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Abstract
This paper documents the annual march of the following processes for the 70°N–20°S region of the Atlantic, including the Gulf of Mexico and Caribbean Sea: net surface heat gains (monthly mean time-scale), subsurface heat storage change (bimonthly), divergence of the “vertically and zonally integrated net meridional heat transport” VZINMHT; (bimonthly). Results for the first three parameters are presented as averages for 10° (5°) zones of the extratropics (tropics)l the VZINMHT's are for the zones' bounding latitude circles.
The net surface heat gain is residually-estimated from sea-air heat exchange calculations. The extratropical North Atlantic is a net loser of heat to the atmosphere for the year as a whole. It experiences a very short period (May–August) of surface heat uptake, during which the maximum rate is as high as 110–130 W m−2, and a more lengthy surface heat loss, much of which exceeds 100 W m−2 and has a 190–250 W m−2 extreme. The tropical Atlantic undergoes a more subdued, and sometimes more irregular, annual march of this process. Between 20°N–5°S the ocean surface gains heat throughout all or almost all of the year, but generally at much lower rates than in the extratropics. April–September surface heat losses between 5–20°S are balanced by October–March gains. Estimation of the subsurface heat storage change is made using 233 957 soundings for the decade 1967–76, a 5° latitude-longitude square spatial resolution, and 14 oceanic layers between the surface and 500 m. Extratropical warming is largely confined to May–August, appears to reach 400 m in some zones, and generally totals 150–225 W m−2. The maximum cooling in this region tends to occur in November–December and, with the exception of 30–40°N, extends to 500 m and totals 250–350 W m−2. Between 30–40°N the storm change is strongly concentrated above 100 m. The annual cycle of this process is more varied and irregular, and of smaller amplitude, in the tropical belt.
The VZINMHT divergence is obtained as the difference between the rates of net surface heat gain and subsurface heat storage change. The extratropical zones import heat throughout all or almost all of January–October, generally at rates of 50–150 W m−2. Only in November–December (40–70°N) and January–February (40–50°N) is this region suggested to export, heat, a result that is rather uncertain. The tropical VZINMHT divergence pattern is dominated by export, especially between 25°N–10°S. The VZINMHT is estimated by successive southward integration of its divergence from assumed near-zero 70°N boundary conditions, a procedure whose uncertainty increases in the same direction and becomes large in the tropics. Northward VZINMHTs prevail throughout the study region during all or almost all of January–October. They tend to be largest in the tropics (150–250×1013 W), especially during July–October, and experience pronounced extratropical decreases, often between 30–50°N. The November–December VZINMHT is suggested to be directed southward throughout much or even all of the study region, and to increase in this direction to a 10–20°S maximum of almost 300×1013 W. However, this result is considered extremely tentative. The annual average VZINMHT is accordingly directed northward at all latitudes. It increases from 50–80×1013 W at 20°S to a 107–115×1013 W maximum in the northern tropics, and then decreases strongly poleward of 30°N, especially between 30–40°N.
Abstract
This paper documents the annual march of the following processes for the 70°N–20°S region of the Atlantic, including the Gulf of Mexico and Caribbean Sea: net surface heat gains (monthly mean time-scale), subsurface heat storage change (bimonthly), divergence of the “vertically and zonally integrated net meridional heat transport” VZINMHT; (bimonthly). Results for the first three parameters are presented as averages for 10° (5°) zones of the extratropics (tropics)l the VZINMHT's are for the zones' bounding latitude circles.
