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Andrew F. Bunker

Abstract

Fluxes of sensible, latent and radiational energy and momentum across the surface of the South Atlantic Ocean have been calculated by substituting ship meteorological observations into bulk aerodynamic and empirical radiation equations. Upper-air measurements of humidity and temperature have been used to supplement the surface empirical infrared radiation formula. North Atlantic fluxes have been updated using upper-air humidities and the same technique. Charts of annual fluxes and meteorological variable averages are presented and discussed in terms of meteorological conditions, oceanic heat advection, upwelling, and horizontal mixing of water in the various regimes of the South Atlantic. Comparisons between meteorological conditions, oceanic currents, and fluxes over the North and South Atlantic have been made. Summations of total heat flux show that the cold South Atlantic gains 4.7 × 1014 W, while the warm North Atlantic loses 6.6 × 1014 W. Oceanographic calculations based on currents and temperatures indicate that a net of 5.4 × 1014 W are transported across the equator from south to north.

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Andrew F. Bunker

Abstract

Regression coefficients have been computed from monthly. seasonal and annual means of eleven meteorological variables and eight energy fluxes by 10° areas over the North and South Atlantic Oceans from January IMS through December 1972. Many linear trends of annual means have been plotted on charts and studied for spatial and flux-variable, relationships. Pressure tendencies showed that pressures, increased under the eastern part of the subtropical high-pressure nets in both hemispheres and decreased east of the mean trough extending southwestward from the Icelandic low-pressure center. Net effects of these trends were to increase the strengths of the westerlies and easterlies in both hemispheres. Meridional winds evolved in such a manner that warm air transport to Greenland increased. Equatoward wind components increased over the eastern tropical Atlantic. Charts presenting trends in air temperature, humidity, clouds, rain and surface fluxes show the relations between these variables, surface fluxes, changing circulation patterns and sea surface temperature. The mixing ratio trend is negative over both oceans with maximum decrease over the Gulf of Mexico and the cut coast of North America. A general decrease in sea temperature is noted over all of the North Atlantic with large decreases off New England and the Maritime Provinces. Long-term sea temperature averages compiled by others indicate that the North Atlantic decrease can be considered as a return to more normal temperatures after two decades with abnormally high temperatures. Upward sea temperature trends are noted in the trade wind region of the South Atlantic. Latent beat flux trends usually determine the trend of the heat gain by the ocean. When latent heat flux trends result from oceanographic changes, i.e., advection or upwelling changes, inverse relations between sea surface temperature and heat gain by the ocean occur. When meteorological changes such as circulation patterns cause trends, direct relations between sea surface temperature and beat gain are produced. From the Middle Atlantic Bight to Greenland sea surface temperature decreased rapidly, presumably through cold water advection causing a large drop in the saturated mixing ratio at the air-sea interface, a decrease in the latent heat flux, and a resulting increase in the heat gain by the ocean. Over nearly all of the rest of the North and South Atlantic Ocean the trend of the heat gain was negative. Over most of the North Atlantic the decrease in heat gain was caused by meteorological events and hence the sea surface temperature also decreased. Over the South Atlantic the sea temperature trend was positive and produced a negative trend of the boat gain by the ocean.

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Andrew F. Bunker

Abstract

Energy fluxes through the surface of the North Atlantic Ocean have been calculated using bulk aerodynamic equations with exchange coefficients which vary with wind speed and stability, and radiation equations. Values of the coefficients were determined from published results of many experiments made at sea, coastal installations and in laboratories. Eight million ship weather reports were used for flux calculations. Reliabilities of monthly meteorological and flux averages are found to be good in areas having SW or move observations per average. A chart of the net annual heat gain by the ocean shows regions with characteristic gains or losses such as the Gulf Stream, Norwegian Sea, Labrador Current, trade winds and upwelling areas. Annual cycles of fluxes, winds, temperatures, clouds and rainfall in eight regions are presented and discussed from the point of view of predominating air–sea interaction processes. Contributions of meteorological variables, oceanic currents, atmospheric circulations and air–sea interaction processes to fluxes over other regions of the Atlantic are appraised.

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Andrew F. Bunker

Abstract

TIROS VII photographs revealed that lines and groupings of clouds off the southwestern coast of India recurred frequently in preferred locations during the northeast monsoon season. Observations made on a meteorological flight of a C-54Q aircraft through this area 3 hr after a TIROS passage allowed a detailed study of the atmospheric conditions associated with this phenomenon. From aircraft observations of clouds, winds, temperatures, humidifies, and turbulence, and from ship and land observations, a description of the phenomenon is given and possible causes are discussed. The offshore air was generally clear except for several lines of small low cumulus clouds which divided the area into lobes of clear air. These lines were located off-shore and to the north of the valleys. The potential virtual temperature of the air in the cloud lines was 1.5C lower than the surrounding air at the flight level and about the same as the air near the sea surface. Either this air had been mixed previously by some mechanism and the clouds are produced by buoyancy forces, or air parcels were lifted by an external force. Convergence, the most likely process which can lift air, was produced by mesoscale eddies leeward of the mountains or by the merging of small jets flowing from the cast through the valleys with the air flowing from the north over the Arabian Sea. Other possible mechanisms capable of producing cloud lines are discussed.

