Kyle Copeland1

Herbert H. Sauer2

Wallace Friedberg1

1

Civil Aerospace Medical Institute

Federal Aviation Administration

Oklahoma City, OK 73125

2

National Geophysical Data Center

National Oceanic and Atmospheric Administration

Boulder, CO 80305

March 2009

Final Report

Solar Radiation Alert System

(Revised 30 May 2008)

DOT/FAA/AM-09/6

Office of Aerospace Medicine

Washington, DC 20591

OK-09-0434-JAH

Federal Aviation

Administration
NOTICE

This document is disseminated under the sponsorship 

of the U.S. Department of Transportation in the interest 

of information exchange. The United States Government 

assumes no liability for the contents thereof.

___________

This publication and all Office of Aerospace Medicine 

technical reports are available in full-text from the Civil 

Aerospace Medical Institute’s publications Web site: 

www.faa.gov/library/reports/medical/oamtechreports


Technical Report Documentation Page 

1. Report No. 2. Government Accession No. 3. Recipient's Catalog No. 

DOT/FAA/AM-09/6 

4. Title and Subtitle 5. Report Date 

Solar Radiation Alert System March 2009 

6. Performing Organization Code 

 

7. Author(s) 8. Performing Organization Report No. 

Copeland K,1 Sauer HH,2 Friedberg W1 

9. Performing Organization Name and Address 10. Work Unit No. (TRAIS) 

 

11. Contract or Grant No. 

1

FAA Civil Aerospace Medical Institute 

P.O. Box 25082 

Oklahoma City, OK 73125 

2

National Geophysical Data 

Center

NOAA, Boulder, CO 80305 

12. Sponsoring Agency name and Address 13. Type of Report and Period Covered 

Office of Aerospace Medicine 

Federal Aviation Administration 

800 Independence Ave., S.W. 

Washington, DC 20591 14. Sponsoring Agency Code 

15. Supplemental Notes 

This work was accomplished under approved task TOXLAB.AV9000 1208AC086110 

16. Abstract 

The Solar Radiation Alert (SRA) system continuously evaluates measurements of high-energy protons made by 

instruments on GOES satellites. If the measurements indicate a substantial elevation of effective dose rates at 

aircraft flight altitudes, the Civil Aerospace Medical Institute issues an SRA via the National Oceanic and 

Atmospheric Administration Weather Wire Service. This report describes a revised SRA system. SRA issuecriteria remain the same but significant improvements have been made in the calculations. The solar proton 

fluence to effective dose conversion coefficients have been recalculated using 2007 recommendations of the 

International Commission on Radiological Protection and the latest release of the Monte Carlo transport code, 

MCNPX 2.6.0. The shape of the <10 MeV secondary neutron spectrum is now accounted for down to 100 eV. 

The flux correction based on spectral index has been revised to smooth the flux spectrum of solar protons. 

Estimates of the >605 MeV spectral shape have been improved by the addition of correction factors for the 

differential interpretation of the >700 MeV integral flux channel. Estimates of galactic cosmic radiation 

background count rates in the GOES data are now median rather than mean values. Estimated solar cosmic 

radiation dose rates are about 10 times higher than those made using the previous version of the SRA system.

 

17. Key Words 18. Distribution Statement 

 

 

Solar Radiation, Monte Carlo Particle Transport Code, 

Solar Protons, Solar Particles, Space Weather, Solar Flare, 

Coronal Mass Ejection

Document is available to the public through the 

Defense Technical Information Center, Ft. Belvoir, VA 

22060; and the National Technical Information 

Service, Springfield, VA 22161 

19. Security Classif. (of this report) 20. Security Classif. (of this page) 21. No. of Pages 22. Price 

Unclassified Unclassified 24 

Form DOT F 1700.7 (8-72) Reproduction of completed page authorized 

iii

ACKNOWLEDGMENTS

For editorial and technical contributions to this report, we thank: E.B. Darden, Jr., Oak Ridge Associated Universities (Ret.), Oak Ridge, TN; M.E. Wayda and F.E. Duke (contract employee), Civil Aerospace Medical Institute, 

FAA, Oklahoma City, OK; D.E. Parker, University of Oklahoma Health Sciences Center, Oklahoma City, OK; M.P. 

Sattler, United States Air Force; and M.A. Shea and D.F. Smart, University of Alabama, Huntsville, AL. 

Contents

Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Background. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Revisions Since the Earlier Version. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

SRA messages. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Method Used to Estimate Effective Dose Rates at Flight Altitudes. . . . . . . . . . . . . . . . . . . . . . . . 6

Basis of SRA System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Calculating Effective Dose Rate at Specific Altitudes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Method Used to Estimate Risk That the Equivalent Dose to a Conceptus Exceeds 500 μSv in

a 10-Hour Exposure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Results and Discussion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Appendix A. Sample Solar Radiation Alert System Messages. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A1

Solar Radiation Alert System

INTRODUCTION

Background

During air travel, aircraft passengers and crew are usually exposed to ionizing radiation at higher dose rates than 

members of the general population. The principal ionizing 

radiation for air travelers is galactic cosmic radiation, a 

main source of which is supernovae (exploding stars). 

Occasionally, a disturbance in the Sun leads to a large 

flux of solar protons with sufficient energy to penetrate 

Earth’s magnetic field, enter the atmosphere, and increase 

ionizing radiation levels at aircraft flight altitudes (geopotential altitudes are reported). For a primer on aircrew 

exposure to ionizing radiation see Reference 1. 

Overview

The Federal Aviation Administration (FAA) has in 

operation a system for continuous evaluation of proton 

flux measurements made by instruments on Geosynchronous Operational Environmental Satellites (GOES). The 

system is illustrated in Figure 1. At present, the primary 

data source is GOES-11; GOES-10 measurements are 

used if there is a problem obtaining data from GOES-11. 

If measurements indicate the likelihood of a substantial 

elevation of ionizing-radiation levels at aircraft flight altitudes at polar latitudes (locations with an effective cutoff 

rigidity of ~0 MV (2)), the FAA’s Civil Aerospace Medical 

Institute (CAMI) issues a Solar Radiation Alert (SRA) to 

the National Oceanic and Atmospheric Administration 

Weather Wire Service (NWWS) (3). 

The specific criteria for issuance of an SRA is that the 

estimated effective dose rate induced by solar protons at 

70,000 ft equals or exceeds 20 microsieverts per hour

(μSv/h) for each of three consecutive 5-minute periods. 

Because of the potential for a delay of 3-20 minutes in 

communication processes and the three 5-minute periods, 

notification of the start of SRA conditions may be 18-35 

minutes after the start of the first 5-minute period. The 

SRA is canceled when the average effective dose rate at 

70,000 ft is less than 20 μSv/h for six consecutive 5-

minute periods. 

