Perturbations in upper tropospheric easterlies and Bay cyclones

Pertu rbat ions in th e form of large amplitude troughs or dosed circu lation s are absen ted todevelop in the weak upper tro posph eric easterlies at 200 and 100 hPs levels over no rthwest Pacific am! adjoiningIndi an Ocean. Occasionally, these are 2 to 3-C colder than their immediate enviro nme nt. These systems areobserved 10 propagate downwards durina their westwa rd tr aversal : while ove r 500 h Ps th ese in teract with andactivate the lower troposph eric cyclonic circ ula tion to intensify into a depression/cyclonic stem}. At this stage, thecyclonic:ci rcu l" tion in upper tropo sph eric levels is observed 10 vanish: this may, however. re-appear subseq uently onfUl1ho r int ensification of the cyclonic sto rm . Evidence of such interaction a nd intensification is adduced with a fewt)'pica) synoptic systems .