ATOC 5051 INTRODUCTION TO PHYSICAL OCEANOGRAPHY Lecture 5 Learning objectives: (1)Know the modern ocean observing system that integrates in situ observations and remote sensing from space (satellite) (2) What is indirect method, why is it necessary, and how does it work? 1. Integrated observing system; 2. Indirect current measurement and application 1. Integrated observing system http://www.pmel.noaa.gov The Pacific

TRITON (Triangle Trans-Ocean Buoy Network)

TRITON array: east Indian & west Pacific (Japan) TAO Buoy and ship

TAO/TRITON buoy data Moored buoy. Example: TAO/TRITON Moored buoy; Tropical Atmosphere Ocean (TAO); TRIangle Trans-Ocean buoy TRITON buoy Network (TRITON).

https://www.pmel.noaa.gov/tao/drupal/ani/ ATLAS (Autonomous Temperature Line Acquisition System)

Data: https://www.pmel.noaa.gov/tao/dru pal/ani/ The Research Moored Array for African-Asian-Australian Monsoon Analysis and Prediction (RAMA) initiated in ~2004; until march 2019: 90% complete

2011: CINDY/ DYNAMO

In-situ: Calibrate Satellite data Piracy Current & future planned IndOOS maps Prioritized actionable recommendations: for next decade

(46-33) Prediction and Research Moored Array in the Atlantic (PIRATA) Argo floats T,S PROFILE & CURRENTS AT INTERMEDIATE DEPTH http://www.argo.ucsd.edu/ Pop-up floats: ~10-days pop up, transmit data to ARGO satellite (~6hours up/down); on the way, collect T and S profile (0~2000m); (Surface: 6~12hours) currents at ~1000m (float drift-parking depth; then dive down to 2000m for T&S Profiling). Life cycles; ~150 repeated cycles. ARGO Floats (each 20-30kg) Argo floats T,S PROFILE & CURRENTS AT INTERMEDIATE DEPTH Float distribution as on August 30, 2019 • Gliders (mount sensors, e.g., ADCP); • Propel themselves by changing buoyancy; • Measure current, T, S, dissolved O2, etc.) from deeper ocean to surface; Good for measuring coastal ocean circulation. 2. Indirect current measurements a. Geostrophic method • T,S,P: density; => vertical shear of geostrophic current component perpendicular to the line connecting a station pair - (indirectly measuring current)

• Make use of all observed data: Obtain 3-Dimensional oceanic circulation Geostrophic method Z V1 A B x z V2

Shear: (V1-V2) Northern Hemisphere(NH) Current at a reference level is needed Geostrophic method: How does it work?

• Large-scale motion satisfies “geostrophy”; • Coriolis force (CF); • Pressure gradient force (PGF); • Geostrophic balance: balance between the Coriolis force and pressure gradient force.

NH, V moves with “high p” to its right, low to its left (Board demo) Direction of V: with high p to its right in NH

z V

y PGF o CF

x

NH X-z section view: conceptual discussion z

p1 x h1 A B x PGF CF p2

h2 V3=0 p3 1000m Geostrophic current: into the paper. Geostrophic balance: equation

Introduce: geopotential anomaly (dynamic height): dp dΦ = gdz, = −ρg, dΦ = −αdp dz p(z) p(r) ΔΦ = Φz = −α dp = α dp r ∫ p(r) ∫ p(z) 1 ∂(ΔΦ) ΔV = V(z)−V(r) = € € f ∂x By omitting Δ sign for convenience, we have: b. Application of geostrophic method

P1 p(r) A B dp P2 Zp(z)

P( r ) P3 is latitude Calculation using hydrographic observations Step 1: Use observed T, S, P derive density and thus α at stations A and B;

Step 2: Calculate from P(r ) to P (z ) at stations A and B by integrating equation: p(r) dp Zp(z) Geostrophic current

Step 3: Calculate geostrophic current:

(i) Level of no motion (ii) Direct observations

Reference level of 500m, 1000m, and 1500m are often used. Dynamic meter

Dynamic meter - dyn m: Dynamic height:

1 dynamic m (D=1): Because

is close to 1.

1 dyn meter is very close to the depth of 1m Pressure level 1dbar is close to 1m.

z is very close to be 1 m. Geostrophic current: example calculation 1000 A = Adp 0db Z500 A B 1000 T,S,P T,S,P B = Bdp 500dbP2 Z500 PGF CF 500dbar P( r ) 0 P3 1000db

Northern Hemisphere Dynamic height: 0-1000db

L

H

H • Advantage: use all useful hydrograhic data to infer general ocean circulation; • Disadvantage: (i) assume level of no motion – measures relative current – current shear; no barotropic component; (ii) if we use known current at the reference level, however, we can obtain “total” geostrophic current at a specific pressure level, which includes both barotropic & baroclinic components; • Surface geostrophic current: sea level measurements: (i) satellite altimetry (TOPEX/POSEIDON/JASON); (ii) coastal sea level stations; [Both barotropic and baroclinic modes) Total motion: Barotropic Baroclinic y V 0 z

V 500db

V 1000 db Shear