Finding the SST gradient from TMI (daily, 1/4°)
==>> This section includes everything that involves u_g due to the SST front!
(A few exceptions include the "Ekman spirals" involving u_ag with the other Ekman stuff in 12 above)
(Lots of confusion about TMI products. The "fusion" product seems to have a significant lag compared to buoy SST. The APDRC 3-day-running mean product is better (still a lag of a little less than a day. Earlier plots here are fusion, plots after about 5 April 2007 are APDRC. Hopefully the labels reflect this! However, for many purposes the lag makes no difference. It really matters only when comparing the phase with buoy values; the statistics and values of the two TMI products are very similar.)
Note that the TMI SST is to nearest 0.05°C: gradient can be funky .... see examples below
- TMI grid structure (on 1/4°, not on integer degrees (interpolation necessary ....):
Over mean SST Over 10 Nov 2004 SST
- Examples of SST gradient:
- Meridional: 5-day averages Daily values
- Zonal: 5-day averages Daily values
- 1.4Mb movie of TMI SST near 2°N,140°W
- Compare the gradient found between gridpoints nearest to 2°N,140°W (1/4° differencing) vs a best-fit line:
Examples: 10th day of each month, June 04 through Feb 05:
- d(SST)/dx: Jun Jul Aug Sep Oct Nov Dec Jan Feb
- d(SST)/dy: Jun Jul Aug Sep Oct Nov Dec Jan Feb
- Example of Ty/Tx (Note that only a few discrete values occur)
- SST gradient, Shear and Wind overlaid on SST map:
- 1/4° differencing: Jun Jul Aug Sep Oct Nov Dec Jan Feb
- Fitted line: Jun Jul Aug Sep Oct Nov Dec Jan Feb
- Maps at 3-day intervals (corresponding to stackplots in 11e above):
Group: 1 2 3 4 4 5 6 7 8 9 All together on one page
- See stackplots including these gradients (plots 11e above)
- Directions of wind, shear, and SST gradient
- Directions
- Difference from Shear direction: V1 From smoothed differences
- High-passed differences
- Example of shear, wind SST gradient on 22 Aug
- Compare 1/4° fitting to 2° fitting (APDRC) (Meghan insisted!)
- Use the SST gradient to compute ug. (Linear eqn of state, thermal wind to find ug(z=0) relative to 20m.)
- Mean u,ug,u-ug components:
- Rel. 20m: Whole period (original TMI) Whole period (APDRC SST) May-Oct
- Rel. 25m: May-Oct
- u and v components: Unsmoothed 5-day triangle Overlay SST 5-day filter
- Note the 0.05°C steps mean there are few possible vector angles
- ug overlaid on SST(y,t): Unsmoothed 5-day filter
- ug overlaid on obs currents: ug u-ug 7-day filter
- TMI gradients: Components Magnitude
- Examples (many examples) showing measured and geostrophic shear, over SST (APDRC)
- Is the shear downwind?
(Comparison between measured shear and geostrophic-adjusted shear vs wind)
- Mean shear: u,ug,uag, and wind: Vectors Variance ellipses Over map of SST
Overlay 10, 15, 20m shear 5,10,15,25m rel 5m (til 15 Oct)
- Wind, ug, uag shear (When does uag tilt the front?)
- Shear rel 10m Overlay both
- Relative directions of wind/uag/front: Scatter diagram of wind/uag angle difference Time series of angles
- Index of warm-over-cold tilting: time series Compare stratification
- SST advection terms: 7-day RM 31-day RM
7-day RM, 1°-gradient Grad(SST)