Solar cycle how long

Our ensemble forecast involving about plausible realizations of the solar surface polar field provides a prediction range that indicates that sunspot cycle 25 would be similar or somewhat stronger than the current cycle It is important to note here the substantial progress achieved over the last decade in our understanding of the predictability of sunspot cycles 17 , 19 , 23 —which was spurred by substantial disagreements and controversy surrounding predictions for sunspot cycle 24 Our ensemble prediction indicates the possibility of a somewhat stronger cycle than hitherto expected, which is likely to buck the significant multi-cycle weakening trend in solar activity.

Our results certainly rule out a substantially weaker cycle 25 compared to cycle 24 and therefore, do not support mounting expectations of an imminent slide to a Maunder-like grand minimum in solar activity. We conclude that near-Earth and inter-planetary space environmental conditions and solar radiative forcing of climate over sunspot cycle 25 i. The basic equation. Since most of the surface magnetic field is confined in the radial direction 47 , we shall solve only for the radial component of the field.

Since we are studying the evolution of B r on the surface of a sphere, the code has been developed using spherical harmonics. Input parameters. As the leading and trailing spots of a tilted BMR reside in different latitudes, the differential rotation increases the longitudinal distance between the two polarities of the same BMR.

The differential rotation has been modeled using an empirical profile This profile has been validated by recent helioseismic observations The supergranular cells in the SCZ effectively diffuse the magnetic field on the solar surface.

Some models 26 , 50 have treated convective motion of supergranules as a discrete random-walk process, rather than using a fixed diffusion coefficient, while others 31 , 39 , have considered a purely advective flux transport model where the convective flows of supergranules are included as a part of the velocity profile. Another large-scale flow, i. Though the flow profiles and peak amplitude of meridional circulation vary from model to model 29 , they all have some fundamental similarities.

To replicate this large-scale flow we have used a velocity profile prescribed by van Ballegooijen 25 ,. Simulations for multiple solar cycles using observed cycle amplitudes show that the polar field systematically drifts and eventually fails to reverse its sign.

The latter is physically motivated and supported by independent simulations of the buoyant rise of flux tubes and we have followed this third prescription in our SFT model.

Replication of flux emergence of sunspots. Modeling of flux emergence requires information of the position of sunspots on the solar surface and the area associated with the spots. Since we do not model the growth of sunspots in our simulation, we take data at the time of their maximum surface area rather than their time of appearance on the photosphere.

We assume all sunspots that appear on the photosphere are BMRs i. To maintain the consistency in area measurement from two different data sources, we multiply a constant factor of 1. This flux is equally distributed among the two polarities of the BMR. Also, we can easily determine the value of radius say, R spot for each of the leading and following polarities from the area information.

We assume that the radial separation say, d between the centroids of leading and following spots is proportional to R spot.

The quantity T n accounts for the variation of tilt angle with cycle strength The factor g is introduced to include the effect of localized inflows towards active regions, that is present on the photosphere apart from the large-scale inflows related to activity belts.

These localized inflows effectively reduce the latitudinal separation between opposite polarities and allow less flux to reach the polar region.

Since the polar flux is proportional to tilt angle, we incorporate the impact of these localized inflows by reducing the tilt angle We choose g to be equal to 0. The initial radial magnetic field associated with the BMR is. Each spot is modeled as 25 ,. B max is the maximum value of magnetic field of each polarity, which is automatically decided by the flux contained in the spot.

Initial field configuration. We use our SFT model to study the evolution of the large-scale photospheric magnetic field for multiple solar cycles, starting from solar cycle 15 around the year As we do not have any full-sun magnetic field data at the beginning of cycle 15, we use an axisymmetric dipolar configuration 25 as an initial field condition to initiate our simulations.

We have tried to minimize the difference between the polar flux associated with this initial field and the polar flux at the beginning of cycle 15 acquired from polar faculae observations However, the actual magnetic field configuration at the beginning of cycle 15 may substantially differ from our choice of initial field.

