Long-term variations in the characteristics of the equatorial stratospheric zonal winds

Stratospheric equatorial zonal winds from 1951 onwards up to the present show considerable long-term variations, more so at higher levels, These are rarely monotonic and often show multi-periodic structures, including a sunspot cycle (II year variations), Stratospheric temperatures and geopotential heights also show multi-periodic variations, A periodicity near 20 years is encountered often.

A Novel Bimodal Forecasting Model for Solar Cycle 25

In this paper, a novel bimodal model to predict a complete sunspot cycle based on comprehensive precursor information is proposed. We compare the traditional 13 month moving average with the Gaussian filter and find that the latter has less missing information and can better describe the overall trend of the raw data. Unlike the previous models that usually only use one precursor, here we combine the implicit and geometric information of the solar cycle (peak and skewness of the previous cycle and start value of the predicted cycle) with the traditional precursor method based on the geomagnetic index and adopt a multivariate linear approach with a higher goodness of fit (>0.85) in the fitting. Verifications for cycles 22–24 demonstrate that the model has good performance in predicting the peak and peak occurrence time. It also successfully predicts the complete bimodal structure for cycle 22 and cycle 24, showing a certain ability to predict whether the next solar cycle is unimodal or bimodal. It shows that cycle 25 is a single-peak structure and that the peak will come in 2024 October with a peak of 145.3.

The Solar Radiation Climate of Greece

The solar radiation climate of Greece is investigated by using typical meteorological years (TMYs) at 43 locations in Greece based on a period of 10 years (2007–2016). These TMYs include hourly values of global, Hg, and diffuse, Hd, horizontal irradiances from which the direct, Hb, horizontal irradiance is estimated. Use of the diffuse fraction, kd, and the definition of the direct-beam fraction, kb, is made. Solar maps of annual mean Hg, Hd, kd, and kb are prepared over Greece under clear and all skies, which show interesting but explainable patterns. Additionally, the intra-annual and seasonal variabilities of these parameters are presented and regression equations are provided. It is found that Hb has a negative linear relationship with kd; the same applies to Hg with respect to kd or with respect to the latitude of the site. It is shown that kd (kb) can reflect the scattering (absorption) effects of the atmosphere on solar radiation, and, therefore, this parameter can be used as a scattering (absorption) index. An analysis shows that the influence of solar variability (sunspot cycle) on the Hg levels over Athens in the period 1953–2018 was less dominant than the anthropogenic (air-pollution) footprint that caused the global dimming effect.

Uniting The Sun’s Hale Magnetic Cycle and ‘Extended Solar Cycle’ Paradigms

Through meticulous daily observation of the Sun’s large-scale magnetic field the Wilcox Solar Observatory has catalogued two magnetic (Hale) cycles of solar activity. Those two (∼22-year long) Hale cycles have yielded four (∼11-year long) sunspot cycles-21 through 24. Recent research has highlighted the persistence of the “Extended Solar Cycle” (ESC) and its connection to the fundamental Hale Cycle-albeit through a host of proxies resulting from image analysis of the solar photosphere, chromosphere and corona. This Letter presents, for the first time, a direct mapping between the ESC, the Sun’s toroidal magnetic field evolution of the Hale Cycle. As Sunspot Cycle 25 begins to accelerate its growth, interest in mapping the Hale and Extended cycles could not be higher given potential predictive capability that synoptic scale observations can provide.

The European Beech Annual Tree Ring Widths Time Series, Solar–Climatic Relationships and Solar Dynamo Regime Changes

In this study, the results from the analysis of annual ring widths (‘Dm’) time series of two “very sensitive” to the climate and solar–climate relationships of long lived European beech (Fagus sylvatica) samples (on age of 209 ± 1 and 245 ± 5 years correspondingly) are discussed. Both series are characterized by very good expressed and relating to the solar magnetic Hale cycle 20–22-year oscillations. A good coincidence between the changes of ‘Dm’ and the growth or fading of the solar magnetic cycle is found. The transition effects at the beginning and ending of the grand Dalton (1793–1833) and Gleissberg minima (1898–1933) are very clearly visible in the annual tree ring width data for the one of beech samples. Some of these effects are also detected in the second sample. The problem for the possible “lost” sunspot cycle at the end of 18th century is also discussed. A prediction for a possible “phase catastrophe” during the future Zurich sunspot cycles 26 and 27 between 2035–2040 AD as well as for general precipitation upward and temperature fall tendencies in Central Bulgaria, more essential after 2030 AD, are brought forth.

Forecasting Solar Cycle 25 using comprehensive precursor combination and multiple regression technique

In this paper, we propose a new model to predict the complete sunspot cycle based on the comprehensive precursor information (peak, skewness, and maximum geomagnetic index aa of the previous cycle, and start value of predicted cycle). The monthly average sunspot original data are processed by Gaussian smoothing and the new model is validated by the observed sunspots of cycle 24. Compared with the traditional 13-month moving average, the Gaussian filter has less missing information and is better to describe the overall trend of the raw data. Through the permutation and combination of multiple parameters in precursor methods of solar cycle forecasting, the multiple regression technique is used to successfully achieve the peak prediction. The regression coefficient (R) of the empirical model established in this paper can reach 0.95. By adding a new parameter to the original HWR function, we provide a complete solar cycle profile showing unimodal structure. It shows that the peak value of cycle 25 will come in March 2024, with a peak of 140.2.

Solar-related and terrestrial drivers modulating the northern polar vortex

<p>The wintertime stratosphere is dominated by the polar vortex, a strong westerly wind, which surrounds the cold polar region. In the northern hemisphere the polar vortex can vary a lot during the winter and these variations affect the surface weather, e.g., in Europe and North America. Earlier studies have shown that the northern polar vortex is modulated by different terrestrial drivers and two solar-related drivers: electromagnetic radiation and energetic particle precipitation. Solar radiation varies in concert with the sunspot cycle by affecting the upper atmosphere at lower latitudes. Energetic electron precipitation (EEP) is driven by the solar wind and affects the polar stratosphere and mesosphere by forming ozone depleting NOx and HOx compounds. However, it is unclear how the effects of these solar-related and other, terrestrial drivers compare to each other. In this study we examine the effects of two solar-related drivers (solar radiation and EEP) and three terrestrial drivers (Quasi-Biennial Oscillation (QBO), El-Nino Southern Oscillation (ENSO) and volcanic aerosols) on the northern polar vortex. We use a new composite dataset including ERA-40 and ERA-Interim reanalysis of atmospheric variables and the multilinear regression analysis to estimate atmospheric responses to these five drivers in years 1957 – 2017. We confirm the findings of earlier studies that westerly QBO wind, cold ENSO, volcanic aerosols and increased EEP are associated with a stronger polar vortex. Furthermore, we find that EEP produces the strongest and most significant effect on the northern polar vortex among the studied variables. Only in December the effect of QBO is comparable to the EEP effect. We also find that EEP effect is strong and significant in the easterly QBO phase, while in the westerly phase it does not stand out from the effects of other drivers.</p>