Solar radiation tidal forcing of radon signals in subsurface air
Steinitz, G., Piatibratova, O., Kotlarsky, P.
Geological Survey of Israel, Jerusalem
[email protected]
Monitoring sites
The reasoning
Geophysical background
High temporal resolution monitoring of radon, using alpha & gamma
detectors, is carried out at several arrays located in arid southern
Israel. Monitoring, at a resolution of 15-minutes, is conducted at
depths ranging from 1.5 to 120 meter.
• Dominance of solar tidal frequencies of annual, and daily scale
• Annual modulation of the amplitude and phase of daily and sub daily
tidal frequencies
• Systematic multi-year variation of signal and periodic characteristics
• Occurrence different locations, at depth to >100 meter
• Similar phenomena in laboratory experiments of radon in confined air
And
• Negation of climatic influences
• [Lack of gravity tidal frequencies]
Signal types, periodicity, Solar tide components
Period
24-, 12-hours
1. Daily signals
Temporal phenomena encountered differ among sites, but have
similar fundamental characteristics.
Radon monitoring arrays along
the Dead Sea Rift (DSR)
Tidal component
S1, S2
2. Multi-Day
(non-periodic)
3. Annual radon
4. Semi-annual radon
5. Ternary annual radon
365.2 days
182.6 days
121.7 days
6. Multi-Year
(non-periodic?)
Rn Acronym
DR
MD
SA
SSA
STA
AR
SAR
TAR
• Array of stations, along a
20 km sector
• 1.5 m deep in unconsolidated
gravel
Solar irradiance related components - S1, S2 dominate
= solar tide
Southern Arava
Elat Granite
80
S1
80
S1
60
40
S2
20
• Array of stations, 20 km sector
• In Precambrian basement
rocks
• Depth 2 to +100 meter
Roded
19W
Day 4100-4700
60
S2
40
0
1
20
1
Granite; Elat; 54m
Cycle / day
gamma radiation emitted from radon in the tank air varies spatially and temporally. A 4-year time series shows
1999
200
2001
2003
2005
and S3. Periodicities indicative for diurnal gravity tide (O1, M2; Lunar influence) are clearly lacking. Profound
100
10000
17W
S2
0
1
external geophysical influence is further indicated by compounded relations that occur as annual modulation of
2007
N2
2
2
NW Gulf Elat, Rn in seawater
Shore gravel; 2m deep, 130 days
the amplitude and phase of the diurnal constituents S1, S2 and S3.
Historgram of values
(17W, Gamma detector)
Further insight is derived from the long term variations in time series from the geological environment and from
1.5e+5
Cycle / day
Granite; Elat; 54m
are dominated by periodicities of 24-, 12-, and 8-hours which are attributed to the Solar tidal constituents S1, S2,
The multi-year rising trend observed at Experiment, 17W and Amram sites. The temporal
pattern is measured by alpha and gamma detectors in Amram and in the Experiment.
M2
Cycle / day
Gravel; NW Dead Sea; 1.5m
radon, the latter diffusing into the upper air volume from U bearing ground phosphorite (376 Kg). Alpha and
multi-year and multi-day signals and especially periodic signals of annual and daily scale. The diurnal variations
0
0
phenomena at depth.
300
0
2
meter. A component of solar irradiation tide was suggested (References) as the driver of these periodic
• Periodicity is forced by solar tide
• A component of solar radiation?
O1 S1
0
in the arid desert of southern Israel demonstrated that the periodic variations, are observed to a depth of >100
recording radon within a confined volume of Air. The setup consisted of an isolated volume (640 L) of air with
Bias
Counts
Amram
Amplitude
• Depth: 1.2 m & 90 meter
• Massive syenite
GAV
400
E-3; Days 4356-4441
100
– multi-year, annual to daily and sub-daily duration. Analysis of extensive data sets from key sites 200 km apart
Gravity tide - rare
Amplitude
Intraplate
temporal variations composed of periodic and non-periodic signals spanning several orders of magnitude in time
IMPLIES
Periodograms of the diurnal components of radon signals in subsurface air
Amplitude
21W
by alpha and gamma activity during the decay of radon and its progeny. Radon in geogas exhibits systematic
The issue of external forcing of radon signals was tested experimentally using alpha and gamma detectors
MY
NW Dead Sea
17W
Radon (Rn-222) occurs at highly varying levels as a trace component in subsurface air (geogas). It is measured
the experiment. In addition to the annual periodicity clear semiannual and ternary annual signals are
5000
demonstrated. They are attributed to the solar tidal constituents Sa, SSa and STa.
1.0e+5
Experimental replication
Gamma-C
Alpha-H
Alpha-L
Cycles
Name
Period (hr)
Principal lunar declinational
O1
25.82
0.9295
Solar diurnal
S1
24.00
1.0000
0
Principal lunar
M2
12.42
1.9324
Principal solar
S2
12.00
2.0000
Counts 1e+5

2008
2009
2010
2011
2008
2009
2010
3e+5
Measured
Long-term bias
Annual Radon (AR)
Long-term (MY)
5.0e+4
Day

2e+5
2500
3000
3500
4000
4500
5000
Elat Granite:
5500
• Measured pattern
• Smoothed time series - AR signal and SAR signal as an asymmetry
• Modulation of the residual time series - AR and SAR signal
Roded: Annual variation of amplitude of the
diurnal periodicities S1, S2
2011
2.5e+5
2004
2006
2008
2010
1999
200
14000
AR
Alpha (BGO)
Alpha-H
Alpha-L
(Rn source)
2.2e+5
1000
5600
5800
6000
6200
6400
6600
5600
6800
5800
6000
6200
6400
6600
6800
Day since 1.1.1992
Day since 1.1.1992
2003
2004
8000
30
SAR
20
10
0
0.000
5e+9
.005
.010
.015
.020
500
MS
MD
AR
DR
Gamma (BGO)
AR Cycle/day
50
0
100
Year
2005
400
40
Amplitude
1100
100
10000
Amplitude
Phosphorite
2002
2009
100
12000
2.3e+5
2007
60
50
1200
2005
S1
Amram
1300
2003
Counts/15-minute
2.4e+5
2001
150
S2
400
200
300
200
0
100
4e+9
PSD SSA
(air)
2002
Alpha (counts)

