Peculiarities of the seasonal variability of the external thermal balance and its components on the surface of the Atlantic Ocean
The results of the investigations of the peculiarities of spatial distribution and seasonal variability of the external heat budget on the surface of the Atlantic Ocean and its components – net radiation budget and latent and sensible heat fluxes, are presented. It is shown that maximum values of th...
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| Цитувати: | Peculiarities of the seasonal variability of the external thermal balance and its components on the surface of the Atlantic Ocean / Yu.V. Artamonov, P.D. Lomakin, E.A. Skripaleva, N.A. Timofeev, A.V. Yurovsky, N.P. Bulgakov // Український антарктичний журнал. — 2004. — № 2. — С. 15-24. — Бібліогр.: 9 назв. — англ. |
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irk-123456789-1281442018-01-07T03:03:02Z Peculiarities of the seasonal variability of the external thermal balance and its components on the surface of the Atlantic Ocean Artamonov, Yu.V. Lomakin, P.D. Skripaleva, E.A. Timofeev, N.A. Yurovsky, A.V. Bulgakov, N.P. Геофізика The results of the investigations of the peculiarities of spatial distribution and seasonal variability of the external heat budget on the surface of the Atlantic Ocean and its components – net radiation budget and latent and sensible heat fluxes, are presented. It is shown that maximum values of the radiation balance are observed on the tropical peripheries of the subtropical centers of high atmospheric pressure in both hemispheres. Extreme values of the sensible and latent flux are in good correlation well with the wind field parameters in the tropical zone of the ocean and in the area of the Antarctic Circumpolar currents as well as with the characteristics of the meridian large-scale currents. Maximum of seasonal variations of external heat balance are characteristic of the Gulf Stream zone, the western Southern subtropical anticyclonic circulation and the Falkland current area. The study was carried out using up-to-date satellite data sets. Представлены результаты исследований особенностей пространственного распределения и сезонной изменчивости внешнего теплового баланса на поверхности Атлантического океана и его компонентов – радиационной составляющей и составляющей, связанной с турбулентным обменом (поток явного тепла и скрытая теплота испарения). Показано, что максимальные значения радиационного баланса наблюдаются на тропических перифериях субтропических центров высокого атмосферного давления в обоих полушариях. Экстремальные значения составляющей, связанной с турбулентным обменом, хорошо коррелируют с параметрами поля ветра в тропической зоне океана и в области Антарктического Циркумполярного течения, а также с характеристиками меридиональных крупномасштабных течений. Максимальные сезонные вариации внешнего теплового баланса характерны для зоны Гольфстрима, западной части Южного субтропического антициклонического круговорота и района Фолклендского течения. Работа выполнена на базе современных массивов спутниковых наблюдений. Представлено результати досліджень особливостей просторового розподілу і сезонної мінливості зовнішнього теплового балансу на поверхні Атлантичного океану та його компонентів – радіаційної складової і складової, пов'язаної з турбулентним обміном (потік явного тепла і схована теплота випару). Показано, що максимальні значення радіаційного балансу спостерігаються на тропічних периферіях субтропічних центрів високого атмосферного тиску в обох півкулях. Екстремальні значення складової теплового балансу, пов'язаної з турбулентним обміном, добре корелюють з параметрами поля вітру в тропічній зоні океану та в області Антарктичної Циркумполярної течії, а також з характеристиками меридіональних великомасштабних течій. Максимальні сезонні варіації зовнішнього теплового балансу характерні для зони Гольфстріму, західної частини Південного субтропічного антициклонічного круговороту і району Фолклендської течії. Робота виконана на базі масивів сучасних супутникових спостережень. 2004 Article Peculiarities of the seasonal variability of the external thermal balance and its components on the surface of the Atlantic Ocean / Yu.V. Artamonov, P.D. Lomakin, E.A. Skripaleva, N.A. Timofeev, A.V. Yurovsky, N.P. Bulgakov // Український антарктичний журнал. — 2004. — № 2. — С. 15-24. — Бібліогр.: 9 назв. — англ. 1727-7485 http://dspace.nbuv.gov.ua/handle/123456789/128144 551.465.521(261) en Національний антарктичний науковий центр МОН України |
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Геофізика Геофізика |