Revisions Since the Earlier Version

This report replaces Office of Aerospace Medicine 

report DOT/FAA/AM-05/14 (4) describing the previous version of the FAA SRA system. Significant changes 

include:

(a) Table 1 has been revised to reflect significant improvements: particle fluences in the atmosphere have been 

recalculated using the most recent release of the Monte 

Carlo transport code, MCNPX 2.6.0 (5). Effective dose 

has been recalculated based on the 2007 recommendations of the International Commission on Radiological 

Protection (6) with the shape of the <10 MeV secondary 

neutron spectrum accounted for down to 100 eV. Also, 

the table values have been restated in terms of dose per 

unit fluence of particles entering the atmosphere, rather 

than unit fluence measured at the satellite.

(b) Step 5 has been revised to smooth the flux spectrum 

of solar protons. Step 8 has been revised to reproduce 

the measured flux by altering the spectral intensity rather 

than the spectral-hardness index. A new Step 10 has been 

added to convert from GOES flux to flux entering the 

atmosphere. 

(c) Estimates of spectral hardness and intensity involv-

ing data from the High-Energy Proton and Alpha Detector 

(HEPAD) have been improved through the addition of 

correction factors for the differential interpretation of 

channel P11 (Table 3). 

(d) Estimates of galactic cosmic radiation “background” count rates in the GOES data are median rather 

than mean values.

The net result of the revisions, combined with bug 

fixes in the source code, is considerably higher dose rates 

at all altitudes. As an example, Figure 2 shows estimates 

made for 20 January 2005 using both versions.

SRA messages

Six different message types are issued to the NWWS 

(3): Test, Alert, Alert Update, Alert Cancellation, Service 

Suspended, Service Resumed. A Test message is sent every 

day at 1500 Coordinated Universal Time (UTC), unless conditions indicate an Alert, Alert Update, or Alert 

Cancellation message should be sent. An Alert message 

is sent when the criteria for an SRA is met. After the 

Alert message, Alert Update messages are sent every 

5 minutes until the conditions indicate that the SRA 

should be cancelled. The Alert Cancellation message is 

then sent. A Service Suspended message is sent when 

the system cannot obtain up-to-date GOES data. Data 

outages can occur during GOES eclipse seasons and 

because of communications trouble between SWPC and 
Figure 1. Solar Radiation Alert system: (1) Occasionally, a disturbance in the Sun (solar flare, coronal mass ejection) leads 

to a large flux of high-energy particles in the vicinity of the Earth. (2) Instruments on a GOES satellite continuously measure 

the radiation, and the information is transmitted to NOAA. (3) From there it is sent to CAMI. A computer at CAMI analyzes 

the measurements. (4) If the measurements indicate the likelihood of a substantial elevation of ionizing radiation levels at 

aircraft flight altitudes, a Solar Radiation Alert is issued to the NOAA Weather Wire Service. Estimated effective dose rates 

for 30-, 40-, 50-, 60-, and 70-thousand feet are included and updated at 5-minute intervals for the duration of the alert. (5) 

The National Weather Service distributes alerts and updates via the NOAA Weather Wire Service and the Internet. 
Table 1. Effective dose per unit incident fluence, Δ(R,H)a

, to an adult at altitude (H), from incident 

exoatmospheric protons of rigidity (R)

Table 1. Effective dose per unit incident fluence, (R,H),a

 to an adult at altitude (H), from incident 

exoatmospheric protons of rigidity (R)

Rigidity (R) Altitude (H) b

MV -50 ft 9722 ft 19,588 ft 29,378 ft 39,197 ft

 183.5 1.00 x 10-16 1.00 x 10-16 1.00 x 10-16 1.84 x 10-11 4.52 x 10-10

 245.6 1.00 x 10-16 1.00 x 10-16 3.08 x 10-13 5.69 x 10-11 1.39 x 10-9

 329.7 1.00 x 10-16 1.00 x 10-16 4.51 x 10-13 2.76 x 10-10 8.16 x 10-9

 444.6 1.00 x 10-16 4.42 x 10-12 5.03 x 10-10 1.77 x 10-8 2.65 x 10-7

 604.4 6.31 x 10-10 6.05 x 10-10 2.03 x 10-8 3.39 x 10-7 2.69 x 10-6

 832.7 2.44 x 10-9 7.11 x 10-8 8.83 x 10-7 5.89 x 10-6 2.45 x 10-5

 1171. 2.43 x 10-8 7.37 x 10-7 7.21 x 10-6 3.78 x 10-5 1.32 x 10-4

 1696. 2.17 x 10-7 4.62 x 10-6 3.79 x 10-5 1.93 x 10-4 6.36 x 10-4

 2549. 8.26 x 10-7 1.49 x 10-5 1.11 x 10-4 4.70 x 10-4 1.24 x 10-3

 3991. 1.92 x 10-6 3.54 x 10-5 2.53 x 10-4 9.84 x 10-4 2.38 x 10-3

 4848. 2.77 x 10-6 4.89 x 10-5 3.37 x 10-4 1.27 x 10-3 3.01 x 10-3

 6494. 5.82 x 10-6 8.75 x 10-5 5.48 x 10-4 1.93 x 10-3 4.19 x 10-3

 10,898. 3.14 x 10-5 2.07 x 10-4 1.06 x 10-3 3.45 x 10-3 7.13 x 10-3

 18,695. 9.98 x 10-5 4.61 x 10-4 2.05 x 10-3 6.14 x 10-3 1.18 x 10-2

 20,917. 1.02 x 10-4 5.54 x 10-4 2.36 x 10-3 6.75 x 10-3 1.25 x 10-2

 32,545. 2.35 x 10-4 9.41 x 10-4 3.65 x 10-3 9.98 x 10-3 1.81 x 10-2

Rigidity (R) Altitude (H) b

MV 48,977 ft 58,749 ft 68,511 ft 78,260 ft 

 183.5 4.18 x 10-9 1.91 x 10-8 5.22 x 10-8 9.68 x 10-8

 245.6 1.52 x 10-8 7.82 x 10-8 2.21 x 10-7 4.25 x 10-7

 329.7 9.16 x 10-8 4.48 x 10-7 1.23 x 10-6 2.33 x 10-6

 444.6 1.64 x 10-6 5.39 x 10-6 1.16 x 10-5 1.89 x 10-5

 604.4 1.11 x 10-5 2.86 x 10-5 5.36 x 10-5 8.15 x 10-5

 832.7 6.87 x 10-5 1.43 x 10-4 4.38 x 10-4 1.78 x 10-3

 1171. 5.30 x 10-4 1.37 x 10-3 1.81 x 10-3 1.88 x 10-3

 1696. 1.25 x 10-3 1.80 x 10-3 2.13 x 10-3 2.26 x 10-3

 2549. 2.20 x 10-3 2.97 x 10-3 3.36 x 10-3 3.41 x 10-3

 3991. 3.91 x 10-3 4.93 x 10-3 5.29 x 10-3 5.17 x 10-3

 4848. 4.84 x 10-3 6.01 x 10-3 6.37 x 10-3 6.16 x 10-3

 6494. 6.32 x 10-3 7.47 x 10-3 7.62 x 10-3 7.17 x 10-3

 10,898. 1.00 x 10-2 1.11 x 10-2 1.07 x 10-2 9.62 x 10-3

 18,695. 1.57 x 10-2 1.65 x 10-2 1.53 x 10-2 1.34 x 10-2

 20,917. 1.62 x 10-2 1.69 x 10-2 1.56 x 10-2 1.36 x 10-2

 32,545. 2.30 x 10-2 2.31 x 10-2 2.08 x 10-2 1.76 x 10-2

a Sv/(incident proton/cm2

)

b

 Geopotential altitude converted from atmospheric depth (11). 

