Investigation%20of%20Mixed%20Layer%20Depth%20in%20the%20Southern%20Ocean%20by%20using%20a%201-D%20mixed%20layer%20model%20Chin-Ying%20Chien%20

1
Investigation of Mixed Layer Depth in the
Southern Ocean by using a 1-D mixed layer
modelChin-Ying Chien Kevin SpeerGeophysical
Fluid Dynamics Institute, Florida State
University
Abstract The atmosphere exchanges mass,
energy, and momentum with the ocean through
atmospheric forcing in the upper few hundred
meters. The forced motions include wind stresses,
heat fluxes, evaporation, and precipitation. The
dynamics of energy and momentum transfer from
wind to water and through the surface mixed layer
to the deep ocean are still not well understood.
In addition, air-sea and fresh water heat fluxes
play an essential role to estimate the heat
budget. Generally, sensible heat and latent heat
fluxes can effect both ocean and atmospheric
temperature. In the atmospheric boundary layer,
wind-driven shear and turbulence cause oceanic
mixed layer deepening. The mixed layer
temperature is largely attributed to the air-sea
heat fluxes. The one-dimensional Kantha-Clayson
Mixed Layer (KCML) model appears to predict ocean
mixed layer well on the various time scales, from
hours to seasonal scale from their studies. In
this study, our goal is to validate KCML model in
the region of the Southern Ocean by combination
of ARGO data, COAPS wind stresses, NCEP/NCAR
fluxes and rain rate. We compare the mixed layer
depth from in-situ data and KCML modeling output.
The relation of mixed layer depth and air-sea
fluxes transfer and base of mixed layer
statistics to Argo is also our interest to study
in the future.
Case (1) ARGO float 5900698

Results
Following ARGO float 5900698 (100 profiles)
start -gt2004/12/17/11Z last-gt 2007/10/27/00Z
Data method (1)
Introduction to Mixed Layer Model Generally,
there are 2 types of upper ocean models. One is
the bulk mixed layer model which suggests the
mixed layer is a well-mixed box. Within this box,
physical and chemical mechanisms/properties are
uniformly distributed. The other one is
turbulence closure model which involves more
about the turbulence processes occurring in the
mixed layer. Herein, consider the regions of the
Southern Ocean with frontal areas which vertical
turbulent mixing is necessary to be considered.
The 1 dimensional KCML model is the latter. In
this study, use the KCML model as a start. The
model accepts a profile and a time-series of the
following inputs

• ARGO temperature (T), salinity (S), depth (D)
• Yomaha velocity data (u v) at parking level

• Calculation of current (U,V) profiles
• UUekUg (Ekman current Geostrophic current).
• Use Yomaha velocity data as I.C. and argo data to
  obtain geostrophic current velocity by applying
  thermal wind equation.
• Use theorem of surface Ekman layer and NCEP wind
  stress data to get Ekman current velocity.

1. Profile for inputs u, v, T, S
2. Surface forcing with time series

• wind stress (zonal meridional stress) N/m2
• incoming solar radiation W/m2
• all other fluxes (long wave radiation, sensible
• heat flux, latent heat flux) W/m2
• evaporation rate m/s
• precipitation rate m/s

• Data (2) Forcing
• Data from NCEP/NCAR reanalysis-1
• Taux momentum flux (zonal)
• Tauy momentum flux (meridional)
• Incoming solar radiation Downward solar
  radiation flux
• All other fluxes Qbrlongwvshf-1.0lhf
• QBR positiveindicates heat loss by ocean
• check TogtTa, so heat from ocean to air, but
  shflt0. Hence change sign of shf
• long wave radiation Net longwave radiation
• sensible heat flux Sensible heat net flux
• latent heat flux Latent heat net flux
• evaporation rate Ev(m/s)LHF/Lv(J/kg)/Qw(kg/m3)
  Lv2.45106(J/kg), Qw1000kg/m3
• precipitation rate precipitation rate

• Output data from model
• MLD based on
• temperature, salinity, and turbulence
• (2) Temperature profile with time series
• (3) Salinity profile with time series
• (4) density profile with time series

Discussions / Work in Progress In this
study, we assume that water mass is the same in
the same ARGO float from the T-S plot. Since the
tracks of floats are between 40S and 50S, the
seasonal cycle of forcing and mixing in the upper
ocean is observed from ARGO float data. However,
the modeling output of mixed layer depth is not
consistent with ARGO data. There are many
possible factors to result in this questionable
results, such as forces, proper input data,
simulating a long time period, and frontal
regions with complicated T/S structures, etc. The
work in progress is to check the possible factors
to impact the modeling results and use a simple
bulk mixed layer model (Price, 1986) to compare
with the results from KCML model.

• Reference
• Kantha, L. H., and C.A. Clayson, 1994. An
  improved mixed layer model for geophysical
  applications. J. Geophys. Res., 99,
  25,235-25,266.
• Price, J. F., R. A. Weller, and R. Pinkel, 1986.
  Diurnal cycling Observations and model of the
  upper ocean response of diurnal heating, cooling,
  and wind mixing, J. Geophys. Res., 91(C7),
  84118427.