Brief Review of Lecture 1 Understanding Science, Oceanography, Physical Oceanography Descriptive or Dynamical Approaches Eulerian or Lagrangian techniques History of oceanography Oceans and ocean basins – oceans are not simply drowned low lying areas on the earth’s crust!

What physical properties do we observe? Temperature Salinity Depth Sea Surface Height Sound Light Current Velocity And many others……waves, met data, etc.

Considerations for Observation Cost Ease of measurement Time taken – ocean is dynamic! Precision – repeat observation without deviation Accuracy – in addition, should be consistent with a reference standard

Temperature Measure of the heat content of a body (SI unit: Celsius) Temperature of ocean can change if heat is lost or gained in situ heat is advected Source of heat: mainly the sun (surface) geo-thermal (bottom) Difference between heating of ocean and atmosphere Ocean body NOT uniform in temperature

Temperature structure with depth Warmer at top, cooler with depth Thermocline – region of rapid change of temperature; permanent seasonal diurnal Higher temperature, lower density

Global range of ocean temperature

Measurement of Temperature Expansion of liquid or metal Differential expansion (eg bimetallic strip) Vapor pressure of liquid Thermocouple Electric resistance (thermistor) IR radiation from sea surface (remote sensing)

Reversing thermometer Temperature affected by pressure. Reversing thermometers allow flow of mercury in one direction only through special capillary tube– thus when flipped, they retain in-situ temperature. Accuracy: ± 0.02°C Nansen bottle (1910)

Thermistors At first-order approximation, resistance is linearly proportional to temperature. ΔR = k ΔT where ΔR = change in resistance ΔT = change in temperature k = first-order temperature coefficient of resistance Accuracy = ±0.1°C Niskin bottle (1966)

Mechanical Bathythermograph Liquid in metal thermometer (toluene in copper) Many limitations (max depth 300 m, hysteresis and creep, can be deployed at low ship speed only) Accuracy < 0.06°C

Expendable Bathythermograph Accuracy = ±0.1°C (??)

IR derived SST – Aug 28, 2006

Salinity

Practical salinity Rule of constant proportions: Ratio between chemical elements more or less constant and range of salinity quite small. Colligative property – based on number of ions/molecules, not type.

Range of salinity 75% of ocean water between 34.5 and 35 Lowest in coastal waters High in enclosed seas and evaporative basins Pacific salinity much lower than Atlantic – important repercussions for circulation and climate! Higher the salinity, higher the density

Global range of salinity

Conductivity-Temperature-Depth sensor T accuracy: ±0.001°C C accuracy: S/m ~ on PSS Response time: Time required for instrument to respond to temperature of a new environment.

TAO/TRITON (formerly TOGA/TAO) Real-time data from 70 moored ocean buoys for improved detection, understanding and prediction of El Niño and La Niña. Uses ARGOS satellite system Supported by USA, Japan and France

TAO/TRITON hardware

ARGO Program Up to 3000 floats in upper 2000 m of ocean International collaboration of about 23 countries Used with Jason satellite

ARGO status

ARGO float

ARGO simple cycle

Current Velocity Current meters Acoustic Doppler Current Profiler

ADCP Based on concept of Doppler shift of frequency when relative positions of source and receiver change F d : Doppler shifted frequency F s : Frequency of sound when everything is fixed V : Relative velocity between sound and receiver C : Speed of sound in medium A : angle between acoustic beam and water velocity The greater the angle of the transducer heads with the vertical, the more surface data is lost

Depth/Pressure Rope/line over a meter wheel Pressure gauge - pressure proportional to depth (hydrostatic balance) – correction for inverse barometric effect (eg. Tide gauge) [1 dB ~ 1 m] Echo sounding – time taken for acoustic signal to make trip to sea-floor and back is proportional to distance traveled.

Something to think about… Ocean varies on different temporal and spatial scales Our ability to understand these variations only as good as our instrumentation What processes we resolve depend on our sampling plan (duration, frequency, extent, ….) What drives ocean variability? How does the ocean respond to such forcing?