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E. Kalnay, M. Kanamitsu, and W.E. Baker

In this paper we describe the global numerical weather prediction system of the National Meteorological Center, and review recent improvements, the evolution in skill, and current research projects and plans.

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M. Halem, E. Kalnay, W. E. Baker, and R. Atlas

This study investigates the degree to which data from the space-borne FGGE observing systems are able to determine the complete state of the atmosphere when incorporated into a global objective analysis cycle. Three data assimilation experiments are performed with the Goddard Laboratory for Atmospheric Sciences (GLAS) analysis/forecast system, using different combinations of the FGGE level II–b data collected during the first Special Observing Period (SOP-1), 5 January through 5 March 1979. The control experiment is an assimilation cycle with the complete FGGE II–b data. The other two assimilation/forecast experiments consist of i) the conventional system without the satellite data and special FGGE data sets; and ii) the FGGE II–b surface and satellite temperature soundings and cloud-track winds, aircraft data, and special FGGE data sets, but without the conventional rawinsonde/pilot balloon network.

From these experiments, we attempt to assess the accuracy of the inferred mass and motion fields over data-sparse regions, by examining their influence on analyses and forecasts over data-rich regions. The sensitivity of the analysis to the FGGE satellite data is shown by comparisons of the 6 h forecast error of the 300 mb geopotential height fields for these three experiments. It is found that large 6 h forecast errors downstream of data-sparse regions are reduced when the satellite observations are incorporated in the analysis. Forecast impact results from the initial states of these assimilation cycles show the geographical influence of the FGGE satellite observing system on short- to medium-range (two to five days) weather forecasting. Over North America and Europe, there is a small improvement in forecast skill from the use of the FGGE II–b data. Over Australia, as expected, the positive impact of satellite data is much larger. The number of skillful four- and five-day forecasts over North America and Europe has been increased substantially by the addition of the FGGE II–b data. Examples of useful eight-day forecasts, which occurred in periods of atmospheric blocking situations also are presented.

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W. E. Baker, R. Atlas, M. Halem, and J. Susskind

Abstract

In this study we examine the sensitivity of forecast to individual components of the First GARP (Global Atmospheric Research Programme) Global Experiment database as well as to some modifications in the data analysis techniques. Several short assimilation experiments (0000 GMT 18 January 1979 through 0000 21 January) are performed in order to test the effects of each database or analysis change. Forecasts are then generated from the initial conditions provided by these experiments. The 0000 21 January case is chosen for a detailed investigation because or the poor forecast skill obtained earlier over North America for that particular case. Specifically, we conduct experiments to test the sensitivity of forecast skill to: 1) the addition of individual satellite observing system components; 2) temperature data obtained with different satellite retrieval methods; and 3) the method of vertical interpolation between the mandatory pressure analysis levels and the model sigma levels.

For the single case examined, TIROS-N infrared land retrievals produced operationally are found to degrade the forecast, while the use of TIROS-N retrievals produced with a physical inversion method as part of an analysis/forecast cycle results in an improved forecast. The use of oceanic VTPR (Vertical Temperature Profile Radiometer) satellite retrievals also results in an improved forecast over North America. The forecast is also found to be sensitive to the method of vertical interpolation between the mandatory pressure analysis levels and the model sigma levels.

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L. Baker Perry, Charles E. Konrad, and Thomas W. Schmidlin

Abstract

Northwest flow snow (NWFS) events are common occurrences at higher elevations and on windward slopes in the southern Appalachians. Low temperatures and considerable blowing and drifting of snow, coupled with significant spatial variability of snowfall, substantially increase societal impacts. This paper develops a synoptic classification of NWFS events in the southern Appalachians using 72-h antecedent upstream (backward) air-trajectory analyses. Hourly observations from first-order stations and daily snowfall data from cooperative observer stations are used to define snowfall events. NCEP–NCAR reanalysis data are utilized to identify NWFS events on the basis of 850-hPa northwest flow (270°–360°) at the event maturation hour. The NOAA Hybrid Single-Particle Lagrangian Integrated Trajectory tool is used to calculate 72-h backward air trajectories at the event maturation hour and composite trajectories are mapped in a geographic information systems format. Analyses of vertical soundings are coupled with NCEP–NCAR reanalysis data to determine the synoptic characteristics associated with each trajectory class. Significant variability of trajectories and synoptic patterns is evident from the analyses, resulting in four distinct backward air-trajectory classes. Trajectories with a Great Lakes connection result in higher composite mean and maximum snowfall totals along portions of the higher-elevation windward slopes when compared with other northwest trajectories, but little effect of the Great Lakes is noted at lower elevations and on leeward slopes.

