Features of climate system since 2016 winter 签发 Zunya Wang, Yongguang Wang, Yuan Yuan National Climate Center, CMA 2017.4.26

Contents Circulations and East Asian winter monsoon SST Snow cover Sea ice

500-hPa geo-potential height anomalies Winter of 2016/2017 3-wave pattern is obvious, with the deep troughs over northern North America, central northern Pacific and Europe. Deep trough is over the Ural mountain and high ridge covers most of Asia. The straight and smooth airflows prevail over mid-high latitudes of Asia.

Positive phase of AO continued. Weak trough controlled most East Asia. After Mar. 1, 2017 Positive phase of AO continued. Weak trough controlled most East Asia. East Asian major trough intensified.

AO and blocking Blocking Positive phase of AO dominated. AO持续正位相，改为AO以正位相为主；增加AAO，最好有指数曲线，不然用环流距平 Positive phase of AO dominated. Ural blocking was inactive, while Okhotsk blocking was active periodically.

500-hPa geo-potential height anomalies over southern hemisphere AAO 500-hPa geo-potential height anomalies over southern hemisphere AAO maintained negative phase during winter and turned to positive phase after early March.

Western Pacific subtropical high Winter of 2016/2017 Intensity After Mar. 1, 2017 Western position of the ridge

The weakest in recent 10 years Siberian high is weaker than normal Intensity index of Siberian high The weakest in recent 10 years

Weak southerly anomalies are observed. Cold air is not so active. 850-hPa wind anomalies Less cold air activities A C Weak southerly anomalies are observed. Cold air is not so active. Winter meridional wind averaged over eastern East Asia at 850 hPa level

Intensity index of East Asian winter monsoon Intensity of EAWM ranks the weakest in recent 10 years Intensity index of East Asian winter monsoon （1951/1952-2016/2017）

Surface air temperature anomalies during 2016 winter 我拿到服务室的一个材料，冬温-1.5度，偏高1.9度 Most parts of the whole world were warmer than normal； 1-3℃ higher than normal over most parts of East Asia.

Anomalies of underlying surface

Sea Surface Temperature NINO 3.4 index reaches 0.11℃ warm conditions dominate central-eastern equatorial Pacific Variations of Niño 3.4 SSTA indices and SOI The below-average sea surface temperatures (SSTs) in the central-eastern equatorial Pacific, which began in June 2016, increased gradually after October 2016. Since February 2017, above-average SSTs have developed in the central-eastern equatorial Pacific again. Recently, warm conditions dominate most central-eastern equatorial Pacific with the Nino 3.4 index being 0.11℃ in March 2017. Sea surface temperature anomalies in March 2017

Indices of key oceanic regions IOD可以不要，增加黑潮指数 Weak negative phase of IOBW Increasing positive SIOD

Posititve NAT index is increasing.

PDO maintains the positive phase

2016 autumn Snow cover Since autumn of 2016, the number of days with snow cover has been more than normal in Eurasia. In Mar. 2017, snow cover over Europe was below normal. Mar. 2017 2016 winter

Snow Cover in China The number of days with snow cover is above normal in Xinjiang and Northeast China and near normal in the Tibetan Plateau. 有2月资料吗？高原积雪偏少吗？

Sea ice anomalies in 2016 Winter Northern hemisphere Southern hemisphere W90° 0° E90° 180° 40°S 50°S 60°S 70°N E90° 0° W90° 180° 40°N 50°N 60°N 70°N 只有90度（1-180之间）可以标注E Sea ice concentration was below normal in most parts, except in the southeastern Indian Ocean and some parts of the Weddell Sea and Amundsen Sea. Below-normal sea ice concentration covered almost all regions.

Variation of sea ice during winter Data source：NCEP Data source：NSIDC

Sea ice anomalies in March 2017 W90° E90° 0° 180° 0° 180° W90° E90° Below-normal sea ice concentration still persists.

Conclusions Positive phase of AO and negative phase of AAO dominate. Straight and smooth airflows prevail over mid-high latitudes of Asia. Intensity of Siberian high is weak. EAWM ranks the weakest in recent 10 years. It is warmer over most East Asia. Warm condition dominates most equatorial Pacific. Positive phase of SIOD and NAT both has been developing. Snow cover is more than normal over northern hemisphere. Arctic and Antarctic sea ice both rank the least since 1978.

Thanks！