A new coupled global NCEP Reanalysis for the period 1979-present is now available, at much higher temporal and spatial resolution, for climate studies. T he first reanalysis at NCEP (all acronyms are defined in the appendix), conducted in the 1990s, resulted in the NCEP-NCAR reanalysis (Kalnay et al. 1996), or R1 for brevity, and ultimately covered many years, from 1948 to the present (Kistler et al. 2001). It is still being executed at NCEP, to the benefit of countless users for monthly, and even daily, updates of the current state of the atmosphere. At the same time, other reanalyses were being conducted, namely, ERA-15 (Gibson et al. 1997) was executed for a more limited period (1979-93) at the ECMWF, COLA conducted a short reanalysis covering the May 1982-November 1983 period (Paolino et al. 1995), and NASA GSFC conducted a reanalysis covering the 1980-94 period (Schubert et al. 1997). The general purpose of conducting reanalyses is to produce multiyear global state-of-the-art gridded representations of atmospheric states, generated by a constant model and a constant data assimilation system. To use the same model and data assimilation over a very long period was the great advance during the 1990s, because gridded datasets available before 1995 had been created in real time by ever-changing models and analysis methods, even by hand analyses prior to about 1965. The hope was that a reanalysis,

NCEP's newly developed second-generation operational seasonal forecast system aims at a seamless suite of forecasts and provides much more comprehensive datasets for users.n April 2000, a new dynamical seasonal prediction system was introduced at the National Centers for Environmental Prediction (NCEP; the acronyms used in this paper are summarized in the appendix). The transition to the new system was hastened by a computer fire in September 1999 and subsequent changeover from a Cray C90 to an IBM-SP computer system. This article will be a reference for people who are using the NCEP numerical seasonal forecast products.The first-generation dynamical seasonal prediction model was based on the notion that the seasonal predictability in the Northern Hemisphere extratropics

No abstract

[1] Evidence is presented that exchanges of water and energy between the vegetation and the atmosphere play an important role in east Asian and West African monsoon development and are among the most important mechanisms governing the development of the monsoon. The results were obtained by conducting simulations for five months of 1987 using a general circulation model (GCM) coupled with two different land surface parameterizations, with and without explicit vegetation representations, referred to as the GCM/vegetation and the GCM/soil, respectively. The two land surface models produced similar results at the planetary scale but substantial differences at regional scales, especially in the monsoon regions and some of the large continental areas. In the simulation with GCM/soil, the east Asian summer monsoon moisture transport and precipitation were too strong in the premonsoon season, and an important east Asian monsoon feature, the abrupt monsoon northward jump, was unclear. In the GCM/ vegetation simulation, the abrupt northward jump and other monsoon evolution processes were simulated, such as the large-scale turning of the low-level airflow during the early monsoon stage in both regions. With improved initial soil moisture and vegetation maps, the intensity and spatial distribution of the summer precipitation were also improved. The two land surface representations produced different longitudinal and latitudinal sensible heat gradients at the surface that, in turn, influenced the low-level temperature and pressure gradients, wind flow (through geostrophic balance), and moisture transport. It is suggested that the great east-west thermal gradient may contribute to the abrupt northward jump and the latitudinal heating gradient may contribute to the clockwise and counterclockwise turning of the low-level wind. The results showed that under unstable atmospheric conditions, not only low-frequency mean forcings from the land surface, such as monthly mean albedo, but also the perturbation processes of vegetation were important to the monsoon evolution, affecting its intensity, the spatial distribution of precipitation, and associated circulation at the continental scale.

