EGU 2009 (Vienna) presentation on "monsoon-modulated ring generation in the eastern gulf of aden"

2. monsoon-modulated ring generation in the eastern gulf of aden
david m. fratantoni
woods hole oceanographic institution
acknowledgements: amy bower, bill johns, hartmut peters
deb glickson, heather furey

3. summer
the western indian ocean is governed by the monsoons
düing (1970)
ncep reanalysis: fratantoni et al. (2006)
wind speed is bold

4. summer winter
schott and mccreary (2001)
the western indian ocean is governed by the monsoons

5. the western indian ocean is dominated by eddies
see al safaani et al. (JGR 2007)

6. the western indian ocean is dominated by eddies and pirates
United Nations Institute for Training and Research Operational Satellite Applications Programme (UNOSAT)

7. red sea outflow experiment (redsox)
amy bower & dave fratantoni (whoi)
bill johns and hartmut peters (miami)

8. rafos floats: eddies fill the gulf of aden

9. satellite ocean color and altimetry
aviso ssh
seawifs chlorophyll
things to notice:
‣ blue colors indicate relatively lifeless oceanic
water
‣ a variety of eddies translate into the gulf of
aden from the east
‣ there is a general pattern of alternately rotating
eddies in the gulf
‣ ring formation appears to occur in oct/nov and
(less clearly) in apr/may

10. time-series of ocean color and altimetry

11. ring characteristics from frontal tracings and altimetry
diameter 250 km
radius of max velocity 80-100 km
azimuthal speed 30-50+ cm/s
translation speed 5-8 cm/s
observed lifetime 5 months
core watermass origin 5° S

12. ring-eddy pairs

13. H1: ring generation occurs during episodes of maximal flow through socotra passage
what do we know?
discrete translating rings composed of near-equatorial indian ocean water are generated in
the eastern gulf of aden in boreal autumn and spring
H2: maximal flow coincides with the fully-established monsoon circulation
need: measurements of socotra passage flow

14. schott et al. (1997): ICM-7 moorings 1995-1996

15. extended time-series of socotra passage flow
H1: YES ring generation occurs during episodes of maximal flow through socotra passage

16. 17 years of socotra passage flow variability: time-series

17. 17 years of socotra passage flow variability: annual cycle
socotra passage velocity anomaly is bold
max flow

18. 17 years of socotra passage flow variability: annual cycle
socotra passage velocity anomaly is bold
monsoon transitions
max flow
max wind
H2: NO maximal flow through socotra passage coincides with the monsoon transitions

19. conclusions
next: new field measurements?
numerical experiments?
discrete translating rings composed of indian ocean water are generated in the eastern
gulf of aden in boreal autumn and spring
maximal flow coincides with the transitions between monsoons
ring generation occurs during episodes of maximal flow through socotra passage
rings with near-equatorial watermass properties appear to form as the “steady”
monsoon circulation regimes collapse