This arbitrariness leads us to exclude the polar field produced by our simulation at the end of cycle 15 from any correlation study or calibration of our model. Numerical modeling parameters. Ideally one should consider all possible values of degree l of spherical harmonics.

The quantity plotted in Fig. It includes data from direct sunspot observations depicted by the gray curve and also the constructed decaying phase of cycle 24 blue and green curves. We calculate the polar flux plotted in Fig.

We consider the magnetic flux to be a better proxy of solar activity than the sunspot numbers. Thus, our synthetic sunspot data profile is mainly based on the flux evolution observed in cycle 24 so far. The time evolution profile of sunspot number during a certain solar cycle can be determined by using a generalized function with the knowledge of its starting time and peak activity For constructing a synthetic input profile, the observed sunspot data of cycle 24 spanning over We further introduce random fluctuations to this mean profile to produce a more realistic observationally input profile.

The total number of sunspots associated with a typical synthetic profile is roughly While assigning area to the spots associated with a synthetic profile, we follow a similar statistical distribution of area obtained by analyzing the observed sunspot data of cycle For the time-latitude allocation of the emerging BMRs on the solar surface, we use an empirical functional form to calculate the mean latitude and the spread of the activity belts The spots are randomly distributed over all possible longitude on the solar surface.

The tilt angles of the BMRs are decided by Eq. We constructed a set of thirty-four different synthetic input profiles by modulating the total flux associated with the sunspots, or by varying the latitudinal spread and interchanging their relative position in the activity wings. Among these thirty-four profiles one closely follows the already observed up to September sunspot distribution of cycle 24, and we regard this profile as a standard one.

Once we have all particulars related to the sunspots of a certain synthetic profile, we consider only the last 3. Introduction of randomness in tilt angle of active region. The scatter around the systematic mean tilt angle decreases with increasing active region area such that the standard deviation of the distribution of tilt angle randomness follows a linear logarithmic relation with active region area We apply this method to every active region of the standard input profile and generate a set of 50 such realizations.

We also consider 60 different input profiles where scatter in the tilt angle is introduced in the strongest and the weakest according to total sunspot-associated flux profiles to model the maximum uncertainty that can be present in the descending phase of cycle Most of the existing solar dynamo models 17 , 42 , 43 , 59 identify Babcock—Leighton mechanism as the sole process for generation of the poloidal component B P from the toroidal component B T of the magnetic field.

In the following section, we shortly describe the model that we have used. The same model has provided satisfactory results previously The axisymmetric dynamo equations solved in kinematic regime are,.

In Eq. The details of every profile and parameter used in this model are elaborately described in an already published work We incorporate results from SFT simulation into the dynamo model only during cycle minima, an approach similar to the earlier effort of predicting cycle 24 using observed surface magnetic field We obtain A SFT on the surface for two hemispheres by using following relations,. We achieve these via two steps. In the first step we calibrate the amplitude of these two quantities at the solar surface by a factor c , which once determined at the minimum of cycle 16, remains constant throughout our simulation.

At every subsequent minimum until cycle 24 minimum, this data assimilation from the SFT to the dynamo model is repeated; this generates our data-driven prediction for cycle In spirit, this assimilation is akin to enforcing the data-driven SFT simulated surface map in the SCZ the dynamo domain.

Vector potential on the solar surface obtained from solar surface flux transport and dynamo simulations at the beginning of cycle The dynamo simulation provides a proxy for the toroidal magnetic field at the base of the SCZ which upon satisfying the magnetic buoyancy 40 , 42 , 43 will appear as sunspots on the solar surface.

We utilize the total erupted field, B Dyn t , as a proxy for total erupted sunspot flux this is possible because each eruption has the same extent in radial and latitudinal grids. Therefore, we can compare B Dyn t with the unsigned flux associated with the observed sunspots as depicted in Fig. The dynamo simulated B Dyn t is calibrated with the observed unsigned magnetic flux through the utilization of a constant factor which remains the same throughout the simulation.