a μSv/(incident proton/cm2)

b

 Geopotential altitude converted from atmospheric depth (11).
Table 2. Conversion factors (k, k') and characteristic rigidities (RP[j] in MV) (7) 

 Channel 

 Conversion 

 factor k a

 Conversion

 factor k' b

 Characteristic

 rigidity (RP[j]) c

 P4 4.64 22.25 225.1 

 P5 15.5 43.04 338.2 

 P6 90. 252.8 563.9 

 P7 300. 1210. 950.0 

 P10 162. 175.6 1225. 

 P11 1565. d 1103. 1700. a k: counts/(particles/(cm2

•sr•MeV)) b k': counts/(particles/(cm2

•sr•MV)) c The characteristic rigidity is a weighted average rigidity, where the weighting depends on 

the instrument sensitivity across the width of the channel and the assumed spectral shape. d k: counts/(particles/(cm2

•sr))

Table 3. Spectral-hardness index correction factors (s) for protons (7) 

a

Channel

ҏSpectralhardness

index, γҏ P4 P5 P6 P7 P10 P11 

 Spectral-hardness index correction factor 

0 1.0000 1.0000 1.0000 1.0000 1.0000 0.289 

 1 0.9565 0.9775 0.9733 0.9300 0.9968 0.289 

 1.5 0.9171 0.9562 0.9483 0.8675 0.9936 0.289 

 2 0.8777 0.9350 0.9233 0.8050 0.9904 0.513

 3 0.7751 0.8764 0.8553 0.6502 0.9808 0.812 

 4 0.6609 0.8060 0.7753 0.4913 0.9683 0.962 

 5 0.5458 0.7284 0.6888 0.3485 0.9529 1.01 

 6 0.4380 0.6476 0.6011 0.2329 0.9348 1.00 

 7 0.3428 0.5674 0.5161 0.1473 0.9142 0.948 

 8 0.2623 0.4904 0.4366 0.08856 0.8914 0.874 

 9 0.1969 0.4186 0.3645 0.05089 0.8666 0.789 

10 0.1453 0.3533 0.3006 0.02811 0.8400 0.702 

a Intermediate correction factors are obtained by linear interpolation.
Table 4. Rigidity limits (in MV) for differential flux spectra

Flux spectrum (i) 1 2 3 4 5 6 

Lower rigidity, Ri,lower 137 338 564 950 1225 1343 

Upper rigidity, Ri,upper 338 564 950 1225 1343 See Step 9 

Figure 2. (a) Original SRA system estimates of effective dose rate on 20 January 2005, during the solar proton event of 16 

January 2005; (b) Revised SRA system estimates of effective dose rate on 20 January 2005, during the solar proton event of 

16 January 2005.
CAMI. Information given with Alert and Alert Update 

messages includes: 

(a) Estimated effective dose rates from solar cosmic 

radiation in μSv/h, based on 5-minute averages, at altitudes of 30-, 40-, 50-, 60-, and 70-thousand feet.

(b) Estimated risk that the equivalent dose to the conceptus will exceed 500 μSv at 40-, 50-, and 60-thousand 

feet in a 10-hour exposure. 

(c) Effective doses for the previous 1, 3, 5, and 10 

hours at 40-, 50-, and 60-thousand feet. 

A sample of each type of message issued by the system 

is in Appendix A. SRA system related messages can be 

identified in three ways:

(a) The Advanced Weather Interactive Processing 

System (AWIPS, 7) identifier is ALTPAV.

(b) The Space Weather Message Code is ALTPAV.

(c) The World Meteorological Organization (WMO) 

header is WOXX50 KWNP.

Subscribers to the NWWS receive SRA messages as 

part of the stream of weather related messages transmitted through the NWWS. Recent SRA and other space 

weather related messages are also available at the National Weather Service Web site: www.weather.gov/view/

national.php?prodtype=space.

The Web site shows the most recent space weatherrelated messages.

METHOD USED TO ESTIMATE 

EFFECTIVE DOSE RATES 

AT FLIGHT ALTITUDES

Basis of SRA System 

Primary Solar Proton Spectrum. GOES-10 and 

GOES-11 proton flux measurements are used to estimate 

solar radiation dose rates in Earth’s atmosphere. They 

are available from the file transfer protocol (ftp) server 

of the Space Weather Prediction Center (SWPC) in near 

real-time and are also available on the Internet (8). The 

measurements are 5-minute averages and are recorded in 

several “channels”: P4-P7 (15-900 MeV energy, 168-1581 

MV rigidity), P10 (510-700 MeV, 1103-1343 MV), 

and P11 (>700 MeV, >1343 MV). Channels P8 and P9 

are excluded from the analysis because their correction 

algorithms are more complex than those of the other 

channels, and their exclusion does not significantly affect 

the calculated dose rates. Fluxes in channels P4-P10 are in 

terms of differential flux (particles/cm2

·steradian·s·MeV). 

Fluxes in channel P11 are in terms of integral flux (particles/cm2

·steradian·s).

In Steps 1-3, fluxes from the SWPC are converted 

to count rates, galactic background count rates are subtracted, and the count rates are reverted to fluxes using 

conversion factors that are appropriate for GOES-10 

and GOES-11 (9). 

In Steps 4-10, the fluxes are used to create a model of 

the proton flux spectrum entering the atmosphere. The 

range of rigidities (R) in the model (137-32,545 MV) 

includes 100% of the flux for over 99% of the solar 

proton events since the 23 February 1956 event (10). 

The model consists of six differential flux spectra (f

i

(R)) 

in the form of Eq. 1, each spanning an adjoining rigidity 

range (Table 4). Parameters in Eq. 1 are flux intensity 

(α) and spectral-hardness index (γ). 

In Step 11, the six spectra are used to calculate effective doses.

