Drivers and Solar Cycles Trends of - PowerPoint Presentation

Slide1

Drivers and Solar Cycles Trends of Extreme Space Weather Disturbances

Emilia Kilpua

University of Helsinki

(emilia.kilpua@helsinki.fi

@

EmiliaKilpua

)Slide2

Key solar wind parameters

magnetic field magnitude and direction

density

speed

level of turbulence

Alfvén

Mach

number (bow shock compression, how plasma flows around the magnetopause, saturation)

dawn

-dusk

(driving) electric field

d

ynamic pressureSlide3

highest

M

A

lowest M

A

p

olar cap potential

s

olar wind driving electric field (mV/m)

Solar wind

Alfvèn

Mach number and saturation

Myllys

et al., 2016Slide4

Effect of dynamic pressure

s

olar wind driving electric field (mV/m)

dynamic pressure (

nPa

)

p

olar cap potential

Myllys

et al., in preparationSlide5

Drivers of

geospace storms four Solar Cycles (1963 -2011)

G1 G2 G3 G4 G5

Coronal Mass Ejections (CMEs) drive nearly all intense

geospace

storms

Richardson and Cane

, 2012

Storm intensity:

Kp

(NOAA scales)Slide6

F

lux Rope

Sheath

Shock

Two principal CME structuresSlide7

Only flux ropes and sheaths have strong enough fields to drive extreme storms

Flux rope

S

heath

CIR

F

ast stream

Normalized occurrence distribution for events in 1997-2014Slide8

Sheaths have clearly higher

Pdyn and

Alfvén Mach number than flux ropes

Flux rope

S

heath

CIR

F

ast streamSlide9

Which CMEs drive the most extreme storms?

intrinsic CME properties

m

odifications during the IP journey

p

re-conditioning of the

heliosphere

“PERFECT STORM SCENARIO”

(

Liu et al

., 2014; 2015)Slide10

Nov 20, 2003 (Strongest

Dst storm of SC 23) driven by “isolated” CMESlide11

November 2001 storm and Halloween storms

impulsive energy injection

Balan et al

., JGR, 2014

V [km/s]

P

dyn

[

nPa

]

B

Z

[

nT

]

Dst

[

nT

]

> 60

nPaSlide12

prevents CME expansion  CME maintains high fields and speeds

t

urbulent and compressed regions (high

P

dyn

and

M

A

)

shock merging (e.g.,

Lugaz

et al., 2015) and shock compression of the preceding ICME (e.g., Lugaz 2016: Statistical analysis based on the Heliospheric

S

hock Database

ipshocks.fi)

Liu et al., Nat Comm., 2014

CME-CME interactions Slide13

V

[

km/s]

n

[

nPa

]

“CME Sandwich”

(March 17, 2015)

Interactions with the other large-scale solar wind structures (CIR, fast stream, HPS)

Kataoka

et al

., GRL, 2015

c

ompresses sheath

and

FR

stronger storm than expected

F

ast stream compression enhances

geoeffectivity

of flux ropes with north-south rotating fields

(see e.g.,

Kilpua et al

.,

Ann.

Geophys

. 2012 and

Fenrich

&

Luhmann

, GRL, 1998)

f

ast

stream

FR

s

heath



B

[

nT

]

B

Z

[

nT

]

Dst

HPS

4

daysSlide14

low density 

minimal drag force  CME maintains high speeds

 large

Ey

and stronger field line draping in the sheath

Liu et al.

, 2014

Preconditioning of the

heliosphere

l

ow density

p

revious weaker CMESlide15

Extreme Substorms

Extreme substorms

 strong ionospheric

currents without significant ring current (Dst) storm (

Huttunen

and

Koskinen

, 2004;

Tsurutani

et al., 2015)

During CME sheath regions (Huttunen and Koskinen 2004)

Triggered by pressure pulses? (Tsurutani et al., 2015)

Strongest GICs occur during CME sheath regions (

Huttunen et al., Space Weather, 2008)Slide16

Strong Van

Allen belt enhancements: Fast streams are important

Kilpua et al., GRL, http://adsabs.harvard.edu

/abs/2015GeoRL..42.3076K, 2015Slide17

Occurrence of extreme storms

Carrington storm

July 22 “super-CME”Slide18

Correlation between solar cycle size and storm occurrence

Pearson correlation

coefficients, confidence intervals calculated with the bootstrap method. From

Kilpua et al., APJ, 2015

mean SSN

m

ax SSN

(14 cycles, SCs 11-23)

95%

confidence



correlation

between the

storm occurrence

and the

solar

cycle strength decreases with increasing storm magnitudeSlide19

Solar cycle phases and storms

Kilpua et al., APJ 2015Slide20

Weaker storms occur predominantly in the declining phase

(see also e.g., Ruzmaikin and

Feynmann, 2001) 

poloidal

field



coronal holes  CIRs and fast

streams

Stronger storms clustered close to maximum time

 toroidal

field  active regions  coronal mass ejection (also probability for CME-CME interactions increases)Solar cycle phases and stormsSlide21

Summary

Extreme storms: strong (+ a few hours) BS, high

V, P

dyn and M

A

 CME sheaths and interacting CMEs

“ Perfect Storm Scenario”: Strong and fast CME(s), favorable modifications during IP journey, pre-conditioning

Extreme space weather may occur also during weaker solar cycles (probability of the next Carrington storm?

Riley

2012: 10-yr occurrence probability 12%)

 smaller-scale dynamo and turbulent fields? Stronger storms occur more near solar maximum