Complex sentence: A second factor which contributes to jet sharpness is more appropriate for the subtropical jet, which forms at the poleward limit of the tropical Hadley cell and to first order this circulation is symmetric with respect to longitude.
Split into simpler sentences: A second factor which contributes to jet sharpness is more appropriate for the subtropical jet. The subtropical jet forms at the poleward limit of the tropical Hadley cell and to first order this circulation is symmetric with respect to longitude.