Nico Rosberg topped the timesheets at Jerez on a day when persistent rain compromised teams programmes and lap times.

With rain showers predicted throughout the four-day test, the first downpour arrived after just one hour of running this morning and conditions remained wet throughout the remainder of the day.

Rosberg had time to complete a couple of short runs in the dry before the rain arrived and his Mercedes team's programme was changed accordingly.

Using wet and intermediate tyres, the German gave the W01 its first run-out in wet conditions, completing 57 laps over the course of the session. Michael Schumacher will take over at the wheel of the car tomorrow.

"The car felt very good today," said Rosberg. "Compared to Valencia where I was sitting too low which affected my visibility and the set-up wasn't perfect, today I felt really comfortable and I could push so it was an enjoyable day and a good start to the test for me. Our objective here is to learn as much as possible, put miles on the car and engine to check the reliability and to make progress on our set-up work. The rain is a little frustrating but the car feels good to drive and that's what's important."

Like most of the other drivers, Sebastien Buemi posted his best time during the dry period right at the start of the session. Furthermore, like most of the other teams, this was the Toro Rosso STR5's first taste of running in the wet.

It's worth noting that the intermediates are a new tyre, with the front sharing the same narrow width as the dry tyres. while the extreme wets are the same tyres as in 2009, however they are mounted on narrower rims for the new season.

Switching between the two types of tyre, the Swiss driver also evaluated mechanical set-up suited to the wet conditions, as well as carrying out some launch simulations. The car ran reliably all day allowing the Faenza team to end its programme ahead of schedule, its entire wet running programme having been completed for the day.

Third quickest was Nico Hulkenberg in the Williams, the German driver completing the most laps today (118) as he continues to acclimatise himself to the new car, indeed, to F1.

For Ferrari, Fernando Alonso worked mainly on overall reliability of the F10 and on the performance of the two types of tyre available for the conditions. The Spaniard covered a total of 88 laps.

"The work was influenced by the bad weather," admitted the Spaniard, "but nevertheless we managed to drive many kilometres and almost did 90 laps. So we're satisfied, because we could collect lots of data, which is important for the reliability.

"We hope that the weather is better tomorrow," he continued, "because it's important to drive on a dry track, too. The car went very well on the wet track though and it's easy to drive. The feeling is good, just like on the dry. All in all I had some positive sensations today."