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Missing Sunspots - Briefing Materials
03.02.11
 

Multimedia Files in Support of the Missing Sunspot Briefing


Plot of monthly sunspot numbers, for the present cycle and the four latest cycles, superimposed over an image of the Sun taken by the Solar and Heliospheric Observatory during the minimum of solar cycle 23, showing a spotless Sun. › View Larger
Plot of monthly sunspot numbers, for the present cycle and the four latest cycles, superimposed over an image of the Sun taken by the Solar and Heliospheric Observatory during the minimum of solar cycle 23, showing a spotless Sun. Credit: NASA/SOHO/Solar Influences Data Analysis Center, Belgium
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NASA sponsored research has resulted in the first computer model developed to explain the recent period of decreased solar activity during the sun's 11-year cycle. The recent solar minimum, a period characterized by a lower frequency of sunspots and solar storms, was the deepest observed in almost 100 years.

Solar scientists around the world were puzzled by the extended disappearance of sunspots in 2008-2009. Results published in the March 3, 2011 edition of Nature indicate the mystery may be solved. The sun’s magnetic field weakened during this deep solar minimum allowing cosmic rays to penetrate the solar system in record numbers making space a more dangerous place to travel. At the same time, the decrease in EUV and UV radiation caused the cooling and collapse of Earth’s upper atmosphere. As a consequence space debris stopped decaying and started accumulating in Earth orbit due to decreased atmospheric drag. These effects demonstrate the importance of understanding the entire solar cycle from minimum to maximum.

Speakers/Presenters

  • Richard Fisher, director, Heliophysics Division, Science Mission Directorate, NASA Headquarters, Washington
  • Dibyendu Nandi, assistant professor, Indian Institute of Science Education and Research, Kolkata, India
  • Andres Munoz-Jaramillo, visiting research fellow, Harvard-Smithsonian Center for Astrophysics, Cambridge, Mass.
  • Delores Knipp, visiting scientist, University of Colorado at Boulder




Presenter: Richard Fisher
Director, Heliophysics Division, Science Mission Directorate NASA Headquarters, Washington

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Presenter: Dibyendu Nandi
Assistant professor, Indian Institute of Science Education and Research, Kolkata, India

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Figure: 1
Graph showing sunspot activity from 1900-2010.

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Total number of spotless days between the maxima of solar cycles. One has to go back to cycle 14 for a deeper minimum. Credit: Based on data provided by David Hathaway (NASA-MSFC). Figure from Nandy, Muoz-Jaramillo& Martens, Nature 3rd March, 2011 issue
 
Figure: 2
An image of the Sun taken with the Solar and Heliospheric Observatory during the minimum of solar cycle 23, showing a spotless Sun.

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An image of the Sun taken with the Solar and Heliospheric Observatory during the minimum of solar cycle 23, showing a spotless Sun. Credit: SOHO/ESA/NASA.
 
Figure: 3
A different phase of sunspot cycle, now also showing the conveyor belt-like North-South meridional flow of plasma (thick black line with arrows indicating direction of flow).

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A different phase of sunspot cycle, now also showing the conveyor belt-like North-South meridional flow of plasma (thick black line with arrows indicating direction of flow). Image credit: William T. Bridgman (NASA/GSFC), Dibyendu Nandy (IISER Kolkata), Andrés Muñoz-Jaramillo (Harvard Smithsonian Center for Astrophysics) and Petrus C.H. Martens (Montana State University).
 
Figure: 4
An image of the Sun taken with the Solar and Heliospheric Observatory during the minimum of solar cycle 23, showing a spotless Sun.

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This collage shows magnetic fields in the interior of the Sun simulated using a solar dynamo model (center) and the observed solar outer atmosphere (corona) at two different phases of solar activity: A quiescent phase during the recent, unusually long minimum in solar activity (right) and a comparatively active phase following the minimum (left). Sunspots originate from the internal magnetic field and are the seats of solar storms that generate beautiful auroras but are also hazardous to our space-based technologies. This computer modeling shows that a deep minimum in solar activity occurs when the magnetic field belts of two successive sunspot cycles (blue and red coloured regions in the right) become separated in space and time due to changes in solar internal meridional plasma flow. This separation of the internal magnetic field belts results in a lack of sunspots eruptions (and solar storms), over a long period of time, between two successive sunspot cycles. Image credit: NASA/Goddard/SDO-AIA/JAXA/Hinode-XRT; Artistic rendering: Cygnus-Kolkata/William T. Bridgman; Conceptualization and simulation data: Dibyendu Nandy (IISER Kolkata), Andrés Muñoz-Jaramillo (Harvard Smithsonian Center for Astrophysics) and Petrus C.H. Martens (Montana State University).



Presenter: Andres Munoz-Jaramillo
Visiting research fellow, Harvard-Smithsonian Center for Astrophysics, Cambridge, Mass.

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Figure: 5
Physical processes of greatest relevance for the solar cycle; (a) Differential rotation, (b) Meridional circulation, (c) Turbulent convection, (d) Sunspot eruption.

