Solar atmospheric model with spicules applied to radio observation

Abstract

Abstract. An atmospheric model was constructed in order to reproduce quantitatively the observations at 17 GHz from Nobeyama Radio Heliograph, namely the brightness temperature at disk center (from 1.4 to 400 GHz), center-to-limb brightening distribution, and radius derived from 17 GHz solar maps. The two dimensional solar atmospheric model, that takes into account the curvature of the Sun, includes spicules, which physical characteristics (such as size, temperature, density, position, and inclination angle) were randomly attributed. After the interferometer instrumental response is taken into account, the results showed than an atmospheric model without spicules produces 36% of limb brightening, approximately the value observed at the solar poles. However, the inferred solar radius from the model (970 ) was 6 smaller than the mean value derived from the solar maps. An improvement of the model is made by including spicules. Results from this upgraded model showed that depending on their physical parameters, limb brightening and solar radius values are obtained in agreement with the radio observations (except for polar regions).

Coronal Magnetic Fields Derived From Simultaneous Microwave and Euv Observations and Comparison With the Potential Field Model

“…The magnetic field at zero height is the photospheric longitudinal magnetic field measured by HMI. This field does not fill the radio-polarized region at a height of 5220 km, which corresponds to the bottom of the corona in the atmospheric model of Selhorst et al (2005). On the other hand, at a height of 20,880 km, the longitudinal magnetic field appears to be distributed throughout the contour of the polarization degree.…”

“…Since the derived coronal longitudinal magnetic fields estimated from EIS observations were still the upper limit, we should estimate the actual coronal magnetic field by using some assumptions. The millimeter-range brightness temperatures in the quiet region have been observed (e.g., Kuseki & Swanson 1976) and modeled (Selhorst et al 2005). According to Selhorst et al (2005), the brightness temperature of the quiet region at 34 GHz is about 9000 K. The height of the optically thick layer at 17 GHz should be higher than that of at 34 GHz because the temperature in the chromosphere is a monotonically increasing function of height.…”

“…The millimeter-range brightness temperatures in the quiet region have been observed (e.g., Kuseki & Swanson 1976) and modeled (Selhorst et al 2005). According to Selhorst et al (2005), the brightness temperature of the quiet region at 34 GHz is about 9000 K. The height of the optically thick layer at 17 GHz should be higher than that of at 34 GHz because the temperature in the chromosphere is a monotonically increasing function of height. Hence, the chromospheric intensity at 17 GHz,I chr,17 , should be greater than 9000 K. If we assume that the chromospheric intensity at 17 GHz is 9000 K, the coronal intensities I cor,17 of the numbered regions range from 1500 to 2500 K. Accordingly, the coronal longitudinal magnetic field is estimated to be 90-130 G, which is still greater than the potential field strength.…”

What determines the radio polar brightening?

“…The atmospheric model previously developed (Selhorst et al 2005) consists of temperature and density (electron and proton) distributions as a function of height, from the photosphere up to 40 000 km in the corona. The SSC model was developed as a bi-dimensional space reproducing one quadrant of the Sun.…”

“…In a previous work, Selhorst et al (2005) developed an atmospheric model (hereafter referred to as the SSC model) in order to reproduce simultaneously three independent radio observations: the brightness temperature at disk center for frequencies ranging from 1.4 to 400 GHz, the observations of the radius and the limb brightening at 17 GHz. Moreover, the SSC is a 2-D model that takes into account the solar spherical curvature in order to study the solar radius and the limb brightening at 17 GHz.…”