Identification of an Oct4 paralogue in chick

An El Niño (La Niña) event is a phenomenon in which SSTs are higher (lower) than normal across a wide area from the centre of the equatorial Pacific to the region off the coast of Peru for a period of between half a year and 1.5 years. El Niño and La Niña events occur once every few years and have an impact on global atmospheric and weather conditions.

34

The prominent El Niño and La Niña episodes in the tropical Pacific are defined using 3-month running mean Nino-3.4 SST anomalies and the following two criteria. (a) The maximum (minimum) SST anomaly exceeds one standard deviation (about 1.0°C), and (b) SST anomalies exceeding 0.5°C persist for at least 8 months. According to these criteria, seven major El Niño (1958, 1965, 1972, 1982/83, 1986/87, 1991/92, 1997/98) and five major La Niña (1970/71, 1973/74, 1975/76, 1984/85, and 1988/89) episodes are identified for the period from 1958 to 1998. (after Wang et al., 2000).

At our site, we findalthough annual averages are slightly lower during La Niña years, summer temperatures are above-average during La Niña years and below-average during El Niño years. For example during La Niña (El Niño July, August and September temperatures were 16.0°C (15.7°C), 18.8°C (17.8°C) and 15.2°C (15.6°C), respectively (Figure 2-17). These findings are also supported by a tree-ring temperature reconstruction in Hokkaido by Davi et al. (2002). The authors found that the temperature reconstruction was significantly and positively correlated with ENSO; with low summer temperatures linked to El Niño and higher summer temperatures linked to La Niña episodes.

Annual precipitation amount between El Niño, La Niña and average years were very similar. Slightly higher annual precipitation values occurred during La Niña years (1727mm) and slightly lower annual precipitation values occurred during El Niño years (1717mm), compared to average values (1723mm). However, it was notable that the months of increased precipitation were different in El Niño and La Niña years. For example, during El Niño years, rainfall increases in July, August and September from average (1958-2014) value of 158mm, 221mm and 249mm to 177mm, 254mm and 324mm, respectively (Figure 2-18). It is notable that increased precipitation in September is also associated with typhoon season in Japan (Lee, 1974, Nogami et al., 1980), suggesting that El Niño conditions influence the strength and/or occurrences of typhoons in this region. Previous studies have also found a connection between the strengthening of typhoons in Japan during El Niño years (Woodruff et al., 2009). Precipitation in January and February also increased during El Niño years. However, precipitation during spring and early summer is lower. We also found that snowfall increased in January and February, and decreased in March during El Niño years (Figure 2-18). During La Niña years, on the other hand, we found that precipitation was

35

increased in March, June and October and was lower in the remaining months (Figure 2-18). Annual snowfall amount was lower during El Niño years (306.4cm) than average years (318.9cm), however there was notably higher values in January and February (Figure 2-19). Annual snowfall amount was similar between La Niña years (318.5cm) and average years (318.9cm), however higher values were noted in March (Figure 2-19).

Figure 2-17: Monthly temperature averages during El Niño (small dashed line) and La Niña (large dashed line) years compared with average (1958-2014) monthly temperature values (solid line).

36 Figure 2-18: Monthly precipitation averages during El Niño (small dashed line) and La Niña (large dashed line) years compared with average (1958-2014) monthly precipitation values (solid line).

Figure 2-19: Monthly snowfall averages during El Niño (small dashed line) and La Niña (large dashed line) years compared with average (1958-2014) monthly snowfall values (solid line).

37

2.2.4.1 ENSO and the EASM

El Niño has been identified as a strong influence on the intensity of the EASM (e.g. Zhang et al., 1996, Wang et al., 2003, Hong et al., 2005). However, classifying EASM intensity simply according to strong El Niño years is not meaningful because the influence of El Niño on the intensity of the EASM occurs in the summer after El Niño reaches its mature phase, rather than the actual year when El Niño develops (Wang et al., 2001). A suggested reason for this is due to the westward movement of the western NPSH in the summer following the mature phase of El Niño, which in turn enhances the EASM (Wang et al., 2001). We find that when we separate El Niño developing years (e.g., 1965, 1968, 1972, 1976, 1982, 1986, and 1997; after Wang and Chan, 2002) and the years after the mature phase of El Niño (e.g., 1970, 1983, 1992, 1995, and 1998;

after Wang and Chan, 2002) there is a clear difference in the intensity of the EASM (Figure 2-20). In the years following the mature phase of El Niño, we find that precipitation at our site increases in June (Baiu precipitation) and August (Shurin precipitation); which is associated with EASM precipitation. However, in El Niño developing years, we find that precipitation is lower in June and August.

Temperature also slightly increased in August and September during the summer following the mature phase of El Niño compared to El Niño developing years. In August and September, temperature was 18°C (17.8°C) and 15.6°C (15.4°C), respectively during the mature phase and developing phase of El Niño. This suggests that during El Niño developing years, El Niño has no influence on the EASM intensity, however, in the summer following the mature phase of El Niño, the EASM intensity increases.

38 Figure 2-20: Monthly precipitation averages during the summer following El Niño (small dashed line) and El Niño developing (large dashed line) years compared with average (1958-2014) monthly precipitation values (solid line).

2.2.4.2 ENSO and the EAWM

The EAWM is weak during El Niño years and strong during La Niña years (Tomita and Yasunari, 1996, Zhang et al., 1996, Chen et al., 2000, Chen et al., 2013, Chen et al., 2014, Wang and Chen, 2014). We identified that a strong EAWM results in increased snowfall, particularly during the month of March (Figure 2-7). We find that during La Niña years snowfall in March increases, suggesting that the EAWM is stronger during La Niña years. A suggested reason for La Niña positively influencing the EAWM is due to the correlation between ENSO and the inter-annual variation of winter northerlies and cold surges near the South China Sea (Zhang et al., 1997). La Niña conditions result in cooling over the equatorial Eastern Pacific, however the western Pacific is not influenced by this cooling and therefore remains warm during La Niña conditions (Chen et al., 2000) During La Niña events, the occurrence of East Asian cold surges increases and also the strength of the northerlies increases (Zhang et al., 1997), this triggers a decrease in temperature in East Asia. As a result, there is a large land-sea thermal contrast during La Niña conditions which results in a movement from the Asian continent towards Japan.

39

2.2.5 Summary

Table 2-1: Sumary table detailing the average temperature, precipitation and snowfall change during stron/weak EASM/EAWM years, the positive and negative phase of the AO/NAO and the PDO and also during El Niño and La Niña years. Average annual values between 1958 and 2014 provided in bold.

Temperature

change Error Precipitation

change Error Snowfall

change Error Average

(1958-2014) 6.8°C ±0.6°C 1723mm ±303mm 319cm ±88mm

Strong EASM No change ↑126 mm ±343mm

Weak EASM ↓0.3°C ±0.7°C ↓115 mm ±100mm

Strong EAWM ↓0.5°C ±0.6°C ↓237 mm ±277mm ↑8cm ±52cm

Weak EAWM ↑0.2°C ±0.3°C ↑114 mm ±282mm ↓31cm ±55cm

Positive AO/NAO ↑0.7°C ±0.5°C ↑48 mm ±363mm Negative

AO/NAO ↓0.1°C ±0.6°C ↓48mm ±297mm

Positive PDO ↓0.6°C ±0.3°C ↓185mm ±268mm Negative PDO ↓0.2°C ±0.5°C ↑ 20mm ±270mm

El Nino No change ↓6mm ±360mm ↓13cm ±70cm

La Nina ↓0.2°C ±0.5°C ↑ 4mm ±404mm No

change