F10.7 and Synoptic Solar Radio Monitoring

Ken Tapping

ken.tapping@nrc-cnrc.gc.ca

Synoptic Solar Monitoring• The parameters we measure should be useful or reflect something useful.• They should be easily measurable and calibratable, and not subject to things that can

cause significant breaks or discontinuities in the data.• They need to be as objective as possible and referable to some stable,

reproduceable calibration standard. Anything based upon empirical processing or correction can be hard to maintain through generations of expertise or instrumentation..

• The data should be adequately sampled, especially if the characteristic timescales of variation themselves vary with time. Otherwise even the effects of undersampling are inconsistent..

• Equipment should be usable for long-term operation, and incrementally upgradable. Total replacement should be done using a long period of parallel operation.

• The equipment should be redundant.• We should understand the physics.• The time-series should be as long as possible.• The instrumentation and measurement/calibration methods should be duplicable.

Solar Monitoring• Space-Based

• Above the atmosphere• Can monitor more things• Can monitor continuously• Expensive• Long-term calibration a problem• Long-term observation easily compromised• Data not long-term, leading to sometimes serious context issues• Upgrading not usually feasible.

• Ground-Based• Accessible and easily maintainable• Easy to upgrade• Relatively Cheap-easy to deploy multiple instruments• Long durations of data reduce context risks• Calibration relatively easy.• Cannot see Sun 24/7 – Multiple instruments needed• Atmosphere reduces the spectrum access and affects some observations

How Does F10.7 Match Up?• F10.7 has found use as an index of solar activity, a calibration datum and for proxying other solar

parameters, such as euv irradiance for ionospheric modelling or upper atmospheric heating..• F10.7 is relatively easy to measure, automatically, and having a hot backup available makes it

easier to avoid data gaps and also to provide a rough calibration check.• The measurements are made objectively using a standardized method, with no manual

intervention. However, in the early years of the project there were manual attempts to filter out bursts, which led to an empirical effect in the early part of the time series.

• Undersampling is a significant issue. Three spot measurements made each day at a single location is not always a good estimate of what happens over 24 hours.

• The equipment is cheap, stable and incrementally upgradeable. A new instrument is under construction, and when complete will be run in parallel with the existing equipment for at least one year before its data is believed (there are no plans to shut down the existing instruments)..

• There are two levels of redundancy, which we are increasing to three.• We understand the physics reasonably well.• The time-series extends back to 1947.• The data are calibrated against a duplicated standard.

WHAT IS F10.7?

• Three measurements made each day of the total emission from all sources present on the solar disc in a 100MHz wide band centred on a frequency of 2800 MHz.

• Measurements made at 1700, 2000 and 2300 UT in the summer and 1800, 2000 and 2200 UT in the winter.

• Each measurement takes 1 hour and is an average of the solar emission within that hour.

• No account is taken of anything happening between those times (although the emission is being recorded all day from sunrise to sunset).

F10.7Monthly Means

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The resonant cavity magnetron, invented by John Randall and Harry Boot of Birmingham University, UK, was the first device ever that could produce high powers at short radio wavelengths.

Tizard, the War, Serendipity and the Magnetron

Where Does F10.7 Come From?

Photosphere and Below

Corona

Free-Free emission from thermal plasma concentration trapped in Active Region Magnetic Fields

Bright emission from thermal electrons trapped in strong magnetic fields overlying sunspots.

Solar Radio Spectrum

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The S-Component Spectrum

corchrom TtTtk

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Flux Monitor 2 (Primary)

Flux Monitor 1 (Secondary)

Solar Radio Monitoring Programme DRAO, Penticton, Canada

One of the Flux Monitors

Feed Horn

Directional Coupler

Receiver A

Demodulator (ch A2)

Control signal to calibration noise source

Control/Data Logging Computer

Two-way splitter

Directional Coupler

Calibration Noise Source

60 cm square x 8 cm thick aluminium slab

Demodulator (ch A1)

Demodulator (ch B1)

Demodulator (ch B2)

Flap Attenuator

Antenna

Test Noise Source

Receiver B

Waveguide Run Channels A1 and B1 are about 20dB more sensitive than Channels A2 and B2 Network

Back to Basics

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ξ is the sensitivity of the antenna compared with the sensitivity at the antenna boresight (on the axis), where it is assumed to be unity. This ideally is what we want over all the solar disc.

Getting a Usable Measurement

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The Compromise

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Antenna Efficiency

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Flux Determination Procedure

Cr File + Flux Determinations

Calibration and Data Checks

The gain of a paraboloidal antenna with a feed is very hard to calculate with any accuracy. On the other hand we can estimate the gain of a horn antenna with high accuracy from the physical dimensions. To calibrate the dish antennas we make periodic parallel (noon) measurements of the solar flux using the horns.

The methods for calculating the gain of horns are getting better. However, for consistency we continue to use the model used by Covington (Steen’s model). Therefore our data might be slightly wrong in absolute terms (a flux unit or two possibly).

Each flux monitor contains two independent receivers, and we have two identical but totally independent flux monitors, providing a high level of redundancy for internal data checks.

On occasion there can be contributions to the flux value by non-thermal emission mechanisms, which are often hard to eliminate.

