A Precursory Signal of June–July Precipitation over the Yangtze River Basin: December–January Tropospheric Temperature over the Tibetan Plateau

Abstract: The prediction of summer precipitation over the Yangtze River basin (YRB) has long been a challenge, especially during June–July (JJ) when the Meiyu generally occurs. This study explored the potential signal for the YRB precipitation in JJ and revealed that the Tibetan Plateau tropospheric temperature (TPTT) in the middle and upper levels during the preceding December–January (DJ) is significantly correlated with JJ YRB precipitation. The DJ TPTT anomaly is closely connected with the JJ one, which may be due to the joint modulation of the DJ ENSO and spring TP soil temperatures. As a result, corresponding to a lower TPTT during the preceding DJ, the TPTT is still lower during the following JJ. The lower TPTT can lead to an anomalous anticyclone to the east of Lake Baikal, an anomalous cyclone at the middle latitudes of East Asia, and an anomalous anticyclone over the western North Pacific. Meanwhile, the East Asian westerly jet shifts southward, which is due to the meridional thermal gradient caused by the colder troposphere extending from the TP to the east of Lake Baikal. The abovementioned circulation anomalies constitute the positive anomaly of the East Asia-Pacific pattern, conductive to more precipitation over the YRB. Since the DJ TPTT contains both the land (TP soil temperature) and ocean (ENSO) signals, it has a closer relationship with the JJ precipitation over the YRB than the DJ ENSO. Therefore, the preceding DJ TPTT can be considered as an alternative predictor of the JJ YRB precipitation.

Keywords:
• Tibetan Plateau,
• thermal condition,
• Yangtze River,
• precipitation,
• prediction