Operational Global Atmospheric Prediction System Research Articles (Page 6)

The evolution of the upper ocean in the strong seasonally forced Arabian Sea, as observed by a mooring deployed in 1994–1995, is investigated using the Naval Research Laboratory Layered Ocean Model (NLOM). Model simulations were sensitive to the choice of surface wind products used for forcing, and results are reported for simulations forced by monthly mean climatologies and 12 hourly 1994–1995 wind products from two operational atmospheric forecast models, the European Centre for Medium‐Range Weather Forecast model and the Navy Operational Global Atmospheric Prediction System model of Fleet Numerical Meteorology and Oceanography Center (FNMOC). The NLOM yields the best prediction of sea surface temperature (SST) and mixed layer depth when using FNMOC forcing. Surface cooling is found to be responsible for the seasonal SST minimum during the NE monsoon. Heat advection is found to be important for supporting the surface cooling during the second half of the NE monsoon. Strong entrainment and appreciable advective cooling are responsible for the SST minimum of the SW monsoon. The NLOM wind experiments strongly suggest that thermal convection may be important in the central Arabian Sea during the winter months.

This study examines the simulation quality of the surface heat flux fields produced during a climate simulation of the Navy Operational Global Atmospheric Prediction System, version 3.4, with a reduced spectral truncation of T63 and 18 levels (herineafter referred to as NOGAPS‐CL). Comparisons are made between a 17‐year NOGAPS‐CL simulation using monthly sea surface temperatures as surface boundary conditions and a number of validating data sets consisting of ship, satellite, and/or reanalysis‐based surface heat fluxes, precipitation, top of the atmosphere radiation budget, water vapor, cloud frequency, surface wind stress, and tropospheric winds. In this extended, long‐range integration, NOGAPS‐CL underpredicts the net surface shortwave flux in much of the subtropical oceans and overpredicts the net shortwave flux in the western Pacific warm pool and the midlatitude oceans, when compared to several satellite‐derived climatological data sets. In addition, NOGAPS‐CL over predicts the latent heat flux in much of the subtropics and under predicts the latent heat flux over the northern ocean western boundary currents and under the storm track regions that extend eastward from them. These shortwave and evaporation biases combine to produce errors in the surface net heat flux, with too little heat entering the subtropical/tropical oceans and too much heat loss in the midlatitudes oceans. Examination of related quantities indicates that the tropical climate biases are coupled to shortcomings in the convective cloud and/or boundary layer parameterizations which leads to the premature release of moist instability from the boundary layer in regions just outside the deep convective zones. This leads to enhanced climatological cloudiness, rainfall, and surface evaporation, as well as to a reduction in the surface shortwave flux and outgoing longwave radiation (OLR), in the subtropical regions. Furthermore, because of this early release of the moist static energy, there is a reduction in clouds, rainfall and water vapor content, as well as enhanced surface shortwave flux and outgoing longwave radiation, in the deep convective zones. The reduction in rainfall and enhanced OLR reduces the strength of the tropical large‐scale circulation, which in turn reduces the strength of the subsidence in the subtropical regions which normally acts to suppress the convection processes in these regions. The implications of these results are discussed in terms of the relationship among the forecast model climatological surface fluxes, convection, clouds, and the dynamical processes, as well as their similarities to other climate models and their possible impact on the simulation of transient systems.

The Navy Operational Global Atmospheric Prediction System (NOGAPS) includes a state-of-the-art spectral forecast model similar to models run at several major operational numerical weather prediction (NWP) centers around the world. The model, developed by the Naval Research Laboratory (NRL) in Monterey, California, has run operational at the Fleet Numerical Meteorological and Oceanographic Center (FNMOC) since 1982, and most recently is being run on a Cray C90 in a multi-tasked configuration. Typically the multi-tasked code runs on 10 to 15 processors with overall parallel efficiency of about 90%. resolution is T159L30, but other operational and research applications run at significantly lower resolutions. A scalable NOGAPS forecast model has been developed by NRL in anticipation of a FNMOC C90 replacement in about 2001, as well as for current NOGAPS research requirements to run on DOD High-Performance Computing (HPC) scalable systems. The model is designed to run with message passing (MPI). Model design criteria include bit reproducibility for different processor numbers and reasonably efficient performance on fully shared memory, distributed memory, and distributed shared memory systems for a wide range of model resolutions. Results for a wide range of processor numbers, model resolutions, and different vendor architectures are presented. Single node performance has been disappointing on RISC based systems, at least compared to vector processor performance. This is a common complaint, and will require careful re-examination of traditional numerical weather prediction (NWP) model software design and data organization to fully exploit future scalable architectures.