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Геофізика Геофізика Artamonov, Yu.V. Lomakin, P.D. Skripaleva, E.A. Timofeev, N.A. Yurovsky, A.V. Bulgakov, N.P. Peculiarities of the seasonal variability of the external thermal balance and its components on the surface of the Atlantic Ocean |
| description |
The results of the investigations of the peculiarities of spatial distribution and seasonal variability of the external heat budget on the surface of the Atlantic Ocean and its components – net radiation budget and latent and sensible heat fluxes, are presented. It is shown that maximum values of the radiation balance are observed on the tropical peripheries of the subtropical centers of high atmospheric pressure in both hemispheres. Extreme values of the sensible and latent flux are in good correlation well with the wind field parameters in the tropical zone of the ocean and in the area of the Antarctic Circumpolar currents as well as with the characteristics of the meridian large-scale currents. Maximum of seasonal variations of external heat balance are characteristic of the Gulf Stream zone, the western Southern subtropical anticyclonic circulation and the Falkland current area. The study was carried out using up-to-date satellite data sets. |
| format |
Article |
| author |
Artamonov, Yu.V. Lomakin, P.D. Skripaleva, E.A. Timofeev, N.A. Yurovsky, A.V. Bulgakov, N.P. |
| author_facet |
Artamonov, Yu.V. Lomakin, P.D. Skripaleva, E.A. Timofeev, N.A. Yurovsky, A.V. Bulgakov, N.P. |
| author_sort |
Artamonov, Yu.V. |
| title |
Peculiarities of the seasonal variability of the external thermal balance and its components on the surface of the Atlantic Ocean |
| title_short |
Peculiarities of the seasonal variability of the external thermal balance and its components on the surface of the Atlantic Ocean |
| title_full |
Peculiarities of the seasonal variability of the external thermal balance and its components on the surface of the Atlantic Ocean |
| title_fullStr |
Peculiarities of the seasonal variability of the external thermal balance and its components on the surface of the Atlantic Ocean |
| title_full_unstemmed |
Peculiarities of the seasonal variability of the external thermal balance and its components on the surface of the Atlantic Ocean |
| title_sort |
peculiarities of the seasonal variability of the external thermal balance and its components on the surface of the atlantic ocean |
| publisher |
Національний антарктичний науковий центр МОН України |
| publishDate |
2004 |
| topic_facet |
Геофізика |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/128144 |
| citation_txt |
Peculiarities of the seasonal variability of the external thermal balance and its components on the surface of the Atlantic Ocean / Yu.V. Artamonov, P.D. Lomakin, E.A. Skripaleva, N.A. Timofeev, A.V. Yurovsky, N.P. Bulgakov // Український антарктичний журнал. — 2004. — № 2. — С. 15-24. — Бібліогр.: 9 назв. — англ. |
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2025-07-09T08:27:48Z |
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| fulltext |
УКРАЇНСЬКИЙ АНТАРКТИЧНИЙ
ЖУРНАЛ
УАЖ, № 2, 15-24, (2004)
15
УДК 551.465.521(261)
PECULIARITIES OF THE SEASONAL VARIABILITY OF THE EXTERNAL THERMAL
BALANCE AND ITS COMPONENTS ON THE SURFACE OF THE ATLANTIC OCEAN
Yu. V. Artamonov, N.P. Bulgakov, P.D. Lomakin, E.A. Skripaleva, N.A. Timofeev,
A.V. Yurovsky
Marine hydrophisical institute, Sebastopol,
e-mail: ocean@mhi2.sebastopol.ua/Fax:380(0692)444253
Abstract. The results of the investigations of the peculiarities of spatial distribution and seasonal variability of the external heat
budget on the surface of the Atlantic Ocean and its components – net radiation budget and latent and sensible heat fluxes, are
presented. It is shown that maximum values of the radiation balance are observed on the tropical peripheries of the subtropical
centers of high atmospheric pressure in both hemispheres. Extreme values of the sensible and latent flux are in good correlation
well with the wind field parameters in the tropical zone of the ocean and in the area of the Antarctic Circumpolar currents as
well as with the characteristics of the meridian large-scale currents. Maximum of seasonal variations of external heat balance
are characteristic of the Gulf Stream zone, the western Southern subtropical anticyclonic circulation and the Falkland current
area. The study was carried out using up-to-date satellite data sets.
Key words: external heat budget, net radiation budget, latent and sensible heat fluxes, seasonal variability.
