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William E. Klein
and
Gordon A. Hammons

Abstract

A new automated system of forecasting maximum and minimum surface temperatures in the conterminous United States has been developed. This system is based on the Model Output Statistics (MOS) approach which effectively combines numerical and statistical methods. A series of screening experiments is described, derivation and interpretation of the MOS equations are discussed, and sample statistics are presented. Verification results, comparing the MOS and perfect prog systems, are summarized. Operational aspects such as facsimile and teletype transmissions, are discussed, and recent changes in procedure are explained. The MOS system replaced the perfect prog technique in the operations of the National Weather Service in August 1973. This has resulted in increased accuracy of the autmated forecasts; at the same time we increased the station coverage from 131 to 228 cities in the conterminous United States.

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John R. Gerhardt
and
William E. Gordon

Abstract

Selected portions of microtemperature data obtained continuously and with near simultaneity at several levels up to six feet over a desert surface are plotted on expanded height-time coordinates. The resulting isotherm patterns are shown to be strikingly consistent at all levels and are qualitatively analyzed in relation to the turbulence field present. Correlation coefficients between temperature fluctuations simultaneously at two levels and at a point for various time intervals are evaluated and their variation with separation, time, wind speed, and thermal stability is discussed. Tentative intensity and scale measures of turbulence derived from iemperature data are presented.

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John R. Gerhardt
and
William E. Gordon

The propagation of radio waves above about 30 megacycles is seriously affected by certain weather phenomena. The meteorological aspects of this effect for a particular case are considered and a forecasting technique proposed.

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Samuel Levis
,
Gordon B. Bonan
,
Erik Kluzek
,
Peter E. Thornton
,
Andrew Jones
,
William J. Sacks
, and
Christopher J. Kucharik

Abstract

The Community Earth System Model, version 1 (CESM1) is evaluated with two coupled atmosphere–land simulations. The CTRL (control) simulation represents crops as unmanaged grasses, while CROP represents a crop managed simulation that includes special algorithms for midlatitude corn, soybean, and cereal phenology and carbon allocation. CROP has a more realistic leaf area index (LAI) for crops than CTRL. CROP reduces winter LAI and represents the spring planting and fall harvest explicitly. At the peak of the growing season, CROP simulates higher crop LAI. These changes generally reduce the latent heat flux but not around peak LAI (late spring/early summer). In midwestern North America, where corn, soybean, and cereal abundance is high, simulated peak summer precipitation declines and agrees better with observations, particularly when crops emerge late as is found from a late planting sensitivity simulation (LateP). Differences between the CROP and LateP simulations underscore the importance of simulating crop planting and harvest dates correctly. On the biogeochemistry side, the annual cycle of net ecosystem exchange (NEE) also improves in CROP relative to Ameriflux site observations. For a global perspective, the authors diagnose annual cycles of CO2 from the simulated NEE (CO2 is not prognostic in these simulations) and compare against representative GLOBALVIEW monitoring stations. The authors find an increased (thus also improved) amplitude of the annual cycle in CROP. These regional and global-scale refinements from improvements in the simulated plant phenology have promising implications for the development of the CESM and particularly for simulations with prognostic atmospheric CO2.

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Robert E. Dickinson
,
Joseph A. Berry
,
Gordon B. Bonan
,
G. James Collatz
,
Christopher B. Field
,
Inez Y. Fung
,
Michael Goulden
,
William A. Hoffmann
,
Robert B. Jackson
,
Ranga Myneni
,
Piers J. Sellers
, and
Muhammad Shaikh

Abstract

Most evapotranspiration over land occurs through vegetation. The fraction of net radiation balanced by evapotranspiration depends on stomatal controls. Stomates transpire water for the leaf to assimilate carbon, depending on the canopy carbon demand, and on root uptake, if it is limiting. Canopy carbon demand in turn depends on the balancing between visible photon-driven and enzyme-driven steps in the leaf carbon physiology. The enzyme-driven component is here represented by a Rubisco-related nitrogen reservoir that interacts with plant–soil nitrogen cycling and other components of a climate model. Previous canopy carbon models included in GCMs have assumed either fixed leaf nitrogen, that is, prescribed photosynthetic capacities, or an optimization between leaf nitrogen and light levels so that in either case stomatal conductance varied only with light levels and temperature.

A nitrogen model is coupled to a previously derived but here modified carbon model and includes, besides the enzyme reservoir, additional plant stores for leaf structure and roots. It also includes organic and mineral reservoirs in the soil; the latter are generated, exchanged, and lost by biological fixation, deposition and fertilization, mineralization, nitrification, root uptake, denitrification, and leaching. The root nutrient uptake model is a novel and simple, but rigorous, treatment of soil transport and root physiological uptake. The other soil components are largely derived from previously published parameterizations and global budget constraints.

The feasibility of applying the derived biogeochemical cycling model to climate model calculations of evapotranspiration is demonstrated through its incorporation in the Biosphere–Atmosphere Transfer Scheme land model and a 17-yr Atmospheric Model Inter comparison Project II integration with the NCAR CCM3 GCM. The derived global budgets show land net primary production (NPP), fine root carbon, and various aspects of the nitrogen cycling are reasonably consistent with past studies. Time series for monthly statistics averaged over model grid points for the Amazon evergreen forest and lower Colorado basin demonstrate the coupled interannual variability of modeled precipitation, evapotranspiration, NPP, and canopy Rubisco enzymes.

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