SIMULATION OF NEAR-SURFACE LAYER OF THE COLOMBIAN PACIFIC OCEAN

Lev Karlin

Description

co colombiano están relacionadas con convección nocturna, mezcla viento-ondas, absorción de energía radiante
y precipitación.

Sujets

• Thermocline
• Halocline
• Cochin International Airport
• NA
• Termoclina
• Haloclina

Informations

• Publié par: erevistas
• Publié le: 01 janvier 2005
• Nombre de lectures: 15
• Poids de l'ouvrage: 1 Mo

Extrait

EARTH SCIENCES
RESEARCH JOURNAL
Earth Sci. Res. J. Vol. 9, No. 2 (Dec. 2005): 110-122
SIMULATION OF NEAR-SURFACE LAYER OF THE
COLOMBIAN PACIFIC OCEAN
1 2Lev Karlin and Nancy Villegas
1 Russian State Hydrometeorological University, San Petersburg, Russia, e-mail: [e-mail]
2 Departamento de geociencias, Universidad Nacional de Colombia,
Sede Bogotá, e-mail:[e-mail]
RESUMEN
Este artículo muestra los resultados obtenidos en el estudio de la estructura fina termohalina de la capa
sub-superficial realizado en la Cuenca del Pacífico colombiano. Se formularon modelos matemáticos para
diferentes regímenes de capas sub-superficiales. Basado en tres estaciones se realizó un análisis horario
de información meteorológica, variación de espesor, temperatura y salinidad de la capa fina. Las leyes
de formación de la estructura fina termohalina para la capa sub-superficial en la Cuenca del Pacífico
colombiano están relacionadas con convección nocturna, mezcla viento-ondas, absorción de energía radiante
y precipitación.
Palabras clave: Capa sub-superficial, estructura termohalina fina, termoclina, haloclina, mezcla viento-
ondas, mezcla convectiva.
ABSTRACT
This paper presents the results provided by the fine-scale thermohaline structure of near-surface layer (NSL)
study done in the Colombian Pacific Ocean (CPO). Mathematical models for different regimes of the near-
surface layer are formulated. Based on three stations, an hourly analysis of meteorological data, thickness
change, temperature and salinity of this layer was done. The principles of formation of the thermohaline
structure for NSL over CPO are related to night convection, wind-wave mixing, volume absorption of
radiant energy and precipitation.
Key words: Near-surface layer, fine-scale thermohaline structure, thermocline, halocline, wind-wave mixing,
convective mixing.
© 2005 ESRJ - Unibiblos
INTRODUCTION
8 m/s), intensive convection (night, autumn-winter,
Fedorov and Ginsburg (1988) found for thermohaline during the cooling or rise of salinity in ocean),
structure formation in the Ocean-NSL, the following Langmuir circulation (wind speed between 3 and
regimes: intensive wind-wave mixing (wind speed > 10 m/s) and desalt due to precipitation.
Manuscript received August 2004,
Paper accepted June 2005
110Simulation of near-surface layer of the Colombian Pacific Ocean
Wind-wave mixing regimeFirst, Karlin et al. (1988) and later Rodhe (1991)
found another regime related to horizontal advection.
The quasi-homogeneity in temperature and salinity Finally, the regime connected to special features
vertical distribution of the mixed layer in diurnal of the offshore thermohaline structure in polar and
time, simplify the differential simulation without loss circumpolar regions was determined (Timokhov,
of accuracy, using integral methods. It is assumed 1989; Timokhov et.al, 1993).
the presence of mixed layer during the calculation We described four mathematical models used
period. The simplified expression of NSL thickness for NSL regimes over CPO provided by data
is:analysis in 3 stations. Hourly weather data and
vertical thermohaline profiles at these stations were
32 m U *examined in detail, obtaining NSL thickness values, h = (1)Tg a qp 0top and bottom boundaries and the corresponding
temperature and salinity (Villegas, 2003). In where, m is an empirical constant of proportion-
conclusion, the predominant NSL regimes of ality; h is the upper mixed layer thickness, m;
CPO are night convection, wind-wave mixing, the t c ua p v
U = is the dynamic speed, m/s; c is the * pvolume absorption of radiant energy and regime t
with precipitation. resistance coefficient; u is the wind speed, m/s; a v p
Tis the thermal expansion coefficient, 1/°C; q is the 0
METHODOLOGY heat flux through water-air boundary, °Cm/s.
The equation to calculate temperature evolution with
The former data was obtained at hydrometeorological constant heat flux is:
stations 14 (4° N , 78° W), 49 (2° N, 80° W) and
111(3° N, 84° W), in August and September, 2001 Tq 0d T = d t (2)(Otero and Pineda, 2001), recording data during 24 0 h
hours, trying to verify the models that describe the
different NSL regimes, see Figure 1. These stations where, d T is the change of upper mixed layer tem-0
