Equinoctial Asymmetry in Solar Quiet Fields along the 120° E Meridian Chain

Equinoctial asymmetry of the range of the solar quiet day variation (Sq) of the horizontal geomagnetic field (H) has been found in some low latitude geomagnetic observatories. This study conducted an investigation of its latitude distribution and the relationship with the solar cycle by using the H field measurements from six observatories along the 120° E meridian chain in the years 1957–2013. Results illustrate a significant equinoctial asymmetry of the SqH range at all observatories. Three main features were identified. First, the signature of the equinoctial asymmetry of the SqH range is opposite for observatories located at the northern and southern sides of the Northern Hemisphere Sq current focus. It shows larger values around spring than autumn equinox at southern observatories, and the converse is seen at northern observatories. Second, the asymmetry increases with the distance from the Sq current focus, suggesting the stronger sensitivity of the distant observatories than observatories around the focus. The result of linear fitting presents a positive dependence of the asymmetry coefficient on geographic latitude, with a reversal of the asymmetry occurring at 28.1° N near the focus of the average Sq current. Third, there is no obvious dependence of the equinoctial asymmetry of the SqH range on solar activity, suggesting a possible cause from some regional factors related to the ionospheric dynamo process.

Stellar magnetic activity and the butterfly diagram of Kepler-63

Context. The study of young solar-type stars is fundamental for better understanding the magnetic activity of the Sun. Most commonly, this activity manifests itself in the form of spots and faculae. As a planet in transit crosses in front of its host star, a dark spot on the stellar surface may be occulted, causing a detectable variation in the light curve. Kepler-63 is a young solar-like star with an age of only 210 Myr that exhibits photometric variations compatible with spot signatures. Because the planet that orbits it is in an almost polar orbit, different latitudes of the star can be probed by the method of spot transit mapping. Aims. The goal of this work is to characterise the spots of Kepler-63 and thus decipher the behaviour of the young Sun. Because planetary orbit is highly oblique, the latitudinal distribution and thus the differential rotation of the spots may be determined. Methods. A total of 150 transits of Kepler-63b were observed in the short-cadence light curve, corresponding to a total duration of about four years. Each transit light curve was fit by a model that simulates planetary transits and allows including starspots on the surface of the host star. This enables the physical characterisation of the spot size, intensity, and location. We determined the spot position in a reference frame that rotates with the star, and thus obtained the latitudinal distribution of the spots. Results. We fit a total of 297 spots and determined their sizes, intensities, and positions. The longitude and latitude of the spots were calculated in a reference frame that rotated with the star. The latitude distribution of spots exhibits a bimodality with a lack of spots around 34°. Moreover, the spot sizes tend to be larger close to the equator, but decrease toward the latitude distribution gap, after which they again increase toward the poles. High-latitude spots dominate the magnetic cycle of Kepler-63. For a mean stellar rotation period of 5.400 d, 59 spots were found at approximately the same longitude and latitude on a later transit. Some of these spots were detected eight transits later. This shows that the lifetimes of spots can be at least 75 d. Conclusions. The geometry of the Kepler-63 system, enabled us to build a starspot butterfly diagram, similar to that of sunspots. It was also possible to infer the differential rotation of Kepler-63 from the spots at different latitudes. This star was found to rotate almost rigidly with a period of 5.400 d and a relative shear close to 0.01% for latitudes lower than 34°, whereas the high latitudes do not follow a well-behaved pattern.

Drift-corrected trends and periodic variations in MIPAS IMK/IAA ozone measurements

Drifts, trends and periodic variations were calculated from monthly zonally averaged ozone profiles. The ozone profiles, among many other species, were derived from level-1b data of the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) by means of the scientific level-2 processor run by Karlsruhe Institute of Technology (KIT), Institute for Meteorlogy and Climate Research (IMK). All trend and drift analyses were performed using a multilinear parametric trend model which includes a linear term, several harmonics with period lengths from three to twenty four months and the quasi-biennial oscillation (QBO). Drifts at 2-sigma significance level were mainly negative for ozone relative to Aura MLS and Odin OSIRIS and negative or near zero for most of the comparisons to Lidar measurements. Lidar stations used here include those at Hohenpeissenberg (47.8° N, 11.0° E), Lauder (45.0° S, 169.7° E), Mauna Loa (19.5° N, 155.6° W), Observatoire Haute Provence (43.9° N, 5.7° E) and Table Mountain (34.4° N, 117.7° W). Drifts against ACE-FTS were found to be mostly insignificant. The assessed MIPAS ozone trends cover the time period of July 2002 to April 2012 and range from -0.5 ppmv decade-1 to +0.5 ppmv decade-1 depending on altitude and latitude. From the drift analyses we derive that the real ozone trends might be slighly more positive/less negative than those calculated from the MIPAS data, by conceding the possibility of MIPAS having a very small (approx. within -0.3 ppmv decade-1) negative drift for ozone. This leads to drift-corrected trends of -0.4 ppmv decade-1 to +0.55 ppmv decade-1 for the time period covered by MIPAS Envisat measurements with very few negative and large areas of positive trends, which is in good agreement with recent literature. Differences of the trends compared with recent literature could be explained by a possible shift of the subtropical mixing barriers. Results for the altitude-latitude distribution of amplitudes of the quasi-biennial, annual and the semi-annual oscillation are also in very good agreement with recent findings.