Due to the requirement of extrapolating the shape 

of the proton spectrum in channel P11, the possibility 

cannot be discounted that the passage of a shock-front 

with a significantly high flux of protons with rigidities 

>1343 MV could result in calculated doses rates that are 

unrealistically high. 

Radiation Transport. The Monte Carlo radiation 

transport code MCNPX 2.6.0 (5) was used to calculate 

particle fluences (particles/cm2

) resulting from the interaction of the exoatmospheric primary protons with 

the atmosphere. Particles transported with the radiation 

transport code include protons, neutrons, pions, kaons, 

photons, electrons, and muons. Previous calculations for 

altitudes of 60,000 ft and below indicate that fluences of 

other particles are too small to be of significance in dose 

calculations (4, 11). 

Earth was modeled as a sphere of liquid water of radius 

6371 km and density 1 g/cm3

. Earth’s atmosphere was 

modeled as 100 spherically symmetric 1-km thick layers

of a gaseous mixture of atoms of nitrogen, oxygen, argon, 

and carbon, in the fractions by weight present in dry air

near sea level (12). The density (g/cm3

) assigned to each 

layer was the density at the geometric altitude of the middle 

of the layer, based on data in NOAA et al. (13). Thus, 

the thickness of the model atmosphere was 100 km, the 

area of its uppermost surface was 5.262 x 1018 cm2

, and 

the total atmospheric depth was 1035.08 g/cm2

. Empty 

space surrounded the uppermost atmospheric layer. 

Fluence-to-Effective Dose Conversion. Table 1 contains coefficients∆(R,H) for estimating effective dose from 

particle fluences traveling into the top of the atmosphere, 

specifically primary solar protons. Secondary particles 

i fi R i R γ α − ( ) = (Eq. 1)
included in the dose calculations (herein designated as 

included secondaries) are muons, photons, electrons, 

positrons, pions, protons, and neutrons. Kaons were not 

included because their contribution to the total dose was 

found to be negligible.

For incident solar protons of all energies, values of 

∆(R,H) (μSv/(particle/cm2)) at each rigidity (R) and 

altitude (H) in Table 1 were calculated as follows: 

(a) For each particle included in the dose calculations, 

the average fluence spectrum at altitude H (particles/cm2

) 

per solar proton of rigidity R entering the atmosphere was 

multiplied by appropriate fluence-to-dose coefficients (6, 

14) to obtain average effective dose to an adult per solar 

proton of rigidity R entering the atmosphere. 

(b) Effective doses to an adult were summed to obtain 

JD, the average effective dose, in μSv at altitude H, per 

incident particle of rigidity R entering the atmosphere.

(c) JD was multiplied by 5.262 x 1018 cm2 (area of 

the uppermost surface of the atmosphere) to obtain

∆(R,H), μSv at altitude H generated by a fluence of 1 

particle/cm2

 of solar protons of rigidity R entering the 

atmosphere. 

A ∆(R,H) of zero was reported as 1 x 10-16 μSv/(particle/

cm2). Coefficients for converting fluence to effective 

dose were obtained by interpolation from coefficients 

reported by Pelliccioni (14), but adjusted to meet 2007 

ICRP recommendations (6). Table 1 is applicable to any 

solar particle event.

Calculating Effective Dose Rate at Specific Altitudes 

Step 1. The uncorrected flux (φ) in each of channels 

P4, P5, P6, P7, P10, and P11 is reverted to total count 

rate (galactic plus solar, C) by multiplying φ by the conversion factor (k) in Table 2: 

GOES-10 and GOES-11 have identical instruments and 

therefore use the same conversion factors.

Step 2. For each channel, the median of the 144 acceptable 5-minute count rates immediately preceding 

the current 5-minute period is used as an estimate of the 

galactic cosmic radiation background (B). Count rates are 

unacceptable if ≤ 0, designated as "bad" by the archiving 

source, or if a solar proton event is ongoing (The SEC 

defines the onset of a solar proton event as the beginning 

of the first of three or more consecutive 5-minute periods 

during which the GOES proton flux with energies ≥10 

MeV exceeds 10 particles/(cm2

·steradian·s) (15)). The 

reduction in count rates during a Forbush decrease (16)

is small, and solar cosmic radiation doses based on GOES 

data during a large solar proton event are not appreciably 

affected; thus their possible influence is not a concern when 

calculating galactic cosmic radiation background. 

The background corrected count rate (C’) is calculated 

as follows: 

(a) Galactic cosmic radiation background count-rate 

(B) is calculated. 

(b) B is subtracted from C, as shown in Eq. 3. 

(c) A negative C’ is changed to 1% of B.

Step 3. A differential flux (φ'), for each of the channels 

listed in Step 1, is calculated by dividing the background 

corrected count-rate (C') by the conversion factor (k') 

from Table 2: 

Step 4. With Eq. 5, derived from Eq. 1, preliminary 

spectral-hardness indices (γi

) are calculated for differential 

flux spectra f

i=1

(R) through f

i=5

(R), using channel pairs 

(P[m] and P[n]): i=1 (channels P[m=4] and P[n=5]), 

i=2 (P[m=5] and P[n=6]), i=3 (P[m=6] and P[n=7]), i=4 

(P[m=7] and P[n=10]), i=5 (P[m=10] and P[n=11]).

Differential proton fluxes (φ'

P4

 through φ'

P11) were 

calculated with Eq. 4 in Step 3. Characteristic rigidities 

(RP[m] and RP[n]) for the channels are from Table 2.

Because the γi are calculated using Eq. 5, the channel 

characteristic rigidities are used as the upper and lower 

rigidity limits of most of the differential flux spectra. 

Exceptions are the lower rigidities of f

1

(R) and f6(R), and 

the upper rigidities of f

5

(R) and f

6

(R). The upper rigidity 

of f

5

(R), which is the lower rigidity of f

6

(R), is the lower 

rigidity limit of fluxes in channel P11. The lower rigid-

ity of f

1

(R)is the lowest rigidity of the model. The upper 

rigidity of f

6

(R) is calculated in Step 9. Rigidity limits 

are in Table 4. 

Step 5. Differential fluxes (φ') are further corrected

(φ'') with Eq. 6, using spectral-hardness index correction 

factors (s) from Table 3. Correction factors are based on 

γi values calculatedwith Eq. 5. Parameters γ1 and γ5 are 

used with φ'

P[j=4] and φ'P[j=11], respectively. 

For φ'

P5

, φ'

P6

, φ'

P7

, and φ'

P10, the γi

 values used to calculate φ''P[j] with Eq. 7 are: for φ''P5

, γ1 and γ2; for φ''P6, 

γ2 and γ3; for φ''P7, γ3 and γ4; for φ''P10, γ4 and γ5. 

