Precipitation variations of Longxi, northeast margin of Tibetan Plateau since AD 960 and their relationship with solar activity

The precipitation variations of Longxi area, northeast margin of the Tibetan Plateau since AD 960 are reconstructed from Chinese historical documentary records. These records show that since AD 960, the precipitation of Longxi decreased and reached the lowest level at the end of the 17th and the 18th centuries. After this period, the precipitation gradually increased. The three short wet periods of Longxi in the last millennium were: from the end of the 10th century to the early years of the 11th century, from the end of the 12th century to the early years of the 13th century and during the first half of the 20th century. The precipitation variations coincide well with variations of the Northern Hemisphere temperature and the atmospheric 14C concentration, as well as the averaged 10Be concentration and the reconstructed solar modulation record which show that solar activity may be an important driving force of the precipitation variations of Longxi on multi-decadal to centennial scales during the last millennium. Solar activity controls the motion of the north edge of the Asian summer monsoon by affecting the Asia summer monsoon intensity, the East Asian winter monsoon intensity and the locations of westerlies, thus further dominating precipitation variations of Longxi. Synchronous variations of Longxi precipitation and Northern Hemisphere temperature may also be ascribed to the same control of solar activity.