Roy L. Jenne

The NCEP/NCAR 40-Year Reanalysis Project

The NCEP and NCAR are cooperating in a project (denoted “reanalysis”) to produce a 40-year record of global analyses of atmospheric fields in support of the needs of the research and climate monitoring communities. This effort involves the recovery of land surface, ship, rawinsonde, pibal, aircraft, satellite, and other data; quality controlling and assimilating these data with a data assimilation system that is kept unchanged over the reanalysis period 1957–96. This eliminates perceived climate jumps associated with changes in the data assimilation system. The NCEP/NCAR 40-yr reanalysis uses a frozen state-of-the-art global data assimilation system and a database as complete as possible. The data assimilation and the model used are identical to the global system implemented operationally at the NCEP on 11 January 1995, except that the horizontal resolution is T62 (about 210 km). The database has been enhanced with many sources of observations not available in real time for operations, provided by differe...

The NCEP–NCAR 50-Year Reanalysis: Monthly Means CD-ROM and Documentation

The National Centers for Environmental Prediction (NCEP) and National Center for Atmospheric Research (NCAR) have cooperated in a project (denoted “reanalysis”) to produce a retroactive record of more than 50 years of global analyses of atmospheric fields in support of the needs of the research and climate monitoring communities. This effort involved the recovery of land surface, ship, rawinsonde, pibal, aircraft, satellite, and other data. These data were then quality controlled and assimilated with a data assimilation system kept unchanged over the reanalysis period. This eliminated perceived climate jumps associated with changes in the operational (real time) data assimilation system, although the reanalysis is still affected by changes in the observing systems. During the earliest decade (1948–57), there were fewer upper-air data observations and they were made 3 h later than the current main synoptic times (e.g., 0300 UTC), and primarily in the Northern Hemisphere, so that the reanalysis is less reliable than for th later 40 years. The reanalysis data assimilation system continues to be used with current data in real time (Climate Data Assimilation System or CDAS), so that its products are available from 1948 to the present. The products include, in addition to the gridded reanalysis fields, 8-day forecasts every 5 days, and the binary universal format representation (BUFR) archive of the atmospheric observations. The products can be obtained from NCAR, NCEP, and from the National Oceanic and Atmospheric Administration/ Climate Diagnostics Center (NOAA/CDC). (Their Web page addresses can be linked to from the Web page of the NCEP–NCAR reanalysis at http:// wesley.wwb.noaa.gov/Reanalysis.html.) This issue of the Bulletin includes a CD-ROM with a documentation of the NCEP–NCAR reanalysis (Kistler et al. 1999). In this paper we present a brief summary and some highlights of the documentation (also available on the Web at http://atmos.umd.edu/ ~ekalnay/). The CD-ROM, similar to the one issued with the March 1996 issue of the Bulletin, contains 41 yr (1958–97) of monthly means of many reanalysis variables and estimates of precipitation derived from satellite and in situ observations (see the appenThe NCEP–NCAR 50-Year Reanalysis: Monthly Means CD-ROM and Documentation

A Comprehensive Ocean-Atmosphere Data Set

Development is described of a Comprehensive Ocean-Atmosphere Data Set (COADS)—the result of a cooperative project to collect global weather observations taken near the oceans surface since 1854, primarily from merchant ships, into a compact and easily used data set. As background, a historical overview is given of how archiving of these marine data has evolved from 1854, when systematic recording of shipboard meteorological and oceanographic observations was first established as an international activity. Input data sets used for COADS are described, as well as the processing steps used to pack input data into compact binary formats and to apply quality controls for identification of suspect weather elements and duplicate marine reports. Seventy-million unique marine reports for 1854–1979 were output from initial processing. Further processing is described, which created statistical summaries for each month of each year of the period, using 2° latitude × 2° longitude boxes. Monthly summary products are a...

The Half-Yearly Oscillations in the Tropics of the Southern Hemisphere

Abstract In the tropics of the Southern Hemisphere the zonal wind in the troposphere above the 500-mb level has a well defined half-yearly oscillation with westerly maxima (easterly minima) in May and November. It is demonstrated that the oscillation is associated with second harmonics of opposite phase in the temperature above the equator and in the subtropics. The temperature oscillations are tentatively explained as being the result of an intensification of vertical motions from autumn to winter. The half-yearly temperature oscillations reverse phase near the tropopause, and again near the 50-mb level. Above this level they are thus in the same phase as in the upper troposphere. The phase reversals imply that the second harmonic of the zonal component of the thermal wind likewise changes phase twice. A marked longitudinal asymmetry is observed with the oscillations being considerably stronger in the Eastern than in the Western Hemisphere.