The net surface heat gain is residually-estimated from sea-air heat exchange calculations. The extratropical North Atlantic is a net loser of heat to the atmosphere for the year as a whole. It experiences a very short period (May–August) of surface heat uptake, during which the maximum rate is as high as 110–130 W m−2, and a more lengthy surface heat loss, much of which exceeds 100 W m−2 and has a 190–250 W m−2 extreme. The tropical Atlantic undergoes a more subdued, and sometimes more irregular, annual march of this process. Between 20°N–5°S the ocean surface gains heat throughout all or almost all of the year, but generally at much lower rates than in the extratropics. April–September surface heat losses between 5–20°S are balanced by October–March gains. Estimation of the subsurface heat storage change is made using 233 957 soundings for the decade 1967–76, a 5° latitude-longitude square spatial resolution, and 14 oceanic layers between the surface and 500 m. Extratropical warming is largely confined to May–August, appears to reach 400 m in some zones, and generally totals 150–225 W m−2. The maximum cooling in this region tends to occur in November–December and, with the exception of 30–40°N, extends to 500 m and totals 250–350 W m−2. Between 30–40°N the storm change is strongly concentrated above 100 m. The annual cycle of this process is more varied and irregular, and of smaller amplitude, in the tropical belt.
The VZINMHT divergence is obtained as the difference between the rates of net surface heat gain and subsurface heat storage change. The extratropical zones import heat throughout all or almost all of January–October, generally at rates of 50–150 W m−2. Only in November–December (40–70°N) and January–February (40–50°N) is this region suggested to export, heat, a result that is rather uncertain. The tropical VZINMHT divergence pattern is dominated by export, especially between 25°N–10°S. The VZINMHT is estimated by successive southward integration of its divergence from assumed near-zero 70°N boundary conditions, a procedure whose uncertainty increases in the same direction and becomes large in the tropics. Northward VZINMHTs prevail throughout the study region during all or almost all of January–October. They tend to be largest in the tropics (150–250×1013 W), especially during July–October, and experience pronounced extratropical decreases, often between 30–50°N. The November–December VZINMHT is suggested to be directed southward throughout much or even all of the study region, and to increase in this direction to a 10–20°S maximum of almost 300×1013 W. However, this result is considered extremely tentative. The annual average VZINMHT is accordingly directed northward at all latitudes. It increases from 50–80×1013 W at 20°S to a 107–115×1013 W maximum in the northern tropics, and then decreases strongly poleward of 30°N, especially between 30–40°N.
Abstract
The heat budget of the atmosphere-ocean-land system in the Indian Ocean region (30°N–30°S, 30–120°E) is studied on the basis of ocean surface heat flux calculations from long-term ship observations and satellite-derived estimates of net radiation at the top of the atmosphere.
The hydrosphere to the north of the equator exports heat at rates of 5 × 1014 W for the year as a whole, and more than 8 × 1014 W during the northern summer (May–October) half-year, respectively. In contrast, the heat budget of the Southern Hemisphere water is dominated by the seasonal storage/depletion of heat transferred through the ocean surface. Oceanic heat export/import is small for this region during both the November–April and May–October half-years, and near zero for the year as a whole. The mean annual net meridional oceanic heat transport is directed southward throughout the study area, reaching a maximum of 8 × 1014 W at 10–15°S. From heat balance considerations, the annual average upwelling north of the equator is calculated to be ∼6 × 10−7 m s−1. Most of the compensatory down-welling must occur outside the tropical Indian Ocean.
Residually determined heat export by the atmosphere north of the equator averages 18 and 4 × 10−14 W during the northern summer and winter half-years, respectively. South of the equator the atmosphere exports heat at a mean annual rate of 19 × 10−14 W, with little seasonal variation. During northern summer, the atmospheric energy export from the southern tropical Indian Ocean is largely in the form of latent heat and is directed northward across the equator. The southern tropical Indian Ocean is the major source of the atmospheric water vapor carried across the coastline of southern Asia during the northern summer southwest monsoon. The larger water vapor flux divergence south of the equator at this time is fed by strong evaporation. This is supported by a combination of the seasonal depletion of the local oceanic heat content and oceanic heat import from north of the equator, in addition to the surface net radiation.
South of about 10°S, the atmosphere must dispose of both the net radiative heat input at the top of the system and the heat imported within the oceanic water body. In contrast, to the north the atmosphere and hydrosphere make similar contributions to the lateral energy export.
