On the Influence of Orography on Large-Scale Atmospheric Flow

The intraseasonal variations in the subtropical jet over the Eurasian continent and the western North Pacific in the northern summer are investigated through a statistical study using the ECMWF objective analysis data for 14 years, from 1980 to 1993. The quasi-stationary Rossby waves are evident in the climatological subtropical jet. They are characterized by well-confined zonal wavenumbers of about 5-7 and less confined spectral peaks at 30-to 45-day and 14-day periods. They are strongly phase-locked in the tonal direction.Through a case study for a typical year (1983), evident standing wave-like disturbances with a 32-day period are found in the subtropical jet. Their propagation routes correspond to the well-defined waveguide for the quasi-stationary Rossby wave formed along the subtropical jet. However, they are not completely confined in the waveguide, but protrude slightly from the waveguide with its southern rim crossing their critical latitude, which lies along the center of the Tibetan High. The vertical structure of the disturbances shows a slight but systematic westward phase tilt, indicating a northward heat flux.In ray-path analysis for barotropic quasi-stationary Rossby waves, temporally and meridionally smoothed basic flows are used in order to take into account temporal and zonal extensions of wave packets. This method is successfully used to diagnose the propagation routes of the observed disturbances.

Section: Methodsmentioning

confidence: 99%

Barotropic Disturbances on Intraseasonal Time Scales Observed in the Midlatitudes over the Eurasian Continent during the Northern Summer

Terao

1998

“…The pattern in A7 or AW can be understood as a response to subtropical mass source/sink distribution under the framework of a linear theory. To show this, the linearized shallow-water equation model by Grose and Hoskins (1979) is used.…”

Section: Interpretation Of Mid-latitude Responsementioning

confidence: 99%

“…The orography is not considered. Other details are the same as in Grose and Hoskins (1979). This map picks up some of the salient features appearing in AW-N in the North Pacific Ocean.…”

Section: Interpretation Of Mid-latitude Responsementioning

confidence: 99%

A Numerical Experiment on Sea Surface Temperature Anomalies and Warm Winter in Japan

Kitoh

1988

Impact of the sea surface temperature anomalies (SSTAs) on atmospheric circulations are studied with emphasis on the winter climate in Japan with the use of an atmospheric general circulation model.The empirical orthogonal function analyses are performed for precipitation, geopotential height at 500mb and surface air temperature. It is shown that leading eigenvectors of precipitation are zonally elongated in the tropics and that the distribution of positive and negative precipitation anomalies is dependent on the SST and precipitation field in the control run. Surface air temperature in East Asia is mostly governed by the temperature contrast between Japan-East China region and the Sea of Okhotsk. This is associated with high pressure anomalies in the North Pacific Ocean, which weakens the cold surge from Siberia. This circulation is found in the first eigenvector in the present experiment El(Z500) and is dominant in the run which uses the composited January SSTA observed during warm winter in Japan. The simulated anomalies in mid-latitude circulation correspond well with the observations.An additional run with the SSTA over the equator east of the dateline gives the largest anticyclonic circulation response over the North Pacific Ocean and the warmest surface air temperature anomalies in East Asia. The pattern relevant to warm winter in Japan is not a simple atmospheric response to tropical heating. It is conceivable that inherently there is a dominant circulation mode like El(Z500) and that this mode can be activated either by a direct and/or an indirect orographic effect or by anomalous heating induced by the SSTA.This pattern can be understood as a response to subtropical mass source/sink distribution under the framework of a linear theory.

“…This is the very reason why the resonant waves can be so easily excited without losing energy to give rise to blocking solutions. The importance of horizontal propagation of barotropic Rossby waves was much emphasized by Grose and Hoskins (1979), Hoskins and Karoly (1981) who showed the Rossby wave trains for a local forcing in the spherical domain. In view of relatively significant role of meridional propagation of Rossby waves it may be by no means relevant to rely on channel models for the proper representation of wave fields.…”

Section: Conclusion and Discussionmentioning

confidence: 99%

The Response of a Barotropic Model Atmosphere with Realistic Topography and a Possibility of Multiplicity of Stationary Solution

Kusunoki

1984