Ahead of today's opening free practice session, the air temperature is 28 degrees C, while the track temperature is 32 degrees C. It's hot, humid (68%) and sunny. There are a few dark clouds in the distance, but nothing too serious.

The lights go green, and as ever the Force Indias lead the way. Vettel and Heidfeld are also eager to get to work, or at least complete the obligatory installation lap.

The big news, other than the ongoing Hamilton/McLaren saga, is that both Toro Rosso are running new engines this weekend.

Five minutes into the session, all but the Ferraris, Piquet, Glock and Barrichello have been out. The Toyotas are sporting an extra long 'dorsal fin', as are the Red Bulls.

McLaren is using pain on the right-hand side of the diffuser on Heikki Kovalainen's car, just as it did in the final pre-season test at Jerez. The only difference being that here the paint is white as opposed to green. With no in-season testing, all the teams must make full use of these sessions, especially those, like McLaren, clearly hurting - whilst bearing in mind the four engine limit.

Coming up to fifteen minutes into the session, Felipe Massa relaxes in the Ferrari garage, along with teammate Kimi Raikkonen he is the only driver not to have gone out yet. Despite the oven-like conditions, the 'Iceman' sits in his car, suited, booted and helmeted, with a small fan blowing cool air on to his visor.

Twenty minutes into the session, Raikkonen heads down the pitlane. Tyres this weekend are soft and hard.

Raikkonen posts the first time of the day, crossing the line at 1:42.194. On his next lap the Finn goes wide at the chicane, when the team ask him what happened, he replies; "don't talk to me when I'm in the middle of a corner". Classic stuff.

No soon has Nakajima gone quicker with a 39.826 than Raikkonen improves again, posting a 39.389. These two are the only drivers on track.

As Raikkonen improves with a 38.707, Hamilton leaves the McLaren garage. Moments later, Nakajima goes quickest with a 38.354.

Hamilton begins his first flying lap as Rosberg, Trulli and Massa leave the pits. The Englishman subsequently posts 39.556.

Rosberg goes third (38.721) but is immediately leapfrogged by Hamilton (38.316) while Massa goes fifth and Trulli sixth.

Trulli spins at the final corner while Massa loses time behind Heidfeld.

A 37.853 sees Massa go second, as Rosberg goes third, ahead of Hamilton, Nakajima and Glock.

On his first lap, Barrichello goes ninth (39.185), the Virgin logos no more prominent on the Brawn than they were last week. Certainly no major change of livery.

As Kovalainen has a big lock-up, Massa goes quickest with a 37.343 only to be demoted by Rosberg who crosses the line at 37.264. Webber improves to third (37.522), ahead of Trulli, Raikkonen and Vettel.

Button goes sixth (37.706) as Fisichella and Massa both have big lock-ups at Turn 1.

Barrichello posts 37.260 to go quickest, as Glock goes wide. Moments later, Rosberg re-takes the top spot with a 36.879.

A lot of the cars very twitchy here, as Webber improves to second with a 37.075. Almost immediately, the Red Bull driver is bounced down to third as Button goes second with a 37.044. Elsewhere, Kubica takes a trip across the gravel.

At 'half-time', it's: Rosberg, Button, Vettel, Webber, Trulli, Barrichello, Piquet and Massa.

Glock improves to second with a 36.980, Toyota now second in the Constructors' Championship. Elsewhere, Fisichella goes quickest in the first sector, finally crossing the line at 37.369 to go tenth.

A high speed 360 for Glock at Turn 6, as Nakajima posts a personal best in the first sector. Elsewhere, Bourdais goes wide at Turn 14 running over the unforgiving rumble strip.

Fisichella moves up to third with a 37.025, as Button begins another flying lap, the Melbourne winner taking the top spot with a 36.676. In the back of the Renault garage, three-time World Champion Nelson Piquet watches his son's progress.