Short-term variability of gamma radiation at the ARM Eastern North Atlantic facility (Azores)

Abstract

This work addresses the short-term variability of gamma radiation measured continuously at the Eastern North Atlantic (ENA) facility located in the Graciosa island (Azores, 39N; 28W), a fixed site of the Atmospheric Radiation Measurement programme (ARM). The temporal variability of gamma radiation is characterized by occasional anomalies over a slowly-varying signal. Sharp peaks lasting typically 2-4 h are coincident with heavy precipitation and result from the scavenging effect of precipitation bringing radon progeny from the upper levels to the ground surface. However the connection between gamma variability and precipitation is not straightforward as a result of the complex interplay of factors such as the precipitation intensity, the PBL height, the cloud's base height and thickness, or the air mass origin and atmospheric concentration of sub-micron aerosols, which influence the scavenging processes and therefore the concentration of radon progeny. Convective precipitation associated with cumuliform clouds forming under conditions of warming of the ground relative to the air does not produce enhancements in gamma radiation, since the drop growing process is dominated by the fast accretion of liquid water, resulting in the reduction of the concentration of radionuclides by dilution. Events of convective precipitation further contribute to a reduction in gamma counts by inhibiting radon release from the soil surface and by attenuating gamma rays from all gamma-emitting elements on the ground. Anomalies occurring in the absence of precipitation are found to be associated with a diurnal cycle of maximum gamma counts before sunrise decreasing to a minimum in the evening, which are observed in conditions of thermal stability and very weak winds enabling the build-up of near surface radon progeny during the night.

Identifying a regional aerosol baseline in the eastern North Atlantic using collocated measurements and a mathematical algorithm to mask high-submicron-number-concentration aerosol events

“…Since our focus here was on summer data at ENA due to the deployment of S1 to constrain C1 measurements, the winter season and vertical characterization of the MBL was beyond the scope here. During the winter, aerosol in the MBL is expected to be less well mixed due to a strong polar front activity and low-pressure system (Barbosa et al, 2017). Therefore, we expect less correlation between the AOS data and the AAF in the winter than what was observed in the summer.…”

Global Electric Circuit research at Graciosa Island (ENA-ARM facility): First year of measurements and ENSO influences

“…It is commonly accepted that the two main sources of atmospheric ionization are cosmic rays and radon, and to this it can be added the breaking of waves near the seaside [32,33] which is the case of Graciosa Island. In fact, being a volcanic Island it can enhance radon migration from the Earth's surface [30]. These co-located measurements of radon are currently under operation and future analysis will consider both radon and PG together.…”

Identifying a regional aerosol baseline in the Eastern North Atlantic using collocated measurements and a mathematical algorithm to mask high submicron number concentration aerosol events

“…Since our focus here was on summer data at ENA due to the deployment of S1 to constrain C1 measurements, the winter season and vertical characterization 5 of the MBL was beyond the scope here. During the winter, aerosol in the MBL are expected to be less well-mixed due to a strong polar front activity and low pressure system (Barbosa et al, 2017). Therefore, we expect less correlation between the AOS data and the AAF in the winter than what was observed in the summer.…”