10.1016/0967-0653(93)95787-7

Abstract The Marine Meteorology Division of the Naval Research Laboratory (NRL), assisted by the Fleet Numerical Meteorology and Oceanography Center, has performed global and mesoscale reanalyses to support the study of Gulf War illness. Realistic and quantitatively accurate atmospheric conditions are needed to drive dispersion models that can predict the transport and dispersion of chemical agents that may have affected U.S. and other coalition troops in the hours and days following the demolition of chemical weapons at Khamisiyah, Iraq, at approximately 1315 UTC 10 March 1991. The reanalysis was conducted with the navy’s global and mesoscale analysis and prediction systems: the Navy Operational Global Atmospheric Prediction System and the NRL Coupled Ocean–Atmosphere Mesoscale Prediction System. A comprehensive set of observations has been collected and used in the reanalysis, including unclassified and declassified surface reports, ship and buoy reports, observations from pibal and rawinsonde, and retr...

Abstract The role of the annual-mean climate on seasonal and interannual variability in the tropical Pacific is investigated by means of a coupled atmosphere–ocean general circulation model. The atmospheric component of this coupled model is the Naval Operational Global Atmospheric Prediction System and the oceanic component is the Geophysical Fluid Dynamics Laboratory Modular Ocean Model. Three sets of experiments are conducted. In case A, no annual-mean flux adjustment is applied so that the coupled model generates its own time-mean state. In case B, an annual-mean flux adjustment for SST is applied. In case C, both the annual-mean SST and surface wind are adjusted. It is found that a realistic simulation of both the seasonal and interannual variations can be achieved when a realistic annual-mean state is presented. The long-term (40 yr) simulations of the coupled GCM demonstrate the importance of the annual-mean climate on seasonal and interannual variability in the Tropics. The mechanism that causes a...

The Yellow Sea is a shallow basin writh an average depth of 44 m located between China and the Korean Peninsula. One of the dominant ocean circulation features of the Yellow Sea is a warm wrater intrusion known as the Yellow Sea Warm Current. This feature is present throughout the year but reaches its farthest northward extension in winter. The circulation of the Yellow, East China, and Bohai Seas was modeled using the Princeton Ocean Model to better understand the dynamics of the Yellow Sea Warm Current. The horizontal resolution of the model varies from 8 km in the Yellow Sea to 25 km in the East China Sea. Twenty‐four sigma levels are used to define the vertical structure. The model uses daily atmospheric forcing from the Navy Operational Global Atmospheric Prediction System for 1993. Open boundary conditions are applied at the Taiwan Strait, the Tsushima (Korea) Strait, an area south of Taiwan, and the Tokara Strait, with a closed boundary south of the Ryukyu Islands. The model results are examined to determine the effect of the wind on the northward extension of the warm water intrusion, using both water mass characteristics and northward velocity components. Sensitivity tests and spectrum analyses, performed to study the influence of the wind on the Yellow Sea Warm Current, show that winds modify the pathway and extent of the Yellow Sea Warm Current. The current's origin, however, appears to be due to external forcing from the current systems developed in the East China Sea.