covered the coastal (station 14), the offshore (station perature for the calculated step on the time d t, °C.
111) and the mixing water zone (station 49), being Equation (1) determines the upper mixed layer thick-
selected according to the quasi-homogeneous ness in wind-wave mixing regime, in the case of its
classification zones (Villegas, 2002). decrease. This happens until maximum heat flux
is observed, when diurnal thermocline is formed.
Thickness remain constant until the heat flux in air-
water boundary decreases, then thickness increases
and expansion of diurnal mixing layer is observed.
In this case, the temperature and thickness evolution
formulas of mixed layer must consider the formed
Tdiurnal thermocline thickness and heat flux q on h
mixed layer bottom boundary. In accordance with
the Similarity Theory of profile T in the thermocline
(Kitaygorodskiy, 1970; Miropolskiy, 1970 and Gar-
nich and Kitaygorodskiy, 1978), we have:
T3 q2 h 2 m U 0*= - 2 t g a h ^ T - T h a ^ T - T h ap 0 H t 0 H T
(3)
T 32 q ] H - h g 1 - a0 2 m U ] T g*d n- - ;2h gh a ^ T - T h ap 0 H T
T 32 q2 T 0 2 m U0 *= - (4)22 t h gh a p
Figure 1. CPO hydrometeorological station locations.
111Lev Karlin and Nancy Villegas
Twhere, T is the water temperature in upper mixed bottom boundary of convective layer, °Cm/s; q 0 0 R
layer, °C; T is the water temperature in bottom is the heat flux through ocean surface caused by H
boundary of mixed layer, °C; a is the dimension- evaporation, turbulent heat exchange and long-wave T
less coefficient of Self-Similarity determined ac- radiation, °Cm/s.
cording to observed data and H is the thermocline Equation (7) requires the expression of turbulent
depth, m. energy balance integrated in limits of convective
Formulas (1), (2), (3) and (4) calculate the thickness layer. The production of energy (generated due to
and temperature evolution of mixed layer in wind- forces of Archimedes) is made until z depth with
wave mixing regime. the Bouguer’s law (radiation flux determined expo-
nentially) and considering dissipation according to
works of Zilitinkevich and Dearfor (1974); Dearfor Convective mixing regime
et al. (1980); Dearfor and Willis (1985); Kofi (1985)
This type of convection, in absence of dynamic fac- and Zilitinkevich (1987), it is possible to write the
tors on water-air boundary, is also called free con- energy balance turbulence equation integrated in the
vection. In this work, convective-wind mixing took limits of convective layer as follows:
place at night, when heat flux on water-air boundary
T Tis negative, the mixed layer descends and heat flux q + q0 R h h 1- rh - rh: Dh + q ] 1 + e g - ] 1 - e g 8)Sthrough mixed layer bottom boundary becomes de- 2 2 r
fined by the involvement hypothesis (Karlin, 1988).
T= 0 . 4 q h0 RThe equations of thickness h ad temperature T evlu-
tion of NSL in convective mixing regime are:
where, q is the short wave emission flux to ocean
S
T 3k q surface, °Cm/s; r is the effective coefficient of weak-2 h q 0 2 m U *= - + ; 5)
-12 t T - T0 H g a h ^ T - T h ening solar energy in sea water, m .p 0 H
TIn expression (8), q is undetermined doing neces-hT 3q2 T 0 U * sary to analyze two stages of NSL evolution, in = 1 . 2 - 2 m . 6)22 t h g a hp the first one, layer thickness increases when solar
energy flux decreases or decreases when heat loss where, k is dimensionless coefficient for free con-
q
increases; causing heat exchange (involvement), the vection (Woods and Barkmann, 1986, Varfolomeyev
Tprevious processes make necessary to estimate q . hand Sutyrin, 1981).
In the second stage, when solar energy flux increases Convective mixing regime is characterized by
or heat loss decreases, the mixed layer thickness layer mixed deepening even for weak wind, due to
decreases, i.e., a new convective mixing layer takes negative heat flux in water-air boundary. These two
place with a thickness smaller than previous one. factors together (intensive refreshing and strong
TWhen h decreases q = 0 then:hwind) contribute to the deepening of layer, causing
the diurnal thermocline vanish.
- rh2 ] 1 - e g
rh = 9)Tq 0 R- rhSunny and weak wind weather regime 1 + e + 0 . 2 c mq S
If in the ocean surface exists a convective mixed Because rh is dimensionless, it is necessary to use the
layer and the mixture of this layer is so strong that the expression h = 1 / r in order to calculate it. Defining*
Utemperature vertical gradient is zeroed, then we use hr = h/ h = h as the thickness of the mixed con-*
U Uheat equation in vertical direction, integrating from vective layer, so h = h/ r. From (9), h is depending
Tsurface