[1] The upper atmosphere and ionosphere exhibit variability on spatial and temporal scales characteristic of tides and planetary waves originating in the lower atmosphere. To study their generation, vertical propagation, possible nonlinear interactions and effects a new Whole Atmosphere Model (WAM) has been developed as part of the Integrated Dynamics through Earth's Atmosphere (IDEA) project. WAM is a 150-layer general circulation model based on the US National Weather Service's operational Global Forecast System (GFS) model extended upward to cover the atmosphere from the ground to about 600 km. First simulations reveal the presence of migrating and nonmigrating tides modulated at planetary wave periods in the upper atmosphere. Comparisons with observations from the TIMED satellite in the lower thermosphere show that WAM reproduces the seasonal variability of tides remarkably well, including the diurnal eastward harmonic with zonal wavenumber 3 (DE3) recently implicated in the observed spatial morphology of the ionosphere. Citation: Akmaev, R.

Abstract. Here we present the first steps in developing a global multi-model aerosol forecasting ensemble intended for eventual operational and basic research use. Drawing

The National Centers for Environmental Prediction (NCEP)/Environmental Modeling Center regional spectral model (RSM) has been improved in several aspects since Juang and Kanamitsu. The major improvements of RSM are its efficiency and functionality. The change of the map factor in the semi-implicit scheme from a mean value to maximal value over the regional domain, the relaxation of the lateral boundary from explicit method to implicit method (or simple blending), and the local diffusion over areas of strong wind allowed the doubling of the model computational time step. The model physics was upgraded with the improvements in the operational global spectral model (GSM) and with an additional explicit cloud scheme. An option to run in either hydrostatic or nonhydrostatic mode has been introduced. Another option to run on a CRAY machine or on a workstation has been fully tested. The nesting process has been changed to provide the capability of nesting into a coarse-resolution RSM, besides the GSM, in a one-way fashion. Thus, multinesting becomes possible, even with different map projections. Regional data assimilation with a gridpoint version of statistical interpolation and the three-dimensional variational method on sigma surfaces has been incorporated. All the output has been encoded in GRIB format, so it can be read on different machines. The authors have tested the improved functionalities of the RSM over a broad range of applications, at resolutions between 80 and 10 km. The daily routine experimental forecasts over North America have acceptable performance. Because the perturbation method, used in the RSM, results in smaller computational error than the full field method, and because the consistency between the GSM and RSM allows for a better treatment of the lateral boundary, the RSM could be used to enhance the reanalysis and regional climate simulations that have long-range integrations. The RSM is also used in the regional ensemble experiments at NCEP. The model was also applied in case studies, such as the case of PYREX in the regional COMPARE project. Several institutions both in the United States and overseas started using the RSM, mostly for regional short-range forecast and climate modeling studies. The RSM has been scheduled to implement into operations at NCEP to possibly enhance the guidance on aviation and on daily weather forecast over Hawaii. The current version of the RSM is available to any institution requesting from the director of NCEP.

Abstract. The first simulation experiment and output archives of the Project to Intercompare Regional Climate Simulations (PIRCS) is described. Initial results from simulations of the summer 1988 drought over the central United States indicate that limited-area models forced by large-scale information at the lateral boundaries reproduce bulk temporal and spatial characteristics of meteorological fields. In particular, the 500 hPa height field time average and temporal variability are generally well simulated by all participating models. Model simulations of precipitation episodes vary depending on the scale of the dynamical forcing. Organized synoptic-scale precipitation systems are simulated deterministically in that precipitation occurs at close to the same time and location as observed (although amounts may vary from observations). Episodes of mesoscale and convective precipitation are represented in a more stochastic sense, with less precise agreement in temporal and spatial patterns. Simulated surface energy fluxes show broad similarity with the First International Satellite Land Surface Climatology Project (ISLSCP) Field Experiment (FIFE) observations in their temporal evolution and time average diurnal cycle. Intermodel differences in midday Bowen ratio tend to be closely associated with precipitation differences. Differences in daily maximum temperatures also are linked to Bowen ratio differences, indicating strong local, surface influence on this field. Although some models have bias with respect to FIFE observations, all tend to reproduce the synoptic variability of observed daily maximum and minimum temperatures. Results also reveal the advantage of an intercomparison in exposing common tendencies of models despite their differences in convective and surface parameterizations and different methods of assimilating lateral boundary conditions.