Особенности внутригодовой изменчивости внешнего теплового баланса и его составляющих на поверхности
Атлантического океана Ю.В. Артамонов, Н.П. Булгаков, П.Д. Ломакин, Е.А. Скрипалева, Н.А. Тимофеев,
А.В. Юровский
Реферат. Представлены результаты исследований особенностей пространственного распределения и сезонной
изменчивости внешнего теплового баланса на поверхности Атлантического океана и его компонентов – радиационной
составляющей и составляющей, связанной с турбулентным обменом (поток явного тепла и скрытая теплота
испарения). Показано, что максимальные значения радиационного баланса наблюдаются на тропических перифериях
субтропических центров высокого атмосферного давления в обоих полушариях. Экстремальные значения
составляющей, связанной с турбулентным обменом, хорошо коррелируют с параметрами поля ветра в тропической
зоне океана и в области Антарктического Циркумполярного течения, а также с характеристиками меридиональных
крупномасштабных течений. Максимальные сезонные вариации внешнего теплового баланса характерны для зоны
Гольфстрима, западной части Южного субтропического антициклонического круговорота и района Фолклендского
течения. Работа выполнена на базе современных массивов спутниковых наблюдений.
Особливості внутрішньорічної мінливості зовнішнього теплового балансу та його складових на поверхні
Атлантичного океану Ю.В. Артамонов, М.П. Булгаков, П.Д. Ломакін, О.О. Скрипальова, М.А. Тімофеєв,
О.В. Юровський
Реферат. Представлено результати досліджень особливостей просторового розподілу і сезонної мінливості
зовнішнього теплового балансу на поверхні Атлантичного океану та його компонентів – радіаційної складової і
складової, пов'язаної з турбулентним обміном (потік явного тепла і схована теплота випару). Показано, що
максимальні значення радіаційного балансу спостерігаються на тропічних периферіях субтропічних центрів високого
атмосферного тиску в обох півкулях. Екстремальні значення складової теплового балансу, пов'язаної з турбулентним
обміном, добре корелюють з параметрами поля вітру в тропічній зоні океану та в області Антарктичної
Циркумполярної течії, а також з характеристиками меридіональних великомасштабних течій. Максимальні сезонні
варіації зовнішнього теплового балансу характерні для зони Гольфстріму, західної частини Південного субтропічного
антициклонічного круговороту і району Фолклендської течії. Робота виконана на базі масивів сучасних супутникових
спостережень.
1. Introduction
Investigations of variability of the heat balance components of oceans and seas are important
for understanding the processes of the ocean-atmosphere interaction. Heat balance essentially affects
the water masses formation, frontal interfaces and current regimes. Due to the heat redistribution
between the low and high latitudes by the oceanic currents systems, various ocean regions influence
the climate in different ways. The papers by Timofeev (1970, 1983) and Strokina (1989) consider
long-term monthly values of the thermal budget characteristics of the World Ocean surface averaged
Yu.A. Artamonov et al.: PECULIARITIES OF THE SEASONAL VARIABILITY OF THE EXTERNAL THERMAL …
16
over 5-grade squares. Being so roughly averaged, regional features’ resolution appeared far from
sufficient. The task of the proposed paper consists in a more detailed research of the features of spatial
distribution and regularities of variability of the intra-year cycle of the external heat balance of the
Atlantic Ocean surface and its components – the radiation component and the component relating to
the turbulent exchange, i.e. the latent and sensible heat fluxes.
2. Data and method
In the present work monthly averaged characteristics of the external heat balance of the
Atlantic Ocean surface and its components in two-grade trapezes for the water area located between
the parallels 40°N and 65°S calculated by N.A.Timofeev and A.V.Jurovsky (1999) based on the
modern arrays of satellite observations were used.
Analyzed fields of the heat balance components are determined using following expressions.
The total amount of heat energy (MJ/m2/day) received (sign plus) or given up (sign minus) by
the ocean through its surface makes the external heat balance )( LEHRB no +−= .
The radiation balance ( nR ) on the water surface (MJ/m2/day) is calculated using the satellite
data by the formula:
[ ] µµ ⋅
⎭
⎬
⎫
⎩
⎨
⎧
−+−+−−⋅
+
−
+= )(5.000037.0017.031.08.6)
04.0sin
0376.0sin06.094.0( 32
aHn ttttt
h
hQR ,
where )()()()( minminmaxmax FFFFAAAA ccnccn −−=−−=µ ; cnA is the albedo of the ocean-
atmosphere system (OAS); cnF is the long-wave radiation of OAS; h is the Sun height; t is the
ocean surface temperature (SST); at is air temperature in the near-surface layer; cc FFAA ,,, minmax
are the tabulated parameters (Timofeev, Yurovsky, 1999); HQ is the total solar radiation at the normal
temperature.
