Ahead of today's opening practice session, the air temperature is 23 degrees C while the track temperature is 27 degrees. It is sunny and warm, very warm, but it's going to get a lot warmer over the course of the weekend with forecaster predicting 'scorchio' for Sunday. That said, it is quite windy.

Two test drivers are on duty this morning, Valtteri Bottas re[laces Bruno Senna at Williams while Jules Bianchi takes over Nico Hulkenberg's Force India.

The lights go green and Kobayashi leads the way, followed by Ricciardo, Vergne, Grosjean, Karthikeyan and Perez.

Tyre choice this weekend is medium (prime) and soft (option), though the softer rubber is unlikely to make an appearance this morning.

As ever, it is very dusty here so we can expect a few 'moments' this morning, and, indeed, this afternoon.

A number of teams have updates here, even though Valencia is a bit of a blip before we return to proper circuits such as Silverstone. At Lotus, Grosjean has a new front wing while the Enstone team has tweaked the floor, rear suspension and steering on his teammate's car.

Under pressure, following a string of poor results, Jenson Button is one of the last to appear, with Webber, Hamilton and Glock showing no sign of wanting to get to work. While the McLaren and Red Bull drivers eventually come out to play it is almost twelve minutes into the session before Glock heads down the pitlane.

Around twenty minutes into the session Kobayashi is the first out for a second run. As the Japanese heads back to his garage after another installation lap, it is the Toro Rosso duo that head down the pitlane.

Vergne gets the weekend underway, the Frenchman crossing the line at 45.619. He subsequently improves to 43.448 as Bottas and Alonso leave their garages. Ricciardo eventually posts a 44.818 as Vergne improves to 43.334.

Thirty minutes into the session, Bottas is the third driver to post a time (46.425), as Karthikeyan is warned of a strong tailwind between turns 10 and 12.

A 49.255 sees Kovalainen go fourth, as Grosjean, Raikkonen and Massa head down the pitlane. Still only four names on the sheets.

A flurry of actions sees the times tumble as Rosberg goes quickest (41.182) ahead of Raikkonen, Grosjean, Massa, Schumacher and Kovalainen.

As expected there a lot of moments with drivers, including Rosberg, locking up at a number of corners, Maldonado lucky to survive an off at Turn 10.

Still to post a time, on his first lap, after running wide at turn 2, Button complains that his KERS isn't working.

Schumacher improves to 41.273 to go second and make it a Mercedes 1-2. Maldonado goes fourth with 41.914 before being demoted by Alonso and his 41.524.

Button posts 42.452 to go eighth, his teammate one of six drivers still to post a time, Webber being one of the others. A 44.799 sees Vettel going fourteenth.

Fifty minutes into the session, Hamilton and Webber are both on track. The Englishman goes sixteenth (43.872) while the Australian goes eighteenth (45.458). Still no times from Kobayashi, di Resta or Glock.

A 40.890 sees Maldonado go quickest, as Alonso goes second ahead of Rosberg and Schumacher. Vettel improves to fifth (41.522) as Button returns to the pits having gone seventh (41.914).

Hamilton goes third with a 41.158, just 0.268s off Maldonado's pace, while Webber remains down in seventeenth (43.277). The Englishman subsequently out-brakes himself at turn 2.

One hour into the session, Vettel goes second with a 40.995, while teammate Webber improves to seventh. Di Resta posts a 41.652 to go eighth while Kobayashi once again comes out to post a time. Glock remains a no-show.

Di Resta improves to fourth with a 41.105, having gone quickest in S2, the Toro Rossos, though quickest through the speed-trap, remain worryingly close to the back end of the timesheets.

A 40.984 sees Webber improve to second, teammate Vettel remaining third.