The effects of vertical resolution and the upper boundary on the structure of the planetary waves in numerical models are investigated with a simplified one dimensional model, using the quasi-geostrophic, mid-latitude β-plane approximation. The results obtained by models with different vertical resolution and different height of the upper boundary are compared with the control solution which is obtained by using a small grid increment of 0.25km and by including large dissipative effects near the upper boundary located at 90km. The influence of lowering the upper boundary is not fatal to the structure of the waves in the troposphere if the upper boundary is placed at the middle stratosphere and a model has several layers in the stratosphere, because Newtonian cooling or other damping effects of realistic magnitudes well attenuate the wave reflected at the top. Stationary planetary waves obtained by low resolution models (5 or 6 layers) show apparent similarity to the true (control) solution in a qualitative sense. But to obtain quantitatively correct solutions, vertical grid increments should be taken as small as Δz=1-2km in the troposphere andΔz=2-3km in the stratosphere and the top should be placed in the middle stratosphere. When the time integration is performed with the use of a low resolution model, using the true data (control solution) as the initial, the waves can no longer be stationary but tend to transform into the model's own stationary state. For resolving this problem we must use higher resolution models as mentioned in the stationary case. Analogous results are obtained for the simulation of the waves in the stratosphere.
In December 1958, the subtropical jet stream displaced, on a large-scale, into North America and then towards the end of the month, also into Western Europe. The largescale displacement of the subtropical jet stream and the related behavior are described in relation to the general circulation of middle- and higher-latitudes. The interaction between the mid-latitude circulation and the tropical one is important for thedisplacement', but the manner in which the former acts upon the latter is different for different places. Over the eastern Pacific, it was done through the formation of an extended and sharp trough of the mid-latitude westerlies. While, over the Atlantic it was performed by the amalgamation of the migrating anticyclone with the subtropical high. Due to the outbursts of cold air in front of the ridge, the subtropical jet stream which had meandered strongly into mid-latitudes was broken-off from the southern part, and was left behind in mid-latitudes, and then disappeared as the subtropical high on its south side declined. The large-scale displacement of the subtropical jet stream acts as a trigger of the change of circulation features, and has a remarkable influence upon the general circulation of the middle- and higher-latitudes. On the south side of the ‘normal’ subtropical jet stream, another core of strong wind is sometimes observed over Cuba and the neighbourhood, near Japan and northern Africa in winter, which seems to be related to the deeply penetrating cold outbreaks over the relatively warm sea surfaces.
The observational study on the thermal and kinematical structure of the cold air-mass and its transformation over Kuroshio region is made for the period of the strong cold air outbreak (23-27 February 1974) based on the data from AMTEX '74. The relatively shallow (1-2km depth) layer of cold air-mass is capped by the well developed inversion layer. The inversion layer distinctly separates the untransformed steady westerly layers aloft from the transformed northerly wind layer below. The vertically uniform profile of θe and V in the subinversion layer, except the lowermost layer, indicates strong vertical mixing there. This “mixed layer” is also characterized by the convective instability due to the large value of θe in the lowermost layer adjacent to the sea surface. The analyzed period is subdivided into “developing stage of the mixed layer” (23-24 February) and “quasistationary stage of the mixed layer” (25-27 February). The “developing stage” is char- acterized by the increase of the thickness of the mixed layer and the upward motion. The “quasi-stationary stage” is characterized by the quasi-stationary state of the mixed layer and the downward motion. The inversion base is, on the whole during the quasi-stationary stage, lower over the northwestern and higher over eastern part of AMTEX area, except some local rising of the inversion base. The budget calculation indicates that the horizontal advection of heat and moisture (cold and dry advection) and the apparent heat and moisture sources are very large in the subinversion layer and they abruptly decrease at the inversion base. The vertical distribution of the convective transport of the heat energy is also obtained. Detailed analysis on the thermodynamical balance in the mixed layer is made for the quasi-stationary stage. The time variation of the static stability in the mixed layer and inversion layer during the developing and quasi-stationary stages is also analyzed on the basis of the heat energy budget calculation.
Based on daily satellite cloudiness data over the tropical belt between 30S and 30N during the northern hemispheric summer from June 1 to September 15 for the eight years 1965 to 1972, cloudiness changes over the monsoon region were found to be positively correlated with those over the Malaysia-Indonesia region, while marked negative correlation was encountered over the African continent, the equatorial Indian Ocean and the western North Pacific. Through computations of time lag correlation, it was found that the zones of either positive or negative correlation propagated northwards through the equatorial Indian Ocean and the Indian subcontinent with an average speed of about 1° latitude per day.
Vertical wind fluctuations were measured simultaneously by two sondes hanged from two tethered balloons, which were located nearly parallel to the mean wind direction with the separation distance of about 120m at the height of several hundred meters from the surface. From the data space-time correlations and coherences were computed. The observed peak values of space-time correlations are in good agreement with the correlations derived theoretically on the hypothesis of the inertial subrange.