Resonant Axion Radiation Conversion in Solar Spicules

It has recently been observed that solar spicules covering almost of all solar surface have strong magnetic field $B\sim {10}^2$G. They are supposed to be plasma jets emitted from chromosphere and they arrive up to $\sim {10}^4$km. Their electron number density is such that $n_e={10}^{10}\mathrm{c}{\mathrm{m}}^{-3}\sim$${10}^{12}\mathrm{c}{\mathrm{m}}^{-3}$. Corresponding plasma frequency $m_p=\sqrt{e^2{n}_e\mathrm{/}{m}_e}$ ( electron mass $m_e$ ) is nearly equal to axion mass $m_a={10}^{-5}$eV$\sim {10}^{-4}$eV. Thus, resonant radiation conversion of axion with the mass can arise in the spicules. We show that radiations converted from axion dark matter possess flux density $\sim {10}^{-6}Jy(m_a\mathrm{/}{10}^{-4}eV)(B\mathrm{/}3\times {10}^2\mathrm{G}{)}^2$. The radiations show line spectrum with frequency $\simeq 24$GHz$(m_a\mathrm{/}{10}^{-4}\mathrm{e}\mathrm{V})$. Our estimation has fewer ambiguities in physical parameters than similar estimation in neutron stars because physical parameters like electron number density have been more unambiguously observed in the sun. But, much strong solar thermal radiations would preclude sensitive observations of such radiations from the axions.