The author has recently completed a global analysis of tropical cyclone genesis (Gray, 1975a). This paper applies the results of that study to a more detailed analysis of tropical cycline genesis in the western North Pacific and of the variation in the seasonal climatology of genesis location and frequency. The first part of this paper presents statistical information on the seasonal frequency of tropical cyclone genesis and discusses the major physical requirements of genesis. The second part of this paper shows how these hypothesized genesis requirements are specified by the product of six seasonally averaged meteorological parameters. The last part of this paper shows how well the product of these seasonally averaged parameters is related to cyclone genesis location and frequency. A cyclone genesis forecast index is proposed.
An analysis is made of the spectral characteristics of the cloud cover observed over Africa for a period of three months. The results indicate the predominance of a 2-2.7 day spectral peak within the vicinity of the Equator (10°N-10°S) with the intensity of this peak much stronger over land than over the ocean. The peak itself may not be detected if the smallest resolved area used in the data analysis is too large. Coherence was found to be maximum in belt-like configurations along certain latitude bands. The phase difference, although very noisy, indicates a horizontal scale on the order of 2000 kilometers.
A partitioning of heat export by the oceanic water body vs. the atmospheric column is presented for the tropical Pacific, on the basis of satellite-derived net radiation at the top of the atmosphere and calculations of the oceanic heat budget. For individual Marsden squares, the divergence of heat transport within the oceanic water body ranges from+169 (export) to-191 (import) percent of the net radiative input to the system at the top of the atmosphere. Heat export within the ocean is particularly important in the band of cold water immediately to the South of the Equator.
Energy transformations involved in the maintenance of kinetic energy in the winter monsoon over the Kuroshio region are investigated with the AMTEX 74 and 75 upper-air observations. The kinetic energy level is very high and the energy transformations are very intense in the winter monsoon over the region. Both the kinetic energy generation and dissipation in the mid and upper troposphere are a few to several times stronger than those in major cyclones of a continental region. A large amount of kinetic energy is supplied to the mid and lower troposphere from the source in the upper troposphere. We may view the winter nonsoon over the region as part of the intense kinetic energy transformations in the general circulation of the Northern Hemisphere winter with the source in the upper and midtroposphere. The cold air outbreak is essentially a surge of energy. The winter monsoon thus maintained over the ocean is then expected to absorb latent and sensible heat from the ocean surface to increase the available potential energy in the general circulation.
Second order finite difference analogues to the two and three dimensional Laplacian operator are presented. These analogues have the property that for a general function there is a minimum of second order error. If a function is defined only at specified points, these analogues are the best possible approximation to the differential operator.
The physical products of splashing water drops were investigated with respect to several parameters: impact velocity, drop size, surface tension, radius of curvature and roughness of the target surface, and the depth of liquid film covering the surface of the target. It is shown that the number of droplets produced by a splash increases with surface roughness, impact velocity and drop size, but decreases with an increase in liquid film depth and with a reduction in surface tension of the drop. For a given drop size, the number of splash products is proportional to the kinetic energy of the drop at impact. The size distribution of splash products is approximately log-normal; the mean size of the ejected droplets (approx. 120μm diameter) increases with drop size, surface roughness and depth of liquid film, but decreases with increasing impact velocity and with a reduction in surface tension. Certain empirical relationships are established which permit the number of splash products, N, to be estimated in terms of the conditions of impact. One such relationship gives N=3.4 R3V2-63, where R(mm) is the radius of a water drop impacting a flat solid surface with velocity V(ms-1). It is also shown that water drops of less than 0.75mm in radius require an impact velocity greater than their terminal velocity if they are to eject droplets.
The results of the turbulent heat flux obtained by airborne measurements over flat terrain and coastal areas are reported, and the structure of the atmospheric boundary layer under the condition of clear daytime is investigated. The main results are summarized as follows: (1) In clear daytime, turbulent heat flux q over land decreases linearly with height in the lower layer and q becomes zero at some height, Zq. It then has a negative peak at about a height of 1.3 Zq and its absolute value is about 20% of the surface value of q. The height Zq coincides with the height of the inversion base of the potential temperature. (2) By the analyses of the balance of turbulent energy in the atmospheric boundary layer under clear daytime conditions, we have reached the conclusion that the buoyant energy production balances the dissipation rate of the turbulent energy. (3) Under sea-breeze conditions, the temperature variation with time can be explained by the heating due to q and the cooling due to the advection of the cool sea-breeze. (4) The height of the internal boundary layer formed by the thermal convection is investigated and the relation between Zq and x/U (where x is the distance from the coastline along the wind direction and U is mean wind velocity) is obtained.
The estimation methods for stress, and heat and moisture fluxes at the sea surface, obtained by combining the resistance-law and the non-dimensional temperature, moisture and mean velocity gradients, is described. In these methods, the geostrophic wind velocity, the temperature and relative humidity near the surface, and the sea-surface water temperature are external parameters.