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J. W. Lavelle, M. A. Wetzler, E. T. Baker, and R. W. Embley

Abstract

Tidal and inertial currents and profuse hydrothermal discharge at recently erupted Axial Volcano, Juan de Fuca Ridge, cause relatively large and rapid temperature (T) changes in the near-bottom water column. Measurements show short-term T variations of as much as 0.13°C at 30 m and 0.18°C at 150 m above bottom and currents that have strong tidal components and means of 3–5 cm s−1. Locations and magnitudes of the hydrothermal sources leading to the observed T variations have been inferred via an inverse calculation. Results imply noncongruent source regions around the mooring site for plumes from low- and high-buoyancy flux sources. Water column and seafloor observations in the volcano’s caldera region generally support the distribution of source types and sites inferred. A high-buoyancy flux, ephemeral venting site, unexpected on the eastern shoulder of the volcano, is also indicated by the inverse calculation and supported by water-column survey data. Over the O(10 km2) calculation region, heat flux from low-buoyancy hydrothermal sources is apparently less than heat flux from high-buoyancy hydrothermal sources, a result that is in disagreement with previous reports on the balance of heat flux between vent source types.

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Robert W. Baker, E. Wendell Hewson, Nicholas G. Butler, and Edward J. Warchol

Abstract

The Pacific Northwest is endowed with substantial resources of both hydro energy and wind energy for electrical power generation. The combination of these energy sources into an integrated and optimized system has the potential for supplying a major portion of the future energy requirements of Oregon, Idaho, Washington, western Montana and northeastern Nevada.

The objective of the Pacific Northwest Wind Regional Energy Assessment Program (PNW WIND-REAP) is to identify areas of high wind-power density and develop an order-of-magnitude estimate of the maximum installed capacity, seasonal and annual energy and possible firm capacity available to the region from wind power when integrated with the Columbia River hydroelectric system. This paper presents an assessment of the potential resource and is not a recommended plan of implementation since obvious nontechnical considerations, i.e., institutional, environmental, aesthetics, etc., must be included in the final decision-making process before sites could be selected and technical specifications for wind energy conversion systems be prepared, ordered and installed.

This resource assessment is being accomplished by installing wind data recording stations in those areas which, because of topography, signs of flagging or carpeted vegetation, and/or soil erosion provide evidence of strong or persistent winds. In. addition to national weather service stations, 33 active data stations, ranging from strip chart recorders to simple wind run recorders, are currently functional.

The proven wind energy resources are concentrated in several regions in the Pacific Northwest, namely, the coastal zone of Oregon and Washington and the adjoining offshore waters, the Columbia River Gorge and adjacent ridge tops running from central Washington to just east of Portland, and portions of northeastern Nevada. Also, most of the higher elevations in the five-state area are believed to have significant wind energy potential, especially during the winter when the storm track moves over the Pacific Northwest. However, wind measurement programs are required in these mountains areas before reliable estimates of wind power potential can be made.

Wind energy potential is examined in terms of the amount of time that power producing winds in the range 4.5–27.0 m s−1 occur. The resulting “effective wind power density” is examined on a seasonal basis at the various sites throughout the five-state area. The analysis indicates that there are large wind power resources not only during storms but also with the clear skies associated with high pressure to the northeast. In summer the dominant high pressure system over the Pacific results in substantial wind power along the coast and through the Columbia Gorge and to the cast.

A preliminary indication of the energy production which could have been produced by a 1175 unit, 2140 MW rated, seven-site network in the Pacific Northwest during the period July 1976-February 1977 is 3.8 × 109 KWh. To obtain the lowest cost per unit energy output the wind turbine generator (WTG) unit should he sized according to the strength of the wind regime. However, a comparison of the cost per kilowatt-hour production for various size WTG ratings reveals that for a minor change in price, a sizable increase (or decrease) in energy output can be experienced.

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M. B. Baker, R. E. Breidenthal, T. W. Choularton, and J. Latham

Abstract

Turbulent mixing of cloudy and cloud-free air may play an important role in determining the overall dynamic and microphysical behavior of warm clouds. We present a model of turbulent mixing based on laboratory and theoretical studies of chemically reacting shear layers, extended to include the effects of buoyancy instabilities and droplet sedimentation. It is found to be consistent with recent observations of microphysical variability in natural clouds.