Evaluation of the effect of meteorological data resolution on Lagrangian particle dispersion simulations using the ETEX experiment

The sensitivity of the atmospheric general circulation model of the Navy Operational Global Atmospheric Prediction System to a parameterization of convective triggering by atmospheric boundary layer thermals is investigated. The study focuses on the western Pacific warm pool region and examines the results of seasonal integrations of the model for the winter of 1987/88. A parameterization for thermal triggering of deep convection is presented that is based on a classification of the unstable boundary layer. Surface-based deep convection is allowed only for boundary layer regimes associated with the presence of thermals. The regime classification is expressed in terms of a Richardson number that reflects the relative significance of buoyancy and shear in the boundary layer. By constraining deep convection to conditions consistent with the occurrence of thermals (high buoyancy to shear ratios), there is a significant decrease in precipitation over the southern portion of the northeast trade wind zone in the tropical Pacific and along the ITCZ. This decrease in precipitation allows for an increased flux of moisture into the region south of the equator corresponding to the warmest portion of the Pacific warm pool. Improvements in the simulated distribution of precipitation, precipitable water, and low-level winds in the tropical Pacific are demonstrated. Over the western Pacific, the transition from free convective conditions associated with thermals to forced convective conditions is found to be primarily due to variations in mixed layer wind speed. Low-level winds thus play the major role in regulating the ability of thermals to initiate deep convection. The lack of coupling with the ocean in these simulations may possibly produce a distorted picture in this regard.

Abstract Experimental wind datasets were derived for two time periods (13–20 July and 24 August–10 September 1995) from GOES-8 observations processed at the University of Wisconsin Cooperative Institute for Meteorological Satellite Studies (UW CIMSS). The first dataset was focused on Tropical Storm Chantal, and the second dataset was focused on the multiple-storm environment that included Hurricanes Humberto, Iris, and Luis. Both datasets feature a processing and quality control strategy designed to optimize the quantity and content of geostationary satellite-derived winds in the vicinity of tropical cyclones. Specifically, the winds were extracted from high-density targets obtained from multispectral imagery, which included three water vapor bands (6.7, 7.0, and 7.3 μm), infrared, and visible. The Navy Operational Global Atmospheric Prediction System (NOGAPS) was used as the vehicle to determine the impact of these winds upon tropical cyclone track forecasts. During the 1995 Atlantic hurricane season the...

The Bohai Bay and Yellow Sea experience sea surface height (SSH) changes of 20 cm and larger during wintertime northerly and southerly wind bursts that have a time scale of a few days. These large SSH changes give rise to coastal shelf waves that subsequently propagate southward along the Chinese coast. Two models provide observations of these waves. The first one is a statistical model based on four years of TOPEX/POSEIDON (T/P) altimeter SSH observations and Navy Operational Global Atmospheric Prediction System (NOGAPS) wind stress fields. The second model is a numerical model forced by the wind stress. The numerical model provides an objective interpretation of the wind stress response based on dynamical equations. The statistical model is based on observations with a linear response to the wind forcing and thus complements the numerical model. The observed waves closely resemble gravest mode shelf waves derived by analytical solutions.

Abstract Existing theories of the Madden–Julian oscillation neglect the feedback between the modification of sea surface temperature by the convection and development of a convective cluster itself. The authors show that the convection-generated SST gradient plays an important role in cluster propagation and development. The relative importance of radiative and evaporative fluxes in SST regulation is also discussed. Various Tropical Ocean Global Atmosphere Coupled Ocean–Atmosphere Response Experiment and Central Equatorial Pacific Experiment observation platforms are used to estimate the effects of equatorial convection on SST changes during March 1993. The data include drifting buoys and TAO-buoy array measurements, combined with the Navy Operational Global Atmospheric Prediction System analyzed surface wind fields and Geostationary Meteorological Satellite cloud-top temperatures. It is shown that during the equatorial convection episode SST is decreasing under and to the west of the convective heat sour...

