J.P. Morgan analyst Mark Moskowitz says in a note to investors — as reported by “AppleInsider” (http://www.appleinsider.com) that checks with Apple’s supply chain indicate that the MacBook Air has continued to be a strong performer for Apple.

He says 420,000 MacBook Air units were shipped in the fourth quarter of calendar 2010, which represented growth of 333% year-over-year, and 326.8% quarter-over-quarter. The level was also three times greater than the product’s previous quarterly high. The number is also much lower than an estimate of over one million units given by another analyst in March, notes “AppleInsider.”

“We believe that the growth rate of the MacBook Air stands to moderate, but we expect the product to exhibit increasing contribution to the overall Mac business,” Moskowitz wrote. “(The fourth quarter of calendar 2010) was the first quarter in which the MacBook Air accounted for greater than 10% of total Apple Mac units. More importantly, the MacBook Air accounted for 15% of total notebook sales during the quarter, versus 5% in the prior year.”