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Glenn H. White

Abstract

Blackmon (1976) used spherical harmonics to determine the root-mean-square (rms) 500 mb geo-potential height in various two-dimensional wavenumber regimes. This paper extends his analysis to 1000 mb and presents for both levels the ratio of rms Z in different wavenumber regimes. This ratio shows the relative spatial scale of atmospheric disturbances. Synoptic-scale disturbances dominate the midlatitude oceans, while planetary waves are most important in high and low latitudes. In summer planetary waves are more important at 1000 mb than at 500 mb.

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Glenn H. White

Abstract

The three-dimensional structure of the extratropical Northern Hemisphere summertime general circulation is documented by making use of twice-daily operational analyses at nine pressure levels (1000–100 mb) for 12 summers (1966–77). Two distinct regimes of standing waves quite unlike the wintertime standing waves appear: a subtropical regime which is clearly a monsoonal response to thermal forcing, and a higher latitude regime in which the standing waves are of smaller scale and much weaker than in winter and tend to be equivalent barotropic in structure with almost no vertical tilt in the mid- and upper troposphere.

While the transient eddies shift poleward from their wintertime location and are weaker in summer, their properties and relation to the mean flow are much the same as Blackmon et al. (1977), Lau (1978, 1979a,b) and Lau and Wallace (1979) found for the winter. In both seasons the regions of strongest transient activity generally coincide with the regions where the height scale of the most unstable baroclinic wave derived by Charney (1947) is large compared to the atmospheric scale height. An exception occurs to the north of the Himalayas where the effect of topography severely limits baroclinic instability.

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Glenn H. White

Abstract

Wintertime and summertime mean 500 mb vertical velocity fields for the extratropical Northern Hemisphere are calculated by several methods from general circulation statistics compiled from National Meteorological Center (NMC) operational analyses for 11 winters and 12 summers and are compared to each other and to seasonal mean patterns of cloudiness and precipitation. The methods are: 1) seasonal averages of NMC 6 h forecasts; 2)solution of the quasi-geostrophic omega equation in the form introduced by Hoskins et al. (1978) involving the Q vector; and 3) integration of the continuity equation employing the divergence calculated as a residual from the seasonal mean vorticity budget. In addition, the adiabatic vertical velocity is calculated from the thermodynamic equation. Plots of the seasonal mean Q vector indicate the pattern of ageostrophic flow in the upper troposphere. The time-mean flow is shown to be more important than the transient eddies in forcing seasonal mean vertical motion.

While little confidence can be placed in the magnitude of the seasonal mean vertical velocity determined from NMC data, the omega equation and the vorticity balance yield very similar vertical motion patterns that, over much of the extratropical Northern Hemisphere, are in agreement with the vertical velocity pattern suggested by cloudiness and precipitation. The other two methods yield somewhat similar patterns that are less successful in matching the pattern suggested by cloudiness and precipitation. The similarity of several features in the adiabatic vertical velocity field to corresponding features in the vertical velocity field calculated from the vorticity balance implies that over many areas of the extratropical Northern Hemisphere diabatic heating is secondary term in the time-averaged mid-tropospheric heat balance.

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Glenn H. White

Abstract

Twelve summers and 11 winters of Northern Hemisphere 500 and 1000 mb geopotential height are used to calculate the third and fourth moments of height in the nondimensional form of skewness and kurtosis. Geopotential height exhibits small but statistically significant departures from a normal distribution in places, especially in low latitudes. Negative skewness and high kurtosis occurs south of the mean jet streams at 500 mb and over the low latitude oceans at 100 mb, while positive skewness appears in high latitudes at 500 mb near the mean troughs. Kurtosis significantly less than that of a normal distribution appears at 500 mb over the midlatitude oceans where large variance of geopotential height and frequent blocking are observed.

At 500 mb skewness and kurtosis appear closely related to the extreme values of geopotential height. Both 500 and 1000 mb surfaces have high maximum values over the eastern portions of the means in regions of blocking.

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Robert M. White and Glenn J. Hung

Abstract

No Abstract Available

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Maurice L. Blackmon and Glenn H. White

Abstract

Eleven winters and twelve summers of twice-daily National Meteorological Center (NMC) analyses of geopotential height and temperature at five levels for the extratropical Northern Hemisphere are partitioned into long-wave fields with zonal wavenumbers m ≤ 5 and short-wave fields with zonal wavenumbers m ≥ 6. The data are also bandpass-filtered to investigate fluctuations of periods 2.5–10 days. From these fields, the standard deviation of 500 mb geopotential height and the poleward geostrophic transient eddy fluxes of sensible heat and zonal momentum are calculated and presented.

The results are compared with theoretical and numerical modeling studies of nonlinear, baroclinic instability. Both the observations and modeling studies produce evidence that baroclinic eddies have a definite life cycle and that the strongest baroclinic eddies are of intermediate size (zonal wavenumbers 6–8). Some interesting differences between observations and modeling results also emerge.

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Glenn H. White and John M. Wallace

Abstract

The annual march of surface temperature is documented on a global basis by mapping the amplitudes and phases of the annual and semiannual cycles in a vectorial format. The annual cycle in Northern Hemisphere geopotential heights is discussed and the amplitude of the annual cycle in 300 mb geopotential height is presented.

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Peter M. Caplan and Glenn H. White

Abstract

The operational model used to generate medium-range forecasts at the National Meteorological Center (NMC) has undergone significant changes in the last few years, resulting in considerable improvement in the skill of its forecasts. The introduction of interactive clouds in late 1988 significantly reduced a cold bias present in model forecasts since April 1985. Model errors during recent Northern Hemisphere summers appear linked to thermal forcing, causing temperatures and upper tropospheric heights over cooler ocean areas to be too low, and heights over the western United States to be too high.

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Duane E. Stevens and Glenn H. White

Abstract

No Abstract.

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Kingtse C. Mo and Glenn H. White

Abstract

Teleconnections are calculated from monthly mean anomalies of sea level pressure and 500 mb geopotential height for the Southern Hemisphere (10–90°S) for five-month winter and summer seasons. The monthly means were calculated from Australian analyses for the period from June 1972 to November 1980.

Zonally averaged anomalies at both sea level and 500 mb display an out-of-phase relation between low and high latitudes and in midlatitudes are negatively correlated with anomalies in the subtropics and polar regions. In winter a striking zonal wavenumber 3 pattern is found over the Southern Ocean. Anomalies in 500 mb geopotential heights at (50°S, 95°E), (58°S, 150°W) and (38°S, 15°W) exhibit strong positive correlations while showing weaker negative correlations with heights over Antarctica and in low latitudes. A similar pattern appears in sea level pressure.

In summer anomalies in 500 mb geopotential height over the three subtropical continents appear to occur out of phase with anomalies over the subtropical oceans and in a zonal wavenumber 3 pattern over the Southern Ocean near 55°S. Much of the pattern appears largely associated with low-frequency variability. A similar pattern with weaker correlations appears in sea level pressure in summer. The strongest teleconnection pattern in summertime sea level pressure features a strong negative correlation between the eastern Indian Ocean northwest of Australia and the subtropical eastern Pacific near Tahiti, which strongly resembles the pattern associated with the Southern Oscillation.

The above features are well-reproduced in both halves of the period and in station data. The features found at 500 mb also appear in patterns obtained from eigenvector analysis.

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