential utility of using rapid temporal changes in drought indices to provide early warning of an elevated risk for drought development over subseasonal time scales is assessed. Standardized change anomalies were computed each week during the 2000–13 growing seasons for drought indices depicting anomalies in evapotranspiration, precipitation, and soil moisture. A rapid change index (RCI) that encapsulates the accumulated magnitude of rapid changes in the weekly anomalies was computed each week for each drought index, and then a simple statistical method was used to convert the RCI values into drought intensification probabilities depicting the likelihood that drought severity as analyzed by the U.S. Drought Monitor (USDM) would worsen in subsequent weeks. Local and regional case study analyses revealed that elevated drought intensification probabilities often occur several weeks prior to changes in the USDM and in topsoil moisture and crop condition datasets compiled by the National Agricultural Statistics Service. Statistical analyses showed that the RCI-derived probabilities are most reliable and skillful over the central and eastern United States in regions most susceptible to rapid drought development. Taken together, these results suggest that tools used to identify areas experiencing rapid changes in drought indices may be useful components of future drought early warning systems.

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R. C. Anderson, D. R. Keefer, and O. E. Myers

Abstract

Air pressure and temperature measurements were made during the 7 March 1970 solar eclipse. A Fourier analysis showed a primary wave with a period of 89 min and an amplitude of 250 μb. Smaller peaks were found with periods of 57, 51, 45, 38, 20.3, 18.2, 15.7 and 12.3 min. The primary wave agreed reasonably well in magnitude and phase with five earlier eclipse measurements dating back as far as 1887. The temperature decreased 3C with a minimum slightly after totality. This occurred under a thick cloud blanket.

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