Ahead of today's second free practice session, the air temperature is 19 degrees and the track temperature is 24 degrees. Once again it is overcast, however, it is not raining, though we can probably expect a shower or two over the next ninety minutes.

It is extremely windy, and as we saw this morning, when the rain did fall the wind soon dried the track once the shower came to an end.

When the lights go green it is Vettel who leads the way, followed by Heidfeld, Liuzzi, Buemi and Rosberg. In the stands a few fans don their plastic macs.

There's no messing about with installation laps this time around, within moments of the session getting underway there are thirteen names on the timesheets with Vettel leading the way from Buemi, Webber, Kobayashi and Heidfeld.

As Barrichello begins his first flying lap of the session, he is slipstreamed and almost left for dead by Liuzzi. The Italian appeared to struggle this morning, some saying he was suffering as a result of his lack of recent race experience combined with the fact that this track runs in an anti-clockwise direction.

Barrichello's first lap sees the Brazilian go eighteenth, improving to seventeenth (14.758) next time around. Teammate Button goes third with a 13.198.

Having gone quickest in the first two sectors, Buemi goes quickest overall, crossing the line at 12.796. Vettel remains second ahead of Kovalainen and Sutil, who posts 13.144.

Having suffered understeer this morning, Jenson Button is now unhappy with the oversteer on his Brawn. Teammate Barrichello moves up to tenth, just 0.3s off the Englishman's pace.

Despite the macs the rain holds off, and the drivers make full use of the dry conditions knowing that the weather is going to remain changeable for the remainder of the weekend.

Vettel improves to 12.714, just 0.004s off Buemi's timesheet topping time.

A 12.696 sees Button go quickest, as the air temperature drops to 18 degrees and the track temperature to 23.

Webber posts personal best in the first two sectors, however, he fails to improve overall and remains sixth overall.

As Trulli goes fifth overall (13.016), Webber goes quickest in the middle sector, finally crossing the line at 12.604 to take the top spot. However, moments later Button up the stakes with a 12.523. Elsewhere, Trulli takes a trip through the Sao Paulo countryside.

At the wrong end of the timesheets we have the Renaults, the BMWs, Kobayashi and Nakajima. That said, the Top 13 are covered by just 0.791s.

Raikkonen goes quickest in the first sector, however, he has a poor middle sector and consequently fails to improve.

Hamilton, currently seventh, posts personal best in the first sector, however, he loses pace in the second and again in the third, consequently he fails to improve.

Buemi posts 12.512 to re-take the top spot, the Swiss driver on the option (super-soft) tyre.

Coming up to half-time, Trulli goes quickest in the second sector, crossing the line at 12.605 to go fourth.

At half-time, it's: Buemi, Button, Webber, Trulli, Vettel, Sutil, Kubica, Kovalainen, Hamilton and Liuzzi.

Though not known for doing a lot of running on GP Friday's Vettel has completed the most laps so far, the German having done 33 laps thus far. Red Bull teammate Webber has done 29. Grosjean and Alonso have done just 30 between them.

Rosberg moves up to fifth with a 12.633 as Kovalainen posts a personal best in the first sector.

Mindful of the fact that Sunday's race comprises 71 laps, a lot of drivers are on long runs, some on the prime tyres some on the option.

Alonso, now running on the option, moves up to twelfth with a 12.997. At which point the first spots of rain begin to appear on the camera lens on his Renault. However, it only appears to be falling (lightly) at a couple of corners (11 and 12).