|TITLE||SUBTROPICAL JETS AND RAINFALL OVER CHILE AND WESTERN US IN RESPONSE TO PALEOCLIMATE FORCINGS|
|AUTHORS||JCH Chiang (1), SY Lee (2), F Lamy (3), JHC Bosmans (4)|
- University of California, Berkeley, USA
- Academia Sinica, Taipei, Taiwan
- Alfred Wegener Institute, Bremerhaven, Germany
- Utrecht University, Utrecht, The Netherlands
|ABSTRACT||One of the pervasive ideas from paleoclimate studies is the meridional shift in the tropical rainband in response to interhemispheric contrasts. The question we ask is if there are subsequent changes to the atmopsheric circulation from the rainband shift: we audition the subtropical jet and its impact on Mediterranean rainfall climates as a direct consequence. A simulation imposing cooling in the North Atlantic - simulating a North Atlantic stadial - leads to a southward ITCZ displacement in the tropical Pacific and a weakening of the South Pacific subtropical jet and strengthening of the North Pacific subtropical jet; they in turn lead to reduced winter rainfall over subtropical Chile and increased rainfall over the western US. The changes to the South Pacific westerlies takes the form of a weakening of the South Pacific Split Jet, seen in today’s interannual variability of the Southern Hemisphere wintertime westerlies.
Changes to the North and South Pacific subtropical jets, and commensurate impacts on the winter rainfall over the subtropical western US and Chile, also occurs in coupled model simulation altering the phase of precession. However, the phasing of the response is somewhat counterintuitive, with the maximum subtropical jet over the South Pacific occurring when perihelion occurs during the Southern Hemisphere summer solstice, rather than during the Northern Hemisphere summer solstice. We attribute this behavior in part to the alteration of the phase of the Eastern Equatorial Pacific cold tongue with precession, and consequent impact on the South Pacific westerlies.|