Ahead of today's opening free practice session, the air temperature is 14 degrees C, while the track temperature is 15 degrees. While it is fine this morning, though cool, rain showers are being forecast for both Saturday and Sunday.

It is three weeks since the Chinese Grand Prix, and once the teams finally got back to their respective bases they were able to get to work on various upgrades and modifications for the start of the European season.

Virtually every team has made changes, some more than others, and while McLaren is seeking to improve its qualifying results, Mercedes has made changes to the wheelbase on Michael Schumacher's car, which, incidentally, is a chassis he previously only used in testing. The German team is also introducing a number of aero upgrades this weekend, including a radical engine cover and roll hoop, while Ferrari has removed that controversial barcode logo.

Paul di Resta is driving Adrian Sutil's car this morning, while Christian Klien is in Karun Chandhok's Hispania. Tyre options are hard (prime) and soft (option).

The lights go green and Liuzzi leads a train of cars, including Webber and Massa, for the obligatory installation lap. While most drivers head back to the pits after their one lap, Liuzzi, Alguersuari, Webber and Vettel stay out for a second. Five minutes into the session, all but Hamilton and Kovalainen have been out.

As Rosberg returns to the pits, having completed four laps but not posted a time, Hulkenberg and Glock head down the pitlane.

Glock posts the first time of the day, the German crossing the line at 1:34.777. Replay shows the German shedding one of his bargeboards.

Felipe Massa goes quickest in the second and third sectors on his out lap. Subsequently, on his first flying lap, the Brazilian posts 24.129, as he is advised by Rob Smedley on how best to use the F-duct.

de la Rosa spins the Sauber, which remains almost totally white despite a new sponsorship deal with Burger King.

Massa raises the benchmark with a 23.536 as Klien goes third (38.583) in the Hispania.

As Klien improves with a 30.383 to go second, teammate Senna posts 32.603 to take third. Still only four names on the timesheets after twenty-seven minutes.

A 28.366 sees Alguersuari go second ahead of Kovalainen, however, they are both eclipsed by Trulli and then Kobayashi (25.929), the Japanese driver really struggling in the Sauber.

Petrov can only manage eighth (31.160) on his first flying lap, as Kobayashi goes quickest with a 23.190. Petrov improves to fourth (25.374).

As Kovalainen complains that his throttle is sticking on various parts of the track, Webber heads down the pitlane. Kobayashi consolidates his top spot with a 22.492.

On his first flying lap, Webber posts 22.985 to go second, improving with a 22.647 next time around.

Vettel goes fourth (23.234) on his first flying lap, taking top spot with a 22.422 on his next lap. In the Lotus garage, Trulli appears happy with his car, the Italian claiming that the various changes made to the car since China are working.

Webber makes it a Red Bull 1-2 when he posts 22.386, elsewhere, Schumacher, Hamilton and Button are on track.

The Williams duo of Hulkenberg and Barrichello go ninth and tenth, but are demoted when Schumacher goes fifth (22.712).

At half-time, it's: Webber, Vettel, Kobayashi, Petrov, Schumacher, Kubica, di Resta, Massa, Alguersuari and Hulkenberg.

Button posts 23.105 to go sixth, as local hero Felipe Massa heads down the pitlane.

Schumacher goes quickest in the second sector, crossing the line at 21.716 to go quickest. Kubica improves to fourth (22.202) only to be demoted by Hamilton who crosses the line at 22.190.

A 21.788 sees Button go second while Rosberg claims seventh with a 22.419. Next time around the world champion crosses the line at 21.672 to go quickest. However, moments later, teammate Hamilton takes the top spot with a 21.330.