C = φ k (Eq. 2)

C′ = C − B (Eq. 3)

φ′ = C′ k′ (Eq. 4)

(Eq. 5 ) ln( ) ln( )

ln( ) ln( )

[ ] [ ]

[ ] [ ]

P m P n

P n P m

i R − R

′ − ′ = φ φ γ

(Eq. 6 ) ( ) P[ j] P[ j] i φ′′ = φ′ s γ
Step 6. For each channel pair in Step 4, the preliminary spectral-hardness index (γi

) (calculated with Eq. 5) is 

recalculated with Eq. 5, but substituting φ''P[m] and φ''P[n]

(calculated with Eq. 6 and Eq. 7) for φ'

P[m] and φ'P[n]

. Any 

negative γi is changed to zero. Any γi of 1 is changed to 

1.000001. For spectrum 6, γi is given the value of γ5.

Step 7. For each differential spectrum, f

1

(R) through 

f

5

(R), αi is calculated with Eq. 8, using characteristic rigidities (RP[j]

) from Table 2, differential fluxes (φ''P[j]) from 

Step 5, and the γi from Step 6. For spectra 1, 2, 3, 4, and 

5, channel numbers are 4, 5, 6, 7, and 10, respectively.

For spectrum 6, αiis given the trial value of α5. 

Step 8. For channel P11, the integral flux (F11) is 

obtained by dividing the corrected count-rate calculated 

in Step 2 (C’) by 0.73 (9). If the relationship of Eq. 9 is 

not satisfied by the trial value of α6

, then a satisfactory 

value for α6 is calculated using Eq. 10. 

The upper limit, 32,545 MV, is the upper rigidity limit 

of the model and encompasses all the available data for 

over 99% of the known solar proton events (10). The 

lower limit, 1343 MV, is the lower rigidity limit of fluxes 

in channel P11.

Step 9. To find R6,upper (the upper rigidity of f

6

(R)), the 

upper limit in Eq. 9 is replaced with 1343 MV and α is 

set equal to α6. The upper limit is then increased in steps 

of 1 MV until the relationship is satisfied. The resulting 

R6,upperis also the upper rigidity of fluxes in channel P11 

(i.e., f

6

(R>R6,upper) = 0). 

Step 10. At this point, all parameters needed to calculate each f

i

(R) have been obtained. To convert each 

f

i

(R) from flux measured at GOES to flux entering the 

atmosphere, the αi values calculated in previous sections 

were each multiplied by π (ref. 11). 

Step 11. Effective dose rates (D(H), μSv/h) to an 

adult, at geopotential altitude (H), from exoatmospheric 

primary solar protons are calculated with Eq. 11. In Eq. 

11: t is a time-scale conversion coefficient (t = 3600 s/h), 

i is the spectrum, Ri,upper and Ri,lower are rigidity limits of 

spectrum i in Table 4, f

i

(R) represents flux spectra, and 

∆(R,H) represents dose rate per unit of incident proton 

fluence.

The integral in Eq. 11 is evaluated numerically in 1 

MV steps. For integration steps with an upper rigidity 

less than R0 (183.5 MV), ∆(R,H) is set equal to ∆(R0,H). 

For all other integration steps, ∆(R,H) is set equal to the 

mean of its values at the upper and lower rigidities of the 

integration step. The values of ∆(R,H) at the upper and 

lower rigidities of the integration step are calculated using 

linear interpolation of ln(R) and ln(∆(R,H)).

Dose rates (D(H)) at altitudes of 30- to 70-thousand 

feet are estimated by calculating D(H) at each of the nine 

altitudes in Table 1 with Eq. 11 and then performing a 

cubic-spline interpolation.

Method Used to Estimate Risk

That the Equivalent Dose to a

Conceptus Exceeds 500 μSv in a

10-Hour Exposure

The FAA and the National Council on Radiation 

Protection and Measurements (NCRP) recommend that 

the equivalent dose to a conceptus not exceed 500 μSv in 

any month after pregnancy has been declared (1, 17). 

Examination of 169 of the 170 solar proton events 

from January 1986 through May 2008 (18) indicated 

that 26 events met the criteria for at least one issuance 

of an SRA (an effective dose ≥20 μSv/h at 70,000 ft for 

at least three consecutive 5-minute periods). Steps 1-9 

given above are only appropriate for analyzing GOES 

data from GOES-8 and more recent satellites (1 March 

1995 to present). For solar proton events from 1 January 

1986 through 28 February 1995, values of α and γ were 

estimated from GOES data using the procedure of section A5 in Ref. 11. A total of 42 SRAs would have been 

issued in the 22-year period. The percentages of these 

SRAs for which an associated 10-hour cumulative dose 

to the conceptus exceeded the recommended monthly 

limit on a polar-latitude flight was 4.8% at 40,000 ft, 

21% at 50,000 ft, and 31% at 60,000 ft. Figure 3 shows 

the risk estimates for 40-, 50-, and 60-thousand feet as 

a function of effective dose rates at 70,000 ft. For each 

data point at a specified altitude, the y-coordinate (Y) is 

a percentage of SRAs, 

where N is the number of SRAs during which the effective dose rate at 70,000 ft equaled or exceeded the 

(Eq. 7) ( ) ( )





 



 + ′′ = ′ +

2

1

[ ] [ ]

i i

P j P j

s γ s γ φ φ

(Eq. 8) i

i P j RP j

γ α φ ( ) [ ] [ ] = ′′

(Eq. 12)

N

n Y =100

(Eq. 11) 

8

∑ ∫ =

= Δ

6

1

,

,

( ) ( ) ( , ) i

R

R i

i upper

i lower

D H t f R R H dR (Eq. 11) 

(Eq. 9) 

8

∫ − ≤ MV

MV F R dR 32,5451343 11 6 γ α

(Eq. 10) 

1 1 1

6 11 6 (1 )(32,545 1343 ) − 6 − 6 − = − − γ γ α F γ
Figure 3. Estimated risk that the equivalent dose to a conceptus in a 10-hour exposure on a polar-latitude flight at 40-, 50-, or 

60-thousand feet will exceed 500 μSv when the lowest of the three highest consecutive 5-minute effective dose rates at 70,000 

ft reaches the dose rate on the x-axis. Data points are based on examination of past solar proton events since 1986 using effective 

doses calculated by the method of this report and equivalent doses to the conceptus from Reference 11. For example, the data 

point at (442, 50) indicates that when the lowest of the three highest 5-minute effective dose rates at 70,000 ft was at least 442 

Sv, the equivalent dose to a conceptus at 40,000 ft exceeded 500 μSv in a 10-hour exposure for 50% of alerts. 
10