The components related to the turbulent exchange – latent (LE) and sensible (H) heat fluxes
(MJ/m2/day), are determined as following:
uttutH a ))(000075.00012.0)(4.0112( −+−= ,
( )ueeutLE aw −+−= )000075.00012.0)(8.0172( ,
where we is the saturation elasticity of water vapor; ae is the water vapor elasticity; u is the wind
speed module.
Based on these data the monthly averaged maps of distribution of the studied Atlantic water
area are constructed. The harmonious analysis permitted to study distributions of the amplitude-phase
characteristics of seasonal variability of the ocean external thermal balance. Analysis and
interpretation of the results also included the maps of geostrophic circulation calculated in
(Artamonov et al., 2001) using the array from (Levitus, Boyer, 1994), horizontal distributions of the
ocean surface temperature (SST) (Levitus, Boyer, 1994) and the monthly averaged fields of the wind
tangential tension above the oceanic surface (Hellerman, Rosenstein, 1983).
3. Analysis of the results
Radiation balance ( nR ). Distribution of the radiation balance on the Atlantic Ocean surface
within a year is basically of the zonal character (Fig. 1). The highest values of nR (more than 20
MJ/m2/day) are observed on the southern and northern peripheries of the zones of high atmospheric
pressure of the Northern and Southern hemispheres where the low cloudy weather promotes the
maximum inflow of radiant energy to the ocean surface. In the near-equatorial latitudes, especially in
the eastern part of the ocean, cloudiness increase results in the considerable reduction of nR up to
14 MJ/m2/day in the Inter-tropical convergence zone (ITCZ). Decrease of nR due to the growth of the
Yu.A. Artamonov et al.: PECULIARITIES OF THE SEASONAL VARIABILITY OF THE EXTERNAL THERMAL …
17
cloudiness cover is also observed in the regions of intensive cyclonic activity in the tropical and
subtropical latitudes – closer to the African and South American coasts. The smallest values of nR are
characteristic of the near-Antarctic waters at the ice edge where its average annual values on the ice-
free water area do not exceed 6 MJ/m2/day. On average the values of nR for a year on the whole ice-
free surface of the Southern Atlantic are positive.
Fig. 1. Radiation balance on the ocean surface (MJ/m2/day).
Seasonal variations of the radiation balance distribution have the following characteristic
features. Since October till February the area of maximum values of nR located southwards of the
equator is clearly traced. In October its center is in the area of 10°S and 30°W (Fig. 1). The area of
such high values of nR is formed in July directly on the equator. Then its center moves to the
southeast and achieves the extreme southern position (25°S and 10°W) in January. During this season
the absolute maximum of nR amounts there to 22 MJ/m2/day. Further to the east along these latitudes
nR is a little bit smaller. In January-May the south-tropical area of high values of the radiation heat
inflow moves to the north with the values of nR being decreased. In June-July the maximum of the
considered characteristic is located almost at the equator where its values do not exceed 15
MJ/m2/day.
Near the South American coast between 25° and 40°S growth of nR is noted from November
to February. In January it increases up to 18 MJ/m2/day. Increase of the radiant energy flow to the
Yu.A. Artamonov et al.: PECULIARITIES OF THE SEASONAL VARIABILITY OF THE EXTERNAL THERMAL …
18
ocean surface is connected with small cloudiness above the Brazil current in summer in the Southern
Hemisphere. In winter when the Brazil current waters weakly penetrate to the south and the cloudiness
increases, the values of nR diminish up to 8-6 MJ/m2/day.
In the Northern Hemisphere in the western tropics the second area of high values of nR is
formed in February-March (Fig. 1). In the seasonal cycle it moves to the northeast, and nR grows. In
February its center is located near 10°N and 55°W, in June – 25°N and 40°W. Here nR varies from
15 MJ/m2/day in February up to 21 MJ/m2/day in July. In this period of a year the southern tropical
maximum of nR is the most weakened.
Owing to the variations of the sun angular height, near the equator the radiation balance
achieves its maximum values two times per year (March and September): on the days of vernal and
autumnal equinoxes.