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Wayman E. Baker, Stephen C. Bloom, John S. Woollen, Mark S. Nestler, Eugenia Brin, Thomas W. Schlatter, and Grant W. Branstator

Abstract

A three-dimensional (3D), multivariate, statistical objective analysis scheme (referred to as optimum interpolation or OI) has been developed for use in numerical weather prediction studies with the FGGE data. Some novel aspects of the present scheme include 1) a multivariate surface analysis over the oceans, which employs an Ekman balance instead of the usual geostrophic relationship, to model the pressure-wind error cross correlations, and 2) the capability to use an error correlation function which is geographically dependent.

A series of 4-day data assimilation experiments are conducted to examine the importance of some of the key features of the OI in terms of their effects on forecast skill, as well as to compare the forecast skill using the OI with that utilizing a successive correction method (SCM) of analysis developed earlier. For the three cases examined, the forecast skill is found to be rather insensitive to varying the error correlation function geographically. However, significant differences are noted between forecasts from a two-dimensional (2D) version of the OI and those from the 3D OI, with the 3D OI forecasts exhibiting better forecast skill. The 3D OI forecasts are also more accurate than those from the SCM initial conditions.

The 3D OI with the multivariate oceanic surface analysis was found to produce forecasts which were slightly more accurate, on the average, than a univariate version.

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N. E. Westcott, S. D. Hilberg, R. L. Lampman, B. W. Alto, A. Bedel, E. J. Muturi, H. Glahn, M. Baker, K. E. Kunkel, and R. J. Novak

In the midwestern United States, the summertime rise in infection rate by the West Nile virus is associated with a seasonal shift in the abundance of two mosquito populations, Culex restuans and Culex pipiens. This seasonal shift usually precedes the time of the peak infection rate in mosquitoes by 2–3 weeks and generally occurs earlier in the summer with above normal temperatures and later in the summer with below-normal temperatures. Two empirical models were developed to predict this seasonal shift in mosquito species, or the “crossover,” and have been run operationally since 2004 by the Midwestern Regional Climate Center located at the Illinois State Water Survey. These models are based on daily temperature data and have been verified by use of a unique dataset of daily records of mosquito species abundance collected by the Illinois Natural History Survey. An unfortunate characteristic of the original temperature models was that the crossover date often was reached with little or no lead time. In 2009, the models were modified to incorporate National Weather Service (NWS) model output statistics (MOS) 10-day temperature forecasts. This paper evaluates the effectiveness of these models to predict the crossover date and thus the period of increased risk of West Nile virus in the Midwest.

For the 8-yr period from 2002 to 2009, 6 yr had at least one model predicting the crossover within one week of the actual crossover date, and for 7 yr at least one of the model predictions was within 2 weeks of the actual crossover date. Incorporation of MOS temperature forecasts for a 10-day period, although not substantially changing the predicted crossover date, greatly improved the forecast lead time by about 9 days. From a disease management point of view, this improvement in advanced notice is significant. In 2009, there was an unprecedented early crossover date and a failed forecast. The poor forecast was likely caused by an unusually early summer prolonged and intense heat wave, followed immediately by a record cold July.

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Karl W. Hoppel, Stephen D. Eckermann, Lawrence Coy, Gerald E. Nedoluha, Douglas R. Allen, Steven D. Swadley, and Nancy L. Baker

Abstract

Upper atmosphere sounding (UAS) channels of the Special Sensor Microwave Imager/Sounder (SSMIS) were assimilated using a high-altitude version of the Navy Global Environmental Model (NAVGEM) in order to investigate their potential for operational forecasting from the surface to the mesospause. UAS radiances were assimilated into NAVGEM using the new Community Radiative Transfer Model (CRTM) that accounts for Zeeman line splitting by geomagnetic fields. UAS radiance data from April 2010 to March 2011 are shown to be in good agreement with coincident temperature measurements from the Sounding of the Atmosphere Using Broadband Emission Radiometry (SABER) instrument that were used to simulate UAS brightness temperatures. Four NAVGEM experiments were performed during July 2010 that assimilated (i) no mesospheric observations, (ii) UAS data only, (iii) SABER and Microwave Limb Sounder (MLS) mesospheric temperatures only, and (iv) SABER, MLS, and UAS data. Zonal mean temperatures and observation − forecast differences for the UAS-only and SABER+MLS experiments are similar throughout most of the mesosphere, and show large improvements over the experiment assimilating no mesospheric observations, proving that assimilation of UAS radiances can provide a reliable large-scale constraint throughout the mesosphere for operational, high-altitude analysis. This is confirmed by comparison of solar migrating tides and the quasi-two-day wave in the mesospheric analyses. The UAS-only experiment produces realistic tidal and two-day wave amplitudes in the summer mesosphere in agreement with the experiments assimilating MLS and SABER observations, whereas the experiment with no mesospheric observations produces excessively strong mesospheric winds and two-day wave amplitudes.

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