Impacts of MJO convection over the Maritime Continent on eastern China cold temperatures Lei Song and Renguang Wu Email: [email protected]; [email protected] Center for Monsoon System Research, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China How can the tropical convection over the Maritime Continent influence cold anomalies over eastern China? What is the difference between the process of the influence by the convection over the tropical Indian Ocean and the Maritime Continent on the happening of cold anomalies over eastern China ? Questions Introduction Previous studies have indicated that tropical convection over the Indian Ocean can exert influence on the occurrence of cold anomalies over eastern China. It is not clear if the tropical heating over the Maritime Continent can lead to robust cold anomalies over eastern China. Data and methodology Summary The anomalous convection over the Maritime Continent can work together with the negative AO in the occurrence of MC convection related cold events over eastern China. The IO convection related cold events over eastern China are caused by both the tropospheric Rossby wave train propagating along the polar front and the poleward wave train trigged by anomalous convective heating over the tropical Indian Ocean. Anomalous overturning circulations caused by the MC and IO convections lead to the development of the Siberian high. Daily NCEP-DOE Reanalysis 2 data (Kanamitsu et al. 2002) from 1979 to 2016 during boreal winter (December-January- February) RMM index (Wheel and Hendon 2004) Daily AO index 30-60-day band-pass filter Selection of the tropical Indian Ocean (IO) convection and the Maritime Continent (MC) related cold events over eastern China Features of the MC and IO convection related cold events Figure Composite surface air temperature anomalies (shading, ° C) from 20° N to 70° N and longwave outgoing radiation (OLR) anomalies (shading, W/m2) between 20° S and 20° N on days (a) -12, (b) -9, (c) -6, (d) -3, (e) 0, (f) 3, (g) 6, (h) 9 of MC (left) and IO (right) convections related intraseasonal cold events over eastern China. The upper color bar is for the temperature anomalies and the lower color bar is for the OLR anomalies. Black dots indicate anomalies significant at the 95% confidence level. The negative AO and the convection anomalies over the Maritime Continent work together in the occurrence of MC convection related cold events over eastern China Figure Time evolution of regional mean surface air temperature anomalies (° C) (red curve) over the region of 20° N-40° N and 100° E-120° E, OLR anomalies (W/m2) (black curve) over the Maritime Continent (15° S-15° N, 110° E- 160° E) (a) and the Indian Ocean (15° S-15° N, 50° E-100° E) (b), the Siberian high index (hPa) (blue curve) and the AO index (green curve) during the life cycle of the MC (a) and IO (b) convection related cold events. Dots on the curves indicate anomalies significant at the 95% confidence level. This study is supported by the National Natural Science Foundation of China grants (41705063, 41530425, 41775080, 41721004, and 41475081). Figure Composite sea level pressure anomalies (shading, hPa) and surface wind anomalies (vector, scale on right bottom) on days (a) - 12, (b) -9, (c) -6, (d) -3, (e) 0, (f) 3, (g) 6, (h) 9 of MC (left) and IO (right) convections related intraseasonal cold events over eastern China. Black vectors denote wind anomalies significant at the 95% confidence level. Figure Composite OLR anomalies (shading, W/m2) between 20 ° S and 20° N, stream function anomalies (contour, blue and red contours indicate negative and positive anomalies, respectively, interval: -8, -6, -4, -3, -2, -1, 1, 2, 3, 4, 6, 8 × 10 6 m 2 /s 2 ), and wave activity fluxes (m 2 /s 2 ) (vector, scale at the right-bottom) at 300- hPa on days (a) -12, (b) -9, (c) -6, (d) -3, (e) 0, (f) 3, (g) 6, (h) 9 of MC (left) and IO (right) convection related intraseasonal cold events over eastern China. Figure Composite anomalies of vertical circulation consisting of divergent meridional wind (m/s) and vertical p-velocity (0.01 Pa/s) along 110° E-140° E of MC (left) and IO (left) convection related intraseasonal cold events over eastern China. Only the anomalies significant at the 95% confidence level are plotted. Anomalous heating over both the Maritime Continent and the tropical Indian Ocean can induce anomalous upper-level convergence and anomalous descending motion over the mid-latitudes through anomalous meridional overturning circulation, which leads to enhancement of the Siberian high. Song, L. and R. Wu, 2019: Impacts of MJO convection over the Maritime Continent on eastern China cold temperatures. J. Climate, https://doi.org/10.1175/JCLI-D-18-0545.1