On the northern boundary of the investigated Atlantic water area, in the Gulf Stream zone
(40°N) the maximum values of nR (17-18 MJ/m2/day) are observed in July, the minimum ones (2-3
MJ/m2/day) – in December. On the southern boundary in the Antarctic latitudes, the maximum values
of nR (10-11 MJ/m2/day) are characteristic in December-January. In winter in the Southern
Hemisphere the radiation balance is negative. The boundary of negative values of nR is located near
the parallel 48°S and a little bit displaced to the south (up to 54°S) in the west of the ocean. Here the
ocean gives away the radiant energy to the atmosphere during 1-2 two months (June-July). Between
60-65°S the cold season is longer and the period with negative values of nR lasts from April till
August. The minimum values of Rn (-2 MJ/m2/day) are typical for June-July.
Turbulent exchange (sensible and latent heat fluxes (H+LE)). Monthly average maps of
LEH + distribution have a more complex structure as compared to the distribution of nR (Fig. 2).
As well as in the case of the radiation balance, in the tropics one can identify two basic areas of the
maximum values of LEH + . In the Southern hemisphere the maximum heat emission
(21 MJ/m2/day) due to the heat expenses on evaporation and the turbulent exchange is observed in
June-July in the region between 10-15°S and 20-30°W. In this period of a year the minimum values of
nR and the maximum speeds of the near-surface wind are observed here.
The intra-year variation of zonal and meridian components of the wind tangential tension based
on the array data from (Hellerman, Rosenstein, 1983) shows that the maximum wind speeds are
characteristic of July. The minimum values of LEH + (13 MJ/m2/day) are observed here in February
when the radiant energy flow is the strongest and the wind speed is minimal.
Seasonal displacements of the south-tropical area of the maximum values of LEH + are
insignificant as compared to the change of the center location of the maximum values of nR . It is
conditioned by the fact that the southeast trade wind axis, with which the extremum LEH + is
connected, slightly changes its position in the course of a year.
Near 5°S in the field of LEH + there is a frontal zone that is aggravated during the autumn-
winter period (March-August) in the Southern Hemisphere (Fig. 2.). At the same time a considerable
meridian gradient in the distribution of the zonal component of the wind tangential tension is observed
here.
Along the South American coast between the parallels 20° and 40° S there is an area of the
increased values of LEH + that is observed in the best way since March till June with its maximum
(15 MJ/m2/day) in April. Comparison with the intra-year variations of nR in this area does not reveal
obvious relations with variations of LEH + as the minimal values of nR are observed here almost
two months later while the analysis of the water temperature distribution in the ocean upper layer
shows that since January till May the Brazil current intensively carries out warm waters from the
analyzed water area to the southern latitudes. The inflow of warm waters to the latitudes where the
colder air masses are located promotes increase of the values of LEH + . This effect grows stronger
Yu.A. Artamonov et al.: PECULIARITIES OF THE SEASONAL VARIABILITY OF THE EXTERNAL THERMAL …
19
in April-May when the winds of southern directions prevail in this region and the advection of cold air
masses from the sub-polar latitudes intensifies.
Fig. 2. Monthly average maps of a sum of heat expenses on the turbulent heat exchange in the ocean–
atmosphere system (sensible and latent heat flux) (MJ/m2/day).
In tropics the Northern hemisphere maximum heat emission (21 MJ/m2/day) is observed in
January-February between 10-15°N and 40-55°W. During the seasonal cycle this extremum of
LEH + moves to the north up to 15-20°N, in so doing the values of LEH + decrease there. High
values of LEH + in this area are due to the strengthening of the northern trade wind (Hellerman,
Rosenstein, 1983). Minimum heat emission (14 MJ/m2/day) is characteristic of July-September.
To the south of 40°S in the zone of the Antarctic Circumpolar current, significant meridian
gradients of LEH + are formed. Their location approximately coincides with that of the axis of zonal
transport in the atmosphere. To the east of 10°W location of the boundary of sharp meridian gradients
of LEH + is marked by the well-pronounced semi-annual signal. To the south of 45°S LEH +
takes negative values two times a year (May-June and October). The semi-annual signal also is well
pronounced in the location of the southern boundary of the zonal western transport in the atmosphere.
Maximum amplitudes of the annual harmonic of LEH + (up to 30 MJ/M2/day) are typical of
the northwestern part of the studied water area. They are characteristic of the Gulf Stream zone where
seasonal variations in the wind field are the highest. The maximum amount of heat (35-40 MJ/m2/day)
the ocean loses here during winter of the Northern Hemisphere and the minimum amount (5-10
MJ/m2/day) – in summer.