Abstract Cloud radiative effects are represented in simulations with the general circulation model of the Navy Operational Global Atmospheric Prediction System (NOCAPS) using ingested cloud field data from the ISCCP dataset rather than model-diagnosed cloud fields. The primary objective is to investigate the extent to which the high temporal resolution ISCCP data can be used to improve the simulation of cloud radiative effects on the general circulation in GCM simulations much as observed sea surface temperatures (SSTs) have been used to avoid simulation errors resulting from inaccurately modeled SSTs. Experiments are described that examine the degree to which uncertainties in cloud field vertical structure impair the utility of the observed cloud data in this regard, as well as the extent to which unrealistic combinations of cloud radiative forcing and other physical processes may affect GCM simulations. The potential for such unrealistic combinations stems from the lack of feedback to the cloud fields i...

Abstract The ability of an atmospheric general circulation model to simulate the observed primary modes of intraseasonal variability in the Northern Hemisphere upper-tropospheric winds during boreal winter is examined. The model used is the Navy Operational Global Atmospheric Prediction System. The authors examine differences between the observed and modeled modes of variability in the context of various model deficiencies, where the observed modes are derived from the European Centre for Medium-Range Weather Forecasts analyses. Rotated empirical orthogonal function analysis is used to determine the primary modes of variability in the Pacific and Atlantic regions. EOFs are computed for both the zonal and meridional wind components. Time-lagged composite analysis is used to examine the temporal evolution of these modes, as well as their relationship to tropical convection. Wave activity flux vectors are used to examine further the characteristics of these intraseasonal modes and their relationship to tropi...

The method of physical initialization, in which one attempts to match observed and model-generated diabatic processes prior to commencing a forecast, is applied to a T47 version of the Navy Operational Global Atmospheric Prediction System (NOGAPS). Particular emphasis is devoted to the matching of observed convective rainfall, inferred from the Microwave Sounding Unit (MSU), with that produced by NOGAPS' Arakawa-Schubert cumulus parameterization scheme. To accomplish the matching, the model's specific humidity field is adjusted at each time step during a preforecast integration period. This adjustment consists of adding a perturbation in relative humidity, with linear vertical profile, to the model's relative humidity; the amplitude of the perturbation is proportional to the difference between observed and model precipitation rates. Results show significantly improved rainfall accumulations during the period in which the model is forced with the observed precipitation. However, this positive impact largely disappears within 24 hours after the forcing is removed, that is, the model has difficulty in maintaining the assimilated rainfall on its own. Possible explanations for this problem are considered, one of the more likely being the model's low resolution.

Abstract In 1991, Typhoon Nat over the western North Pacific made four directional reversals due to its interactions with two other tropical cyclones (TCs), Luke and Mireille. This paper analyzes the performance of three global and two regional models in predicting the movement of Nat to determine the extent to which each of the models was capable of correctly simulating such binary interactions. The global models include those of the European Centre for Medium-Range Weather Forecasts (ECMWF) and the U.K. Meteorological Office (UKMO) and the U.S. Navy Operational Global Atmospheric Prediction System (NOGAPS). The regional models studied are the Typhoon Model (TYM) of the Japan Meteorological Agency and the One-Way Tropical Cyclone Model (OTCM) of the U.S. Navy. It was found that in general the global models made better predictions than the regional ones, especially when the large-scale flow was well defined. During the interaction periods, the UKMO model and the TYM were the best. The ECMWF model was also...

Abstract In June 1990, the assimilation of synthetic tropical cyclone observations into the Navy Operational Global Atmospheric Prediction System (NOGAPS) was initiated at Fleet Numerical Oceanography Center (FNOC). These observations are derived directly from the information contained in the tropical cyclone warnings issued by the Joint Typhoon Warning Center (JTWC) and the National Hurricane Center. This paper describes these synthetic observations, the evolution of their use at FNOC, and the details of their assimilation into NOGAPS. The results of a comprehensive evaluation of the 1991 NOGAPS tropical cyclone forecast performance in the western North Pacific are presented. NOGAPS analysis and forecast position errors were determined for all tropical circulations of tropical storm strength or greater. It was found that, after the assimilation of synthetic observations, the NOGAPS spectral forecast model consistently maintained the tropical circulations as evidenced by detection percentages of 96%, 90% ...

