ihy 2008, sozopol, bulgaria1 n. a. kilifarska 1, y. k. tassev 2 1 geophysical institute, bulgarian...

IHY 2008, Sozopol, Bulgaria 1

N. A. Kilifarska1, Y. K. Tassev2

1Geophysical Institute, Bulgarian Academy of Sciences

2 Solar-Terrestrial Influences Laboratory, Bulgarian Academy of Sciences


Motivation for this study

• Major stratospheric warmings (MSWs) affect dramatically the whole winter atmosphere till the surface;

• Mechanisms relevant to SSW are still not clear;

• Existence of solar and internal atmospheric modes (i.e. QBO, AO, ENSO) in the polar atmospheric variability is broadly documented;

• 2 main types of MSWs:− Vortex displacement− Votex spliting After: Charlton and Polvani, J. Climate, Feb.2007


Data and Methods

Data:• CRs (energetic particles measured by GOES satellites at 30 000 km) for

three winters 1987-1988, 1998-1999 and 2001-2002 in which 2 MSWs had occured;

• Ground-based μ monitor at Climax (42.21N; -85.37W);

• Daily values of F10.7;

• T, winds and O3 mixing ration – from ERA 40 6 hourly analyses, for the period 1957-2002;

• Indices of internal atmospheric modes, i.e. Arctic oscillation index (AO) and QBO (quasi biennial oscillation of the equatorial stratospheric winds)

Methods: multiple regression and lagged correlation analyses


The aim of this study:

• To reveal the existence of causal relationships between some observed atmospheric parameters and forcing factors (i.e. solar and CRs variability and atmospheric internal modes like QBO, AO, etc.)

• To offer an explanation for existing great variety of Stratospheric Warmings, i.e.:– minor; – major (splitting type and displacement type); – Canadian.


Zonal wind distribution

0 10 20 30 40 50 60 70 80 90

10

20

30

40

Hei

ght

/km

'd isp lacem ent type ' SSW s; H igh Solar

Zonal W ind

0 10 20 30 40 50 60 70 80 90

10

20

30

40

10

20

30

40

Hei

ght

/km

'sp liting type ' SSW s; H igh Solar Zonal W ind

0 10 20 30 40 50 60 70 80 90

10

20

30

40

Hei

ght

/km

'd isp lacem ent type ' SSW s; Low Solar Zonal W ind

0 10 20 30 40 50 60 70 80 90

10

20

30

40

10

20

30

40

Hei

ght

/km

'sp liting type ' SSW s; Low Solar Zonal W ind

G eodetic Latitude [deg] G eodetic Latitude [deg]

0 10 20 30 40 50 60 70 80 90

10

20

30

40

10

20

30

40

Q BO (E) U in [m /s]; regular case

0 10 20 30 40 50 60 70 80 90

10

20

30

40

10

20

30

40

Q BO (W ) U in [m /s]; regular case

G eodetic Latitude [deg]


Some elementary statistics for MSWs:

• Initial guess: possible influence of highly energetic cosmic rays on polar atmospheric thermodynamics due to a strong control of active solar wind on CRs intensity.

• Correl. Coeff. for F10.7 and CRs time series: - 0.93 (west QBO)

- 0.67 (east QBO)

Displacement type MSWs Splitting type MSWs

High Solar

( 5 )

Low Solar

( 8 )

High Solar

( 5 )

Low Solar

( 9 )HS(e) HS(w) LS(e) LS(w) HS(e) HS(w) LS(e) LS(w)

2 3 6 2 4 1 3 6


MSWs during Low Solar radiation conditionsI. Wind correlation with ground based measurements of CRs

0 10 20 30 40 50 60 70 80 90

10

20

30

40

Hei

ght

/km

Zonal W ind regressed on C R (E )

0 10 20 30 40 50 60 70 80 90

10

20

30

40

10

20

30

40

Hei

ght

/km

Zonal W ind regressed on C R (w )

G eodetic Latitude [deg] G eodetic Latitude [deg]

"sp liting" type; w eak Q BO (w ) & LS

0 10 20 30 40 50 60 70 80 90

10

20

30

40

10

20

30

40

Hei

ght

/km

G eodetic Latitude [deg]0 10 20 30 40 50 60 70 80 90

10

20

30

40

Hei

ght

/km

"d isp lacem ent" type strong Q BO (e) & LS



II. Temperature and wind correlations with CRs measured on GOES satellite – winter 1987-1988 (west QBO)

4 0 5 0 6 0 7 0 8 0 9 0

10

20

30

Heigh

t /km

CRs = 4 - 15 M eV

CRs = 4 - 15 M eVTem perature

Zonal W ind

G eodetic Latitude [deg] G eodetic Latitude [deg]3 0 4 0 5 0 6 0 7 0 8 0 9 0

10

20

30

40

10

20

30

40

Heigh

t [km

]

10

20

30

40

3 0 4 0 5 0 6 0 7 0 8 0 9 0

10

20

30

40

Heigh

t [km

]

U corr. coeff. w ith C R s (C lim ax); 1987-1988

4 0 5 0 6 0 7 0 8 0 9 0

10

20

30

40

10

20

30

40

Heigh

t /km

U during MS W s w ithin 1987- 1988

Conclusion:

Intense CRs precipitation within periods of Low Solar radiation and west QBO favor decrease of Polar Vortex size eroding its equatorward edge.