We select this particular constant as the scaling factor which operates upon the whole B Dyn t time-series. The result is depicted in Fig. A similar multi-cycle calibration technique is implemented to generate the amplitude prediction and range of the ensemble forecast in terms of the yearly mean sunspot number for cycle 25 as reported in Table 1. This is achieved by calibrating the observed annually averaged peak sunspot numbers for cycles 17 to 24 maxima with the simulated peaks of the corresponding cycles.

At no point in our century-scale simulations is any individual scaling done to the amplitude of any single cycle, or any model driving parameters fine-tuned. This maintains the sanctity of these long-term data-driven simulations.

Informed requests from established scientists for numerical simulations pertaining to this study may be entertained by the Center of Excellence in Space Sciences India. Such requests may be made through email to the corresponding author. The century-scale solar cycle simulation data and solar cycle 25 prediction data would be made available based on email requests to the corresponding author after a period of one year following publication.

Schrijver, C. Space Res. Versteegh, G. Solar forcing of climate. Space Sci. IPCC Climate Change Synthesis Report. Pachauri and L. Meyer eds. Hale, G. On the probable existence of a magnetic field in Sun-spots.

The magnetic polarity of Sun-spots. Charbonneau, P. Dynamo models of the solar cycle. Living Rev. Parker, E. Hydromagnetic dynamo models. Babcock, H. Leighton, R. A magneto-kinematic model of the solar cycle. Dasi-Espuig, M. Sunspot group tilt angles and the strength of the solar cycle. Cameron, R. The crucial role of surface magnetic fields for the solar dynamo.

Science , — Bushby, P. On predicting the solar cycle Using mean-field models. Pesnell, W. Predictions of solar cycle Dikpati, M. Predicting the strength of solar cycle 24 using a flux-transport dynamo-based tool. GeoRL 33 , L ADS Google Scholar. Choudhuri, A. The beginning of a solar cycle is a solar minimum , or when the Sun has the least sunspots.

Over time, solar activity—and the number of sunspots—increases. The middle of the solar cycle is the solar maximum , or when the Sun has the most sunspots. As the cycle ends, it fades back to the solar minimum and then a new cycle begins.

Evolution of the Sun in extreme ultraviolet light from through , as seen from the telescope aboard Europe's PROBA2 spacecraft. Giant eruptions on the Sun, such as solar flares and coronal mass ejections, also increase during the solar cycle. These eruptions send powerful bursts of energy and material into space. This activity can have effects on Earth. For example, eruptions can cause lights in the sky, called aurora , or impact radio communications.

Extreme eruptions can even affect electricity grids on Earth. Some cycles have maximums with lots of sunspots and activity. After all, at its heart, our Sun is a huge nuclear bomb!

Much of the Sun's tempestuous nature comes from its core. At its core is dense, electrically charged gas. Electrically charged gas is a special form of matter called a plasma. This roiling, boiling plasma generates the Sun's powerful magnetic field. Like Earth's magnetic field, the Sun's magnetic field has a north pole and a south pole. On the Sun, however, the magnetic fields are much messier and more disorganized than on Earth.

About every 11 years, the Sun's magnetic field does a flip. In other words, the north pole becomes the south pole, and vice versa. This flip is one aspect of the roughly year activity cycle the Sun experiences as its magnetic field evolves slowly over time. As the cycle progresses, the Sun's stormy behavior builds to a maximum, and that's when the magnetic field reverses. Then the Sun settles back down to a minimum, only to start another cycle.

Evolution of the Sun in extreme ultraviolet light from through , as seen from the telescope aboard Europe's PROBA2 spacecraft. Sunspots are areas of particularly strong magnetic forces on the Sun's surface. They appear darker than their surroundings because they are cooler. Even so, scientists have discovered that when there are lots of sunspots, the Sun is actually putting out MORE energy than when there are fewer sunspots.

During solar maximum, there are the most sunspots, and during solar minimum, the fewest. Through special filters, sunspots may look like the picture on the left.