Abstract
The heat budget of the atmosphere-ocean-land system in the Indian Ocean region (30°N–30°S, 30–120°E) is studied on the basis of ocean surface heat flux calculations from long-term ship observations and satellite-derived estimates of net radiation at the top of the atmosphere.
The hydrosphere to the north of the equator exports heat at rates of 5 × 1014 W for the year as a whole, and more than 8 × 1014 W during the northern summer (May–October) half-year, respectively. In contrast, the heat budget of the Southern Hemisphere water is dominated by the seasonal storage/depletion of heat transferred through the ocean surface. Oceanic heat export/import is small for this region during both the November–April and May–October half-years, and near zero for the year as a whole. The mean annual net meridional oceanic heat transport is directed southward throughout the study area, reaching a maximum of 8 × 1014 W at 10–15°S. From heat balance considerations, the annual average upwelling north of the equator is calculated to be ∼6 × 10−7 m s−1. Most of the compensatory down-welling must occur outside the tropical Indian Ocean.
Residually determined heat export by the atmosphere north of the equator averages 18 and 4 × 10−14 W during the northern summer and winter half-years, respectively. South of the equator the atmosphere exports heat at a mean annual rate of 19 × 10−14 W, with little seasonal variation. During northern summer, the atmospheric energy export from the southern tropical Indian Ocean is largely in the form of latent heat and is directed northward across the equator. The southern tropical Indian Ocean is the major source of the atmospheric water vapor carried across the coastline of southern Asia during the northern summer southwest monsoon. The larger water vapor flux divergence south of the equator at this time is fed by strong evaporation. This is supported by a combination of the seasonal depletion of the local oceanic heat content and oceanic heat import from north of the equator, in addition to the surface net radiation.
South of about 10°S, the atmosphere must dispose of both the net radiative heat input at the top of the system and the heat imported within the oceanic water body. In contrast, to the north the atmosphere and hydrosphere make similar contributions to the lateral energy export.
Abstract
Monthly multi-annual mean heat budgets are calculated for the Caribbean Sea; previous results from the Gulf of Mexico are included to portray fields for the combined Central American seas. Oceanic heat storage rates (QT ) for the upper 200 meters in the Caribbean are calculated directly from vertical subsurface temperature data for the decade 1967–76; spatial distribution of QT are contoured on maps for February, May, August and November. In the Gulf of Mexico, QT was found to be determined principally by the surface heat exchange. In the Caribbean Sea, QT is related primarily to convergence and divergence of heat transport; QT patterns in the southern Caribbean can be associated with Ekman pumping and heat advection due to currents. The monthly mean surface heat exchanges are defined by the averages of Bunker's unpublished data and the atlas data of Hastenrath and Lamb. Comparisons are also made with the results of both Budyko and Coló in the Caribbean Sea for historical perspective. Monthly mean oceanic heat transport divergences are then derived as residuals in the heat budget equation. Partial verification is obtained by directly computing the horizontal component of heat advection using estimates of water transport in the Central American seas.
Estimates of the seasonal freshwater budgets in the Central American seas are calculated using the oceanic precipitation rates (P) of Dorman and Bourke and the averaged evaporation rates (E) obtained from Bunker and from Hastenrath and Lamb. Annual mean E – P values of 104 and 112 cm are obtained for the Caribbean Sea and Central American seas, respectively. The freshwater continuity is examined by including estimates of river discharge rates; it is shown that river discharge does not compensate for the net water loss caused by an excess of evaporation over precipitation. An analysis of the freshwater flux in the Central American seas, using typical salinity data, indicates a convergence of freshwater over the region consistent with the earlier observation of excessive evaporation.
