Rather than Sonic Sparkleboom it is a Twilight Starburst.



For one, we don't hear a BOOOOOOOOOOOOOOOOMing sound like with RD's Sonic Rainboom.

Also there's no air shockwave messing with manes and trees like when RD breaks through the soundbarrier.

Next while such a circluar wave of colors is "possible" (as in more possible than a starshaped one) such a starshaped can't be made with speed.

Add to that that Twi's purple Star was gone very quickly unlike RD's rainbow circle which stayed and spread afar for quite a while.

Plus there's the fact that Twi channeled magic on her horn before she took flight.

And then we need to consider that her element is magic and she trained magic her entire life while RD trained her entire life speed and such.

Given that we have words from the creators that Twi's "Sonic Rainboom" is in truth a spell made by her while she just flies straight ahead, this all points us to one conclusion:



Twilight never flew a "Sonic Sparkleboom" (which we all could have guessed anyway with her lacking speed and experience in flying, after all RD needed YEARS and a friend falling to her death to be able to do the Sonic Rainboom for a second time!), but instead used a spell with her immense magic to create a flashing star as symbol of the Twilight arriving and passing in an instant as Princess Luna and Celestia sink the moon and raise the sun together for the first time in a thousand years (cause normally we see the sun settle first and then the moon raise while here we see the two orbs passing each other with Twi flying through them the moment they pass each other!!!).



So we shouldn't compare it to RD'S speedy Rainboom and rather to Trixie's fireworks which are also flashy stuff made into the sky via spell/magic. Thus, if you don't mind, I would propose to name Twi's spell/display of her magic "Twilight Starburst" as in my first sentence.^^