Physics Department Nuclear Physics Laboratory Aristotle University of
Physics Department, Nuclear Physics Laboratory Aristotle University of Thessaloniki 54124, Greece 7 Be 25 th Annual Symposium of the Hellenic Nuclear Physics Society HNPS – 2016 Time lag between the tropopause height and the levels of 7 Be concentrations in surface air Presenting author: Ioannidou Eleftheria June 3 – 4, 2016, Athens, Greece
CONTENTS • Theoretical introduction ü Environmental radioactivity ü Radioactive isotope 7 Be ü Atmospheric aerosols ü Radioactive aerosols ü Atmosphere – tropopause • Experimental part ü Air sampling of 7 Be ü Calculation of 7 Be concentrations ü Determination of the height of the tropopause ü Time lag definition • Results – discussion ü Evaluation of results ü Conclusions
Environmental radioactivity sources Natural sources Cosmic rays Terrestrial radiation Radioactive decay series of 238 U, 232 Th, 235 U Man – Made sources o Medical sources o Industrial sources o Nuclear explosions Ø 3 H Ø 14 C Ø 22 Na Ø 26 Al Ø 32 P Ø 33 P Ø 32 Si o Nuclear power o Nuclear accidents and Radiation
Cosmic ray radiation Atmospheric cosmic rays, which produced Cosmic rays may be Half termed Radionuclide - life Secondaryproduction rate are (atoms Radiation of ‘’primary’’ or ‘’secondary’’. by interactions of the-2 primary rays and s-1) of subatomic extraterrestrial origin, Those, which have not yet atmosphere, consistmlargely which rain 3 interacted with matter in the particles, such as pions, muons and 12. 33 yearselectrons. 2500 continuously upon the. He earth’s atmosphere, lithosphere earth, is termed 7 Be or hydrosphere, are 53. 28 termed the observed cosmic days At sea level, nearly all 810 ‘’cosmic rays’’ primary. These consist radiation consists of secondary cosmic rays, 10 Be 1. 6(∼ 85%) x 106 years principally of protons with some 68% of the 450 flux accounted for by and alpha particles (~14%), muons and 30% by electrons. 14 C 5730 years 25000 with much smaller fluxes (<1%) Less than 1% of the flux at sea level consists 22 Naof heavier nuclei. 2. 60 years of protons. 0. 86 The fact that this 26 Al 7. 3 x 105 years 1. 4 highly penetrating radiation was 32 280 years 1. 6 impinging upon the Si sharply with A considerable number of earth from space, 32 P Cosmic ray intensity increases 14. 28 isdays 8. 1 are continuously elevation until a maximum reached at an radionuclides rather than emanating From in the atmosphere by from the earth, was 33 P altitude of about 20 km. 25. 3 days 20 km to the produced 6. 8 deduced from balloon limit of the atmosphere (up to 50 km), the cosmic ray interactions with 35 matter. 14 Most of these 87. 2 days experiments in which S intensity decreases. are produced as ionization is also related to latitude. radionuclides 36 Cl Cosmic ray intensity 3. 01 5 years x 10 11 fragments, but some are formed measurements were At a given altitude, the cosmic flux increases of stable atoms made at various 37 Ar from the equator to latitude of 50 to 60°. The by activation 34. 8 days 8. 3 altitudes from sea flux remains roughly constant from 50 to 60° with neutrons or muons. 39 Ar level to 9000 m. 269 years 56 to the poles. 81 Kr 2. 1 x 105 years 0. 01
Cosmogenic isotope 7 Be • The production features of cosmogenic nuclides depend primarily by latitude and altitude. • 7 Be is found both in the troposphere and the stratosphere, where the concentration is longer. The production rate reaches a maximum in the lower stratosphere , ~ 20 km and decreases with decreasing altitude. • The 7 Be concentration in the stratosphere is expected to remain stable over time, except for a few changes at a rate ~ 10%, due to changes in the activity of sunspots. • The main process in which the 7 Be can penetrate the stratosphere in the 7 Be measured troposphere by mixingofthem, because of thethe folding of the tropopause. The temporalisvariations near surface is a potential tracer of the dynamics of the troposphere, the stratosphere – troposphere coupling and the fluctuations in the flow of cosmic rays due to solar activity.
Production rate of 7 Be • It depends on the flow of cosmic ray particles. The factors by which the change in flow depends on are three: The 11 year periodic solar cycle • The intensity of galactic cosmic radiation is inversely proportional to the solar activity. The result is to have decreased production of 7 Be with increasing density of the solar wind. The geomagnetic latitude • The higher values of production rate are displayed around the magnetic poles and the lower values in the equatorial region. The height of the sea surface • Considering that the intensity of cosmic rays decreases during their passage through the atmosphere, the 7 Be production rate decreases with atmospheric depth, combined with the increase in air density.
