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  • Author or Editor: ROBERT F. STRICKLER x
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Robert D. Elliott
and
Robert F. Strickler

An analysis of a series of cloud seeding projects conducted in three different Pacific-slope watershed areas, each during several seasons, is presented. Seven separate project-seasons are involved in each of which identical seeding procedures were used. Silver iodide smoke generators were operated at ground level for a total of well over 10,000 generator-hours during these operations.

Snowpack and other official precipitation records are examined and target-to-control-area comparisons made in order to bring out the effects of the seeding and apply statistical tests thereto.

It is concluded that this evaluation procedure, as applied to the available data, is capable of discerning the effectiveness of cloud seeding in increasing precipitation over a period of several seasons, but is not capable of bringing into focus the many details of interest to the cloud seeder.

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REGINALD H. CLARKE
and
ROBERT F. STRICKLER

Abstract

A nine-level hemispheric primitive-equation model is applied to make a 14-day experimental prediction for the Southern Hemisphere; this is the first numerical prediction on the hemispheric scale for the Southern Hemisphere and the first attempt to use the model for summertime forecasting.

The predictions are verified against hemispheric data, the inadequacy of which is clear. They are also verified in the Australasian sector where the data are more adequate.

For the first 2 days, especially over areas with good data, the forecasts were generally of high quality, decreasing in accuracy with height above the surface. After a serious decline in skill on the fourth day, a recovery is noted. Australian rainfall during the first 2 days was also predicted with useful skill.

Some properties of the model atmosphere are compared with those of the observed Southern Hemisphere atmossphere, and deficiencies in the performance of the model, as well as in the analysis and initialization, are brought out by the comparison. However, on the whole, good agreement is found.

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Syukuro Manabe
and
Robert F. Strickler

Abstract

The states of thermal equilibrium (incorporating an adjustment of super-adiabatic stratification) as well as that of pure radiative equilibrium of the atmosphere are computed as the asymptotic steady state approached in an initial value problem. Recent measurements of absorptivities obtained for a wide range of pressure are used, and the scheme of computation is sufficiently general to include the effect of several layers of clouds.

The atmosphere in thermal equilibrium has an isothermal lower stratosphere and an inversion in the upper stratosphere which are features observed in middle latitudes. The role of various gaseous absorbers (i.e., water vapor, carbon dioxide, and ozone), as well as the role of the clouds, is investigated by computing thermal equilibrium with and without one or two of these elements. The existence of ozone has very little effect on the equilibrium temperature of the earth's surface but a very important effect on the temperature throughout the stratosphere; the absorption of solar radiation by ozone in the upper and middle stratosphere, in addition to maintaining the warm temperature in that region, appears also to be necessary for the maintenance of the isothermal layer or slight inversion just above the tropopause. The thermal equilibrium state in the absence of solar insulation is computed by setting the temperature of the earth's surface at the observed polar value. In this case, the stratospheric temperature decreases monotonically with increasing altitude, whereas the corresponding state of pure radiative equilibrium has an inversion just above the level of the tropopause.

A series of thermal equilibriums is computed for the distributions of absorbers typical of different latitudes. According to these results, the latitudinal variation of the distributions of ozone and water vapor may be partly responsible for the latitudinal variation of the thickness of the isothermal part of the stratosphere. Finally, the state of local radiative equilibrium of the stratosphere overlying a troposphere with the observed distribution of temperature is computed for each season and latitude. In the upper stratosphere of the winter hemisphere, a large latitudinal temperature gradient appears at the latitude of the polar-night jet stream, while in the upper statosphere of the summer hemisphere, the equilibrium temperature varies little with latitude. These features are consistent with the observed atmosphere. However, the computations predict an extremely cold polar night temperature in the upper stratosphere and a latitudinal decrease (toward the cold pole) of equilibrium temperature in the middle or lower stratosphere for winter and fall. This disagrees with observation, and suggests that explicit introduction of the dynamics of large scale motion is necessary.

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SYUKURO MANABE
,
JOSEPH SMAGORINSKY
, and
ROBERT F. STRICKLER

Abstract

A numerical experiment with a general circulation model with a simple hydrologic cycle is performed. The basic framework of this model is identical with that adopted for the previous study [35] except for the incorporation of a simplified hydrologic cycle which consists of the advection of water vapor by large-scale motion, evaporation from the surface, precipitation and an artificial adjustment to simulate the process of moist convection. This adjustment is performed only when the relative humidity reaches 100 percent and the lapse rate exceeds the moist adiabatic lapse rate. The radiative flux is computed for the climatological distribution of water vapor instead of using the distribution calculated by the prognostic equation of water vapor. A completely wet surface without any heat capacity is chosen as the lower boundary. The initial conditions consist of a completely dry and isothermal atmosphere. A state of quasi-equilibrium is obtained as a result of the time integration of 187 days. A preliminary analysis of the result is performed for the 40-day period from 148th day to 187th day.

According to this analysis, the hemispheric mean of the rate of precipitation is about 1.06 m./yr. which is close to the estimate of the annual mean rainfall obtained by Budyko [5]. In the Tropics rainfall exceeds evaporation and in the subtropics the latter exceeds the former in qualitative agreement with observation. The difference between them, however, is too exaggerated, and an extremely large export of water vapor from the dry subtropics into the wet, Tropics by the meridional circulation takes place. In the troposphere, relative humidity increases with decreasing altitude. In the stratosphere it is very low except at the tropical tropopause, and the mixing ratio of water vapor is extremely small in qualitative agreement with observation. Although water vapor is transported from the troposphere into the stratosphere, it is then transported toward low latitudes and condenses at the tropical tropopause where the temperature is very low and the relative humidity is high.

Based upon a harmonic analysis of the flow field and the surface pressure field, it, is concluded that the effect of condensation tends to increase the wave number of the tropospheric flow and surface pressure field. Also, the incorporation of the moist process in the model seems to increase the intensity of meridional circulation in the Tropics. As a result of this increase, the transport of momentum and heat by the meridional circulation in the Tropics is much larger than that obtained from the previous study. In middle latitudes, the poleward transport of total energy in the moist-model atmosphere is less than that in the dry-model atmosphere because of the effect of the poleward transport of Intent energy or the heat of condensation.

The latitudinal distributions of radiative fluxes at the top of the atmosphere and at the earth's surface coincide very well with those obtained by London [17] for the actual atmosphere. Bowen's ratio increases with increasing latitude and its magnitude coincides reasonably well with that obtained by Budyko [5] or Jacobs [11] for the ocean surface.

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