The nighttime ionospheric response to a geomagnetic storm that occurred on 23–29 September 2020 is investigated over the South American, Atlantic, and West African longitude sectors using NASA's Global-scale Observations of Limb Disk measurements. On 27 solar wind conditions were favorable for prompt penetration electric fields influence equatorial ionosphere extended longitudes. ionization ano...

We present an overview of the observational results related to the existence of long-lived sunspot active longitudes. These are affected by the solar differential rotation. The existence of such migrating active longitudes imposes an important constraint on the dynamo theory. We review different approaches to model non-axisymmetry in solar dynamo models and find that, in principle, plausible me...

The lifetimes of chromospheric active regions and active region complexes (\active longitudes") for 35 lower main sequence stars observed at Mount Wilson Observatory are estimated from the relative distribution of pooled variance at diierent time scales. The time scale of active region evolution (i.e., the lifetime of large active regions) is approximately 50 days, while the lifetime of active ...

We present an analysis of a sequence of light curves of the RS CVn-type binary II Pegasi extending from 1974 to 1998. The distribution of the spotted area versus longitude is derived by Maximum Entropy and Tikhonov regularized maps, assuming a constant spot temperature (Lanza et al. 1998a). The spot pattern on the active K2 IV star can be subdivided into a component uniformly distributed in lon...

A total of 6 new surface images of II Peg obtained for the years 1997 and 1998 confirms the recently revealed permanent active longitude structure. The lower limit of the active longitudes’ lifetime is now extended up to 25 years. A new “flipflop” phenomenon, redefined as a switch of the activity between the active longitudes, has started in summer of 1998. It coincides reasonably well with the...

The result of Da Prato and Sinestrari [3] concerning the non-autonomous evolution operators of hyperbolic type for the equation u′(t) = A(t)u(t) + f(t), t ∈ [0, T ], w(0) = w0, is applied to the study of u′(t) = A(t) [ u(t)+ ∫ t −∞ G(t, s)u(s)ds ] +K(t)u(t)+f(t), t ∈ [0, T ], u(s) = φ(s), s ≤ 0, which models linear viscoelasticity. Here A(·) satisfies all the requirements of Kato’s semigroup ap...