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J. P. Pandolfo

Abstract

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P. S. Brown Jr.
,
J. P. Pandolfo
, and
S. J. Thoren

Abstract

The numerical model of air-sea interaction previously described in Jacobs (1978), Pandolfo and Jacobs (1972) and Pandolfo (1969) is inserted at one horizontal grid point in the GATE III Gridded Global Data Set to calculate a model-generated, local interface temperature over a two-day interval (0000 GMT 4 September-0000 GMT 6 September 1974) of GATE Period III.

The experiment provides a preliminary demonstration of the accuracy achievable in predicting sea-surface temperature over multi-day scales with limited-domain models nested within global data sets. It also demonstrates the degree of sensitivity of the model-generated sea-surface temperature to the inclusion of parameterized convective adjustments in the oceanic and atmospheric sub-layers under the general conditions prevailing during the period studied.

Initial and boundary data were provided to the local model on a relatively coarse vertical grid and with relatively coarse (12 h) temporal resolution. Linear spatial and temporal interpolation was used to produce the higher resolution data required by the model. (A 6 min time step and grid intervals as small as 1 m were used in the experiments described in this paper.) Therefore, the nested local model provides, in this preliminary experiment, increased resolution only in the vertical and temporal dimensions. It also adds greater physical complexity to the global-scale model used in the generation of the GATE III gridded data set (and described in Miyakoda et al., 1980) by coupling the atmosphere-ocean boundary layers to allow the prediction (rather than the prespecification) of sea-surface temperature, and by taking into account model-generated temporal variations in the vertical structures of the atmospheric transmissivity with regard to solar and infrared radiation.

The two-day period used for this demonstration is characterized by moderately disturbed tropical marine conditions with intermittent periods of light wind as contrasted to the generally steady trade-wind and midlatitude conditions previously treated in the papers cited above. Nevertheless, the air-sea interaction model, when suitably refined to include parameterized convective adjustment in the, coupled air-ocean layers, again yields model-generated sea-surface temperatures which generally differ from those observed by less than the uncertainty of measurement, and with accuracy well within that estimated in Charney et al. (1966) as required in order to extend the temporal range of weather forecasts in numerical models of the atmosphere.

In one model run of the experiment the atmospheric convective adjustment was eliminated from the model. The result is an unrealistic accumulation of heat in the ocean surface layer. In another model run of the experiment the ocean-surface layer convective adjustment was eliminated from the model. The result is a somewhat cooler model-generated nighttime interface temperature.

Interaction between the parameterized convective processes of the coupled air-sea model layers is also evident from the results. When the parameterized atmospheric convective adjustment is omitted from the model, significant alteration of the model-generated oceanic “convection depth” takes place; conversely when the parameterized oceanic convective adjustment is omitted, there occurs a substantial alteration of the model-generated atmospheric “convective condensation level.”

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P. S. Brown Jr.
,
J. P. Pandolfo
, and
G. D. Robinson

Abstract

The numerical model of air-sea interaction previously described in Brown et al. (1982), Pandolfo and Jacobs (1972) and Pandolfo (1969) is applied over a limited horizontal portion of the GATE III Gridded Global Data set (including continental grid points) to calculate a model-generated interface temperature field over a two-day period of GATE Period III.

The experiment provides a further estimate of the accuracy achievable in predicting sea-surface temperature over multi-day scales with limited-domain models nested within global data sets. It also demonstrates the degree of sensitivity of the model solutions to the inclusion of three additional atmospheric radiators (viz., an hypothesized tropical haze over the entire area simulated, a Saharan dust layer over its northern portions, and model-generated cloud); and to the thermodynamic effects of the parameterized cloud and rain-generating mechanism.

The initial oceanic temperature field was subjectively analyzed from GATE ship data and supplemented by climatological data. The sea-surface temperatures thus derived were qualitatively consistent in pattern with independent analysts of daily mean temperature based on GATE satellite and ship data. Both analyses show a belt of maximum temperature extending from the western boundary of the simulated area north-eastward to the African coast. In both analyses sea-surface temperatures decrease rapidly toward the southeast of the axis of maximum temperature. In our synoptic field it decreases more slowly toward the northwest. Actual values of analyzed temperature may differ locally by up to 2°C at locations sparse in ship data, but by less than the 0.50°C accuracy suggested by Krishnamurti et al. (1976) in data-rich portions of the limited area.

When the haze and model-generated cloud are included in the numerical simulation, model-generated daily mean temperatures change from the first to the second day of simulation in a manner that is also qualitatively consistent with that exhibited by day-to-day changes of the independently analyzed mean temperature. In the absence of these additional radiators the model-generated temperatures exhibit unrealistic warming of sea-surface temperatures. The sensitivity of daily average model-generated interface temperature to the presence of individual radiators shows patterns of difference similar in intensity and scale to those of the day-to-day changes.

Model-generated hourly-average temperature fields show isolated, shallow, cool-water pools at locations with intense model-generated cloud and rain and at data-sparse locations of the limited area simulated. At their most intense, they are similar in scale and intensity to a feature observed at another time, and under similar conditions, in the vicinity of the AB-scale GATE array. Their presence in the model-generated solutions is directly attributable to inclusion of the salinity-stabilization mechanism suggested by Katsaros (1976). These features appear with greatest intensity when all three atmospheric radiators are included, and diminish noticeably in intensity as the atmospheric dust is removed. They are completely absent in a simulation in which model-generated cloud and rain are also omitted.

In that simulation, an isolated, shallow, warm-water pool appears in the presence of generally strong insulation, and at a location with light surface wind. It is similar in scale and intensity to a feature observed at another time, and under similar conditions, within the GATE-AB scale array (Peters, 1978).

A noticeable nocturnal temperature maximum in the northern coastal regions of the simulated area is present in the initial data, and is repeated in the model-generated nighttime temperature fields thereafter. It is complemented by a repeated model-generated coastal daytime temperature minimum slightly to the south. Observational data are not available to confirm this most pronounced diurnally-varying feature of the simulated sea-surface temperature fields.

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