Yu.A. Artamonov et al.: PECULIARITIES OF THE SEASONAL VARIABILITY OF THE EXTERNAL THERMAL …
20
Semi-annual variations of LEH + with the amplitude up to 5 MJ/m2/day are observed in the
eastern part of the Tropical Atlantic, between the equator and the parallel 10°N. Semi-annual
harmonics in the intra-year variation of the radiant energy coming to the ocean surface and in the
variability of the wind field characteristics are noted here (Hellerman, Rosenstein, 1983).
External thermal balance ( oB ). Fig. 3, a shows the annual average distribution of the external
heat balance in the ocean. As nR exceeds LEH + , in the near-equatorial and partially in the tropical
latitudes of both hemispheres the ocean surface receives heat during the whole year. In the higher
latitudes heat accumulation by oceanic waters decreases.
-70 -60 -50 -40 -30 -20 -10 0 10 20
-70
-60
-50
-40
-30
-20
-10
0
10
20
30
40
-70 -60 -50 -40 -30 -20 -10 0 10 20
-70
-60
-50
-40
-30
-20
-10
0
10
20
30
40
а b
c d
Fig. 3. Distribution of the harmonics of the ocean external heat balance: (a) annual-average balance; amplitude of
(b) annual and (c) semi-annual variations and (d) phase of the annual variation (MJ/m2/day).
The basic maximum of the annual average positive values of oB (>6 MJ/m2/day) is observed in
eastern part of the tropical zone and in the Guinea Gulf. The second extensive area of the increased
values of oB is observed between the parallels 45˚ and 55˚S. Within the limits of this area there are
two local maximums (>3 MJ/m2/day) near the South America coast and in the eastern part of the
ocean in those latitudes where the Antarctic Circumpolar current is located. Some increase of the
values of oB is also observed in the central parts of subtropical anticyclonic circulations in both
hemispheres.
Yu.A. Artamonov et al.: PECULIARITIES OF THE SEASONAL VARIABILITY OF THE EXTERNAL THERMAL …
21
On the average in the course of a year negative values of oB are found in the Northern Atlantic,
in the region of the Gulf Stream and the western boundary layer, in tropics; on the southern periphery
of South subtropical anticyclonic circulation, in the zone the currents Аgulyas re-circulation, in the
central part of the Weddell Sea circulation. Especially significant negative values of oB are marked in
the Gulf Stream zone (<-15 MJ/m2/day) and in the region of a recirculation cell of the current Agulyas
(<-9 MJ/m2/day).
Maximal amplitudes of the annual harmonic oB are characteristic of the Gulf Stream zone (>20
MJ/m2/day), the eastern part of the South subtropical anticyclonic circulation (>10 MJ/m2/day) and the
region of the Falkland current (>9 MJ/m2/day) (fig. 3, b). Semi-annual fluctuations of the value oB are
marked within the limits of the western boundary layer, in tropics, in the eastern part of the Tropical
Atlantic, between the equator and 10˚N, in the tropical zone of South Atlantic between the parallels
10˚ and 20˚S and in the Antarctic Circumpolar current region (fig. 3, c).
Maximum values of oB in the Northern Hemisphere are observed mainly in July, and in the
Southern Hemisphere – in December. The line of a season change of the external heat balance is
located in the tropical zone approximately along the southern boundary of the intertropical
convergence zone (fig. 3, d).
Two areas of violation of this general regularity are noted. One of them is in the Guinean sector
between the equator and 10˚N. Here the main maximum of oB falls on April, the second, a weaker
one, – on September. Another more extensive area where the main maximum is observed in January is
located in the eastern part of the Atlantic sector of Southern Ocean.
Regional peculiarities of seasonal variability of oB and their relation with the gradient large-
scale water circulation can be understood better after the monthly average maps of the ocean external
heat balance (fig. 4) are analyzed.
