The behavior of mean zonal wind and planetary-scale geopotential height disturbances during the 1973 sudden warming is investigated in terms of their dynamical interactions, with use of the data of Nimbus 5 Selective Chopper Radiometer and conventional radiosonde. From the survey of the stratospheric temperature field in the 1972/73 northern hemisphere winter, it is found that two mid-winter warmings occurred successively at an interval of about 16 days. Examination of previous studies based on satellite observations reveals that a major or minor warming occurs about two weeks before a spectacular major warming, and an emphasis is laid on the effect of the first warming on the second one. A large easterly region of mean zonal wind appeared in the stratospheric high latitudes in the second warming (Warming 2) while not in the first warming (Warming 1). With Warming 2, initially the easterly accelerations occurred in middle latitudes while the westerly accelerations in high latitudes in the upper stratosphere and these accelerations owe its existence generally to the momentum flux convergence mainly by wavenumber 2 disturbances. Eventually there occurred the intense easterly accelerations both in middle and high latitudes which brought about the circulation reversal in the stratosphere, which were due to the predominance of the Coriolis torque acting on the equatorward mean meridional flow induced mainly by wavenumber 1 disturbances. During pre-warming period for Warming 2, wavenumber 1 geopotential height disturbances propagated from the lower troposphere upward to the middle stratosphere and attained very large amplitude. This amplification of wavenumber 1 seems to come from the response to a characteristic mean zonal wind profile which continued through about 10 days after Warming 1. The wind profile is such that a westerly maximum lies in the high latitudes 40km level and then a region of large positive β-effective (latitudinal gradient of zonal mean quasi-geostrophic potential vorticity) in the high latitude stratosphere is surrounded by negative β-effective regions. It is speculated that this wavenumber 1 amplification is the result of resonance of planetary Rossby wave discussed by Tung and Lnidzen (1979).
This paper describes the numerical simulation of the air-mass transformation by a three dimensional model. The model has a relatively high vertical resolution in the lower troposphere to improve the treatment of the vertical turbulent transfer processes in the boundary layer. The physical processes taken account of in the model are: (1) surface exchange of heat, moisture and momentum based on the similarity theory, (2) vertical turbulent transfer of heat, moisture and momentum based on the turbulent closure model of level 2 (Mellor and Yamada, 1974), (3) the parameterization of convection (the moist convective adjustment) and the condensation of moisture, (4) orographic effect, and (5) sub-grid scale lateral diffusion. The model is applied to the observed meteorological situation under the northwest monsoon over the Sea of Japan. The simulated heat, moisture and momentum budget due to the sub-grid scale processes are discussed. The results are encouraging. However further improvement is required.In particular, the moist convective adjustment causes unrealistically large cooling and too humid stratification near the surface. Preliminary result of a sensitivity test which is relevant to future improvement and remaining problems are also discussed.
Average structure and large-scale heat, moisture and momentum budgets of a convective mixed layer during cold air outbreaks are examined. The atmosphere is divided into a mixed layer, an inversion layer and a layer above which is not affected by the air-sea interaction processes. Potential temperature and winds are generally uniform in the mixed layer and have large increases in the inversion layer. Mixing ratio of the water vapor slightly decreases with height in the mixed layer and falls rapidly in the inversion layer. There exists divergence in the mixed layer and convergence above. Large-scale downward motions dominate the whole layer with a maximum in the inversion layer. Large apparent heat and moisture sources are found in the mixed layer. Net heat sinks and large moisture sources exist in the inversion layer mainly due to evaporation. There are large momentum sinks in the subcloud layer, but small sources and sinks in the cloud layer. Large downward momentum fluxes due to subgrid-scale eddies exist in the subcloud layer but small upward fluxes exist in the cloud layer.A diagnostic cloud model is applied to the heat and moisture budgets to determine spectral distributions of cloud mass fluxes. Sallower clouds have larger mass fluxes than deeper clouds. Large net heat sources are resulted from condensation heating in the lower cloud layer, but net cooling occurs in the inversion layer due to evaporation cooling effects. Vertical flux convergence of the water vapor due to clouds is important for the moisture balance as well as condensation and evaporation effects. Difference in momentum between inside and outside clouds is evaluated by combining the results of budget and cloud model computations. Momentum inside clouds is very close to that in the environment indicating that the clouds over the AMTEX region quickly adjust their momentum to that in the environment. Vertical eddy fluxes of heat, moisture and momentum obtained by the budget computations are compared with those measured by the NCAR Electra. The fluxes computed by the budgets agree quite well with those directly measured by the aircraft.
Extremely high sea states are known to occur to the right of the direction of movement in typhoons. A well documented case of such extreme sea heights in the western North Pacific is examined and compared with results obtained from a numerical spectral ocean wave model. The wind and sea state field of the numerical model compares favorably with the observed data. An examination is also made to determine how extreme sea states relate to tropical cyclone intensity, forward speed of movement, and circulation size or wind distribution. The results indicate that all three are important with intensity being the primary factor, speed of movement being of secondary importance and circulation size or wind distribution being the least important factor.
In a transitional airmass situation cloud droplet measurements were made from stratocumulus and fair-weather cumulus using newly devised MgO type instrument, on which brief description is given in this paper. It was found that an extremely large number of large drops were existing in a growing cumulus tower from the strato-cumulus, though the cloud depth is relatively thin, around 1200m. Cloud droplet size and concentration seem to vary very sensitively to the evolutional life time of the cloud tower, in a manner that with larger drops and water content in the mature stage and vice versa in the decaying stage. In this paper the frequency of parameters, number concentration N, liquid water content L, and median volume diameter D50 are given for reference as well as the mean size distributions of cloud droplets.
The frequency of occurrence of so-called “peculiar shapes of snow crystals” was observed at the Arctic Canada. When the peculiar crystals were observed, the predominant common crystals were combination of bullets, column and crossed plates. The falling frequency of the peculiar crystals against other common crystals was 3 to 4% in average. The minimum temperature of the ice saturation layer in which the peculiar crystals grew, which was estimated from the sounding curves, was warmer than -35°C in all groups of those crystals.
The ability of planar ice crystals to assume horizontal orientations during fall is examined as a function of crystal diameter. After reviewing fall velocity measurements for the various planar crystal types, the fall attitude predictions from model experiments are compared to the results of photographic analyses of light pillar displays, an atmospheric optical phenomenon generated by near-horizontally aligned ice crystals. It is concluded that the prediction for stable fall in terms of Reynolds number (Re) through the range 1.0<Re<100 is generally valid in the atmosphere. It is further shown that planar crystals with Re≈10 display the most stable fall attitudes, and that crystal diameters >0.1-0.2mm are required to generate the optical displays. It also appears that the distribution of ice crystal orientations from the horizontal plane is Gaussian in character owing to the effects of turbulence. The implications of these findings for other optical phenomena and the active remote sensing of cloud composition are discussed.
Characteristics of the spectra in the relatively lower frequency ranges of the strong katabatic winds observed by the ultra sonic anemometer-thermometers (SAT) at Syowa Station, Antarctica are studied. The great snow smokes which are the very high drifting snow and rotating roll clouds on the Antarctic coastal slope not far from Syowa Station are observed at Syowa Station. The great snow smokes indicate clearly the existence of the hydraulic jump of the katabatic winds. The relationship of the great snow smokes to the vertical wind and temperature spectra of the katabatic winds is investigated.