Assessment of GA4/GL4/GO4/GSI4 and progress in ... - Met Office

Figure 2: DJF precipitation <strong>in</strong> N96 AMIP simulation.The changes to convective cloud condensate <strong>and</strong> improved representation <strong>of</strong> fall<strong>in</strong>gice have <strong>in</strong>creased the tropospheric humidity, improv<strong>in</strong>g the relative humiditystructure <strong>in</strong> the tropics, but <strong>in</strong>creas<strong>in</strong>g the moist bias <strong>in</strong> the southern mid-latitudes.3.2 Global ocean biases assessment & PEG reportThe climatological mean SST bias is generally similar between GA3 <strong>and</strong> <strong>GA4</strong> with aSouthern Ocean warm bias <strong>and</strong> North Atlantic cold bias. The large North Atlanticcold bias <strong>in</strong> GA3 N96ORCA1 is reduced <strong>in</strong> <strong>GA4</strong> (Figure 3), although the LabradorBas<strong>in</strong> rema<strong>in</strong>s cooler than configurations us<strong>in</strong>g the higher ocean resolution(ORCA0.25) which is able to capture the turn <strong>of</strong> the North Atlantic current aroundNewfoundl<strong>and</strong>. The reduction <strong>in</strong> this cold bias is, <strong>in</strong> part, due to the fix<strong>in</strong>g <strong>of</strong> a bugaffect<strong>in</strong>g the SW flux at coastal sea-ice po<strong>in</strong>ts, however a sensitivity test has shownthat this change alone cannot fully expla<strong>in</strong> the SST improvement.