Metal tank, tight
Alpha
1400
Gamma (counts)
Counts/15-min
Gamma
0
6000
Counts/15-minute
Main components
(Day-1)
3e+9
0
50
2e+9
SAR
-200
1e+9
-100
0
4000
1360
2008
27.0
2009
2010
26.2
1355
1345
1335
1340
26.1
5650
5660
5670
5680
5690
1330
5700
C
26.8
2.405e+5
2.430e+5
5640
o
2008
26.0
1335
2.400e+5
1330
6020
6030
6040
6050
6060
26.6
6070
Day since 1.1.1992
1400
27.4
2.428e+5
o
2009
26.2
2010
2.425e+5
1390
1300
1200
Gamma-C
Alpha-H
Alpha-L
Temperature
2.3e+5
27.2
Alpha
Gamma
2.435e+5
1400
Gamma
Alpha
C
2.4e+5
1385
27.0
2.423e+5
25
5750
6000
6250
6500
4000
5000
6000
o
C
10
2008
Spectral analysis:
SA. SSA, STA periodicities
6750
80
2009
2010
2008
Alpha H
2009
2010
75
4
gamma-C
6430
6750
6760
6770
6780
6790
Day since 1.1.1992
6800
6810
CWT analysis:
Annual modulation of the
amplitude of DR signal (S1
and S2) occurs as a
compounded feature
2
20
2500
0
0.00
0.01
0.02
0.03
0.04
0.05
Cycle/day
Mean of two
alpha detectors
75
1
Gamma C
10
5
2
0
14
Alpha L
2005
2006
2007
2008
2009
S1
50
2001
2003
2005
2007
6
25
2
Cycle/day
Spectra of alpha and gamma
measurements (Experiment - 4yrs)
show clear peaks characteristic for
annual and semiannual periodicity
(365.2 and 182.6 cycle/day).
0
5500
0
4800
5000
2004
2005
2006
S2
2007
2008
1000
500
0
6
GAV: Annual modulation of the amplitude of the diurnal
periodicities S1 and S2
150
S2
3000
4000
5000
Days since 1.1.1992
6000
S1
100
50
15
0
2003
10
2004
2005
2006
2007
2008
REFERENCES
4500
0
6000
6500
Days since 1.1.1992
5500
S1
S2
S3
5000
5500
6000
6500
Days since 1.1.1992
0
0.05
S1
S2
0
2
4
0.04
4600
4
6
0.03
2
2
8
0.02
4400
5
10
25
2003
2009
4
0
6
12
0.01
4200
0
50
0.00
4000
7
Amplitude (x1000)
Day since 1.1.1992
6420
2004
6
Phase (rad)
6410
3800
GAV: Daily averages at 1.2 meter
4
5
Amplitude (counts x103)
6400
1999
Phase
60
Day since 1.1.1992
3600
Days since 1.1.1992
6
Amplitude
Amplitude
6390
26.8
3400
6000
Days since 1.1.1992
15
Amplitude
6380
1375
5000
diurnal periodicities S1, S2
40
2.420e+5
6740
4000
7000
Amplitude and phase are extracted by applying FFT windowing,
where each point represents a (consecutive) 21-day time interval.
5000
26.0
3000
Roded: Multi-year variation of phase of the
20
1380
2.430e+5
6370
0
Spectra for alpha and gamma measurements (9 yrs) show clear peaks characteristic for annual
and semi-annual periodicity (365.2 and 182.6 cycle/day).
Smoothed pattern of
• AR & SAR signals
• (maxima of T – lags)
1100
o
C
Counts/15-min (alpha)
26.3
2.410e+5
Counts/15-min (gamma-C)
2.435e+5
C
Day
30
1400
Alpha
1350
26.4
o
Gamma
2007
Alpha
Gamma
1355
.020
Cycle/day
2011
2.440e+5
.015
Daily mean (counts)
2.415e+5
26.5
.010
amplitude
30 days
Semi-annual radon signals are superimposed on the annual signal recorded by alpha-L and
gamma-C. A similar semi-annual pattern is absent in the ambient temperature.
.005
phase (rad)
Gamma-C
Alpha-H
Alpha-L
Temperature
Amplitude (x1000)
Nuclear radiation - summer peak times of
annual signal
0.000
6000
6500
Days since 1.1.1992
Annual modulation of the periodic components (amplitude
& phase) of the DR signal in Experiment.
• Annual variation of the amplitudes of the daily
components is dissimilar for gamma and alpha time
series - showing opposite temporal patterns!
21W: Annual and semi-annual modulation of the
amplitude of the diurnal periodicities S1 and S2
1. Steinitz, G., O. Piatibratova, and S. M. Barbosa, 2007. Radon daily signals in the Elat Granite,
southern Arava, Israel, J. Geophys. Res., 112, B10211, doi:10.1029/2006JB004817.
2. Steinitz, G., Piatibratova, O., 2010a. Radon signals in the Gavnunim intrusion, Makhtesh Ramon,
Israel. Geophys. J. Int. 180, 651–665.
3. Steinitz, G. and Piatibratova, O., 2010. Radon signals at the Roded site, Southern Israel, Solid
Earth, 1, 99-109, doi:10.5194/se-1-99-2010.