Figure 4. The map is divided into four regions based on the degree of geomagnetic shielding that air travelers are provided 

by the Earth’s magnetic field (23, 24, 25). Region 1 is the polar-latitude region where the magnetic field provides little to no 

protection from solar cosmic radiation. The highest dose rates occur in Region 1; estimated probabilities that the total dose to 

the conceptus will exceed the recommended limit are as shown in Figure 3. In the absence of a geomagnetic storm, dose rates 

in Region 2 will be lower than those in Region 1. During a G5 geomagnetic storm (24), dose rates throughout Region 2 can 

be as high as those in Region 1. In Region 3, a total dose to the conceptus that exceeds the recommended limit is possible in 

a 10-hour exposure at 40- to 60-thousand feet (11), but dose rates will always be lower than in Regions 1 and 2. Dose rates in 

Region 4 never exceed a few percent of dose rates in Region 1. In Region 4, in the period studied, the highest 10-hour dose to 

the conceptus from solar cosmic radiation at 50,000 ft was <10% of the recommended limit.
11

x-­coordinate for three consecutive 5-minute periods 

and n is the number of the N SRAs for which a 10-hour 

dose to a conceptus exceeded 500 μSv at the altitude of 

interest. The risks are estimated using Eq. 13-15, which 

are fits to the data for 40-, 50-, and 60-thousand feet, 

where D is the lowest of the three highest consecutive 

5-minute effective dose rates at 70,000 ft.

Estimated risk at 40,000 ft = 5.900 (1 - exp-0.00004429 D) 0.6992 (13)

Estimated risk at 50,000 ft = 1.009 (1 - exp-0.0006916 D) 0.7088 (14)

Estimated risk at 60,000 ft = 1.010 (1 - exp-0.01988 D) 1.016 (15)

Dose estimates for the solar proton event of 7 July 1991 

could not be reliably estimated because of several gaps in 

the HEPAD data. However, the peak >10 MeV flux was 

only 2300 pfu (18) and there was no associated ground 

level event (19, 20). Of the 169 events examined, 160 

had peak >10 MeV fluxes <10,000 pfu. There were only 4 

of these 160 events during which the 10-hour equivalent 

dose to the conceptus exceeded the recommended limit 

and all 4 were associated with very intense ground level 

events (20). Thus, it is very unlikely that during the 7 July 

1991 event the 10-hour equivalent dose to the conceptus 

exceeded the 500 μSv recommended limit.

RESULTS AND DISCUSSION

Influences not accounted for in the dose rate calculations are: (a) ions other than protons (e.g., alpha particles) 

in the primary solar particle flux, (b) shielding by Earth's 

magnetic field, (c) anisotropy in the solar proton flux, and 

(d) shielding by aircraft structure. In estimating dose rates 

for the SRA system, only solar protons are used because 

they are the dominant contributor to the ionizing radiation from the Sun at aircraft flight altitudes and data are 

available in near real-time. Other radiation information, 

such as GOES alpha particle measurements and data 

from the worldwide network of neutron monitors, would 

enable more complete calculations, including anisotropy 

effects (21), but not with the immediacy required of an 

alert system. Earth’s magnetic field, including effects of 

geomagnetic storms, while important at lower latitudes, 

can be neglected at polar latitudes (Fig. 4). Aircraft 

structure has very little effect on dose rates. In a study of 

the solar proton events of 29 September 1989, 14 July 

2000, and 16 January 2005, calculations indicated that 

0.6 g/cm2 of aluminum (approximate “skin” of a Boeing 

747) at altitude 40,000 ft changed by <1% the effective 

dose of solar plus galactic cosmic radiation. Ferrari et al. 

(22) investigated the effect of aircraft structure and its 

contents on the effective dose of galactic cosmic radiation, 

with a simulated fully-loaded Airbus 340. They found 

that at a vertical cutoff rigidity of 0.4 GV and altitude 

10.7 km (approximately 35,000 ft), aircraft structure and 

contents reduced the effective dose by 0-8%, depending 

on location in the aircraft. 

Using the method of Reference 11, which incorporates 

ground-level neutron monitor data and includes dose rates 

from solar alpha particles, dose rates at 50,000 ft during 

the seven solar proton events with the highest 10-hour 

polar-latitude doses at 50,000 ft were calculated. When 

compared with these, 77% of the dose rates estimated 

by the method in this report (but using the same fluence-to-dose conversions as Reference 11) were within 

20% (mean 5.1% lower, median 5.4% lower, standard 

deviation 20%), indicating that dose rates generated by 

the revised SRA system (this report), which uses easily 

and rapidly available data, are good estimates at aircraft 

flight-altitudes at polar latitudes. 

REFERENCES

1. Friedberg, W., and Copeland, K. What Aircrews Should 

Know About Their Occupational Exposure to Ionizing 

Radiation. Washington, DC: U.S. Department of 

Transportation, Federal Aviation Administration, 

Office of Aerospace Medicine, Report No. DOT/

FAA/AM-03/16 (2003). Available through the 

National Technical Information Service, Springfield 

VA 22161 and at: www.faa.gov/library/reports/medical/oamtechreports/2000s/media/0316.pdf (accessed: 

1 June 2007).

2. Clem, J.M., Bieber, J.W., Evenson, P., Hall, D., 

Humble, J.E., and Duldig, M. Contribution of 

obliquely incident particles to neutron monitor 

counting rate. Journal of Geophysical Research

102(A12): 26919-26 (1997).

3. National Weather Service. Solar Radiation Alerts are 

distributed to subscribers of the NOAAWeather 

Wire Service (NWWS). The NWWS is administered by Computer Sciences Corporation, phone 

(703) 818-4940. Messages are identified by the 

first 11 characters of the WMO header “WOXX50 

KWNP” and AWIPS identification “ALTPAV.” 

The most recent space weather messages are 

available without subscription at: www.weather.

gov/view/national.php?prodtype=space (accessed: 18 

July 2008).
12

4. Copeland, K., Sauer, H.H., and Friedberg, W. Solar 

Radiation Alert System. Washington, DC: U.S. 

Department of Transportation, Federal Aviation 

Administration, Office of Aerospace Medicine, 

Report No. DOT/FAA/AM-05/14 (2005). Available through the National Technical Information 

Service, Springfield VA 22161 and at: www.faa.

gov/library/reports/medical/oamtechreports/2000s/media/0514.pdf (accessed: 1 June 2007). 

5. Los Alamos National Laboratory. Monte Carlo NParticle Transport Code System for Multiparticle 

and High Energy Applications (MCNPX 2.6.0), 

released April 2008. Available from the Radiation 

Safety Information Computational Center at the 

Oak Ridge National Laboratory. 

6. International Commission on Radiological Protection 

(ICRP). ICRP Publication 103: Recommendations 

of the ICRP, London, Elsevier (2007). Available 

at: www.elsevier.com/wps/find/bookbibliographic 

info.cws_home/713998/description#bibliographic

info (accessed: 9 January 2009). 

7. NOAA, National Oceanic and Atmospheric Admin-

istration. Overview of the AWIPS System www.

crh.noaa.gov/lmk/?n=awipsoverview (accessed: 27 

February 2008).