Abstract
Monthly multi-annual mean heat budgets are calculated for the Caribbean Sea; previous results from the Gulf of Mexico are included to portray fields for the combined Central American seas. Oceanic heat storage rates (QT ) for the upper 200 meters in the Caribbean are calculated directly from vertical subsurface temperature data for the decade 1967–76; spatial distribution of QT are contoured on maps for February, May, August and November. In the Gulf of Mexico, QT was found to be determined principally by the surface heat exchange. In the Caribbean Sea, QT is related primarily to convergence and divergence of heat transport; QT patterns in the southern Caribbean can be associated with Ekman pumping and heat advection due to currents. The monthly mean surface heat exchanges are defined by the averages of Bunker's unpublished data and the atlas data of Hastenrath and Lamb. Comparisons are also made with the results of both Budyko and Coló in the Caribbean Sea for historical perspective. Monthly mean oceanic heat transport divergences are then derived as residuals in the heat budget equation. Partial verification is obtained by directly computing the horizontal component of heat advection using estimates of water transport in the Central American seas.
Estimates of the seasonal freshwater budgets in the Central American seas are calculated using the oceanic precipitation rates (P) of Dorman and Bourke and the averaged evaporation rates (E) obtained from Bunker and from Hastenrath and Lamb. Annual mean E – P values of 104 and 112 cm are obtained for the Caribbean Sea and Central American seas, respectively. The freshwater continuity is examined by including estimates of river discharge rates; it is shown that river discharge does not compensate for the net water loss caused by an excess of evaporation over precipitation. An analysis of the freshwater flux in the Central American seas, using typical salinity data, indicates a convergence of freshwater over the region consistent with the earlier observation of excessive evaporation.
Abstract
The formation of a recirculating subsurface core in an internal solitary wave (ISW) of depression, shoaling over realistic bathymetry, is explored through fully nonlinear and nonhydrostatic two-dimensional simulations. The computational approach is based on a high-resolution/accuracy deformed spectral multidomain penalty-method flow solver, which employs the recorded bathymetry, background current, and stratification profile in the South China Sea. The flow solver is initialized using a solution of the fully nonlinear Dubreil–Jacotin–Long equation. During shoaling, convective breaking precedes core formation as the rear steepens and the trough decelerates, allowing heavier fluid to plunge forward, forming a trapped core. This core-formation mechanism is attributed to a stretching of a near-surface background vorticity layer. Since the sign of the vorticity is opposite to that generated by the propagating wave, only subsurface recirculating cores can form. The onset of convective breaking is visualized, and the sensitivity of the core properties to changes in the initial wave, near-surface background shear, and bottom slope is quantified. The magnitude of the near-surface vorticity determines the size of the convective-breaking region, and the rapid increase of local bathymetric slope accelerates core formation. If the amplitude of the initial wave is increased, the subsequent convective-breaking region increases in size. The simulations are guided by field data and capture the development of the recirculating subsurface core. The analyzed parameter space constitutes a baseline for future three-dimensional simulations focused on characterizing the turbulent flow engulfed within the convectively unstable ISW.
Abstract
The formation of a recirculating subsurface core in an internal solitary wave (ISW) of depression, shoaling over realistic bathymetry, is explored through fully nonlinear and nonhydrostatic two-dimensional simulations. The computational approach is based on a high-resolution/accuracy deformed spectral multidomain penalty-method flow solver, which employs the recorded bathymetry, background current, and stratification profile in the South China Sea. The flow solver is initialized using a solution of the fully nonlinear Dubreil–Jacotin–Long equation. During shoaling, convective breaking precedes core formation as the rear steepens and the trough decelerates, allowing heavier fluid to plunge forward, forming a trapped core. This core-formation mechanism is attributed to a stretching of a near-surface background vorticity layer. Since the sign of the vorticity is opposite to that generated by the propagating wave, only subsurface recirculating cores can form. The onset of convective breaking is visualized, and the sensitivity of the core properties to changes in the initial wave, near-surface background shear, and bottom slope is quantified. The magnitude of the near-surface vorticity determines the size of the convective-breaking region, and the rapid increase of local bathymetric slope accelerates core formation. If the amplitude of the initial wave is increased, the subsequent convective-breaking region increases in size. The simulations are guided by field data and capture the development of the recirculating subsurface core. The analyzed parameter space constitutes a baseline for future three-dimensional simulations focused on characterizing the turbulent flow engulfed within the convectively unstable ISW.
