Dataset: mixed_layer
Deployment: TT054

Mixed layer depths

Principal Investigator:

Wilford D. Gardner (Texas A&M University, TAMU)

Co-Principal Investigator:

John M. Morrison (North Carolina State University - Marine, Earth and Atmospheric Sciences, NCSU MEAS)

BCO-DMO Data Manager:

Cynthia L. Chandler (Woods Hole Oceanographic Institution, WHOI BCO-DMO)

Project:

U.S. JGOFS Arabian Sea (Arabian Sea)

Version:

June 6, 2002

Deployment Synonyms:

TTN054, TN054, TTN-054

Version Date:

2002-06-06

Data URL:

https://osprey.bco-dmo.org/dataset-deployment/450696/data

Expand/Collapse All

Description

  PI:             Wilford Gardner (Texas A&M University),
                  Jan Gundersen (Texas A&M University)
                  John Morrison (North Carolina University)
  dataset:        Mixed layer depths
  dates:          January 08, 1995 to December 26, 1995
  location:       N: 22.5  S: 10  W: 57.3  E: 68.75
  project/cruise: Arabian Sea - All Process Cruises
  ship:           Thomas Thompson

  Wilford Gardner - based on temperature changes
  John Morrison - based on density changes						
  Arabian Sea Mixed Layer Depths - all process cruises

  PI Notes
  PI Notes on density vs. temperature calculation

 

Mixed layer depths are based on a temperature increase of 0.1 and 0.5
degrees C from the second temperature value listed in the CTD files, which
corresponds roughly to a density increase of 0.03 and 0.125 density units.

The second TEMPERATURE value was used because there occasionally appeared to
be questionable numbers as the first value.  The temperature change of 0.1
degree C was recommended by Dr. Craig Lee (WHOI) after looking at the data
and the 0.5 degree C value is the Levitus standard used in his NOAA global
atlases.  These are also the values used in the US JGOFS EqPac program.

Please note variable initial (starting) depths.

Calculations were made by Jan Gundersen. (TAMU).

Wilford D. Gardner
Dept. of Oceanography
Texas A&M University
College Station, TX 77843-3146

From Wilf Gardner, Texas A & M University, August 8, 1997

to Arabian Sea investigators and all interested others

Since the New Hampshire meeting [July, 1997], we have compared the MLD
based on the temperature criteria of 0.1 and 0.5 degrees C compared with
the density differences of 0.03 and 0.125 density units.  About 75% of
the time the values are identical.  There are other occasions, however,
where there are significant differences, especially for the 0.1 degrees
C/0.03 comparison. When there is a difference, the temperature
calculations generally give deeper MLDs than density calculations.
Differences most often occur when there is a salinity increase below
the surface.  Temperature criteria are often used for MLDs on moored
data as salinity sensors are sometimes subject to greater drift than
temperature sensors.

None of the above criteria identify the "mixed-layer depth" perfectly in
all cases, but examination of depth plots where there are differences
suggest that the density criteria more reliably identify the depth of most
recent mixing.  For consistency, we recommend that the MLDs based on
density be used when you are trying to calculate mass budgets.  In some
situations, such as sometimes during the TN045 intermonsoon period, there
is no true mixed layer - just a depth at which the MLD criteria are finally
exceeded.  We suggest that you look at an expanded plot of the density
profile if your calculations are critical.

Methods & Sampling

Dataset acquisition description

See Platform deployments for cruise specific documentation

Deployment-specific acquisition description

   PI:             Wilford Gardner (Texas A&M University),
                   Jan Gundersen-temperature-based (Texas A&M University) and
                   John Morrison-density-based (North Carolina State University)
   dataset:        Mixed layer depths
   dates:          November 30, 1995 to December 26, 1995
   location:       N: 22.5171  S: 9.9673  W: 57.2992  E: 68.7849
   project/cruise: Arabian Sea Process Cruise 7, TTN-054 (Early NE Monsoon)
   ship:           Thomas Thompson


Mixed layer depths are based on a temperature increase of 0.1 and 0.5
degrees C from the second temperature value listed in the CTD files, which
corresponds roughly to a density increase of 0.03 and 0.125 density units.

The second TEMPERATURE value was used because there occasionally appeared to
be questionable numbers as the first value.  The temperature change of 0.1
degree C was recommended by Dr. Craig Lee (WHOI) after looking at the data
and the 0.5 degree C value is the Levitus standard used in his NOAA global
atlases.  These are also the values used in the US JGOFS EqPac program.

