Ahead of today's second practice session, the air temperature is 21.8 degrees C, while the track temperature is 29.2 degrees. It remains bright and sunny.
Sebastian Vettel topped the timesheets earlier, ahead of Max Verstappen, Lewis Hamilton and Valtteri Bottas. However, neither Mercedes driver tried the hypersoft compound.
Daniel Ricciardo was sidelined for much of the session, other than damaging his floor when running wide, the Australian's car was subsequently shrouded in smoke on its return to the pits.
With for reserve drivers on duty, this afternoon will see Perez, Ericsson, Sainz and Alonso get their first taste of Sochi 2018, a circuit which witnessed a number of incidents earlier as drivers struggled for grip.
Changes of engines and their various components means that no loss than five drivers are demoted to the back of the grid on Sunday, those five being the Bulls, the Toro Rosso duo and Alonso.
Ahead of the green light, Alonso and his teammate are already waiting at the end of the pitlane, they are followed by the newly-retained (for 2019) Haas duo.
Both duos are on different tyres, Alonso and Magnussen on softs and Vandoorne and Grosjean on ultras.
Vandoorne posts 37.819, Magnussen (37.936), Grosjean (40.866) and Alonso (55.422).
Hamilton is among the first to go wide, the Briton getting it wrong in T7.
Alonso improves to 39.933 but is demoted when Vettel stops the clock at 35.382. The German is on ultras.
A 36.686 sees Gasly go second, ahead of Grosjean, Magnussen, Leclerc and Vandoorne.
No sooner has Vettel improved to 34.984 than Verstappen posts a 34.433.
As Hamilton begins his first flying lap of the afternoon, Ricciardo goes third with a 35.574.
With barely a cloud in the sky, Raikkonen asks if it is raining as he has spotted some water on the track. The team confirms it is definitely not raining.
A 35.170 sees Hamilton go third, only to be demoted when teammate Bottas posts 34.643 to go second.
Verstappen ups the ante with a 34.164, as Raikkonen goes sixth with a 35.639, ahead of Gasly, Sainz, Leclerc and Hartley.
"I have a vibration," reports Vettel, and we suspect it's not a good one.
Unhappy with the handling of his car, Grosjean demands more laps.
On the ultrasofts, Hamilton improves to second with a 34.245.
Twenty-five minutes in and Ocon and Vandoorne have the track to themselves.
Though he has posted a time, and is currently fourth (34.927), Ricciardo is back in his garage and not looking to go out any time soon.
While Verstappen's pace-setting time was on hypers, the next four drivers were on ultras, while sixth placed Raikkonen posted his time on softs. Seventh-placed Gasly is the next highest hyper runner while thirteenth-placed Perez is the next best soft runner.
Verstappen improves to 34.079, increasing the gap to Hamilton to 0.166s.
Now on the hypers, Bottas goes quickest with a 33.584, despite an off in t final corner, as Hamilton also fits the pink-banded rubber. The Briton subsequently posts 33.548 to take the top spot.
Going quickest in S2, Bottas subsequently backs off, the Finn concerned at the temperature of his tyres.
Ericsson improves to sixth, as Vettel aborts his first flying lap.
Hartley is warned he is losing too much time in the middle sector as Leclerc runs wide in T5.
Gasly improves to seventh with a 35.137, the next eight drivers covered by just under a second.
At 'half-time', it's: Hamilton, Bottas, Verstappen, Ricciardo, Vettel, Raikkonen, Gasly, Ocon, Ericsson and Magnussen.
The McLaren duo appear to be helping one another with tows, first Vandoorne helps Alonso then the Spaniard reciprocates.
Attention now switches from qualifying to Sunday afternoon.
On the ultras, Verstappen is third, 0.442s off the pace, but let's not forget that grid penalty.
Instructed to make a number of changes to his steering wheel display settings, Verstappen reports back that its telling him there's a safety car.
Now on their longer runs, the Mercedes pair split strategies, Hamilton on ultras and Bottas on hypers.
Asked about balance, Verstappen reports that the "left-front is not good". Told to "stick with it", he replies "it's not easy to drive, that's the problem".
A spin for Vettel at T13 as the rear steps out. Though all is OK, he opts to head back to his garage.
Like his teammate, Ricciardo reports issues with his front-left. The Australian is on ultras but it is the hypers that are really degrading.
Not so Sainz however, who reports that his tyres are "coming back a bit".
Again, Vettel is unhappy that he finds himself in traffic.
"Something is broken," reports Stroll after an off over the kerbs, but the team feels it is actually graining that is causing him issues.
The session ends, Hamilton is quickest, ahead of Bottas, Verstappen, Ricciardo, Vettel, Raikkonen, Perez, Gasly, Ocon and Ericsson.
Magnussen is eleventh, ahead of Sainz, Leclerc, Hulkenberg, Grosjean, Hartley, Alonso, Vandoorne, Sirotkin and Stroll.
With the Bulls demoted, this weekend is very much Mercedes versus Ferrari, and on the evidence thus far the German team has the edge.
However, tyre strategy is clearly going to be an issue and it remains to be seen if Ferrari has learned from some of its recent mistakes.
Speaking to Sky Sports in the moments after the session, a downcast Vettel admits: "We've got some catching up to do".