8. National Oceanic and Atmospheric Administration, 

Space Weather Prediction Center Web Site: www.

swpc.noaa.gov/ftpmenu/lists/pchan.html. Files to select are G11pchan_5m.txt and G10pchan_5m.txt 

(accessed: 1 January 2008). 

9. Sauer, H.H. Analysis of GOES Particle Data and 

the Development of a Processing Procedure in Support of FAA Requirements for Radiation Exposure 

Estimation at Aircraft Altitudes, Boulder, CO: 

CIRES/NOAA-NGDC (2003). Prepared for the 

FAA under contract number DTFA0201P09198. 

6973H5 FAA Aero Center AMQ-300. Appendix 

C contains the instrument manufacturer’s calibration report Calibration Report for the EPS DOME 

Sensor Response to Protons, NXT-CAL-102, May 30, 

1995, Panametrics, Inc. for Space Systems/Loral, 

Inc. The FAA-contracted report is in the library of 

the Civil Aerospace Medical Institute, Oklahoma 

City, OK.

10. Swinson, D.B., and Shea, M.A. The September 

29, 1989 ground-level event observed at high 

rigidity. Geophysical Research Letters 17(8): 1073-5 

(1990). 

11. Copeland, K., Sauer, H.H., Duke, F.E., and Friedberg, W. Cosmic radiation exposure of aircraft occupants on simulated high-latitude flights during 

solar proton events from 1 January 1986 through 

1 January 2008. Advances in Space Research 42: 

1008-29 (2008).

12. ICRU, International Commission on Radiation Units 

and Measurements. Stopping Powers and Ranges 

for Protons and Alpha Particles. Bethesda, MD:

International Commission on Radiation Units and 

Measurements, ICRU Report 49 (1993).

13. National Oceanic and Atmospheric Administration, 

National Aeronautics and Space Administration, 

and United States Air Force. U.S. Standard Atmosphere, 1976. NOAA S/T 76-1562, Washington, 

DC: U.S. Government Printing Office (1976).

14. Pellicioni, M. Overview of fluence-to-effective 

dose and fluence-to-ambient dose equivalent 

conversion coefficients for high energy radiation 

calculated using the FLUKA code. Radiation 

Protection Dosimetry 88(4): 279-97 (2000). 

15. National Oceanic and Atmospheric Administration, 

Space Weather Prediction Center Web Site: swpc.

noaa.gov/tiger/SolarProtons.html (accessed: 1 

January 2008). 

16. McCracken, K.G. Anisotropies in radiation of solar 

origin, in: MacDonald, F.B. (Ed.), Solar Proton 

Manual. Washington, DC: National Aeronautics 

and Space Administration, NASA Technical Report R-169 (December 1963) (Forbush decrease, 

pp. 73 and 74).

17. NCRP, National Council on Radiation Protection 

and Measurements. Limitation of Exposure to Ionizing Radiation. Bethesda, MD: National Council 

on Radiation Protection and Measurements, Report 

No. 116. (1993) (NCRP recommends a monthly 

equivalent dose limit of 0.5 mSv (i.e., 500 μSv) to 

the embryo-fetus, p. 38.).

18. NOAA, National Oceanic and Atmospheric Administration, Space Weather Prediction Center, at 

www.swpc.noaa.gov/ftpdir/indices/SPE.txt (accessed: 

18 December 2007).

19. HAARP, The High Frequency Active Auroral Research 

Program. Glossary of Solar and Geophysical Terms. 

Available at www.haarp.alaska.edu/haarp/glos.html

(accessed: 4 September 2007).
13

20. IZMIRAN. Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radiowave Propagation, 

Russian Academy of Sciences. List of ground level 

events with dates. Available at ftp://cr0.izmiran.rssi.

ru/COSRAY!/FTP_GLE/DOC/GLEBASES.TXT

(accessed: 20 February 2008).

21. Smart, D.F. and Shea, M.A. The local time dependence of the anisotropic solar cosmic ray flux. 

Advances in Space Research 32(1): 109-14 (2003).

22. Ferrari, A., Pelliccioni, M., and Villari, R. A mathematical model of aircraft for evaluating the effects 

of shielding structure on aircrew exposure. Radiation 

Protection Dosimetry 116 (1-4): 331-5 (2005).

23. Smart, D.F. and Shea, M.A. A review of geomagnetic cutoff rigidities for earth orbiting spacecraft. 

Advances in Space Research 36: 2012-2020 (2005) 

(Regions were selected based on boundaries of constant L value, calculated using Eq. 6, p. 2013.).

24. Papitashvili, N., Papitashvili, V., Belov, B., Popov V., 

and Moretto, T. Computer program GEO_CGM.

FOR(EXE) version 2001 (2001) (Used to convert 

from geomagnetic to geocentric coordinates. Geocentric coordinates differ from geographic coordinates at a level of precision not visible in the figure. 

See nssdc.gsfc.nasa.gov/space/cgm/ for details.).

25. NOAA, National Oceanic and Atmospheric Administration, Space Weather Prediction Center, at www.swpc.noaa.gov/NOAAscales/index.

html#GeomagneticStorms (accessed: 6 March 

2008).

A1

APPENDIX A 

Sample Solar Radiation Alert System Messages

 The following six messages are samples of the messages that would have been issued during the solar 

proton event that started 16 January 2005, if the revised system had been operational. The samples begin with 

Test, Service Suspended, and Service Resumed messages that would have been issued on 19 January 2005. 

Dose rates on 20 January 2005 were high enough to warrant the sending the Alert message, which would have 

been followed by Alert Update messages until the conditions warranted the issuance of the Alert Cancelled 

message on 21 January 2005. Numbers in tables are reported to two significant digits. 

1. Test

000

WOXX50 KWNP 141506

ALTPAV

Space Weather Message Code: ALTPAV

Serial Number: 9989

Issue Time 2005 Jan 19 1455 UTC

TEST ALERT: Message Delivery Test - Solar Radiation Alert

Comment:

This is a message delivery test of the SOLAR RADIATION ALERT

system. Test messages are sent each day at 1500 UTC unless

a SOLAR RADIATION ALERT is in progress.

Information on the Solar Radiation Alert system is at

www.faa.gov/education_research/research/med_humanfacs/

aeromedical/radiobiology/solarradiation 

 . . .

CARI users:

heliocentric potential was 583 in December 2004

 . . .

# Issued by the US DOT, FAA, Civil Aerospace Medical Institute

# Send questions to kyle.copeland@faa.gov

2. Service Suspended

000

WOXX50 KWNP 191938

ALTPAV

Space Weather Message Code: ALTPAV

Serial Number: 9990 

Issue Time: 2005 Jan 19 1938 UTC

WARNING: GOES Satellite Data Unavailable

Comment:

The Solar Radiation Alert system is currently inactive.
A2

GOES satellite data used in estimating radiation levels at flight altitudes are 

unavailable. The system will resume normal operation as soon as GOES data become

available. 