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Andrew F. Bunker

Abstract

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Andrew F. Bunker

Abstract

Turbulent transports of sensible heat and water vapor have been measured from an airplane within southerly-flowing air masses over the western North Atlantic Ocean. It is found that the lower levels of these air masses are unstable and warmed by the transport, of heat from the water below, while the higher levels are stable and warmed by diffusion from the subsidence-inversion air aloft. Average values of the upward flux of sensible heat were found to be 2.1 mcal cm−2 sec−1 in the middle latitudes and 0.1 mcal cm−2 sec−1 in the tropics. The downward heat flux was 0.3 mcal cm−2 sec−1 in the region above the potential temperature minimum formed between the warm air aloft and the water-warmed air below. The flux of latent heat of condensation in the form of water vapor was found to be less than the flux of sensible heat from the ocean in the middle latitudes within 300 km of the east coast and about one order of magnitude greater than the sensible flux farther offshore and in the tropics. The observations are discussed in relation to various theories of heat transport and the process by which the atmosphere accumulates heat from the earth's surface.

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Andrew F. Bunker

Abstract

The meridional circulation over the equatorial central Pacific Ocean in April 1967 was found to consist of a shallow northern Hadley cell, an extensive equatorial cell centered south of the equator with maximum subsidence over the equator, and a strong southern Hadley cell. Part of the high-level outflow of the southern Hadley cell subsides across the equator and decreases the activity of the northern convergence zone. The divergence of the equatorial easterlies and the resulting subsidence is increased by a low value of the shearing stress which was observed over the cool upwelling equatorial waters. Transfer of energy by radiation, turbulence, precipitation and advection is determined from observations and calculation. Energy budgets are constructed for three regions between 13N and 13S to obtain as a residual the transport of energy by cumulus and cumulonimbus convection. The budget shows that the mid-tropospheric layer of the low energy is maintained by the efficient vertical transfer of energy by cumulus convection through the layer and the loss of energy by radiation.

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Andrew F. Bunker

Abstract

A method of measuring the horizontal and vertical turbulent components of the wind has been developed to meet the need for these measurements over the open ocean. An anemometer, a vertical accelerometer, and a gyroscope mounted in an airplane (U. S. Navy PRY-6A) yield simultaneous records of the total airspeed, vertical accelerations, and the attitude of the airplane. From these records, and from airplane-lift theory and the characteristics of the particular type of aircraft, the vertical and horizontal fluctuations of the wind, the root-mean-square deviation velocities, and the shearing stress can be computed. The method allows the phugoid oscillations of the airplane to contribute nearly periodic velocity terms to both components; these must be eliminated by a computational step. A different reduction method can give phugoid-free vertical velocities, but an additional instrument will be required for phugoid-free horizontal velocities. The airplane lift has a response of from 80 to 100 per cent to gusts of radius 20 meters or more, and the method fails to measure reliably gusts larger than 350 m. This limits the contributions to the quantities presented to those by gusts within the 20- to 350-m range. In the lower levels of polar-continental air masses, root-mean-square vertical velocities have been observed to attain 191 centimeters per second over land and 120 cm/sec over water, while stresses reached maxima of 16.6 dyne/cm2 over land and 3.8 dy/cm2 over water. Shearing stresses in the lowest 60 m in the trade winds averaged 0.2 dy/cm2 over seven days, while vertical velocities averaged 26 cm/sec. The influence of atmospheric stability and convective activity upon the turbulent velocities is discussed.

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Andrew F. Bunker

Abstract

The entrainment equations of Houghton and Cramer have been extended to include the effects of diffusion of heat and momentum and the frictional pressure drag. The equations developed from these considerations show that certain combinations of parcel size, temperature difference, vertical velocity, and turbulence permit buoyant air parcels to pass from the bottom to the top of the turbulent ground layer. Other combinations lead to rapid dissipation of the parcel's temperature difference and velocity. The equations have been checked against three sets of observations within unstable, dry air masses. Observed properties of buoyant parcels existing in super-adiabatic atmospheres agree, within observational error, with combinations leading to extended survival of air bubbles as predicted by the equations. One set of data leads to the approximation of the value of the coefficient of pressure drag, 0.1, associated with an air parcel moving through the air.

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Andrew F. Bunker

The humidity indicated by the rapidly rising radiosonde lags behind the true humidity of the air, making moisture gradient determinations uncertain by a factor of 4. Application of isothermal laboratory determinations of the lag to the readings may be misleading because the radiosonde, in rising through the atmosphere, usually passes from warm air to cooler air. The lag of the strip may be quite different under these circumstances. By comparison of radiosonde reports with airplane humidity soundings, it is found that in the case of the radiosonde moving from warm, dry air (about − 5°C) to cooler, moister air (about − 18°C) the lag may increase to 165 seconds. When it passes to cooler, drier air, the lag decreases to 10 to 20 seconds. Using these lags and assuming an exponential approach to the final value, more nearly correct values of the humidity at particular heights can be computed from the radiosonde records.

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