The characteristic feature of seasonal variability of spatial distribution of oB consists in the
changes of the boundary position between the regimes of water heating and cooling in the Northern
and Southern hemispheres. Since October till March it is located approximately between the equator
and 10˚N (fig. 4). To the north the ocean gives out heat and gets it to the south. It is noticeable that in
the northwest part of the Atlantic tropical zone the period of the upper layer cooling is by a few
months longer than that in the central part of the Northern subtropical anticyclonic circulation. Thus,
on 20˚N the heating phase begins in March, whereas on 10˚N – only in June. It is connected with the
fact that in the first half of a year the northern trade wind intensifies and maximum heat emission to
the atmosphere due to the sensible and latent flux is observed. In the middle of a year when the values
of LEH + decrease the ocean receives heat.
In the first half of a year in the Northern Hemisphere the distribution of oB qualitatively
repeats the distribution of LEH + . It is connected with the fact that on the major part of the ocean
water area the radiant energy inflow is insignificant, and heat for evaporation and turbulent heat
exchange with the atmosphere is spent basically due to heat power resources of the oceanic currents.
Thus an absolute maximum of heat inflow from the under-laying layers to the ocean surface is
observed in the Gulf Stream zone (more than 40 MJ/m2/day).
In the Southern Atlantic in the zone of the Brazilian and Falkland currents merging and in the
region of the Weddell Sea circulation, the values of oB become negative in March, and in April
practically the whole water area of the Southern Atlantic (to the south of 5-10˚S in the west and 15˚S
in the east) gives out heat to the atmosphere. Since May till August the boundary between positive and
negative values of oB is manifested in a form of the high-gradient frontal zone located between the
parallels 5˚ и 10˚S. Its location coincides with the frontal zone in the field LEH + (fig. 2) and with
the well pronounced geostrophic flow of the western direction (the central branch of the Southern
trade current) in the field of dynamic heights. To the north of the frontal zone between the equator and
5˚S, to the east of 30˚W the local maximum of oB is formed in May and observed till December
(fig. 4). During this period the values of LEH + near the equator are low. The well pronounced
Yu.A. Artamonov et al.: PECULIARITIES OF THE SEASONAL VARIABILITY OF THE EXTERNAL THERMAL …
22
equatorial temperature minimum and the shallow gully of the dynamic relief that testify to the
intensification of the Lomonosov current and its elevation to the surface, are also noted.
Fig. 4. External heat balance of the ocean (MJ/m2/day).
In November-January in the eastern half of the ocean, approximately between the parallels 20˚
and 30˚S, the area of the increased values of heat inflow to the ocean is distinguished. Intensive
heating of these waters is promoted by the high values of nR , and rather weak winds during this
period provide low values of LEH + . To the southwest from this area the values of oB decrease. The
analysis of the water temperature distribution on the ocean surface shows that during these months the
cold water within the system of the Bengel and Southern trade currents is brought from the south. To
the southwest, warm waters brought by the Brazil current from the west to the east is observed.
The boundary of two oppositely directed water flows coincides with the boundary where the
meridian component of the wind tangential tension changes its sign. During this period of a year it is
in its extreme northern position. The Southern equatorial countercurrent is poorly manifested in this
period.
In May-August the Southern equatorial countercurrent intensifies (the dynamic relief crest near
10˚S is better pronounced) that results in the intensive coming of warm waters on this latitude to the
Yu.A. Artamonov et al.: PECULIARITIES OF THE SEASONAL VARIABILITY OF THE EXTERNAL THERMAL …
23
east and in the increase of heat consumption for evaporation. On the other hand, strengthening of the
southern trade wind is observed here. That is accompanied by the increase of heat consumption for the
turbulent exchange with the atmosphere. As a result, LEH + exceeds heat amount coming due to the
solar radiation. Since May till August the local extremum of negative values of oB (up to 10
MJ/m2/day) is formed here.
Significant heat return by the under-laying layers through the ocean surface to the atmosphere
is observed in the zone of the Brazilian and Falkland currents merging, in the South Atlantic current
and in the zone the Agulyas current recirculation.
Maximum heat return in the zone of the Brazilian and Falkland currents merging is typical for
May-June (10-12 MJ/m2/day). In the given area maximum wind speeds and maximum values of
LEH + are observed in this period of a year. Thus minimum of nR occurs approximately a month
later – in July-August, and SST minimum – in August-September. In other words, the extreme
negative values of oB are conditioned by warm water advection to the south by the Brazil current in
the conditions of maximum wind speeds. The ocean receives the greatest amount of heat (10-12
MJ/m2/day) in January in the region of the Falkland current above the Patagonian shelf. During this
period the maximum flow of radiant energy and minimal wind speeds are observed. In the central part
of the region in the area of the South Atlantic current the ocean gives out the maximum amount of
heat (up to 10 MJ/m2/day) in May-July when minimum values of nR are noted. It is typical that in the
seasonal cycle the extremums of oB and LEH + occur first between the parallels 50˚ and 60˚S in
April. Then they move to the north and in May-July they are located between the parallels 30˚ and
40˚S. Similar displacement is observed in location of the maximum of the zonal component of the
wind tangential tension.
