Transcript Document

CLIMATE AND METEOROLOGY I:
ATMOSPHERIC TRANSPORT
TOPICS FOR TODAY
1.
How are changing transport patterns important for
atmospheric composition?
2.
Some robust transport changes
3.
Changes in mid-latitude cyclones
4.
Changes in the storm track (NAO)
5.
El Nino and atmospheric transport
HOW ARE CHANGING TRANSPORT PATTERNS
IMPORTANT FOR ATMOSPHERIC COMPOSITION?
1.
2.
3.
4.
5.
Changing lifetimes of pollutants (longer at higher altitudes)
Changing vertical mixing, ventilation
Changing transport efficiency
Changing locations of down-wind impact
Changing winds affecting emission (dust, sea salt)
?
?
Can impact tropospheric background and local pollution events
TOPICS FOR TODAY
1.
How are changing transport patterns important for
atmospheric composition?
2.
Some robust transport changes
3.
Changes in mid-latitude cyclones
4.
Changes in the storm track (NAO)
5.
El Nino and atmospheric transport
DISPLACEMENT AND INTENSIFICATION OF STORM TRACKS
Winter-time cyclone counts
The JFM changes over the North Atlantic are associated with the
mean position of the storm track shifting about 181 km northward
[Wang et al., 2006]
IMPORTANCE OF MID-LATITUDES CYCLONES
IN AIR POLLUTION METEOROLOGY
Cold fronts from mid-latitude cyclones are the principal ventilation process
for U.S. Midwest/Northeast, western Europe, China
Clean air sweeps
behind cold front
IPCC shows decrease in frequency, increase in intensity and a poleward shift of
cyclones in 1950-2000 climatological data
TRENDS IN BLOCKING
Blocking: persistent high-latitude ridging and displacement of mid-latitude westerly winds
Atlantic
Europe
W Pacific
E Pacific
NH: “a significant trend toward weaker and less persistent events”
[Barriopedro et al., 2006]
NORTH ATLANTIC OSCILLATION (NAO)
Dominant pattern of near-surface atmospheric circulation variability in N Atlantic, present
throughout the year.
Positive NAO index (MSLP Lisbon-Iceland) = enhanced westerly flow in winter (warmer
maritime air over EU, dry conditions over S EU and N. Afr, also associated with a
northeastward shift in Atlantic storm activity
http://www.giub.unibe.ch/klimet/wanner/nao.html
Many other modes of variability… Pacific Decadal Variability, Southern Annular
Mode, Atlantic Multi-Decadal Oscillation… Can all impact relevant transport
WINDS & WAVES
Trend in wave height (1950-2002)
Affecting MBL chemistry, ocean emissions (DMS, sea salt…)?
[IPCC, 2007]
EL NINO – SOUTHERN OSCILLATION (ENSO)
Starts with the warming of tropical Pacific surface waters  global impact on T &
precipitation (eg. 1997 ENSO  1998 highest global mean T on record, until 2005)
Southern Oscillation Index:
MSLP (Tahiti-Darwin)
Correlation of SOI w/ T
Correlation of SOI w/ precip
Links to drought and temperature….
[IPCC, 2007]
MONSOONS
Monsoon: seasonal on-shore prevailing winds (generally bringing moisture) due to
land-ocean T contrasts
 Like a large sea-breeze effect
Strength of
monsoonal
circulation is
diagnosed by
upper-level
divergence
(dotted line)
Observed some diminished monsoonal circulations over the period of
record, but little recent trend (uncertain record)
[Chase et al., 2003]
TOPICS FOR TODAY
1.
How are changing transport patterns important for
atmospheric composition?
2.
Some robust transport changes
3.
Changes in mid-latitude cyclones
4.
Changes in the storm track (NAO)
5.
El Nino and atmospheric transport
EFFECT OF CLIMATE CHANGE ON REGIONAL STAGNATION
GISS GCM simulations for 2050 vs.
present-day climate using pollution
tracers with constant emissions
weather map illustrating
cyclonic ventilation of the eastern U.S.
2045-2052
summer
1995-2002
Pollution episodes double in duration in 2050 due to decreasing frequency of
cyclones ventilating the eastern U.S; expected result of greenhouse warming.
Mickley et al. [2004]
EVOLUTION OF OZONE CONCENTRATIONS AS CYCLONE
PASSES
cyclone
cold front
EPA ozone levels
L
Stalled high pressure
system increases
ozone due to:
• increased biogenic
emissions
• clear skies
• weak winds
• high temperatures.
cold front
85-104 ppb
105-124 ppb
L
3 days later
Cold front pushes
smog poleward
and aloft on a
warm conveyor
belt.
Loretta Mickley (Harvard)
CORRELATIONS AND TRENDS OF POLLUTION EPISODES
AND CYCLONES IN THE NORTHEAST
# pollution episode days (O3>80 ppb) and # cyclones tracking across SE Canada
in summer 1980-2006 observations
# cyclones
# episodes
Cyclone frequency is predictor of pollution episode frequency.
1980-2006 decrease in cyclone frequency would imply a corresponding
degradation of air quality if emissions had remained constant
[Leibensperger et al. 2008]
TOPICS FOR TODAY
1.
How are changing transport patterns important for
atmospheric composition?
2.
Some robust transport changes
3.
Changes in mid-latitude cyclones
4.
Changes in the storm track (NAO)
5.
El Nino and atmospheric transport
WINTER-TIME OZONE IN EU LINKED TO NAO
UK Unified Model simulation (shown to correspond well to TOMS O3)
Correlation between O3 and the NAO
O3 (high-low NAO)
Given observations [Hurrell et al., 1995] and predictions [Shindell et al., 1999] that
there may be a positive trend in the NAO, we may expect ozone over parts of
central and northern Europe to decrease, possibly enhancing an already existing
negative trend (due to emission reductions.
[Braesicke et al., 2003]
SPRING-TIME OZONE AT HIGH LATITUDE SITES IN EU AND
NA CONTROLLED BY NAO (OR AO)
Arctic Oscillation (AO) and North Atlantic Oscillation (NAO) are related
North America
Europe
MAM (sondes)
JFM
In the NH spring, much of the year-to-year variability in tropospheric ozone is
dynamically driven is not dominated by variations in ozone precursors emissions.
Air quality improvements (associated with + NAO) extending to North America?
[Lamarque and Hess, 2004]
TOPICS FOR TODAY
1.
How are changing transport patterns important for
atmospheric composition?
2.
Some robust transport changes
3.
Changes in mid-latitude cyclones
4.
Changes in the storm track (NAO)
5.
El Nino and atmospheric transport
ENSO AND OZONE INTERANNUAL VARIABILITY OVER EU
Ozone mass fluxes
La Nina years
Southern Oscillation Index (SON)
R=-0.65
Tropospheric Ozone Column over EU (JFM)
El Nino years
R=-0.50
Surface Ozone over EU (JFM)
Positive anomalies in tropospheric O3 column and in surface O3 are
found over Europe in the spring following an El Nino year – linked to
pollution transport from Asia and enhanced biomass burning.
[Koumoutsaris et al., 2008]
EL NINO (NEGATIVE PHASE ENSO) MAY ALSO LEAD TO
ENHANCED STE
“ENSO affects global total tropospheric O3 not only via its effects on chemical
processes (temperature-dependent chemistry, water vapour concentrations,
emissions, etc.) but also via its profound effect on STE in the extratropics.”
[Zeng and Pyle, 2005]
EL NINO INFLUENCING NATURAL EMISSIONS
[Stevenson et al., 2005]