Transcript The impact of tropical convection and interference on the extratropical circulation Steven Feldstein and Michael Goss The Pennsylvania State University IUGG, Prague, June 25,

The impact of tropical convection and
interference on the extratropical circulation
Steven Feldstein and Michael Goss
The Pennsylvania State University
IUGG, Prague, June 25, 2015
Questions:
1. What is the relationship between interference, Arctic sea
ice, and tropical convection and how does it impact the
extratropical
circulation?
2. What is the relative impact of different centers of tropical
convection
on
the
extratropical
circulation?
Methods:
Composites,
Self-Organizing
Idealized
Map (SOM)
Numerical
analysis,
Model
Data: ERA-Interim Reanalysis, NOAA OLR, NSICD sea ice
Sea Ice
Tropical convection
Sea Ice
6.5-7.5 day timescale for patterns
SOM patterns, trend, and frequency of occurrence
Poleward Jet Shift in the Northern Hemisphere
Lagged-correlations between Arctic sea ice and SOM frequency
positive sea ice
anomaly leads
SOM1
negative sea ice
anomaly leads
SOM3
positive sea ice
anomaly leads
AO
Zonal-mean zonal wind
SOM1
SOM3
SOM1 (preceded by positive sea ice anomaly) EP Fluxes
Zonal wave 3 and above
Zonal wave 1 and 2
Negative Interference
occurs in SOM1
-60 to -45 days
-30 to -10 days
-45 to -30 days
-10 to 0days
Positive Interference
occurs in SOM3
-60 to -45 days
-30 to -10 days
-45 to -30 days
-10 to 0days
Sea-ice concentration anomalies
Days -60 to -45 prior to SOM1
Anomalously high sea ice concentration
Days -10 to 0 prior to SOM3
Anomalously low sea ice concentration
Summary of impact of sea ice
(4) Strong polar vortex
a)
(3) Weaker ver cal
wave ac vity flux into
the stratosphere
(1) cooling
(2) Destruc ve
interference with
climatological high
(4) weaker polar vortex
(b)
(3) Stronger ver cal
wave ac vity flux into
the stratosphere
(1) warming
(2) Construc ve
interference with
climatological high
Question: What is the relationship between
interference, tropical convection, and surface air
temperature, sea ice, the stratospheric polar vortex,
and the Arctic Oscillation?
Stationary wave index (SWI): Defined as the projection
of the daily 300-hPa streamfunction onto the 300-hPa
climatological stationary eddies.
Evolution of 300-hPa streamfunction
Positive SWI days
Negative SWI days
Evolution of outgoing longwave radiation
Enhanced
convection
Positive SWI days
Negative SWI days
Evolution of 2-m temperature
Positive SWI days
Negative SWI days
Arctic Sea-Ice Concentration evolution
Positive SWI days
Reduced
Sea ice
Negative SWI days
Time evolution: OLR  SWI  sea ice  stratospheric
polar vortex  AO (for k=1,2)
Surface Air Temperature: Constructive interference with and
without Warm Pool convection
Western Pacific
OLR < -0.5
Western Pacific
-0.5 < OLR < 0.5
Western Pacific
OLR > 0.5
• Question: What is the extratropical
response to individual tropical convection
anomalies?
Convective Precipitation
-> PNA-
-> PNA+
-> PNA+
-> PNA-
Convective heating anomalies
Anomalous 0.3σ Geopotential Height (7-10 days)
MJO Phase 1
El Nino
Anomalous 0.3σ Geopotential Height (7-10 days)
MJO Phase 5
La Nina
CONCLUSIONS
• Interference and changes in Arctic sea ice: Reduced sea ice  constructive
interference  enhanced vertical wave activity propagation into
stratosphere  deceleration of stratospheric polar vortex  excitation of
negative AO.
• Interference and changes in Warm Pool (WP) tropical convection:
Enhanced convection  constructive interference  warming of the
Arctic & melting of sea ice  deceleration of the stratospheric polar vortex
 excitation of the negative AO
• MJO phase 1 and El Nino have a similar pattern in tropical convection yet
they excite the opposite phases of the PNA (also, between MJO phase 5
and La Nina). Possible Explanation: Competing influences of warm pool
(WP) and central Pacific (CP) convection.
Implications
• For medium-range and climate models, if a single
tropical convection anomaly is wrong, the
extratropical response could be rather inaccurate.
MJO Phase 1 Anomalous Convective
Precipitation
MJO Phase 5 Anomalous Convective
Precipitation
Correlation between sea-ice area (Barents and Kara
Seas) and SOM frequencies
Composites of AO index
Composite eddy-momentum flux convergence & zonal wind
SOM1
synoptic waves
planetary-scale waves
SOM2
synoptic waves
SOM3
synoptic waves
planetary-scale waves
planetary-scale waves
SOM4
synoptic waves
planetary-scale waves
CONCLUSIONS
•
Four distinct teleconnection (SOM) patterns in the Northern Hemisphere,
associated with GHG driving/ENSO and Arctic sea ice (time scale 6.5-7.5
days, driven by storm track eddies)
•
Poleward shift of subtropical jet associated with GHG driving and Arctic sea
ice decline
•
GHG driving contributes to poleward shift of eddy-driven jet and Arctic sea
ice decline to an equatorward eddy-driven jet shift (implications for AO trend)
•
Up-to 12 month predictability based upon Arctic sea ice
•
Our understanding of inter-decadal variability hinges in part on (1) the
dynamics of intraseasonal time scale processes (2) the mechanism by which
external forcing (GHG, sea ice) alter the frequency of intraseasonal time
scale teleconnection patterns.
•
Impact of SOMs manifested through change in tropical convection.