According to the model experiments of Scott and Dritshel, 2006 => volumes’ ratio of Aleutian Anticyclone and Polar vortex plays an important role in the process of vortex splitting


Vortex-Vortex interactions in the Winter Polar Atmosphere I.

After: R. Scott and D. Dritshel, J. Atmos.Sci., 63, 726, 2006

Volumes’ ratio (Aleutian high/Polar Vortex)=0.6

t=0 t=2 days t=4 days

t=6 days t=8 days t=10 days


Vortex-Vortex interactions in the Winter Polar Atmosphere II.

t=0 t=8 days t=16 days

Volumes’ ratio (Aleutian high/Polar Vortex)=0.2


“Displacement” type MSWs

CRs showers during Low solar radiation and east QBO, however seems to force anticyclonic circulation trough decrease of westerlies over the Polar Cap;

Distortion of equilibrium between Aleutian high and Polar vortex could provoke a movement of the anticyclone toward the Pole and displacement of Polar Vortex;

The mostly affected by CRs is Nort-East part of Canada (due to the less geomagnetic cutoff) => creation of anticyclonic vortex in North Atlantic

1987


MSWs occurred within periods of High Solar Irradiance

0 10 20 30 40 50 60 70 80 90

10

20

30

40

Hei

ght

[km

]

"d isp lacem ent" type; Q BO (W ) & HS"spliting" type; Q BO (e) & HS0 10 20 30 40 50 60 70 80 90

10

20

30

40

Hei

ght

/km

0 10 20 30 40 50 60 70 80 90

10

20

30

40

10

20

30

40

Hei

ght

/km

Zonal W ind regressed on AO (W )Zonal W ind regressed on AO (E)

0 10 20 30 40 50 60 70 80 90

10

20

30

40

Hei

ght

[km

]

10

20

30

40

G eodetic Latitude [deg]G eodetic Latitude [deg]

Lagged cross-correlation analysis of forcing factors show:

• within QBO(e) phase AO is significantly influenced by F10.7 (+0.42) and QBO amplitude (+0.30)

• during QBO(w) phase AO index has stochastic character


U regression coefficients for winter 2001-02, HS, QBO(w), “displacement” type

3 0 4 0 5 0 6 0 7 0 8 0 9 0

10

20

30

40

Heigh

t /km

W inter 2001-2002

10

20

30

40

U corr. coeff. w ith F10.7

3 0 4 0 5 0 6 0 7 0 8 0 9 0

10

20

30

40

Heigh

t /km

10

20

30

40

U corr. coeff. w ith Q BO

3 0 4 0 5 0 6 0 7 0 8 0 9 0

10

20

30

40

Heigh

t /km

U corr. coeff. w ith C R


10

20

30

40


Zonal wind correlations with CRs measured on GOES satellite – winter 2001-2002

3 0 3 5 4 0 4 5 5 0 5 5 6 0 6 5 7 0 7 5 8 0 8 5 9 0

10

20

30

40

Heig

ht /k

m

CRs = 15 - 40 M eV

3 0 3 5 4 0 4 5 5 0 5 5 6 0 6 5 7 0 7 5 8 0 8 5 9 0

10

20

30

40

Heig

ht /k

m

CRs = 40 - 80 M eV

3 0 3 5 4 0 4 5 5 0 5 5 6 0 6 5 7 0 7 5 8 0 8 5 9 0

10

20

30

40

Heig

ht /k

m

CRs = 80 - 165 M eV

3 0 4 0 5 0 6 0 7 0 8 0 9 0

10

20

30

40

Heig

ht /k

m

CRs = 165 - 500 M eV


3 0 3 5 4 0 4 5 5 0 5 5 6 0 6 5 7 0 7 5 8 0 8 5 9 0

10

20

30

40

10

20

30

40

Heig

ht /k

m

Tim e Lag for 15-40 M eV

3 0 3 5 4 0 4 5 5 0 5 5 6 0 6 5 7 0 7 5 8 0 8 5 9 0

10

20

30

40

5

15

25

35

Heig

ht /k

m


3 0 3 5 4 0 4 5 5 0 5 5 6 0 6 5 7 0 7 5 8 0 8 5 9 0

10

20

30

40

10

20

30

40

Heig

ht /k

m


3 0 4 0 5 0 6 0 7 0 8 0 9 0

10

20

30

40

10

20

30

40

Heig

ht /k

m




CONCLUSIONS

An attempt for setting in order the great variety of conditions for occurrence of Major Strat. Warms is made. It was found that:

1. within periods of Low Solar irradiance CRs’ showers may affect the dynamical structure of Polar Atmosphere as well as to be the key factor for occurrence of different types Major Stratospheric Warmings, namely “spliting” and “displacement” types;

2. During High Solar activity periods: • For QBO(e) phase solar electromagnetic radiation and the

amplitude of QBO affect significantly dynamical regime of the Polar Atmosphere operating more effectively trough AO index;

• For QBO(w) AO index have stochastic character and this reduces possibilities for predictions;

3. In periods of very active Sun, solar electromagnetic radiation and corpuscular particles in a “trio” with QBO may affect strongly atmospheric dynamics at middle and high latitudes.

ihy 2008, sozopol, bulgaria1 n. a. kilifarska 1, y. k. tassev 2 1 geophysical institute, bulgarian...

Documents