Stronger local overturning in convective-permitting regional climate model improves simulation of the subtropical annual cycle

Journal article

Global climate models fail to represent the annual cycle of tropical-extratropical cloud bandsand produce too much summer rainfall over subtropical southern Africa. This study demonstrates thatrunning a regional convective-permitting climate simulation alleviates these biases, counteracting biasesthat are present in the parent model. The improvement emerges from stronger vertical mass flux in thetropics, which forces a stronger local Hadley overturning into the summer hemisphere. This enhancedoverturning increases upper-level subsidence in the subtropics and amplifies the forcing of the localsubtropical jet. Together, these improvements halve the wet subtropical rainfall bias and are associatedwith a 50% increase to an 80% match bet ween the simulated and observed annual cycle of crucialtropical-extratropical cloud band rainfall systems. The results advocate for the increased use ofconvective-permitting climate models with domains that include regional tropical convection hot spots, inorder to fully benefit from the explicit representation of deep convection.

Authors: Hart, N; Washington, R; Stratton, R

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: American Geophysical Union
• Journal: Geophysical Research Letters
• Volume: 45
• Issue: 20
• Pages: 11,334-11,342
• Publication date: 2018-10-09
• Acceptance date: 2018-10-05
• DOI: 10.1029/2018GL079563
• EISSN: 1944-8007
• ISSN: 0094-8276
• Keywords: convective‐permitting; tropical‐extratropical interactions; Hadley cell; model bias; regional climate; climate modeling