Snow anomaly events from historical documents in eastern China during the past two millennia and implication for low‐frequency variability of AO/NAO and PDO

Abstract

Models and instrumental data indicate that the spatial and temporal variations of snow cover are significantly related to atmospheric circulation (e.g. the AO/NAO). Here, we present historical snow anomaly events during the past two millennia that provide a unique temporal window to studying long‐term AO/NAO, a prominent phenomenon in wintertime. Direct descriptions such as “no snow during the winter” and “pray God for snow” are interpreted as convincing evidence for snow anomalies. The variations of positive/negative snow abnormal events show clear decadal to century variations during the past two millennia. Based on the previous instrumental research and comparison with other reconstruction data, we suggest the Index of Abnormal Snow (IAS) may be an AO‐like atmospheric variability. The winter during the Medieval Warm Period (MWP) (AD 900–1300) might be strongly influenced by a predominantly positive AO with less snow condition, whereas the Little Ice Age (LIA) (AD 1300–1900) by negative AO concomitant with heavier snowfalls in East Asia. Our data show that a warm climate period (the MWP)/a cold period (the LIA) can be perturbed by a cold spell/a warm spell which are linked with a change in atmospheric circulation. Low‐frequency variability of snow records may be intrinsic to the natural climate system. Although the dynamic mechanisms linking snow anomalies with atmospheric circulation (the AO/NAO, the PDO) is unclear on the decadal to century time scales, Pacific Ocean may play an important role in regulating atmospheric circulations since the IAS is highly correlated with the reconstruction of PDO.

A 1000-year chironomid-based salinity reconstruction from varved sediments of Sugan Lake, Qaidam Basin, arid Northwest China, and its palaeoclimatic significance

“…First, the southward shift of the westerlies and the stronger pole-equator thermal gradient, associated with low temperatures during the LIA, could have resulted in an increase of cyclonic activity over the mid-latitudes and thus more precipitation [57,58] . Second, the predominantly negative NAO winter index during the LIA [59] could have lead to an increase in precipitation at mid-latitudes of continental Asia. This inverse association was suggested by statistical analyses of meteorological data from relevant hydro-climatic stations [60] .…”

Relationship between NAO and drought disasters in northwestern China in the last millennium

“…to reduce the bias of abundant historical documentation over time (see Chu et al, 2008), where NDA is the number of years with negative drought anomalies per decade, PDA is the number of years with positive drought anomalies per decade, and x represents a threshold which defines the drought anomalies. For IDA 1 , only drought that reached Grade 1 or above would be considered as positive drought anomalies.…”

Natural disasters in northwestern China, AD 1270–1949

“…Because previous research showed a significant relationship between atmospheric circulation and the precipitation anomalies over China (Xin et al 2006, Su & Wang 2007, Chu et al 2008, Wei et al 2008, we hypothesized PC2 to be related to atmospheric circulation, and we compared it with some general atmospheric circulation parameters in the Northern Hemisphere for verification. Three atmospheric circulation parameters were selected to investigate their possible influence on PC2 in the GNQR.…”

“…Although much attention has focused on the disasters (flood and drought in particular) in eastern and southern China (Liu et al 2001, Jiang et al 2005, Stige et al 2007, Chu et al 2008, Zhang et al 2008b, 2009, Yin et al 2009), few studies have carefully considered the disasters in northwestern China. This phenomenon may be attributable to the fact that historical documents are less abundant in northwestern China than in eastern and southern China.…”

“…Although historical records may be biased by the perception of different observers, they provide both reliable time scales of and direct information about the disasters. Also, their easy availability is an asset (Glaser & Stangl 2003, Chu et al 2008.…”