Impact of ENSO on extreme temperatures in Vietnam

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Impact of ENSO on extreme temperatures in Vietnam. This paper presents the results of research on the effects of ENSO to extreme temperature in Vietnam [1] through the frequency deviation of the occurrence extreme temperatures during ENSO and non-ENSO seasons. The results demonstrate that in an El Niño winter, the frequency of absolute maximum temperature decreased over mountainous areas of the temperature in comparison to those under the influence of a non-ENSO winter. In summer, the effects of El Niño and La Nina generally led to a reduction in the frequency of maximum temperatures in comparison to the non-ENSO condition. For minimum temperatures, the effect of El Niño winter led to a decrease in the appearance of the temperatures, while the effect of La Nina led to an increase in the appearance of this characteristic. In contrast, the effects of El Niño and La Nina led to a reduction in the frequency of minimum temperatures during summer. Generally, in both El Niño and La Nina conditions, significant changes were observed in the distribution of frequency deviation with regard to both patterns and values of seasons, in which the South obviously exhibited more changes than the North.
EnvironmEntal SciEncES | Climatology
Impact of ENSO
on extreme temperatures
in
Vietnam
Duc Ngu Nguyen*
Centre for Hydro-Meteorological and Environmental Sciences and Technologies
Received 25 May 2017; accepted 30 October 2017
Abstract:
in
the
frequency
distribution
and
This paper presents the results of research on the effects of ENSO to extreme
intensity of climatic extremes that affect
temperature in Vietnam [1] through the frequency deviation of the occurrence
production, and more importantly, can
extreme temperatures during ENSO and non-ENSO seasons. The results
cause
severe
natural
disasters
such
demonstrate that in an El Niño winter, the frequency of absolute maximum
as
heat
waves,
cold
weather,
floods,
temperature decreased over mountainous areas of the temperature in
prolonged
droughts,
unusually
strong
comparison to those under the influence of a non-ENSO winter. In summer,
the effects of El Niño and La Nina generally led to a reduction in the frequency
of maximum temperatures in comparison to the non-ENSO condition. For
minimum temperatures, the effect of El Niño winter led to a decrease in the
appearance of the temperatures, while the effect of La Nina led to an increase
in the appearance of this characteristic. In contrast, the effects of El Niño
and La Nina led to a reduction in the frequency of minimum temperatures
during summer. Generally, in both El Niño and La Nina conditions, significant
changes were observed in the distribution of frequency deviation with regard
to both patterns and values of seasons, in which the South obviously exhibited
typhoons, among others.
This study investigates the
distribution of extreme temperature
in the seasons of El Niño (E), La Nina
(L), and non-ENSO (N) during winter
and summer across regions spread
throughout the country. The impacts
of ENSO on extreme temperatures
in Vietnam have been assessed, an
more changes than the North.
evaluation that facilitates the creation of
Keywords: effects of ENSO, extremes temperature, winter.
forecasting and early warning methods
that can contribute to the prevention and
Classification number: 6.2
reduction of damage caused by natural
disasters.
Data and methods
Data
Introduction
Research on weather and climate
extremes is of particular importance for
both scientific and practical purposes.
Most climate extremes occur under
conditions of abnormal variability in
terms of atmospheric circulation or
solar radiation. In the context of global
climate change, some of the weather
to occur more frequently in the 21st
century [2]. In fact, the variation in
extreme weather and climate has been
exhibited in many places; further, even
the moderating climate of local climate
conditions also causes to extreme
changes [3]. The climate extreme has
occurred increasingly more, especially
the El Niño and La Nina (ENSO)
To investigate the distribution of
extreme temperature, we have utilized
the average maximum and minimum
temperature and monthly absolute
maximum and minimum temperature
data from 38 meteorological stations
from the period 1961-2000 and ENSO
data from the period 1951-2000.
Methods
and climate extreme events are likely
phenomenon [4] that effects a change
The periods of ENSO (El Niño and
*Email: nguyenducngu@yahoo.com.
December 2017 Vol.59 Number 4
Vietnam Journal of Science,
Technology and Engineering
89
p
EnvironmEntal SciEncES | Climatology
La Nina) that occurred during the period
temperature in non-ENSO seasons).
