May 1st 2008SWPC/NOAA SWW Workshop New Ionosphere Products Proposed for SWPC Tim Fuller-Rowell,...

May 1st 2008 SWPC/NOAA SWW Workshop

New Ionosphere Products Proposed for SWPC

Tim Fuller-Rowell, Mihail Codrescu, Rashid Akmaev, Eduardo Araujo-Pradere, Mike Husler, and Herb Sauer1

NOAA Space Weather Prediction Center and/or

CIRES University of Colorado1National Geophysical Data Center


New SWPC “Ionosphere” Products:in transition or proposed

• D-Region absorption upgrade - FY08

• GPS Ionosphere Positioning Correction (GIPC) - FY08

• US-TEC short-term forecast - FY09


Effect of Solar X-rays on D-Region and HF Propagation.

• D-Region Absorption Product based on GOES X-Ray Flux (SEC Product)– The map shows regions affected by the increased D-region ionization resulting

from enhanced x-ray flux during magnitude X-1 Flare

D-Region absorption in response to solar X-ray flare

Driver: GOES X-rays

• Dayside response to flare• Zenith angle dependence• Frequency dependence• Estimated recovery time based on current X-ray flux


Combined flare and Polar Cap Absorption (PCA)(Provided by Michael P. Husler, NOAA SEC)

June 21, 2000 00:00 UT Kp= 3

Color scale denotes frequency at which the ionospheric absorption equals 1 dB

Day/Night Absorption

• Algorithms developed by Sellers et al*

• Provides 30 MHz absorption estimates

• Driven by proton fluxes obtained in real-time by NOAA GOES

• Day/night differences due to electron attachment to O2 in absence of UV radiation

Day-time Abs Ad = 0.115 [ J(E>5.2 MeV)]1/2 dB

Night-time Abs An = 0.020 [J(E>2.2 MeV)]1/2 dB

*Sellers, B., F.A.Hanser, M.A. Stroscio, and G.K.Yates, The night and day relationships between polar cap riometer absorption and solar protons, Radio Sci., v12, pp779-789, 1977.

• Twilight absorption bi-linear fit to values at 10 solar elevation angle

A = Ad [ El + 10] / 20 – An [ El – 10 ] / 20

• Recovery time-scale based on current GOES flux levels

Geomagnetic Latitude Dependence- Determine Cutoff Energy Effects

•The absorption at lower than polar cap latitudes are obtained from application of geomagnetic cutoff energies which include their dependence on geomagnetic activity (Kp) as derived from the results of Smart et al* and illustrated below.

*Smart, D.F., M.A.Shea, E.O.Fluckiger, A.J.Tylka, and P.R.Boberg., Changes of calculated vertical cutoff rigidities at the altitude of the International Space Station as a function of geomagnetic activity,

Proc. Int’l Cosmic Ray Conf., v7, pp337-340, 2001

Frequency Dependence

•The absorption at a frequency, f, other than 30 MHz (Af) is obtained from the approximate dependence of ionospheric absorption on the inverse power law of the frequency (e.g.: Patterson et al*)

Af = (30/f)1.5 A30

*Patterson, J.D., T.P.Armstrong, and C.M.Laird, Correlation of solar energetic protons and polar cap absorption, J.Geophys. Res.,

106, A1, pp 149-163,2001.

Specimen Comparison with Observation: Thule 30 MHz Riometer

Panel a): GOES particle fluxes.Panel b): Observed absorption with calculated day and night absorptionPanel c): Observed and fully estimated absorptionPanel d): Calculated solar elevation angles

a)

b)

c)

d)

Comparison of Calculation with observations provided by AFGL’s Thule Riometers for 11 largest events 1986-2002

Top panels: GOES particle fluxes.2nd panels: Observed absorption with calculated day and night absorption3rd panels: Observed and fully estimated absorption4th panels: Calculated solar elevation angles


Combined X-ray and PCA


Polar Region Display - 10dBPCA depends on solar illumination

O2 - e- attachment process in the D-region


US-TEC Target Users:

•Positioning and Navigation community

•Collaboration between SWPC, NGS, FSL, and NGDC

•Kalman filter over CONUS + ground-based GPS data, IRI background model, solve for receiver biases

•15-minute cadence

•15 to 30 minute latency

•2 - 3 TEC unit accuracy (~34 - 48 cm delay at L1 frequencies)


