**2.2 Results**

In 2010, record heat and sunshine occurred in Japan because a strong North Pacific High covered the country during summer. The total solar radiation between 0000 and 1200 during the flower opening time observation periods ranged from 1.0 to 13.3 MJ m−2. Sunshine hours in the former and latter halves of August 2010 were 6.58 and 9.75, respectively. The normal sunshine hour in August is 6.47. This suggests that average solar radiation during the flower opening time observation periods was higher than usual in that year. The vapor-pressure deficit between 0000 and 1200 during the flower opening time observation period ranged from 1.9 to 18.3 hPa.

The maximum and minimum air temperature between 0000 and 1200 during the flower opening time observation period ranged from 24.6 to 36.7°C and from 19.4 to 27.3°C, respectively (Fig. 2). In particular, the mean air temperatures between the latter part of July and August in 2010 reached record-high levels. The maximum and minimum air temperature increased rapidly from mid-July through early August. The maximum air temperature was higher than 34°C (temperatures >34°C at the time of flowering may induce flower sterility and decrease yield) for 23 days, however, in normal years, the maximum air temperature was rarely higher than 34°C.

Fig. 1. Total solar radiation and average vapor-pressure deficit between 0000 and 1200 during the observation period.

Fig. 2. Maximum and minimum temperatures between 0000 and 1200 during the observation period.

Average wind speed and atmospheric pressure ranged from 0.0 to 1.4 m s−1 and from 1001 to 1017 hPa, respectively, between 0000 and 1200 during the flower opening time observation period. The wind speed and atmospheric pressure were stable because a strong North Pacific High covered Japan during the summer of 2010.

Significant correlations existed between the meteorological variables. In particular, the correlation between air temperature and vapor-pressure deficit was high (r = 0.715, *p* < 0.001). The correlation between solar radiation and air temperature and that between solar radiation and vapor-pressure deficit were also relatively high (r = 0.532, *p* < 0.001; r = 0.664, *p* < 0.001, respectively). Wind speed and atmospheric pressure had relatively weak correlations (r < 0.5) with other meteorological variables.

Vapor pressure difference (hPa)

Fig. 1. Total solar radiation and average vapor-pressure deficit between 0000 and 1200

Fig. 2. Maximum and minimum temperatures between 0000 and 1200 during the

North Pacific High covered Japan during the summer of 2010.

July August September

Flower opening time observation period

correlations (r < 0.5) with other meteorological variables.

Average wind speed and atmospheric pressure ranged from 0.0 to 1.4 m s−1 and from 1001 to 1017 hPa, respectively, between 0000 and 1200 during the flower opening time observation period. The wind speed and atmospheric pressure were stable because a strong

Significant correlations existed between the meteorological variables. In particular, the correlation between air temperature and vapor-pressure deficit was high (r = 0.715, *p* < 0.001). The correlation between solar radiation and air temperature and that between solar radiation and vapor-pressure deficit were also relatively high (r = 0.532, *p* < 0.001; r = 0.664, *p* < 0.001, respectively). Wind speed and atmospheric pressure had relatively weak

during the observation period.

Solar radiation (MJ m-2)

Temperature (oC)

40

35

30

25

20

15

10

July August September

Flower opening time observation period

p p

observation period.

Solar radiation

Vapor pressure difference

Maximum temperature Minimum temperature

Fig. 3. Average vapor-pressure deficit and average wind speed between 0000 and 1200 during the observation period.
