Temporal variation of atmospheric heat sourcesink

The analysis on the temporal variation of seasonal and annual mean <Q1> values of the whole TP during 1961~1995 indicates that the <Q1> value of winter ranges from -65 to -40 W-m-2 (figure not shown). It exhibits a greatly decreasing trend in 1960s and early 1970s with the minimum value of -66 W-m-2 in 1977 and a noticeable rise from 1978 to 1983 with the sub-maximum value of -48 W-m-2 in 1983. In spring, the <Q1> values are positive, which indicates a heat source, and show a decreasing trend in the 1960s with the minimum of 3 W-m-2 in 1969. A significantly rising trend is observed from the 1970s to the middle 1990s, peaking at 27 W-m-2 in 1989. In summer, the <Q1> value is 50~80 W-m-2 and displays a decreasing trend from 1961 to 1977 with a minimum of 53 W-m-2 in 1977 and oscillations in later years. It is noticed that the <Q1> values in summers of 1962, 1974, 1980, 1984, 1987 and 1993 exceed 70 W-m-2 with a maximum in 1962, corresponding to the relatively strong heat source over the TP, and in the summers of 1967, 1972, 1975, 1977 and 1978 are below 60 W-m-2 with the minimum in 1977, corresponding to the relatively weak heat source. In autumn, the <Q1> value varies between -15 and -35 W-m-2. It shows a conspicuous decreasing trend from 1971 to 1976 and then an in creasing trend till the end of the 1980s and again a decreasing trend in the 1990s. Additionally, the <Q1> values experience more remarkable interde-cadal variation in winter, spring and autumn. All values of these four seasons have the minimums or sub-minimums around 1976~1977. This feature is also seen from the temporal curve of the annual mean <Q1> values over the TP (Figure not shown). The annual mean <Qi> value exhibits a decreasing trend in the 1960s and an increasing trend in late 1970s and early 1980s. The obvious interdecadal change occurs around 1977. The annual mean <Q1> averaged over the periods of 1967~1976 and 1978~1987 are -3.6 and 1.6 W-m-2, respectively. The analysis using the moving Z-test method for these two means shows that the difference between them is remarkable (at a significance level of 0.001) and maximizes in this case.

Fig. 6.1 Climatological distribution of <Q1> for (a) January, (b) April, (c) July, (d) November. The thick dashed line is the 3000m contour of topography (Zhao and Chen, 2001)

Fig. 6.1 Climatological distribution of <Q1> for (a) January, (b) April, (c) July, (d) November. The thick dashed line is the 3000m contour of topography (Zhao and Chen, 2001)

Table 6.1 The climatological mean monthly SH, Rnet, LP and <Q1> for the southwest and east parts of the TP and the whole TP. units: W-m-2 (Zhao and Chen, 2001)

Month

Jan Feb Mar Apr MayJun Jul Aug Sep Oct NovDec Annual mean

SH

6

31

62

88 100

99

73

61

54

36

15

1

52

SWTP

Rnet

-68

-58

-59

-58

-54

-53

-79

-83

-74

-63

-71

-79

-67

LP

3

5

6

5

12

29

64

67

31

9

3

3

20

<Q1>

-59

-22

10

36

57

75

58

45

11

-1 8

-54

-75

5

SH

9

22

39

55

64

58

50

44

33

24

14

6

32

ETP

Rnet

-73

-67

-68

-63

-56

-56

-60

-68

-78

-77

-77

-80

-69

LP

3

5

11

20

39

76

91

77

63

23

5

3

35

<Q1>

-60

-40

-1 9

12

47

79

81

53

19

-30

-58

-71

1

SH

9

24

45

63

73

69

56

48

38

27

14

5

39

TP

Rnet

-72

-64

-66

-62

-55

-55

-65

-72

-77

-74

-75

-80

-69

LP

3

5

9

17

32

64

84

75

55

20

4

3

31

<Q1>

-60

-34

-12

18

50

78

75

51

17

-27

-57

-72

2

0 0

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