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Physical processes of greatest relevance for the solar cycle.
  1. (a) Differential rotation: Not all layers of the Sun rotate at the same speed: the equator rotates faster than the poles and deep in the interior, the Sun rotates as a solid body. Differential rotation is the main source of energy for the solar cycle because it wraps and strengthens the magnetic field into rings around the axis of rotation. Once the field is strong enough, sunspots erupt from these rings. Credit: University of Hong Kong, department of physics.
  2. (b) Meridional circulation: Global flow that transports magnetic field towards the poles at the surface and towards the equator at the bottom of the convection zone. It plays a crucial role in determining the strength of the polar field, as well as the duration of the cycle and the cycle’s minimum. Credit: Andrés Muñoz-Jaramillo (Harvard-Smithsonian Center for Astrophysics) in collaboration with Dibyendu Nandy (Indian Institute of Science Education and Research-Kolkata), Petrus Martens (Montana State University) and Tom Bridgman (NASA).
  3. (c) Turbulent convection: Responsible for the transfer of thermal energy from the inside of the sun towards the surface, it plays an important role in the transport of magnetic field due to the random scatter of magnetic elements. The simplest way of modeling it is through a diffusion process. Credit: Big Bear Solar Observatory - New Jersey Institute of Technology
  4. (d) Sunspot eruption: Consequence of the buoyant rise of magnetic fields from the bottom of the convection zone. The collective effect of all erupted sunspots during a cycle is responsible for recreating the polar magnetic field and setting the stage for the future cycle. Credit: Solar Optical Telescope – Hinode
 
Figure: 6
Physical processes of the solar cycle as ingredients in our kinematic dynamo model of the solar cycle; (a) Differential rotation, (b) Meridional circulation, (c) Turbulent convection, (d) Sunspot eruption.

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Physical processes of the solar cycle as ingredients in our kinematic dynamo model of the solar cycle.
Before using the kinematic model to study the nature of the extended solar minimum, each of the aforementioned physical processes (see Figure 5) was revisited and improved upon:
  • (a) Differential rotation: It is one of the greatest successes of Helioseismology (which uses the propagation of waves to probe the interior of the Sun). The description use in the model is that of Charbonneau et al. ApJ 527, 445–460 (1999).
  • (b) Meridional circulation: Measured by helioseismology on the top 10% of the convection zone. The model uses a profile constrained observationally. The details can be found in Muñoz-Jaramillo, Nandy & Martens ApJ 698, 461–478 (2009).
  • (c) Turbulent Magnetic Diffusivity: responsible for modeling the way turbulence interacts with the magnetic field in the Sun. The model uses a profile which reconciles what is typically used in the dynamo community with what is suggested by theory. Details about this work can be found in Muñoz-Jaramillo, Nandy & Martens ApJL 727, L23 (2011).
  • (d) Sunspot Eruption: The most relevant improvement for studying the solar minimum. Having sunspots in the model allows one to understand the mechanisms that produce a large amount of spotless days. Furthermore, the algorithm used captures successfully the dynamics of the surface magnetic field (see Figure 7). Details about this work can be found in Muñoz-Jaramillo et al. ApJL 720, L20 (2010).
  • Credit: Andrés Muñoz-Jaramillo, Harvard-Smithsonian Center for Astrophysics.
 
Figure: 7
Comparison of the improved model with observations and other models

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Comparison of the improved model with observations and other models
The main observational constraints for models of the solar cycle come from observations of the surface magnetic field. The way the cycle is usually represented is called the butterfly diagram (a), where one can see the time evolution of the longitudinally averaged magnetic field. The main features of the solar cycle (which can be observed in the figure) are the emergence of sunspots which gradually shifts towards the equator as the cycle progresses, the migration of field towards the poles (produced by sunspot decay) and the reversal of the field polarity from cycle to cycle. Up until now, models of the solar cycle didn’t include the emergence of sunspots (b) which resulted in smooth and large surface fields. The introduction of sunspots into the model (c) produces important changes on the evolution of the magnetic field at the surface which are crucial for understanding the extended solar minimum. Credit: (a) David Hathaway, NASA; (b-c) Andrés Muñoz-Jaramillo, Harvard-Smithsonian Center for Astrophysics.



Presenter: Delores Knipp
Visiting scientist, University of Colorado at Boulder

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Figure: 8
Plot of monthly sunspot numbers, for the present cycle and the four latest cycles.

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Plot of monthly sunspot numbers, for the present cycle and the four latest cycles. Credit: Solar Influences Data Analysis Center, Belgium
 
Figure: 9
When the atmosphere has an prolonged contraction, low-Earth-orbiting spacecraft  (and space debris) encounter fewer atmospheric atoms and molecules.  The result is less drag and a longer time on orbit.

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When the atmosphere has an prolonged contraction, low-Earth-orbiting spacecraft (and space debris) encounter fewer atmospheric atoms and molecules. The result is less drag and a longer time on orbit. This is good news for operational satellites but bad for space junk accumulation. Space mission operators may have to maneuver spacecraft to avoid collisions. In some cases no maneuvers are possible. Credit: ESA