WASHINGTON — The sun has now rebounded from what experts say was an unusually quiet solar minimum, and with a host of new space sensors on orbit or launching soon, the new solar cycle promises to be an enlightening one.

The sun’s magnetic energy ramps up and down in cycles that typically last around 11 years. Over the next few years, the sun’s magnetic field will grow stronger, and the amount of ultraviolet radiation and particles that reach the Earth will increase. The changes in the solar magnetic field have a number of effects on Earth, some of which can be disruptive to critical technologies such as GPS and the electric power grid.

When the sun is in a state of low magnetic activity, which it has been for the past several years, its magnetic field is less effective at shielding Earth from cosmic rays. This past solar minimum was the lowest in a hundred years, and as such, the amount of cosmic rays reaching the Earth were the highest they have been since measurements first began, Chris Scolese, NASA’s associate administrator, said June 8 at the Space Weather Enterprise Forum in Washington. The effects of cosmic rays on the Earth are not well understood.

“Life is going to change for us,” Scolese said. “We have some uncertainties about what happened during this minimum that have really provided some food for thought.”

Changing levels of solar magnetic activity also affect the Earth’s upper atmosphere, or ionosphere. The difference in the height of the ionosphere can vary by hundreds of kilometers from solar minimum to solar maximum, according to Richard Fisher, director of NASA’s heliophysics division. The difference in height can alter how much drag satellites in low Earth orbit experience, and thus impact how much fuel they consume to stay at a desired altitude.

Ironically, the most recent solar minimum was so low that the ionosphere fell to a point where a satellite recently launched to study that region of the upper atmosphere was unable to do so.

That satellite was the U.S. Air Force’s Communications/Navigation Outage Forecasting System spacecraft launched in April 2008. One of the payloads was designed to monitor the concentration and energy of various structures in the ionosphere that can impact high-frequency communications and GPS signals. At first the satellite had nothing to monitor, but the ionosphere is slowly rising again, Fisher said.

One of the most important instruments for monitoring the sun is an aging spacecraft 1.6 million kilometers from Earth. NASA’s 13-year-old Advanced Composition Explorer (ACE) satellite sits at the first Lagrange point, directly between the Earth and the sun at all times. When the sun blasts out a plume of particles that could potentially cause disruptions on Earth, ACE gives scientists as much as an hour of advance warning.

The space weather community for years has been sounding the alarm that the satellite could fail at any time. Heeding the warning, Congress added $5 million to NASA’s 2010 budget to refurbish and launch the Deep Space Climate Observatory, which had been shelved since 2001, to replace ACE. NASA and the National Oceanic and Atmospheric Administration will be responsible for getting the satellite ready for launch, and the Air Force will provide the launch vehicle in 2013.

NASA’s two Solar Terrestrial Relations Observatory spacecraft also will be witnessing their first solar maximum in the coming years. Launched in 2006, these two satellites follow Earth’s orbit, one in front of the Earth and one behind it, to provide a stereoscopic view of the sun.

NASA launched the Solar Dynamics Observatory in February and it began full-fledged science operations in May. The satellite is providing a view of the sun more detailed than ever before, and three instruments are contributing new space weather data. Over the summer more and more space weather data products will be made available from the Solar Dynamics Observatory, but it will be an ongoing process to develop predictive models for the data, Fisher said.

The Johns Hopkins University’s Applied Physics Laboratory in Laurel, Md., is building two of NASA’s next solar missions. The twin Radiation Belt Storm Probe spacecraft are on track to launch in 2012, and preliminary design work is being done for the Solar Probe Plus mission, which could launch as early as 2015.

The next solar missions the United States will pursue will be influenced by the upcoming 2013-2022 Decadal Survey in Solar and Space Physics. The survey will be led by Dan Baker, director of the University of Colorado’s Laboratory for Atmospheric and Space Physics, Arthur Charo of the National Research Council said at the forum. The rest of the panel will soon be announced and meetings will begin this summer with a full report due March 31, 2012, Charo said.