More information at

www.faa.gov/education_research/research/med_humanfacs/

aeromedical/radiobiology/solarradiation 

# Issued by the US DOT, FAA, Civil Aerospace Medical Institute

# Send questions to kyle.copeland@faa.gov

3. Service Resumed

000

WOXX50 KWNP 192008

ALTPAV

Space Weather Message Code: ALTPAV

Serial Number: 9991 

Issue Time: 2005 Jan 19 2008 UTC

ATTENTION: Satellite Data Now Available 

Comment:

GOES satellite data are now available for estimating radiation 

levels at flight altitudes. SRAS service has resumed. 

More information at

www.faa.gov/education_research/research/med_humanfacs/

aeromedical/radiobiology/solarradiation

# Issued by the US DOT, FAA, Civil Aerospace Medical Institute

# Send questions to kyle.copeland@faa.gov

4. Alert

000

WOXX50 KWNP 200708

ALTPAV

Space Weather Message Code: ALTPAV

Serial Number: 9992 

Issue Time: 2005 Jan 20 0705 UTC

ALERT: Solar Radiation Alert at Flight Altitudes

Conditions Began: 2005 Jan 0650 UTC

Comments:

Satellite measurements indicate unusually high levels of ionizing radiation coming from the Sun. This may lead to excessive radiation doses to air travelers on 

trans-polar and other high-latitude flights. See map at 

www.faa.gov/education_research/research/med_humanfacs/

aeromedical/radiobiology/solarradiation
A3

The following dose, dose rate, and risk estimates do not

include any shielding by the Earth’s magnetic field.

Table 1. Effective dose rate estimates at selected altitudes 

based on the latest GOES solar proton flux measurements

Altitude Effective dose rate

 (ft) (microsieverts/hour)

---------------------------------

 30,000 40

 40,000 160

 50,000 450

 60,000 890

 70,000 1300

---------------------------------

Table 2. Effective doses for periods of selected length at

selected altitudes*

 Effective Dose (microsieverts)

 -------------------------------------------------

Altitude Previous Previous Previous Previous 

 (ft) 1 hour 3 hours 5 hours 10 hours

-------------------------------------------------------------

 30,000 16 16 16 16

 40,000 55 55 55 56

 50,000 140 140 140 140

 60,000 260 260 260 260

 70,000 350 350 350 350

-------------------------------------------------------------

*Includes contributions made before the SRA was issued

Table 3. Estimated risk that the equivalent dose to a 

conceptus in an aircraft at the indicated altitude will

exceed 500 microsieverts in a 10 hour exposure.

Altitude Risk

 (ft) (%) 

------------------------

 40,000 20 

 50,000 85 

 60,000 98 

------------------------

To avoid possible excessive radiation exposure to the 

conceptus, a pregnant aircrew member or passenger may want to

avoid flight altitudes of 40,000 ft or more in regions 1-3 

shown on the aforementioned map. 

# Issued by the US DOT, FAA, Civil Aerospace Medical Institute

# Send questions to kyle.copeland@faa.gov
A4

5. Update Alert

000

WOXX50 KWNP 200713

ALTPAV

Space Weather Message Code: ALTPAV

Serial Number: 9993 

Issue Time: 2005 Jan 20 0710 UTC

UPDATE ALERT: Update for Solar Radiation Alert

Alert Conditions Began: 2005 Jan 20 0650 UTC

Comments:

Satellite measurements indicate unusually high levels of 

ionizing radiation coming from the Sun. This may lead to

excessive radiation doses to air travelers on trans-polar

and other high-latitude flights. See map at 

www.faa.gov/education_research/research/med_humanfacs/

aeromedical/radiobiology/solarradiation

The following dose, dose rate, and risk estimates do not

include any shielding by the Earth’s magnetic field.

Table 1. Effective dose rate estimates at selected altitudes 

based on the latest GOES solar proton flux measurements

Altitude Effective dose rate

 (ft) (microsieverts/hour)

---------------------------------

 30,000 51

 40,000 200

 50,000 590

 60,000 1200

 70,000 1800

---------------------------------

Table 2. Effective doses for periods of selected length at

selected altitudes* 

 Effective Dose (microsieverts)

 ------------------------------------------------ 

Altitude Previous Previous Previous Previous 

 (ft) 1 hour 3 hours 5 hours 10 hours

-----------------------------------------------------------

 30,000 20 20 20 20

 40,000 72 72 72 72

 50,000 190 190 190 190

 60,000 350 350 350 360

 70,000 500 500 500 500

-----------------------------------------------------------

*May include contributions made before the SRA was issued
A5

Table 3. Estimated risk that the equivalent dose to a 

conceptus in an aircraft at the indicated altitude will

exceed 500 microsieverts in a 10 hour exposure.

Altitude Risk

 (ft) (%) 

-------------------------

 40,000 75 

 50,000 100 

 60,000 100 

-------------------------

# Issued by the US DOT, FAA, Civil Aerospace Medical Institute

# Send questions to kyle.copeland@faa.gov

6. Alert Cancelled

000

WOXX50 KWNP 210138

ALTPAV

Space Weather Message Code: ALTPAV

Serial Number: 1008 

Issue Time: 2005 Jan 21 0015 UTC

END ALERT: Solar radiation levels not excessive

Alert Conditions Began: 2005 Jan 20 0650

Alert Conditions Ended: 2005 Jan 21 0010

Comment:

The alert issued at 2005 Jan 20 0705 UTC has ended.

The following 2 tables summarize peak effective dose rate

estimates and peak effective dose estimates at polar latitudes:

Table 1. Peak effective dose rate estimates at selected 

altitudes based on the latest GOES solar proton flux 

measurements

Altitude Effective dose Rate

 (ft) (microsieverts/hour)

----------------------------------

 30,000 130

 40,000 460

 50,000 1200

 60,000 2000

 70,000 2700

----------------------------------
A6

Table 2. Peak effective doses for periods of selected length

at selected altitudes*

 Effective Dose (microsieverts)

 ------------------------------------------------

Altitude Peak Peak Peak Peak

 (ft) 1 hour 3 hours 5 hours 10 hours

-------------------------------------------------------------

 30,000 37 58 67 77 

 40,000 140 230 270 310 

 50,000 390 660 790 920 

 60,000 770 1300 1600 1900 

 70,000 1100 2000 2500 2900 

-------------------------------------------------------------

*May include contributions made before the SRA was issued

Information on the Solar Radiation Alert system is at

www.faa.gov/education_research/research/med_humanfacs/

aeromedical/radiobiology/solarradiation 

# Issued by the US DOT, FAA, Civil Aerospace Medical Institute

# Send questions to kyle.copeland@faa.gov