Cosmogenic isotope 7 Be • Stratospheric component of 7 Be is intense at latitudes of about 45°, where there is an exchange of stratospheric and tropospheric air. Increase of 7 Be concentrations in the atmosphere • On an annual basis, the stratosphere contributes by 25% at concentrations of 7 Be. • During the spring season and summer the stratospheric component is 40%. • The concentration of beryllium in the atmosphere depends on various weather and atmospheric factors as: v The temperature (Azahra M. et al, 2003) The deposition of 7 Be in v The atmospheric pressure (Likuku A. S. , 2006) the earth’s surface varies v The relative humidity (Meresova J. , 2008) with season, latitude and v The rainfall (Al-Azmi D. et al, 2001) local weather conditions. v The snowfall (Ioannidou A. & Papastefanou C. , 2006) Dry deposition v The cloudiness (Durana L. et al, 1996) Wet deposition
Tropopause • It is the atmospheric layer which constitutes the boundary between the troposphere and the stratosphere. • The height of the tropopause varies, depending on the latitude and season. The tropopause zone is not continual. The height varies daily, without a specific rule. • Main feature of the tropopause is that within this no vertical temperature variation occurs. • Rule: the reduction of the height of the tropopause by increasing the latitude. Ø 6 -8 km at the poles Ø 12 km in mid – latitudes Ø ~18 km at the equator
Tropopause • It is a transition zone between the troposphere and stratosphere, despite a specific boundary. • It is a discontinuous surface, and presents a gradient from the equator towards the poles. During the year, present a discontinuity (interruption) in the region with latitude 30°-40°. Discrimination between Tropical and Polar tropopause. • Fluctuations in the level of the tropopause caused firstly to seasons of the year, on the other hand, the prevalence of various barometric systems. • The height of the tropopause is higher during the transitional period from summer to autumn and smaller during the period from winter to spring. • -70°C to -80°C over the equatorial regions. • -55°C to -60°C in the mid and high latitudes. • There is a strong positive dependence of the height of the tropopause by temperature.
Sampling of 7 Be (air sampling) • 3 regions of Finland Ø Ivalo (68° 64’N, 27° 57’E) Ø Rovaniemi (66° 51’N, 25° 68’E) Ø Kotka (60° 483184’N, 26° 918078’E) • Special air sampling devices (TFIA-2 Staplex) • Filters of rectangular cross section, 8’’x 10’’ cm (TFAGF 810 glass – fiber). • The duration of each sampling was one week (7 -8 days), thus covering the entire year 2009. • A total of 52 measurements from each area during 2009. High-volume air sampler Staplex TFIA-2. Glass fiber filter TFAGF 810.
Evaluation of 7 Be concentrations • The filters constitute the radioactive radiation sources. • Processing for the appropriate geometry filter (cutting and compressing: diameter 5. 8 cm, height – thickness 2 mm). • Installation in high resolution and accuracy low background Ge detectors (HPGe). • Receiving characteristic gamma radiation spectrum from each filter. Characteristic peak of 7 Be at 477. 6 ke. V.
Experimental results • For each region we have mean weekly values of 7 Be, an average value of each week. • 2009: year of a solar minimum about solar activity. 7 Be concentrations get the maximum value in the atmosphere When the solar wind is weak, the Earth is more exposed to cosmic radiation which is responsible for the production of 7 Be Thus, we measure from the beginning (default) high concentrations, which help us to become more easily visible anyone time variation or fluctuation due to changes of meteorological factors
Experimental results • Strong positive dependence between the average monthly activity of 7 Be and temperature. • High concentrations during summer. Ioannidou & Kotsopoulou, 2010. • Explanation: heating air which has the effect of favoring unstable atmospheric conditions with turbulent eddies, which play a key role in vertical transport of air masses. • 7 Be as a radioactive nuclide of cosmogenic origin generated normally high in the atmosphere, it is easier to trap in this rotation of air masses, which is responsible for the transport of air masses, rich in 7 Be, from the place of production along the atmospheric column, lower in the surface of the Earth.
Calculation of the height of the tropopause Daily calculation of the height. Daily data concerning various meteorological factors. Use of special computer statistical models. Network – grid of approximate calculation of natural meteorological quantities for all latitudes. Create cell enclosing each one area. Create a program in Matlab to calculate the height on a daily base, for the year 2009.
Calculation of the height of the tropopause Ivalo, Finland. Rovaniemi, Finland. The maximum height of the tropopause occurs normally during the summer months Kotka, Finland.
Correlation between the two factors 2009: solar minimum max tropopause in the summer max 7 Be Elevation of the tropopause in the summer Strong dependency between 7 Be and T Longer stirring of air masses max 7 Be in the summer More 7 Be in the surface layer Theoretical approach: Positive dependence between the height of the tropopause and 7 Be concentrations. Valid for mid latitudes (Greece).
Correlation between the two factors • Next step Finding the time lag • Understanding the behavior of 7 Be concentrations an how they depend on several factors. Time lag Represents the time we have to wait until the concentrations of 7 Be in the Earth’s surface layer to respond to changes in the level of the tropopause. • Empirically, we expect a time difference of days, without excluding a delay of hours or weeks.
Time lag calculation 2 values columns 52 7 Be concentration measurements (average weekly values): calculate the deviation from the moving average Get the average day of the week for the week that I have 7 Be: I consider it as a day that became the measurement 365 calculation tropopause heights rage e v a t the e g , t igh the k e f h o t s A heigh ding wee spon e r r o c Matlab: creation program for the calculation of the correlation coefficient for each step. Get the average weekly heights for weeks that I have 7 Be measurements: 52 heights Day 0 Stable column with 52 values of 7 Be Alternating values of heights
Results • For Ivalo and Rovaniemi the Rmax were found in the fourth day. • For Kotka the Rmax was found in the first day. Ivalo: Rmax = 0. 1686 Rovaniemi: Rmax = 0. 2252 Kotka: Rmax = 0. 1751 0<R<1 Stochastic – random dependence Small values of the coefficients
Results • Chaotic nature of the atmosphere. • Incessant movements of the atmosphere have a consistency. • 7 Be is also influenced by other factors. • Statistical error of the computing model – errors in measurement of 7 Be. Conclusions v In latitudes above 60°N, the correlation between the height of the tropopause and the 7 Be concentrations is weak. v Factors affecting the concentrations of 7 Be in the surface layer, in Finland, are basically of atmospheric origin. v Kotka: the influence of air masses from the East affects more to 7 Be than the height of the tropopause. v Finland: changes in transport mode of air masses mainly related to NAO (North Atlantic Oscillation) has been determined to be the main factor in the variation of surface concentrations of 7 Be.
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