GLOBAL CHANGES IN OUR ATMOSPHERE: a top-down point of view

Atmospheric Science 101 Structure of atmosphere Important relationships

The Northern Hemisphere Annular Mode (NAM) NAM patterns Significance

Vortex variation Amplifier mechanism Implications and trends

Var Limpasuvan1 and Kumar Jeev2

1Department of Chemistry and Physics and 2Department of Computer Science Coastal Carolina University, Conway, South Carolina

Goals:

To demonstrate that changes in our atmosphere above 30,000 feet can influence surface climate

To see global changes in a new perspective (“top- down view”)

2

Orientation: Atmospheric Science 101

30oN

equator

60oN altit

ude30oN

equator

60oN

NP

60oN

30oN

equator

altit

ude30oN

equator

60oN

NP 60oN 30oN equator

altit

ude

latitude

30oN

equator

60oN

NP60oN30oNequator

altit

ude

latitude

12 km (~39,300 ft )troposphere

50 km (~164,000 ft )

stratosphere

mesosphere

tropopause

stratopause

3

Basic Atmospheric Structure

30oN

equator

60oN

sun

west-east wind(“zonal wind”)

sun

West-east (zonal) wind (m/s) Temperature (deg K)

Longitudinally Average

winter wintersummer summer

VORTEX VORTEX

Pressure (density) decreases rapidly with altitude

Where is the coldest region in atmosphere?

Note the jet reversal near 90 km

4

Simple Atmosphere

sun

West-east (zonal) wind (m/s) Temperature (deg K)

Longitudinally Average

winter wintersummer summer

270

250

290

230190210

170

150

130

50

100

200

150

250

300

-50

-100

Radiatively determined state

Look markedly different than observations

Wind & temperature are governed by physics Near geostrophic and hydrostatic balance Latitudinal temp gradient ~ vertical wind shear

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Atmospheric Waves and Circulation

Planetary waves (~ mountain; land-sea contrast; > 5000 km)

Gravity Waves (~ convection; adjustment; < 1000 km)

Close-off jetsClose-off jets

cooling

warming

Synoptic Waves (~weather storm; instability; between 1000-3000 km)

6

Basic Atmospheric Structure Revisited

West-east (zonal) wind (m/s) Temperature (deg K)

Longitudinally Average

winter wintersummer summer

270

250

290

230190210

170

150

130

50

100

200

150

250

300

-50

-100

Atmospheric waves are important to maintain structure.

Circulating gyres due to waves spread response.

Balance between dynamics and radiative effects

Latitudinal temp gradient ~ vertical wind shear

VORTEX VORTEX

Thermal Wind Relationship

7

Wintertime Climatology (DJF)

Sea Level Pressure & Surface Winds Zonal Wind (Jet) @ 10 km & Storm Tracks

40-year average using NCEP/NCAR Reanalyses

every 5 hPa

12 m/s

H

L

H

L

H

every 5 m/s

track

Jetstream

Weather systems

Aleutian

Icelandic

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Modes of Variability

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The Northern Hemisphere Annular Mode (NAM)

NAM Pattern NAM Index

HIGHLOWHIGH

“See-Saw” across Arctic Circle

30% of winter variance North Atlantic Oscillation (NAO)

Jet Stream Shift (storm activity)

Storm activity

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The NAM SummaryHIGH PhaseLOW Phase

Natural Mode of variability

Strong troposphere and stratosphere coupling

Characteristic of rotating fluids (i.e. other planets) Changes that project on NAM will be amplified

Connects polar vortex with surface conditions Rethinking of surface climate and weather

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Stratospheric Influence of Surface Climate?

Impossible !!!

Growing evidence for “downward” influence

75 % of the atmospheric mass in troposphere. Atmospheric waves mostly originate from near-surface.

Strong variation in polar vortex strength appears to reach surface This variation occurs naturally within the system during winter

Surely, troposphere affects stratosphere. One way interaction!

Dynamics of this natural downward influence? How? (Mr. Jeev)

Alti

tude

(km

)

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Atmospheric Wave Amplifier

VORTEX

warm cold

JET

NORTH POLEEQUATOR

TROPOSPHERE

STRATOSPHERE

TROPOPAUSE

ALT

ITU

DE

(km

)

WINTERTIME

heat flux

colder

JET

VORTEX

heat flux

colder

JET

HIGH NAM Positive feedback by waves

Turning the troposphere on itself

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How Can the Polar Vortex Change?

Naturally with the atmospheric system

Solar Variability: 11-year solar cycle (Sunspots)

Stratospheric ozone and UV changes (10-20% of solar irradiance )

Polar vortex becomes stronger and colder during UV increase

El Chicon (1982, 17oN)

Volcanic eruptions: stronger, colder vortex after eruption Pinatubo (1991, 15oN)

North poleEquator

Aerosols (sulfuric acid + water) dark

warm cold

JETJET

Wave amplification HIGH NAM

Similar mechanism to above

ozone

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Observed Trends in Northern Hemisphere

Polar stratospheric cooling ~3-5 degrees since 1979

NAM Index

Polar Stratospheric Clouds (PSC)

Kiruna, Sweden

Polar Mesospheric Clouds

Edmonton, Alberta Canada

Trend toward positive NAM index

Stronger polar vortex (PSCs)

Change in wave propagation

Change in overturning gyres

Surface Air Temperature

Incipient ozone loss (~SH)

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Summary

Dramatic changes above 30,000 ft (tropopause) are present sporadic: volcanic eruptions, sudden vortex changes cyclical: solar cycle trends: stratospheric/mesospheric cooling future NASA missions (EOS-AURA, SABER, AIM)

Their influence can extend downward and affect surface amplification process due to atmospheric waves projection on to preferred mode of variability (NAM)

Strong stratospheric-tropospheric coupling stratosphere ignored in the past; future models must extend up improving mid-range forecasting

Support: National Science Foundation – RUI; CCU