Monsoon dynamics: An idealized GCM results Precipitation a 30N Numerical results from idealized aqua-planet model: ocean surface all the globe .no orography only vary depth of the ocean mixed 30S OBS layer b 20 20 30N Model Hsur=1m 10 OBS (s w)n 0 Hsur=100m -10 30S Hsur=1m 0 90 180 270 360 Day Julian Day A monsoonal circulation can observed only (Bordoni and Schneider,2008,nature-geosci.) when the surface heat capacity is small enough. 授课教师： 张洋3授课教师：张洋 13 Monsoon dynamics: - An idealized GCM results x 20 12 x 12 x Figure 1: Rapid shifts of precipitation zones. Seasonal cycle of zonal- and pentad-mean pre￾cipitation (color contours, mm day−1) and sea-level air temperature (SAT) (grey contours) from observations in the Asian monsoon sector (a) and from aquaplanet simulations with ocean mixed￾layer thickness 1 m (b) and 100 m (c). SAT is evaluated at 1000 hPa in the observations and at the lowest model level in the simulations. The contour interval for precipitation is 1 mm day−1 in (a) and 2 mm day−1 in (b) and (c); for SAT, it is 2◦C, with the solid grey line marking the 24◦C isoline. Precipitation rates in the simulations can exceed observed precipitation rates be￾cause the lower boundary in the simulations is entirely water-covered. The thick dashed line in (a) shows the latitude at which the zonal-mean topography in the Asian monsoon sector rises above 3 km. Arrows at the time axes in (a) and (b) indicate the centers of the 20-day periods for which circulations are shown in Figs. 2 and 4. Observed precipitation is from Global Precipitation Cli￾matological Project29 data for the years 1999–2005. In this and subsequent figures, zonal means for the Asian monsoon sector are averages between 70◦–100◦E. Results are robust to changes in the averaging sector and do not change substantially if Southeast Asia is included in the averages. 13 Numerical results from idealized aqua-planet model: •ocean surface all the globe •no orography •only vary depth of the ocean mixed layer Hsur=1m Day OBS Model Figure 3: Rapid changes in near-surface zonal wind at 15◦N. Seasonal cycle of zonal- and pentad-mean near-surface zonal wind at 15◦N from observations in the Asian monsoon sector (green) and from aquaplanet simulations with ocean mixed-layer thickness 1 m (yellow) and 100 m (orange). The near-surface zonal wind is evaluated at 850 hPa in the observations and at σ = 0.85 in the simulations, where σ = p/ps is pressure p normalized by surface pressure ps. 15 OBS Hsur=1m Hsur=100m Precipitation A monsoonal circulation can observed only when the surface heat capacity is small enough. (Bordoni and Schneider, 2008, nature-geosci.)