The Russians have been moving aircraft into their new base just south of Latakia, Syria. The nature and numbers of these aircraft make Russian intentions a lot clearer.
The planes that have been generating the most comment in the Western press are 4 advanced SU-30 multirole fighters. While capable of ground attack, these are primarily air-superiority fighters. The Russians also have an unknown number of surface-to-air missiles set up at the base. Western newspapers point out that ISIS has no real air force and are quick.to suggest that the Russians intend to challenge the anti-ISIS air coalition.
The Pentagon says however that these kind of assets appear consistent with force protection, able to raise the cost for anyone who tries to attack the Russian base from the air, but not sufficient to challenge the coalition aircraft attacking ISIS. The Russians appear to have moved several hundred naval infantry (marines) to the base as well, along with 6 top-of-the-line tanks, about 35 armored personnel carriers and several artillery batteries, which also appear to be intended for force protection and base security. It makes sense, seeing as how a number of Assad military bases have been attacked by rebels and overwhelmed (sometimes leading to mass killings of captured POWs). Jaish al Islam says that it attacked the Russian base in just the last few days, boasting of destroying a Russian transport aircraft with a rocket. Satellite imagery reportedly shows no signs of damage at the base and Russian activities continue.
Ok, if we've established that the Russians want to protect their base, what do they intend to use the base for? The rest of their aircraft inventory gives some indication of that.
September 20 satellite imagery shows 12 SU-25 ground attack jets. There also appear to be 15 MI-24 Hind attack helicopters.
Video on the internet seems to show 4 SU-24 long range attack jets flying over Syria, and leaks from US intelligence suggest that 12 of these planes have arrived in Syria subsequent to Sept 20.
All of this amounts to 43 aircraft total, of which 39 are ground attack jets and helicopters. So pretty clearly, the Russians intend to be flying air support for the Syrian army.
https://www.stratfor.com/analysis/russian-fighter-aircraft-arrive-syria