Mercedes driver Nico Rosberg topped the timesheets on a day when the rain made a somewhat surprising, and wholly unwelcome, visit to Barcelona.

After two days of near ideal conditions, the penultimate day of pre-season testing was hit by intermittent rain which started around ninety minutes into the session and lasted until the end of the lunch-break.

Just 24 hours after Michael Schumacher cast doubt on the pace of the W01, teammate Nico Rosberg gave the German team a significant boost, setting his best time early in the session on a low fuel run.

The German spent the morning working on qualifying simulations and developing the car's set-up before completing a race simulation in the afternoon. Despite the intermittent showers, he was able to complete 128 laps.

"We had a good day today," said Rosberg, "and made some significant progress in terms of set-up which was nice to see. We hadn't got the most out of the car in terms of performance over the last couple of days, but we made a step in the right direction today. We went through some big changes this morning step by step and found some good improvements. The longer runs this afternoon were interesting. We learnt a lot as there were other cars running similar programmes at the same time so we were able to do some comparisons. There is still plenty of room to improve but overall we're looking in pretty good shape."

Second quickest was Sebastien Buemi in the Toro Rosso as the weather caused the Italian team was change its planned programme. "Today's programme was supposed to be a repeat of yesterday's - pit stop practice in the morning, followed by a race simulation in the afternoon - with Sebastien taking over from Jaime," said chief engineer, Laurent Mekies. "However, the morning rain slightly altered the plans, though we were able to complete the race simulation, as there were only two periods of light drizzle in the afternoon."

"Despite the rain, my first day in Barcelona has gone well," said Buemi. "Carrying out a race simulation was very useful and it was particularly interesting to see how the tyre behaviour changed depending on the fuel load. In the races, it will be important to drive smoothly, as on full tanks it is very easy to damage the tyres if you slide too much. Today was good and so we can try and improve a bit more tomorrow, our last chance before Bahrain."

"With just one more day of pre-season testing remaining, It is very encouraging that we have successfully completed two race simulations on two consecutive days," added the team's technical director, Giorgio Ascanelli.

It was the final day of testing for the reigning world champion, Jenson Button, who had his running compromised and limited McLaren's learning of a number of new components.

As a result, the morning was spent conducting a number of shorter installation runs to establish set-up. Subsequently, as the track dried over the lunch hour, Button was able to complete a race simulation in the afternoon - a run that was only mildly disrupted by late red flags. This also provided the opportunity for the race team to undertake a series of live pit stops, all of which went without problem.

According to the Woking team, today's long-run times have established a benchmark for the final day of pre-season running tomorrow, which will be carried out by Lewis Hamilton.