Please note variable initial (starting) depths.

Calculations were made by Jan Gundersen. (TAMU).

Wilford D. Gardner
Dept. of Oceanography
Texas A&M University
College Station, TX 77843-3146

From Wilf Gardner, Texas A & M University, August 8, 1997

to Arabian Sea investigators and all interested others

Since the New Hampshire meeting [July, 1997], we have compared the MLD
based on the temperature criteria of 0.1 and 0.5 degrees C compared with
the density differences of 0.03 and 0.125 density units.  About 75% of
the time the values are identical.  There are other occasions, however,
where there are significant differences, especially for the 0.1 degrees
C/0.03 comparison. When there is a difference, the temperature
calculations generally give deeper MLDs than density calculations.
Differences most often occur when there is a salinity increase below
the surface.  Temperature criteria are often used for MLDs on moored
data as salinity sensors are sometimes subject to greater drift than
temperature sensors.

None of the above criteria identify the "mixed-layer depth" perfectly in
all cases, but examination of depth plots where there are differences
suggest that the density criteria more reliably identify the depth of most
recent mixing.  For consistency, we recommend that the MLDs based on
density be used when you are trying to calculate mass budgets.  In some
situations, such as sometimes during the TN045 intermonsoon period, there
is no true mixed layer - just a depth at which the MLD criteria are finally
exceeded.  We suggest that you look at an expanded plot of the density
profile if your calculations are critical.

Data Processing Description

Dataset Processing Description

More information about this dataset deployment

Funding

Award Number	Funding Source
unknown Arabian Sea NSF	National Science Foundation
unknown Arabian Sea ONR	Office of Naval Research

Instruments

CTD - profiler

Supplied Name: Conductivity, Temperature, Depth

Supplied Description:

CTD measurements taken, CTD unit unidentified

Instrument Type

Generic Name: CTD - profiler

Community Identifier: http://vocab.nerc.ac.uk/collection/L05/current/130/

Generic Description:

The Conductivity, Temperature, Depth (CTD) unit is an integrated instrument package designed to measure the conductivity, temperature, and pressure (depth) of the water column. The instrument is lowered via cable through the water column. It permits scientists to observe the physical properties in real-time via a conducting cable, which is typically connected to a CTD to a deck unit and computer on a ship. The CTD is often configured with additional optional sensors including fluorometers, transmissometers and/or radiometers. It is often combined with a Rosette of water sampling bottles (e.g. Niskin, GO-FLO) for collecting discrete water samples during the cast.

This term applies to profiling CTDs. For fixed CTDs, see https://www.bco-dmo.org/instrument/869934.

Parameters

Supplied Name	Supplied description	Supplied Units	Standard Name
event	event number, from event log		event
sta_std	Arabian Sea standard station identifier		no_bcodmo_term
sta	station number		no_bcodmo_term
cast	CTD cast number		cast
MLD_0d1_t	depth of mixed layer based on a .1 deg. C change in temperature	meters	no_bcodmo_term
MLD_0d5_t	depth of mixed layer based on a .5 deg. C change in temperature	meters	no_bcodmo_term
depth_start_temp	starting depth used in computation based on temperature	meters	no_bcodmo_term
MLD_0d03_dp	depth of mixed layer based on a .03kg/m^3 change in density	decibars	no_bcodmo_term
MLD_0d05_dp	depth of mixed layer based on a .05kg/m^3 change in density	decibars	no_bcodmo_term
MLD_0d125_dp	depth of mixed layer based on a .125kg/m^3 change in density	decibars	no_bcodmo_term
LD_0d25_dp	depth of mixed layer based on a .25kg/m^3 change in density	decibars	no_bcodmo_term
depth_start_dens	starting depth used in computation based on density	decibars	no_bcodmo_term
MLD_0d25_dp	depth of mixed layer based on a .25kg/m^3 change in density	decibars	no_bcodmo_term

Database

Contribute Data

Dataset: mixed_layer
Deployment: TT054

From Wilf Gardner, Texas A & M University, August 8, 1997

Dataset acquisition description

Deployment-specific acquisition description

From Wilf Gardner, Texas A & M University, August 8, 1997

Dataset Processing Description

Database

Contribute Data

Dataset: mixed_layerDeployment: TT054

From Wilf Gardner, Texas A & M University, August 8, 1997

Dataset acquisition description

Deployment-specific acquisition description

From Wilf Gardner, Texas A & M University, August 8, 1997

Dataset Processing Description

Dataset: mixed_layer
Deployment: TT054