The response of a general circulation model to a change in its treatment of cloud solar forcing is investigated. Radiation field data from the forecast model of the Navy Operational Global Atmospheric Prediction System for five Julys (1979–1983) are presented in an investigation of the effect of a change from grid cell averaged clouds to maximally overlapping clouds in the model's solar radiation scheme. The model results are compared with Nimbus 7 Earth Radiation Budget top of the atmosphere (TOA) solar and longwave irradiances and with derived surface solar irradiance data. Although the maximal overlap scheme performs considerably better than the grid cell averaging scheme (reducing maximum deficiencies in TOA and surface solar irradiance by over 100 W m−2), significant errors remain. The simulated correlation between TOA net solar and longwave irradiance improves at low latitudes in the northern hemisphere, with little change at higher latitudes. This improved correlation is consistent with the greater consistency between the treatments of solar and longwave cloud radiative forcing brought to the model by the new solar radiation scheme. The change in the radiation treatment is shown to have the greatest direct effect on solar radiation over convective regions, a consequence of the scarcity of optically thick clouds produced by the model's cloud parameterization in other regions. The model responds with an increase in convective activity over land and an increase in the flux of moisture from sea to land. Planetary cooling over the oceans increases because of a decrease in cloud cover. From mid to high latitudes in the northern hemisphere, there are scattered regions of increased cloud water content associated with increased tropospheric temperatures. Over land the model response in terms of TOA downwelling solar irradiance tends to counter the increase in solar irradiance caused by the model change in all latitudinal zones in the northern hemisphere. This response is caused primarily by changes in the cloud fields, which thus act as a negative feedback following the change in cloud solar forcing. The significance of this response is examined with respect to the perturbation in solar irradiance represented by the model change. An estimate of this perturbation is obtained by taking the difference in solar irradiance diagnosed by the two cloud solar forcing treatments for simulations employing the grid cell averaging scheme. The response is significantly greater in magnitude in the tropics than at midlatitudes, both in an absolute sense and as a percentage of this perturbation. Because TOA longwave irradiance exhibits a positive response in the tropics, and a negative response at midlatitudes, however, the percentage response in net TOA downwelling irradiance is actually greater in magnitude at midlatitudes. In a number of regions the cloud feedback is very large, showing the importance for cloud field prediction of improvements in the treatment of cloud solar forcing. Such cloud feedback also explains the small improvement seen here in the prediction of TOA solar irradiance in certain regions/Increases in surface sensible heating and longwave cooling are generally considerably less than increases in surface latent heating, though a notable exception occurs in arid central Asia. A large ground temperature increase in that region is strongly correlated at low levels with the atmospheric temperature increase observed at midlatitudes in the northern hemisphere.

Abstract The purpose of this paper is to discuss the major systematic errors of the U.S. Navy Operational Global Atmospheric Prediction System (NOGAPS), version 3.2, and to describe several tuning experiments of NOGAPS parameterizations. It is found that despite its overall good performance, major systematic errors exist in the forecast model. These errors lead to a warmer atmosphere with less precipitation and eddy kinetic energy than is observed. Some of the errors may be attributed to the lack of horizontal and vertical resolution, but most of the errors are due to inadequacies and incorrect assumptions in the physical parameterizations. We present a list of the systematic errors of the operational 5-day forecasts and results of a 1-yr integration with climatological sea surface temperatures. One of the prominent features of NOGAPS integrations is a large diurnal oscillation in the global mean averages. This oscillation is traced to large differences in total albedo over the land and sea areas. We pres...

The paper evaluates the meteorological quality and operational utility of the Navy Operational Global Atmospheric Prediction System (NOGAPS) in forecasting tropical cyclones. It is shown that the model can provide useful predictions of motion and formation on a real-time basis in the western North Pacific. The meterological characteristics of the NOGAPS tropical cyclone predictions are evaluated by examining the formation of low-level cyclone systems in the tropics and vortex structure in the NOGAPS analysis and verifying 72-h forecasts. The adjusted NOGAPS track forecasts showed equitable skill to the baseline aid and the dynamical model. NOGAPS successfully predicted unusual equatorward turns for several straight-running cyclones.