Ahead of today's opening free practice session, the air temperature is 17 degrees C, while the track temperature is 27 degrees. It is bright and sunny, but there has been a fair amount of rain in the last couple of days with more expected over the course of the weekend.

Tyre options this weekend are the same as Canada, soft (prime) and supersoft (option). The teams also have two extra sets of medium 'development' tyres at their disposal today.

For the first time this season, there are two DRS activation zones, one the main straight that leads to the pit entrance and final chicane, and also on the pit straight. DRS detection is at the hairpin (Turn 10).

Nico Hulkenberg replaces Adrian Sutil in this session while Daniel Ricciardo replaces Sebastien Buemi.

Most of the teams are running updates this weekend, including parts specifically for this high downforce circuit.

Kovalainen gets the weekend underway, the Lotus driver followed by d'Ambrosio, Ricciardo and Liuzzi.

Four minutes into the session all but Vettel, Massa, Petrov and Alguersuari have been out, Lewis Hamilton waving to the fans on his installation lap. The rear wing on Alonso's Ferrari is covered in high-vis paint. The Italian team is comparing different types of rear wing configuration.

Fifteen minutes into the session, Barrichello is the first driver to come out for a second run. Williams finally having opened its 2011 points account two weeks ago. Shortly afterwards he is joined by Rosberg.

Ricciardo posts the first time of the weekend (1:26.560) as more and more drivers pour onto the circuit. Alonso, who goes quickest in all three sectors, posts a 22.158 at the line. Replay shows the Spaniard getting very out of shape at the hairpin.

Showing no signs of any after effects from his Monaco crash, Perez posts a 26.299 as Schumacher goes second and Alonso improves (19.981).

Schumacher improves with a 18.821 to go quickest as Hamilton goes third with a 20.357. Next time around the McLaren driver improves to second with a 18.914.

An 18.395 sees Hamilton go quickest, ahead of Schumacher, Alguersuari, Alonso and Ricciardo as Webber improves from 28.469 to 20.722.

A great close up of Rosberg riding the kerbs in the final chicane, the German posting 19.642 to go fifth. Moments later he's demoted when Hulkenberg posts a 19.611.

Vettel has yet to post a time, the German suffering a front brake problem… not what you want at this circuit. Problems also for Hamilton whose car is being stripped right down much to the McLaren driver's obvious frustration.

Massa goes straight to the top of the timesheets with a 17.707 as Webber also improves, the German going second with an 18.104.

At half-time, it's: Massa, Rosberg, Webber, Alonso, Hamilton, Ricciardo, Schumacher, Button, Alguersuari and Hulkenberg.

Vettel gets mighty close to the wall on the back end of the circuit as Button improves to fourth with an 18.266. As the world champion posts 22.171 to go seventeenth, Petrov remains the only driver yet to post a time.

It's unclear exactly why but the marshals are waving the 'slippery surface' flag on the back straight.

No sooner has Alguersuari gone cross country than Vettel, one of the first drivers to witch to options, goes into the champions' wall. The session is immediately red flagged as the German climbs from his car. Replay shows his right-front locking up, the car getting out of shape, riding the kerb and heading into the wall. On the pit wall Christian Horner and Adrian Newey hold their heads. He was carrying far too much speed into the chicane.

After six minutes the session is re-started.

Heidfeld improves to fourth with an 18.172, as Massa does very well to keep out of the wall at Turn 9. Elsewhere, di Resta, after numerous lock-ups, makes a pig's ear of the final chicane. Indeed, as they switch to the softer rubber more and more drivers are having moments.

No such problems for Alonso who posts a 17.102 to make it a Ferrari 1-2. Hamilton is back on track as onboard camera reveals that there is no data display on his steering wheel.