Daniel Ricciardo tops the Thursday morning timesheets in Spain as F1 rediscovers the phenomenon of 'porpoising'... and we're not talking Flipper!

As was the case on Wednesday, a McLaren driver was first out on track this morning to get proceedings underway, only in this case it was Daniel Ricciardo.

And while teammate Lando Norris toped the timesheets on the opening day, Ricciardo heads into the lunch break as this morning's pace setter.

However, the big issue today was the reappearance of porpoising... and we're not talking Flipper.

The issue was first notice yesterday afternoon when Lewis Hamilton experienced issues, and this morning a number of other teams, including Red Bull, were experiencing the same.

Porpoising was peculiar to ground effect cars when they previously raced in F1, and is the result of airflow separation causing the cars to bounce and rock. Having only run this new generation of car on simulators or in the windtunnel the effect hadn't come to light, but it is now clear that the teams have a problem on their hands.

The solution is to try and harmonise the air flow between the front wing and floor in order that it doesn’t separate and instead keeps the car bolted to the ground, and as a result a number of teams have modified their floors overnight, while others have brought in new floors from their factories.

It’s been suggested that ‘porpoising becomes less noticeable when DRS is open – however, that’s not going to be a long term solution.

Such was the concern that in the opening phase of the session - where once again the aero rakes were much in evidence - lap times were way off the pace as drivers were ordered to slow on the pit straight as the teams studied the phenomenon.

Another issue noticed this morning is that some cars are also bottoming out, particularly noticeable at Turn 1, while the German media is reporting that getting down to the new minimum weight (795 kg) is proving to be an issue for some teams and as a result some are running 10 kg or more above it.

This morning saw the first red flag of the test, with Sergio Perez grinding to halt at Turn 13 just over half-an-hour before the break.

Following yesterday's issues, things appear a lot better for Haas, with Mick Schumacher completing 66 laps and posting the sixth best time of the morning.

However, Alfa Romeo's issues continue and as a result Valtteri Bottas has completed just 21 laps.

As was the case yesterday, McLaren and Ferrari look good, while it has been a return to earth with a hefty bump for Red Bull.

Esteban Ocon was the early pace setter before Lance Stroll and then Carlos Sainz went quicker, only for Ricciardo to top them all.

The C3 tyre is still the preferred option, but Hamilton and Perez were the main exceptions.

There is uncertainty over tomorrow's weather, and while there is talk of rain it has been said that if it remains dry the track will be artificially dampened in order to allow some wet running.

A number of teams witness a change of driver this afternoon, most notably Alfa Romeo where Guanyu Zhou will make his official debut.

Check out our Thursday gallery from Barcelona, here.