Prestwick Airport, which is currently up for sale after its New Zealand-based owners said it was under-performing, has welcomed the extra Ryanair flights, which will launch next year.
As the no-frills firm announced the services to two Polish airports, it said a move to Glasgow International Airport had been ruled out.
The airline also unveiled six new routes from Edinburgh.
Tom Wilson, chief executive of Prestwick's owners, Infratil Airports Europe, said it would help reassure potential investors about the future of the Ayrshire hub, which was put up for sale in March.
He added: "This expansion is good news. Despite tough economic times we are actually seeing passenger numbers rise and it's good for the business and for Ayrshire and Scotland."
Ryanair is planning to increase the frequency of its existing services at both Edinburgh and Prestwick and reverse two years of decline in which passenger numbers have fallen by 18%.
At Edinburgh, it will launch new services to Bologna, Beziers, Cagliari, Corfu, Katowice and Santander, taking the total number of destinations to 38, while increasing flights from 232 to 246 a week.
Prestwick will see new routes to Rzeszow and Warsaw Modlin, taking the total to 27 routes and increasing the number of weekly flights from 86 to 95.
Overall passenger numbers in Scotland are expected to reach 3.2 million in 2013, an increase of 15% and just shy of the peak of 3.3 million seen in 2010.
Ryanair said the enhanced route network would deliver 400 new jobs between Prestwick and Edinburgh, though the industry formula it uses to calculate the figure has been widely described as overly optimistic in the past.
The announcement follows a turbulent few years for Ryanair, which cut its winter schedule at Edinburgh earlier this year following a disagreement over landing charges with the hub's previous owner, BAA, and has presided over a steep drop in passenger numbers at Prestwick.
The airline's chief executive Michael O'Leary, in Glasgow yesterday, admitted a deal struck with Global Infrastructure Partners (GIP), which took over the running of Edinburgh Airport in the summer, did not include the reduction in landing fees which he had tried and failed to secure with BAA.
But he said GIP, which also owns Gatwick Airport, was "committed to growth".
He blamed the downturn at Prestwick on increases in air passenger duty (APD), which is paid on all departing UK flights.
This had a particularly damaging impact on short-haul flights and spelled the demise of the Prestwick to Stansted service, he said.
"We haven't been growing significantly in Scotland in recent years and that's because APD has hit domestic aviation very strongly," Mr O'Leary said.
"Passengers are suffering both sides of the route – on the departure and return flight – and as a low-fare airline, the effect is even worse.
"We have been campaigning with the Scottish Government to have this changed. I'm a great believer in Scottish independence – as long as we get rid of APD, I'm all in favour of it."
Gordon Dewar, chief executive of Edinburgh Airport, said it was clear he had to repair the relationship with Ryanair when he was appointed.
"It's great to find a new, long-term relationship with what is the most important airline in terms of growth going forward," he added.
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