In the zone of the Agulyas current recirculation (40˚S) two maximums of heat emission – in
April (up to 12 MJ/m2/day) and in July (up to 16 MJ/m2/day) are observed. The main maximum of the
heat inflow to the ocean (up to 6 MJ/m2/day) is noted in February. The intra-year variation of the
zonal component of the wind tangential tension and the values of LEH + contain a semi-annual
harmonic. It is typical that on the water area between the parallels 50-55˚S warm season lasts almost
two months longer, and in winter the minimum heat emission is observed. Here in the course of the
major part of a year, except for September-November, the values of LEH + are positive, and the
wind speed maximum is located to the north of these latitudes. SST maps and the schemes of dynamic
topography show that in these latitudes the southern boundary of the maximum meridian temperature
gradient that coincides with the southern boundary of the Antarctic Circumpolar current is located.
Here during the major part of a year, northern winds prevail. They bring warm air to the water area
occupied by cold Antarctic water masses. On the boundary of cold waters the ocean receives heat
practically within the whole year. To the south where the air masses lose their heat supply this effect
is not manifested. Similar seasonal variability of oB on the boundary of cold waters is observed on the
whole water area of the Atlantic sector of the Southern ocean to the east of 10˚W.
The above described peculiarity of seasonal variability of the value oB is not manifested in the
western half of the ocean where the boundary of cold Antarctic water masses is located much to the
south (55-63˚S) and the winds with the southern component prevail.
4. Conclusion
Based on the array of monthly average climatic data of satellite observations investigated are
the regularities of spatial distribution and seasonal variability of external heat balance oB of the
Atlantic Ocean surface and its components – radiation component nR , turbulent exchange LEH +
(the sensible and latent flux).
It is shown that distribution of the radiation balance nR is mainly of a zonal character. Its
maximum values are observed on the tropical peripheries of the subtropical centers of high
atmospheric pressure in both hemispheres. Minimum nR is typical of the water areas located near the
Yu.A. Artamonov et al.: PECULIARITIES OF THE SEASONAL VARIABILITY OF THE EXTERNAL THERMAL …
24
Antarctic ice edge. On the prevailing part of the Atlantic Ocean seasonal fluctuations of nR are
characterized by harmonic of the annual period with the maximum amplitude 10-15 MJ/m2/day in the
tropical zone. In the equatorial area the intra-year cycle of fluctuations of nR contains harmonic of the
semi-annual period with the amplitude about 5 MJ/m2/day.
Distribution of the heat balance component connected with the turbulent exchange, and its
seasonal variations are more complex in comparison with the changes of nR . Extreme values of
LEH + correlate well with the wind field parameters in the tropical zone of the ocean and in the area
of the Antarctic Circumpolar currents and with the characteristics of the meridian large-scale currents.
The maximum amplitudes of the annual harmonic LEH + are observed in the northwest part of the
Atlantic, in the Gulf Stream zone (30 MJ/m2/day), in the northern and southern tropics (10
MJ/m2/day). Well pronounced semi-annual harmonic in the seasonal cycle of variability of LEH +
with the amplitude 2-3 MJ/m2/day is observed between the equator and the parallel 10˚N, in the
eastern part of the Antarctic sector of the Atlantic and in the field of the Antarctic Circumpolar
current.
Maximum seasonal variations of external heat balance are characteristic of the Gulf Stream
zone (amplitude ≈22 MJ/m2/day), the western part of the Southern subtropical anticyclonic circulation
and the Falkland current area (amplitude ≈10 MJ/m2/day). Minimal annual fluctuations of oB with the
amplitude 1-2 MJ/m2/day are noted in the region of the Inter-tropical convergence zone and in the
Guinean Gulf. The role of the semi-annual signal in the seasonal variability of the ocean surface heat
exchange with the under-laying layers is most significant in the western boundary layer, in the
Guinean sector of the Tropical Atlantic, on the northern periphery of the Southern subtropical
anticyclonic circulation and in the region of the Antarctic Circumpolar current.
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