Yamauchi et al: Effect of the ionizing radiation on the rain-time atmospheric electric field (PG) 2 week rain Chernobyl PICO 09:36 (EGU ) Fukushima Helsinki PG

Rain time peaks (a)Distribution of PG peak values every 15 min in logarithmic bins (25% stepping in horizontal axis). (b)Relative PG values compared to the peak during 5 min before (right) and 5 min after (left) the negative peaks (when peak PG < -0.2 kV/m). The same period of the year (14 March to 30 April) is plotted for (gray triangles), average (black line) and 2011 (red cross).

Effect of the ionizing radiation on the rain-time atmospheric electric field M. Yamauchi 1, M. Takeda 2, M. Makino 3, and T. Owada 4 (1) Swedish Institute of Space Physics (IRF), Kiruna, Sweden (2) Kyoto University, Japan (3) National Institute of Advanced Industrial Science and Technology, Tsukuba, Japan (4) Kakioka Magnetic Observatory, Japan Meteorological Agency, Ishioka, Japan PICO (EGU ) / GI1.4

Effect of ionizing radiation ionization Electric field reduction Instrument to measure E-field

Extra ionization causes the atmospheric E-field (PG) decrease

Atmospheric E-field (PG) after the accident (EGU-2012) 2 week rain Chernobyl Fukushima Helsinki PG PG suddenly decreased!

Combine with dose rate and rain data Interpretation: PG obs for different contamination

 At Kakioka, 150 km SW of the FNPP1 (EGU-2012) (A) March = floating radionuclide 14 March: Dry deposition on 14 March at Kakioka, 150 km March: Strong re-suspension by wind. (B) - 20 April = some re-suspension March: Wet deposition at Kakioka by the first substantial rain April : Re-suspension by daily wind. Transport from highly- contaminated to moderately-contaminated areas. (C) afterward - summer: minor plumes from the FNPP-1.

Today, we examine rain-time PG Analyses is not possible without < 5 min resolution PG data (i.e., impossible for Chernobyl). Case-study is very difficult for very variable phenomenon Difficulty: PG under rain-cloud is highly variable and dynamic. Therefore, we examine statistically (Kakioka PG sampling is 1 Hz. Data is calibrated and compared with backup measurement)

PG vs. rain (hourly value) Less spread of right after FNPP accident?

Is “less spread” real?  Statistic of all peaks We used 1-min value instead of hourly value We examine all positive and negative peaks in 15-min bins Remove double-counted peaks between neighboring 15-min bins Remove even minor peaks (see illustration) We removed this type of small peaks from the statistics

Result: distribution of the peaks (a)Distribution of PG peak values every 15 min in logarithmic bins (25% stepping in horizontal axis). (b)Relative PG values compared to the peak during 5 min before (right) and 5 min after (left) the negative peaks (when peak PG < -0.2 kV/m). The same period of the year (14 March to 30 April) is plotted for (gray triangles), average (black line) and 2011 (red cross).

Quick decay & development for March-April 2011 (red/black). May (blue) and March/April is different because of different types of rain cloud (seasonal effect). May is already back to normal (consistent with the end of re- suspension). The characteristic time of the negative peaks

Summary For the first time, effect of the floating radioactive materials on the rain-time PG was examined, using PG data at Kakioka (150 km SW of FNPP1). (1) one-hour averaged rain-time PG after the accident is not as much scattered to the negative side as those during the same season at different years. (2) The range/distribution of the peak value is not changed very much. (3) But the time scale of negative peaks after the accident is shortened compared to those before the accident. The observed short time scale can be interpreted in two ways: (1) Quick development and decay of the electric charges in the cloud nuclei. (2) Shielding of the charge of horizontally moving cloud when the charges are not exactly the above the PG measurement.

extra slides for questions

Low PG even after 1 year because of radiocesium (half-life is 134 Cs = 2 yr, 137 Cs = 30 yr). seasonal effect

weather (00 UT) (00 UT) (00 UT) (00 UT) (00 UT)

Fallout (a) (b) (c) Three types of fallout (a)(b)(c)

PG drops after nuclear test (Harris, 1955) and Chernobyl Accident (Tuomi, 1988) 24 hours 2 weeks PG at Tuscon after Navada Test Shower Harris, 1955 (JGR) Shower 26/4 29/4 1/5 10/5 PG at Helsinki after Chernobyl Accident Rain Past (wet deposition)

detailed analyses (EGU-2012)

q: production (by cosmic ray, radon, and  -ray) α ： neutralization, β ： attaching to aerosol (density N) Ion density n: dn/dt = q - αn 2 - βnN aerosol  + positive ion         molecule negative ion

With atmospheric electric field aerosol          negative ion positive ion E

MainSub ElectrometerElectrostatic sensor typeField mill type Collector TypeWater-dropperMechanical Height2.55 m1.00m Separation from the wall1.17 m Sampling1 sec LatitudeLongitude 36  13'56"N140  11'11"E PG measurement at Kakioka