Nico Rosberg topped the timesheets on the third day of testing at Barcelona, on a day of changing weather conditions.

The action got underway on a wet track, the rain and heavy cloud lifting as the day progressed, finally giving way to some sunshine

Like his rivals, the damp track meant Rosberg's programme was restricted to several exploratory runs to gain experience of the Pirelli intermediate tyre. However, as conditions improved for the start of the afternoon session, the team was able to complete its programme.

Rosberg continued his familiarisation with the KERS system in conjunction with set-up comparisons over longer runs to further develop the team's understanding of car and tyre behaviour. His day concluded with qualifying simulations, including operation of KERS and the adjustable rear wing.

"It was interesting running with the intermediates this morning and, although the warm-up is tricky, we definitely improved our understanding of the tyres," said Rosberg. "Our long runs this afternoon included some aero work in preparation for our next upgrade package before going into lower-fuel, new-tyre running at the end of the day. We made good progress in understanding the car and the tyres, and the reliability was solid once again. Overall, I've enjoyed two positive and productive days here in Barcelona."

Second quickest was Vitaly Petrov as Lotus Renault GP gathered data on the intermediates. The R31 was fitted with a different spec of exhaust tail pipe today and aero data was collected to assess its effect on car performance.

"We used the intermediates to begin with," said the Russian, "it was one of our first opportunities to do a lot of laps with them. The only issue we had was warming them up because it was very cold early on. The plan was to do a race distance in the morning and we managed quite a lot of long runs while the track was wet. Then, we put the slicks on just before lunch and started improving the set-up. We learned a lot of new things and I'm starting to understand the tyres more and how to get the most from this car."

"It was a slow start to the day with the wet conditions," added Alan Permane, "but we did some long runs on the intermediates. However we were interrupted by several red flags. For the afternoon, Vitaly started a set-up programme, and we made some good progress with the suspension changes at the front and rear. We also did some work with tyre pressures and found some more improvements. Overall the car has responded well to the changes today and Vitaly has been much happier."

Lewis Hamilton's day began with some installation laps on wet tyres - his first experience of Pirelli's intermediate and full wet compounds. The morning was spent focusing on shorter runs, with some brief downtime shortly before lunch to correct a minor mechanical issue. In the afternoon, the Englishman conducted longer runs, evaluating tyre behaviour over the course of a stint.

"This was a positive day," said Hamilton, "we've been focusing on our programme, trying to complete as many laps as possible, improve reliability and understand the Pirelli tyres. We're learning more and more about them every day.

"We've had a few technical issues with this car, but the guys have been working incredibly to rectify them. To get more than 90 laps under my belt today was a big positive, and I'm looking forward to a trouble-free day tomorrow."