Tracking an Atlantic Wave Storm with Jason-2 Altimeter

Tracking an Atlantic Wave Storm with Jason-2 AltimeterTracking an Atlantic Wave Storm with Jason-2 AltimeterTracking an Atlantic Wave Storm with Jason-2 AltimeterTracking an Atlantic Wave Storm with Jason-2 Altimeter

Sérgio Muacho - IPMASérgio Muacho - IPMA

- Operational oceanography (waves and wind)

- Mean Sea Level

- Tides

- Ocean large-scale circulation

- Ocean currents and eddies

- Bathymetry

- Tsunamis

Altimetry applications for oceans and seas:

- Operational oceanography (waves and wind)

- Mean Sea Level

- Tides

- Ocean large-scale circulation

- Ocean currents and eddies

- Bathymetry

- Tsunamis

Altimetry applications for oceans and seas:

here we will focus on…

Do you know other applications of altimetry? Yes No

- Ice (Ice sheets; Sea ice)

- Climate (ENSO; NAO; Decadal oscillations)

- Atmosphere (Cyclones; Rain)

- Hydrology & land (Lake level; River level)

Chapter I: IntroductionJason-2 radar

http://www.eumetsat.int/Home/Main/Satellites/Jason-2/MissionOverview/index.htm?l=en

-Satellite does not measure individual waves…

- Satellite beam is about 1-2 km minimum in diameter;

- Measurements are averaged (over 1s, ~7km along the track) to remove noise.

Some considerations about altimetry:

The radar altimeter receives the reflected wave (echo), which varies in intensity over time.

If sea surface is flat (a), the reflected wave's amplitude increases sharply from the moment the leading edge of the radar signal strikes the surface.

In rough seas (b), the wave strikes the crest of one wave and then a series of other crests which cause the reflected wave's amplitude to increase more gradually. *

We can derive ocean wave height from the information in this reflected wave: the slope of the curve representing its amplitude over time is proportional to wave height.

* from http://www.altimetry.info/html/alti/principle/waveform/ocean_en.html

Satellite

Radar wave

Radar wave as seen from above the surface

Shape of the power as received back by the onboard radar

How do satellite altimeters measure ocean waves?

- Over ocean surface, the echo waveform has a characteristic shape that can be described analytically (Brown model);

- The edge slope is related to the significant wave height (SWH)

How do satellite altimeters measure ocean waves?

This is an ascending or descending orbit? Ascending Descending

Can we use altimetry data in an operation way? Yes No

No, because the satellite goes over the same point every cycle (10 days at least, up to 35 days depending on the satellite)

In my opinion, yes…!

If a satellite goes over your region of interest (ROI), you can have data 2 hours after the measurements. This is relevant in oceans and sea zones with a lack of observations (buoys), such as West Iberian coast and more off-shore areas.

The Atlantic wave storm (17 – 20 April 2012)

Wave storm life cycle: The early stages (synoptic conditions)

Plot: surface wind >10 m/s

Azores

Plot: surface wind >10 m/s

Azores

Steady southwesterly flow with several cyclogenesis, some of them originate deep lows with very strong winds

Azores

Omega Block between 14 and 20th april 2012 with some minor changes in position

Wave storm generation and propagation

Adapted for http://www.co.fc.ul.pt/

Wave storm propagation (03UTC 17 April-12): model results (WAM/ECMWF) and Jason-2

Wave storm propagation (17 and 18 Apr 2012): model results (WAM/ECMWF)

Approaching shore in Bay of Biscay and West Iberian coast (19 and 20 Apr 2012): model results

(WAM/ECMWF)

Let’s track the storm… with Jason-2!

Jason-2 data and wave model forecast (03 UTC 17-Apr)

Important ideas:

• We collect 5 passages during a three days period (17, 18 and 19 April 2012) in our ROI;• Jason-2 data is in good agreement with wave model and buoys (~2400 points with a mean difference of 3,5cm);• We can use altimetry information to supply the lack of buoys in off-shore areas (we can monitor sea conditions!).

Important ideas:

• We collect 5 passages during a three days period (17, 18 and 19 April 2012) in our ROI;• Jason-2 data is in good agreement with wave model and buoys (~2400 points with a mean difference of 3,5cm);• We can use altimetry information to supply the lack of buoys in off-shore areas (we can monitor sea conditions!).

But…. It is difficult to track a storm only with the altimetry data:

• Altimetry doesn’t give you an idea of sea conditions in all your ROI;• Miss important information for marine forecasters, such as wave direction.

Jason-2 data against buoys data in West Iberian coast

~1,4m 02h45m, 18-Apr

Jason-2 data against buoys data

º ~7,8m 17h17m, 18-Apr

Additional issues:

Jason-2 near costal regions (e.g., NW Iberian coast)

Jason-2 near islands (e.g., Azores)

North swell: Wave refraction is well represented by altimetry

Update – Atlantic ePort !

Atlantic ePort (http://eumetrain.org)Atlantic ePort (http://eumetrain.org)

Archive:

10 April 2012onwards

Portuguese Hydrographical Institute (www.hidrografico.pt)

Spanish Hydrographical Institute (www.puertos.es)

Acknowledges

- Thank you! - - Thank you! -

Tracking an Atlantic Wave Storm with Jason-2 Altimeter

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