Oscillations in the Winter Stratosphere: Part 1. Description

Abstract Two patterns dominate changes of monthly mean temperature and pressure-height in the stratosphere. In the one, the middle latitudes vary oppositely to low and high latitudes, and in the other the changes at higher latitudes are out of phase with those at lower latitudes. A shorter trend consisting of opposite changes at middle and high latitudes is superposed on the above variations which a cross-spectrum analysis shows has a preferred time scale of one to three weeks. The contrast between middle and high latitudes thus undergoes a series of corresponding fluctuations and we show that these are associated with amplitude changes in waves 1 and 2 in that the meridional contrast decreases when the amplitude of one or both waves is large, and vice versa.

Estimates of Seasonal Mean Temperature, Using Persistence between Seasons

Abstract We have tested three methods of estimating the level of a coming seasons mean temperature at a station where the statistical association between two selected seasons is as high as one can expect in extratropical regions. The methods are contingency tables, regression equations, and the use of the last few decades if there is a trend at the station which will separate the mean of these decades a fair distance from the long-term mean. A moderate amount of skill was achieved, but the degree of seasonal association in our test case was exceptionally high, and generally these methods will provide only a small improvement over a probability based on knowing only the observed frequency distribution.

The Kinetic Energy of Large-Scale Atmospheric Motion in Wavenumber-Frequency Space: 11. Mid-Troposphere of the Southern Hemisphere

Abstract The wavenumber-frequency spectra of the kinetic energy of the zonal and meridional components of the motion in the mid-troposphere of the Southern Hemisphere show a definite spectral domain of wave activities. This spectral domain is generally oriented from a region of low wavenumbers and low frequencies to a region of high wavenumber and negative frequencies designated for waves moving from west to east. The wavenumber-frequency spectra of the large-scale motion indicate that wave activities in the summer have the same intensity as in the winter in the Southern Hemisphere, whereas in the Northern Hemisphere the wave intensity in summer is about 50% of that in winter. The frequency spectra of the kinetic energy of the zonal and meridional components of the motion show similar distributions at all latitudes and seasons for the respective components of the motion. In the high-frequency range, the frequency spectra of both the zonal and meridional motion are approximately proportional to the –1 powe...

Spectral characteristics of the meridional transport of angular momentum in the mid-troposhere of the Southern Hemisphere

SummaryThe wavenumber-frequency spectra of the meridional flux of angular momentum at 20°, 30°, 40°, 50°, 60° and 70°S, at 500 mb, show a definite domain of wave interactions between the zonal and meridional components of the velocity at various latitudes. In middle latitudes, the spectral band of the meridional flux of angular momentum is oriented from a region of low wavenumbers and low frequencies to a region of high wavenumbers and negative frequencies assigned for waves moving from west to east. In low latitudes, however, the spectral domain is confined to a narrow band centered near the zero frquency.In contrast to the meridional flux of angular momentum in the Northern Hemisphere in which the intensity in winter is about twice that in Summer, in the Southern Hemisphere the meridional flux shows same intensity for all seasons.In the Southern Hemisphere, most of the meridional flux of angular momentum is directed toward the south pole and is accomplished by the eastward moving waves. In the Northern Hemisphere, however, most of the meridional flux is directed toward the north pole and is contributed by the stationary waves.

Data collection and management for Global Energy and Water Cycle Experiment (GEWEX) Continental‐Scale International Project (GCIP)

[1] The Global Energy and Water Cycle Experiment (GEWEX) Continental-Scale International Project (GCIP) was focused on the Mississippi River basin to take advantage of the existing meteorological and hydrological networks that were upgraded with new Doppler radars, wind profilers, and automatic weather stations together with an upgraded version of the Geostationary Operational Environmental Satellites (GOES) operated by the United States. The Mississippi River basin encompasses a wide range of climate, soil moisture conditions, vegetation types, and surface topography. The GCIP Science Plan identified the major phase of GCIP as the 5-year Enhanced Observing Period (EOP), targeted for 1995 to 2000, during which original data sets would be assembled for the GCIP database. GCIP organized these data into in situ, model output and satellite remote sensing data. Data from three mesoscale models were included with the start dates ranging from May 1995 to April 1997. A number of GCIP Initial Data Sets (GIDS) were prepared, starting in 1993, to provide the data services support during the buildup period before the 5-year EOP. The data sets were compiled for on-line access by GCIP investigators and were also published on CD-ROM. A number of special data sets, in addition to the EOP data sets, were compiled during the course of GCIP. Some of the most significant special data sets are summarized in this paper.

Standard Deviations of 24-Hour 10-Mb Height and Temperature Changes in the Northern Hemisphere

Abstract This note deals with the standard deviations of 24-hr changes in 10-mb temperatures and heights. The standard deviations are differently distributed in disturbed and in quiet winter months. In the disturbed months their largest values form a coherent area at high latitudes; in the quiet months they surround the polar region as a ring with its center on the Atlantic side.