Slant-Path TEC Maps2-D maps of of slant path TEC over the CONUS for each GPS satellite in view updated every 15

minutes

Applications: 1. Ionospheric correction for single frequency GPS2. Support dual-frequency integer ambiguity resolution for more rapid

decimeter and centimeter accuracy positioning

Sat. 1

Sat. 5

Sat. 14

Sat. 29

….etc

A

A

A

A B

B

B

B

C

C

C

C

C


Ionosphere phase delay/advance for NGS in new RINEX format

US-TEC slant TEC provides ionospheric

correctors for RINEX files

Sat. 29

A B

C


Mid-latitude day-to-day variability in ionospheric total electron content


The challenge in forecasting the ionosphere and total electron content

15 minute units

12hrs 24hrs

15 min intervals

1hr forecast 0.92 hr forecast 0.8


VTEC Short-term ForecastUsing USTEC 10-day average to predict the

ionospheric behavior in to the next 1 to 2 hours.,

USTEC 10-day averageUSTEC 15-min data

time

Now

– Departure of “now value” from the 10-day average.

Now-24 h

Now-24+t

– TEC in the 10-average between the value at now-24 h and now-24+tt < 6hrs

Now+t


Latitude dependence


US-TEC Validation SummaryDifferential TEC:Slant = 2.4 TEC unitsVertical = 1.7 TEC units

“Absolute” FORTE ray tracing:Slant = 2.7 TEC unitsVertical = 1.9 TEC units

•Estimated US-TEC slant path total electron content uncertainty < 3 TEC units (equivalent to about 45 cm of signal delay at L1 frequencies)•Estimate US-TEC vertical total electron content uncertainty < 2 TEC units (equivalent to about 30 cm of signal delay at L1 frequencies)

***************************************************************************************************


“Differential” Validation

€

RMSE(n−m )k =ΔTECnk

L − ΔTECnkU

( )

Mi=1

M

∑

• Integrate through US-TEC model at two different times.

• Compare directly to the phase difference in the original RINEX data file.

• As time separation increases, errors in US-TEC map become uncorrelated and approach true uncertainty.

Araujo-Pradere et al. 2006


US-TEC “Differential” Validation

• Validation stations not included in assimilation process

• Build up statistics every 5th day over 6 months

• Daily average RMSE for each site

Slant path RMSE

US-TEC

IRI

Validation Statistics: “differential” TEC

2.4 TEC units


Absolute validation: FORTE Fast Onboard Recording of Transient Events satellite

(Los Alamos, Abe Jacobson)

• Phase or arrival time as function of frequency

• Separate O and X traces

• Fit to k/f2 dependence provides TEC estimate

Time of arrival

Fre

qu

ency

•Broad-band RF receiver 30-300 MHz at 800 km altitude•Designed to monitor lightning•Pulse transmitted from Los Alamos (simulated lightning)•Possible to estimate line-of-sight TEC between transmitter and FORTE satellite•Broad-band signal/receiver eliminates phase ambiguity so produces an “absolute” TEC estimate (uncertainty estimate is about 1 to 2 TEC units)•Issues are

–bending of the rays, –plasmaspheric content, and having to sub-sample US-TEC vertical domain


US-TEC/FORTE Statistics“Absolute”: using 178 FORTE observations between

June 30, 2000, and November 27, 2001

• All values in TECU

( ) nMFn

iii∑

=

−=1

2RMSE

Approximate Number of

CORS Stations

All data

{178}*

Elevation angles

> 55 deg. {36}*

Data < 60

TECU {84}*

Elevation angles > 55 deg. and

data < 60 TECU {28}*

133 2.705 1.676 1.708 1.148

105 2.751 1.689 1.731 1.240 73 2.768 1.763 2.134 1.519

60 2.872 1.878 2.316 1.659

44 3.019 1.903 2.601 1.783

21 4.221 2.739 3.902 2.438 * The number in brackets indicates the number of values used in the calculation .

Minter et al. 2006


OPUS – GIPC (GPS Ionospheric Positioning

Correction)

TRANSITION: 4th quarter ‘08

May 1st 2008SWPC/NOAA SWW Workshop New Ionosphere Products Proposed for SWPC Tim Fuller-Rowell,...

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