Dual Horn Calibration System

A Typical Horn Observation

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Universal Time on 9 July, 2010

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Calibration Noise Source

Flap Termination

Solar Transit

Comparison of FM#1 and FM#2 Flux Values

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The Flare Problem

2006/12/06 Event: Value of Low-Sensitivity Channels

Rose’s Cantina, El Paso, Texas

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OHHC 52

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Swinging Saloon Doors

(Transfer Function: a(t))

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F10.7

• It is a very good indicator of the general level of solar magnetic activity.• It is a successful basis for proxies for various solar emission components

and solar parameters.• It is easy to measure and monitor with high objectivity. It is highly but not

totally observer-independent.• We have a consistent, continuous database covering more than 60 years.

• It contains contributions from at least two emission components (thermal free-free and thermal gyroresonance). The former is related to plage and the latter to sunspots.

• It is not therefore fully clear what it is an index of.• Since sunspot and plage area are not consistently proportional to one

another, this can degrade its applicability to proxies (as our needs get tighter and tighter).

What’s Right About It What’s Wrong With It

New Technology: The Next Generation Solar Flux Monitor

• F10.7 is a very useful index of solar activity, but it is a composite of up to three emission mechanisms; more specialized applications require those mechanisms to be separated, which in turn needs multiple-wavelength measurements. The Next Generation Solar Flux Monitor can monitor six spot wavelengths between 2 and 20 cm, and the entire spectrum between those wavelengths with millisecond time resolution.

• Observing with high time resolution will provide better flare detection and hopefully the radio signatures of the lifting off of coronal mass ejections, which are the main cause of large magnetic storms.

• Experience with F10.7 has shown that users always come up with new needs. To (hopefully) avoid some of these issues, the NGSFM is designed to obtain all the data within its physical capabilities and budget.

• Others are interested in duplicating the capabilities of the NGSFM.

Next Generation Solar Flux Monitor - Requirements

• To make precise flux determinations at enough wavelengths for the spectrum to be estimated and f-f and g-r emission contributions separated. To make these values truly comparable they should be measured using the same instrumentation, at the same time and in the same manner.

• To record data for each wavelength at a high enough sampling rate to address any reasonable burst monitoring/event patrol requirements.

• To record dynamic spectra over the whole wavelength range.• To use orthogonal linear polarizations to achieve receiver channel

redundancy (backup receiver system).

Specification for the NGSFM

Antenna half-power beamwidth to stay in the range 3 – 5 degrees over the wavelength range 21 – 3 cm (1.4 – 10 GHz).

Multi-wavelength operations: 21 cm, 18 cm,10.7 cm, 6 cm, 4 c m, 2.8 cm (and “broadband” for testing).

Dual orthogonal linear polarization (not primarily for science, for redundancy and backup).

Three precise flux determinations a day plus a “continuous record” from sunrise to sunset, for each polarization and wavelength.

Time resolution in continuous record better than 10ms, target is 1ms.

Modular system that can be duplicated totally or in part in the construction of other instruments.

An Under-Illuminated Dish

NGSFM Beamwidth w ith Bipol Horn

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NGSFM Design Wavelength Range

As the wavelength changes, so does the fraction of the antenna, so that to a first order, the beamwidth of the feed/antenna combination remains unchanged.

Trials Using the Broadband Test Receiver

Next Generation Solar Flux Monitor

Test Receiver

Production Receiver

Installing the Test Receiver

Queen’s University Radio Spectrometer

Antenna

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NGSFM – First Light: 2011-09-08

Broadband Tests: 20110908(1.5 - 8.5 GHz)

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Solar Radio Monitoring• Solar radio monitoring can be done from the ground. It is

inexpensive and easy to do for long periods with a smooth maintenance/upgrade strategy.

• Such programmes can be continued for long periods of time (will be 70 years in 2017).

• Consistency of calibration is easy to maintain over long periods.

• Undersampling is an issue.

• Cannot be done 24/7/12 from any ground-based location; multiple stations are needed. This can be achieved through international collaboration, through linkage of stand-alone systems into larger arrangement.

• We are now reaching the point where a new generation of instrumentation is needed.

• BUT NOT AT THE EXPENSE OF THE MEASUREMENTS WE HAVE BEEN MAKING FOR DECADES.

S-Component Spectrum (Flux Density)

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Initial NGSFM Operating Wavelengths

Possibilities for the additional wavelengths

The Problems With F10.7

For better proxies, and science, we need to separate the contributions from thermal gyroresonance and thermal free-free emission. The former makes the bump in the spectrum and the latter the monotonic decrease with increasing wavelength. To separate them requires the spectrum, not a single-wavelength measurement.

During the solar activity cycle, the spectrum of the S-component changes both amplitude and to a small extent, the wavelength of the spectral peak. A single-wavelength measurement reflects both variations inseparably.

There are occasionally contributions by non-thermal emission mechanisms, which are often hard to eliminate.

Although we want to keep our current measurements of F10.7 going indefinitely, it would be very useful if we could measure the S-component spectrum, and provide additional indices hopefully reflecting the contributions by different emission mechanisms.

FM#2 v. FM#1 Values

y = 1.0036x

R2 = 0.9962

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F10.7 and the Sun’s Energy Output

Antenna Arrangement

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Angular diameter of the patch of dish “seen” by the horn (horn diameter is d:

Diameter of patch of dish seen by the horn:57Hfx

Beamwidth of antenna at that wavelength:f

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Beamwidth is independent of wavelength until x=>D

We want a beamwidth of 3-5 degrees over the wavelength range 3-21 cm. This will require a dish diameter of at least 3.6m

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