Short‐period solar cycle signals in the ionosphere observed by FORMOSAT‐3/COSMIC

We analyze 2 years of the FORMOSAT‐3/COSMIC GPS radio occultation data to study the response of the Earth's ionosphere to the solar rotation (27‐day) induced solar flux variations. Here we report electron density variations in the ionosphere (∼100–500 km) associated with the 27‐day solar cycle. The peak‐to‐peak variation in electron density at low latitudes in the F2 region is about ∼104–105 electrons cm−3 or 20–40%, and can be as high as 60% depending on altitude, latitude, and season. The half and double periods of the 27‐day are also observed at an amplitude comparable to that of the 27‐day. The results place useful constraints for modeling chemical and dynamical processes in the ionosphere.