Update on the Worsening Particle

Radiation Environment

Observed by CRaTER

N A Schwadron, F Rahmanifard, J. Wilson, A P Jordan,

H E Spence, C J Joyce, J B Blake, A W Case, W d Wet,

W M Farrell, J C Kasper, M D Looper, N Lugaz, L Mays,

J E Mazur, J Niehof, N Petro, C W Smith, L W

Townsend, R Winslow and C Zeitlin

Radiation

Hazards,

Interactions • Galactic Cosmic

Rays (GCRs)

– Steady Background

– Career limit in ~ 1-3 years

• Solar Energetic Particles (SEPs)

– Acute Sources

– ESPs versus impulsive component

– Time-dependent response

ACE &

Ulysses

Comp.

Pro

ton

sp

ee

d

Norm

aliz

ed

density

Norm

aliz

ed

tem

p

Dynam

ic

pre

ssure

Reduced

Density

and

Dynamic

Pressure

McComas et al., 2008

Schwadron and McComas, 2008

Open Flux Depletion

Connick et al., Astrophys. J., 2011.

There is a 2-phase depletion of open field lines: first during

the “normal phase” of solar min when ICME activity is

small, and then later when ICME activity is virtually zero.

Rahmanifard et al., 2016

Integration into Heliospheric Models

|B| = 2/4R12 where

R1 = 1 AU;

ICME = 1 x 1013 Wb;

D = 1/2;

ic = 40 days;

0 = 2.5 years;

d = 4.4 years;

Flo = 0.5 day1;

fhi = 3 day1;

flr = 4 x 1014 Wb (|B| = 2

nT). More recent theoretical

coniderations are predicting

a lower flux floor.

Schwadron et al., Astrophys. J. Lett., 722, L132, 2010.

Continued Decay of Magnetic Flux in

the Dalton-like Minimum

Goelzer et al., ApJ, 2013

Strong Reduction in Field

Possible – Much Higher GCR Flux

Rahmanifard et al., 2016

SCHWADRON ET AL., SPACE WEATHER, 2014a

• Highest GCR doses

in space age in

recent cycle 23 solar

minima

• Continues trend

observed by

Ulysses, ACE

Schwadron et al., Space Weather, 2017

0 2 4 6 8 10 12 14 16 1950 1960

1970 1980

1990 2000

2010 0 200

400

600

800

1000

1200Lunar Surface Dose Rate (cGy/yr)

Sunspot Number

Year

ACECRaTER

Sunspot Number

Model

Solar Proton Model Prediction/Validation After Schwadron et al., 2012

SEP Events During 2012:

Indicators of Larger SEP Events

in the New Cycle (24)

• Shown here are the major SEP events of 2012

and the comparisons between CRaTER

observations (blue) and prediccs predictions (red

and green).

• Agreement reveals overall accuracy of models,

while deviations likely reveal heavy ion

contributions to dose observed by CRaTER

60 65 70 75 80DOY

100

101

102

103

104

105

Dose

Ra

te(u

Gy/h

r)

CRaTER (blue) EMMREM (red)

134 136 138 140 142 144 146DOY

100

101

102

103

104

105

Dose

Ra

te(u

Gy/

hr)

CRaTER (blue) EMMREM (red)

Ja

n.

23

rd ,

2012 E

vent

Mar

7, 2012 E

vent

May 1

6,

20

12 E

vent

MeWaldt et al., 2015 Schwadron et al., 2017

SCHWADRON ET AL., SPACE WEATHER, 2014a

Joyce et al., 2015

Schwadron et al., 2017

Schwadron et al., 2017

10-2

10-1

100

101

102

Lu

na

r D

ose

Ra

te (

cG

y/d

ay

)

CRaTER D1D2

CRaTER D3D4

CRaTER D5D6

CRaTER Microdosim eter

10-3

10-2

10-1

100

101

102

Lu

na

r D

ose

Ra

te (

cG

y/d

ay

)

PREDICCS Al 0.3, H2O 10 g/cm 2

PREDICCS Al 1, H2O 10 g/cm 2

PREDICCS Al 5, H2O 10 g/cm 2

PREDICCS Al 10, H2O 10 g/cm 2

17/09

/04

17/09

/06

17/09

/08

17/09

/10

17/09

/12

17/09

/14

17/09

/16

17/09

/18

17/09

/20

10-4

10-2

100

102

104

pro

ton

/cm

2-s

-sr-

Me

V

PREDICCS Al 0.3, H2O 1 g/cm 2

PREDICCS Al 1, H2O 1 g/cm 2

PREDICCS Al 5, H2O 1 g/cm 2

PREDICCS Al 10, H2O 1 g/cm 2

2.5 MeV

6.5 MeV

11.6 MeV 30.6 MeV 63.1 MeV 165.0 MeV 433.0 MeV

X9 Flare

Sep 10X8 Flare

Sep 6

X9.3 Flare

Sep 6

X8.2 Flare

Sep 10• Example of a

large event

during

decline of

cycle 24

• Note

importance of

seed

population

Schwadron et al., 2017

• First event

had clear

shock, and

ESP

• Second event

shows

prompt

acceleration

Schwadron et al., 2017

Conclusions

• Radiation levels continue to increase due to

weakening solar activity

• Dose rates even higher than predicted in

2014

• Large events (Sep 2017) in decline of cycle

24 indicate that weak activity does not

exclude large SEP events

• Overall, SEP event probabilities still quite

low during cycle 24