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  • Author or Editor: C. Bruce Baker x
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C. Bruce Baker
,
William R. Kuhn
, and
Edward Ryznar

Abstract

Direct normal and diffuse solar irradiances and 500 nm aerosol optical depths measured at the University of Michigan departed far from normal on 26 October 1982, when it is concluded that the main stratospheric cloud from the El Chichon volcanic eruption arrived at the 42°N latitude of the radiation measurement facility. For clear-sky data analyzed through 19 January 1983, direct solar is about 25% less than normal and diffuse solar is about 85% greater. For the same aerosol optical depths and solar zenith angles, the ratio of diffuse to direct is about 30% greater for about 0.3 cm of precipitable water but nearly the same for 0.9 cm. Aerosol optical depths are nearly three times greater for wind directions that naturally advect the cleanest air. The effect of circumsolar irradiance on the methods used to measure direct normal and diffuse irradiances cause the former to be overestimated and the latter to be underestimated.

Full access
Matteo Colli
,
Roy Rasmussen
,
Julie M. Thériault
,
Luca G. Lanza
,
C. Bruce Baker
, and
John Kochendorfer

Abstract

Recent studies have used numerical models to estimate the collection efficiency of solid precipitation gauges when exposed to the wind in both shielded and unshielded configurations. The models used computational fluid dynamics (CFD) simulations of the airflow pattern generated by the aerodynamic response to the gauge–shield geometry. These are used as initial conditions to perform Lagrangian tracking of solid precipitation particles. Validation of the results against field observations yielded similarities in the overall behavior, but the model output only approximately reproduced the dependence of the experimental collection efficiency on wind speed. This paper presents an improved snowflake trajectory modeling scheme due to the inclusion of a dynamically determined drag coefficient. The drag coefficient was estimated using the local Reynolds number as derived from CFD simulations within a time-independent Reynolds-averaged Navier–Stokes approach. The proposed dynamic model greatly improves the consistency of results with the field observations recently obtained at the Marshall Field winter precipitation test bed in Boulder, Colorado.

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Jon K. Eischeid
,
C. Bruce Baker
,
Thomas R. Karl
, and
Henry F. Diaz

Abstract

One of the major concerns with detecting global climate change is the quality of the data. Climate data are extremely sensitive to errant values and outliers. Prior to analysis of these time series, it is important to remove outliers in a methodical manner.

This study provides statistically derived bounds for the uncertainty associated with surface temperature and precipitation measurements and yields a baseline dataset for validation of climate models as well as for a variety of other climatological uses. A two-step procedure using objective analysis was used to identify outliers. The first step was a temporal check that determines if a particular monthly value is consistent with other monthly values for the same station. The second step utilizes six different spatial interpolation techniques to estimate each monthly time series. Each of the methods is ranked according to its respective correlation coefficients with the actual time series, and the technique with the highest correlation coefficient is chosen as the best estimator. For both temperature and precipitation, a multiple regression scheme was found to be the best estimator for the majority of records. Results from the two steps are merged, and a combined set of quality control flags are generated.

Full access
Fong Ngan
,
Christopher P. Loughner
,
Sonny Zinn
,
Mark Cohen
,
Temple R. Lee
,
Edward Dumas
,
Travis J. Schuyler
,
C. Bruce Baker
,
Joseph Maloney
,
David Hotz
, and
George Mathews

Abstract

A series of meteorological measurements with a small uncrewed aircraft system (sUAS) was collected at Oliver Springs Airport in Tennessee. The sUAS provides a unique observing system capable of obtaining vertical profiles of meteorological data within the lowest few hundred meters of the boundary layer. The measurements benefit simulated plume predictions by providing more accurate meteorological data to a dispersion model. The sUAS profiles can be used directly to drive HYSPLIT dispersion simulations. When using sUAS data covering a small domain near a release and meteorological model fields covering a larger domain, simulated pollutants may be artificially increased or decreased near the domain boundary because of inconsistencies in the wind fields between the two meteorological inputs. Numerical experiments using the Weather Research and Forecasting (WRF) Model with observational nudging reveal that incorporating sUAS data improves simulated wind fields and can significantly affect mixing characteristics of the boundary layer, especially during the morning transition period of the planetary boundary layer. We conducted HYSPLIT dispersion simulations for hypothetical releases for three case study periods using WRF meteorological fields with and without assimilating sUAS measurements. The comparison of dispersion results on 15 and 16 December 2021 shows that using sUAS observational nudging is more significant under weak synoptic conditions than under strong influences from regional weather. Very different dispersion results were introduced by the meteorological fields used. The observational nudging produced not just an sUAS-nudged wind flow but also adjusted meteorological fields that further impacted the mixing calculation in HYSPLIT.

Open access