洋流 - 专业级别的资料,适合地理工作者,地理爱好者和潜水爱好者收藏研究

Right Hand Rule: Curl your fingers on your right hand (northern hemisphere) in the direction of spin. If you thumb points upward the vorticity is positive. If you thumb points downward, vorticity is negative.
North Pole (High planetary Vorticity f)
Right Hand Rule: Curl your fingers on your right hand (northern hemisphere) in the direction of spin. If you thumb points upward the vorticity is positive. If you thumb points downward, vorticity is negative.
- The idea of Convergence
- Conservation of Vorticity
- Geostrophic Balance
Convergence/Divergence
This idea is nothing more then the piling up or moving of water away from a region. Conservation of VOLUME: (du/dx+dv/dy+dw/dz=0) Rearranging... du/dx + dv/dy = -dw/dz If water comes into the box (du/dx + dv/dy)>0 there is a velocity out of the box: dw/dz < 0 DOWNWARD
- Ekman transport (and spiral)
- The idea of Convergence
- Conservation of Vorticity
- Geostrophic Balance
What drove Deep Currents?
Ekman spiral: Wind Driven (τ)
4 Primary things that need to be understood
- Ekman transport (and spiral)
- The idea of Convergence
- Conservation of Vorticity
- Geostrophic Balance
Vorticity (I think the 3rd time we’ve talked about it)
洋 流
Ocean Circulation
Wind-driven surface currents
Ocean Circulation Animation
Figure 7-4
Measuring surface currents
Direct methods
Float meters (lagrangian: float with current) Intentional Inadvertent Propeller meters (eularian: stay in one place)
Off the equator (to the north) Planetary Vorticity (f) > 0. Since (f + ξ )=0, ξ must be < 0. The water begins to spin. A parcel of water moves off the equator its vorticity on the equator (f+ ξ )=0.
Deep ocean characteristics
Conditions of the deep ocean:
Cold Still Dark Essentially no productivity Sparse life Extremely high pressure
Identification of deep water masses
So lets go back to Ekman…and see where water is piled up and where it is emptied.
Convergence (Divergence) across a mid ocean gyre
Understanding the formation of currents
Figure 7-24
Atlantic Ocean subsurface water masses
Figure 7-25
Conveyer-belt circulation: Deep Currents
Figure 7-27
Understanding the formation of SURFACE currents 4 Primary things that need to be understood
Vorticity is analagous to angular momentum. Vorticity is a conserved quantity (Conservation of Vorticity) When we talked about Coriolis we introduced the idea of Planetary Vorticity (f). Every object on earth has a vorticity given to it by the rotation of the earth (except an object on the equator). This vorticity is dependent on latitude. Each object on earth can have Relative Vorticity as well. An ice skater who is spinning has Relative Vorticity. A skater who becomes more skinny spins faster (greater relative vorticity). But remember that water is incompressible. So if a water column becomes ‘skinny’ it MUST become taller at the same time!
Deep water masses are identified by measuring temperature (T) and salinity (S), from which density can be determined T-S diagram Characteristics set at surface
As the parcel hits the bump, H decreases. We know that (f + ξ)/H=Constant. So if H decreases, (f + ξ) must decrease. If f decreases, the parcel moves equatorward. If ξ decreases the parcel spins clockwise. Ocean Surface
Deep currents
Affect deep water below pycnocline (90% of ocean water…I think it is more like 75%) Driven by density differences Larger and slower than surface currents
Indirect methods
Pressure gradients Satellites Doppler flow meters
Figure 7B
Ocean currents
Surface currents
Affect surface water within and above the pycnocline (10% of ocean water…I think it is more like 25% of ocean water) Driven by major wind belts of the world
Ekman spiral describes the speed and direction of flow of surface waters at various depths Factors:
Wind Pushes Water through Wind Stress (τ) Coriolis effect pushes water to right(left)
NO CLEAR CUT DELINEATION
Deep water masses and currents
Deep water masses:
Form in subpolar regions at the surface Are created when high density surface water sinks Factors affecting density of surface water:
Temperature (most important factor) Salinity
Deep currents which transport deep waters are also known as thermohaline circulation