Rising/Falling diphthongs

I found an old msg. of Trebor Jung's concerning this terminology, which was
never properly answered, and got to wondering:

Are things like [aj] [oj] [iw] etc. (Vowel +glide) called "falling
diphthongs"?  I believe they are.

Converserly, then, [ja] [jo] [we] are called "rising" diphthongs, I believe.

AIUI, it's the Vowel > glide vs glide > vowel makeup that's the determining
factor, rather than the articulatory positions of the vowel/glide
components. One could, after all, envision diphthongs with _central/low_
glides-- [i_@, @_o]; Thai IIRC has diphthongs like [1_a] (high central V +
low glide).

What say you all? In particular, what says Trask's Dictionary, or the other
one that's often cited (whose author I disremember).

Thanks.

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