interactions between equatorial waves and tropical cyclones paul e. roundy wwosc august 2014
TRANSCRIPT
Interactions Between Equatorial Waves and
Tropical CyclonesPaul E. Roundy
WWOSC August 2014
Intraseasonal variability of tropical cyclones
Diagnose the most favored relationships in space and time between TC genesis andMJOEquatorial Rossby wavesMixed Rossby Gravity (MRG) wavesKelvin waves
Diagnostics
Follow a simplified approach after Frank and Roundy (2006)Filter OLR and wind anomaly data at 850 hPa for
broad bands of different “wave” types. Generate TC-genesis centered composites of filtered
data including only periods of enhanced activity in the filter bands
10 years of additional data allows me to increase the wave activity thresholds for including an event
Madden Julian Oscillation
Eastward-moving global intraseasonal feature of circulation and convection, no broad agreement on its dynamics
Madden Julian Oscillation
Eastward-moving global intraseasonal feature of circulation and convection, no broad agreement on its dynamics
Influences TC genesis in all basins, although most directly through modulation of convection in the Eastern and Southern Hemispheres
Madden Julian Oscillation
Eastward-moving global intraseasonal feature of circulation and convection, no broad agreement on its dynamics
Influences TC genesis in all basins, although most directly through modulation of convection in the Eastern and Southern Hemispheres
Interaction with the extratropical circulation and Kelvin waves allows it to strongly influence the northeast tropical Pacific basin
Madden Julian Oscillation
MJO impacts on the Atlantic basin are also substantial, including through its modulation of synoptic wave activity, the vertical distribution of moisture, and vertical wind shear
Equatorial Rossby Waves
Intraseasonal Westward-moving waves
MRG waves
Form circulations centered on the equator
Waves disperse energy eastward while the waves move westward
TCs can be sources of MRG waves, but MRG waves can modulate TC genesis (e.g., Dickinson and Molinari 2002 JAS)
From Kiladis et al. (2009)
From Roundy and Janiga (2012)
Kelvin Waves
Waves move rapidly eastward ~10-30 ms-1
Kelvin Wave Theoretical Structure
Wind, Pressure (contours), Divergence, blue negative
Kelvin Waves Frank and Roundy (2006) did not achieve robust results
in our composite analysis consistent with Kelvin waves, suggesting that Kelvin waves might not contribute systematically to TC genesis. Some theoretical arguments supported this point of view.
Kelvin Waves Frank and Roundy (2006) did not achieve robust results
in our composite analysis consistent with Kelvin waves, suggesting that Kelvin waves might not contribute systematically to TC genesis. Some theoretical arguments supported this point of view.
Bad conclusion
Kelvin Waves Frank and Roundy (2006) did not achieve robust results
in our composite analysis consistent with Kelvin waves, suggesting that Kelvin waves might not contribute systematically to TC genesis. Some theoretical arguments supported this point of view.
Bad conclusion
First clue to me was from watching numerous wave events over the Indian basin followed by TC genesis over the Bay of Bengal
From Ventrice et al. 2012, Mon. Wea. Rev.
Kelvin Waves and Atlantic TC Genesis:
Why?
Theoretical Kelvin waves include no potential vorticity signature because the thermodynamics directly compensate for the dynamics
Convectively coupled Kelvin waves modulate convection, and that convection generates a PV response, yielding PV “wakes” behind the waves (MacRitchie and Roundy 2012, JAS).
From Ventrice et al. 2012, Mon. Wea. Rev.
Kelvin Wave @ 70°E
Negative PV anomalies prior to Kelvin wave passage
Abrupt jump to positive PV anomalies following Kelvin wave passage
Legend (contours are 4 W/m2)
MJO Active OLR
Kelvin Active OLR
Kelvin Wave @ 70°E
Negative PV anomalies prior to Kelvin wave passage
Abrupt jump to positive PV anomalies following Kelvin wave passage
Legend (contours are 4 W/m2)
MJO Active OLR
Kelvin Active OLR
+
-
+
-
Kelvin Wave @ 90°E
Negative PV anomalies prior to Kelvin wave passage
Abrupt jump to positive PV anomalies following Kelvin wave passage
Legend (contours are 4 W/m2)
MJO Active OLR
Kelvin Active OLR
Kelvin Wave @ 110°E
Negative PV anomalies prior to Kelvin wave passage
Abrupt jump to positive PV anomalies following Kelvin wave passage
Legend (contours are 4 W/m2)
MJO Active OLR
Kelvin Active OLR
Composite
Negative PV anomalies prior to Kelvin wave passage
Abrupt jump to positive PV anomalies following Kelvin wave passage
Legend (contours are 4 W/m2)
MJO Active OLR
Kelvin Active OLR
Lag -3 Days
For Reference:
Lag -2 Days
For Reference:
Lag -1 Days
For Reference:
Lag 0 Days
For Reference:
Lag +1 Days
For Reference:
Lag +2 Days
For Reference:
Lag +3 Days
For Reference:
Conclusions
The MJO and equatorial waves modulate the locations and timing of TC genesis events over all basins
Kelvin waves modulate TC formation and are far more important than originally reported by Frank and Roundy (2006)