Results and discussions
1951-2010 are determined with red to
the following regulations:
Determine the extreme temperature
values for the 95th, 90th, 5th, and 10th
For the above definition, the years
and seasons of El Niño (N), La Nina
-
El
Niño
(La
Nina)
forms
a
percentile
utilized
as
the
“threshold”
(L), and non-ENSO (N) are presented
continuous
period
of
no
less
than
6
values of the “warm” (“cold”) events
in Table 1
months with a 5-month moving average
of the monthly mean sea surface
temperature anomalies in NINO.3 (5oN-
5oS, 150oW-90oW) that is greater than
or equal to 0.5oC (less than or equal to
- 0.5oC) [3].
- Define months and seasons as (3
months) El Niño (E), La Nina (L), and
non-ENSO (N):
From the El Niño and La Nina periods
defined as above, the months E, L, and
N are determined. To determine the
ENSO seasons (El Niño and La Nina),
each season is defined as constituting
3 months, wherein the spring stretches
from March to May, summer from June
to August, Autumn from September to
November, and winter from December
to February, while the average sea
surface temperature anomaly (SSTA) in
the NINO.3 area is in accordance to the
following criteria:
SSTA ≥ 0.5oC El Niño (E)
- 0.5oC ≤ SSTA< 0.5oC neutral or non-ENSO (N)
with the following rules: The “extreme”
events occur when maximum/minimum
temperature in the ENSO seasons are
higher (lower) than the “threshold”
values that correspond to the 90th, 95th
(5th, 10th) percentile for the non-ENSO
(normal) seasons.
- Calculate the frequency of
occurrence of extreme temperatures
in ENSO seasons, with the extreme
temperature as higher (lower) than the
“threshold” of extreme temperatures
with percentiles 90th, 95th (5th, 10th) in
non-ENSO seasons of the corresponding
seasons.
- Calculate the frequency deviation
(Panom) of extreme temperatures in ENSO
seasons that correspond to the percentiles
90th, 95th (5th, 10th) (“threshold”) in
non-ENSO seasons of the corresponding
seasons through the application of by the
formula given below [5]:
Panom = 100(100 m 1)
Mean winter, summer of E, L,
N seasons’ extreme temperature
distribution (spring and autumn cases
are omitted)
Monthly average maximum
temperature (Tx ):
- Winter:
In the North-West, the values of
monthly Tx in E seasons were found to
be higher in N and L seasons with 0.5-
2oC. The difference between the highest
value and the lowest value of the average
monthly maximum temperature (x) in
E and L seasons was determined to be
nearly 8-10oC, values that are
comparatively lesser than that in N
seasons (about 12oC).
In the North-East, monthly Tx in E
seasons was found to be greater than that
in L seasons, but at the same level as that
of N seasons. In contrast, the maximum
value of monthly Tx in E seasons was
found to be greater than L and N seasons
of 2-3oC, while the minimum value for
SSTA < - 0.5oC La Nina (L)
where:
the monthly Tx in E seasons was
determined as being greater than that in
Each season must comprise at least
p forms the frequency of extremes for
L seasons and less than that in N seasons
two consecutive months to satisfy one
ENSO seasons higher (lower) than the
of about 1-2oC. x in E seasons is 10-
of the above provided criteria. In the
case where there are no two consecutive
months that fulfill the above criteria,
the average SSTA of 3 months must
meet that criterion. The frequency and
frequency deviation of temperature
extremes in ENSO (El Niño, La Nina),
and non-ENSO seasons are calculated as
follows:
“threshold” values for the m percentile
in the non-ENSO seasons (base seasons)
of the corresponding seasons;
m represents the number of percentiles.
Thus, the frequency anomaly reflects
the increase or decrease in the frequency
of extremes during ENSO seasons
in comparison to their occurrences
11oC higher than that in L seasons (9-
10oC) and N seasons (7-9oC).
In North central and South central
regions, monthly Tx in E seasons was
found to be higher in N and L seasons,
especially in the North central region (2-
5oC) (in the South central, it was only
0.5-1oC). x in E seasons in the North
central reached 9-10oC, while for N and
- Calculates the 5th, 10th, 25th, 50th,
during
non-ENSO
seasons
for
the
L seasons it was only 7-8oC. In the South
75th, 90th, 95th percentile of the extreme
corresponding seasons.
central
region,
the
value
of
this
90
Vietnam Journal of Science,
Technology and Engineering
December 2017 Vol.59 Number 4
EnvironmEntal SciEncES | Climatology
Table 1. ENSO (E, L) and non-ENSO (N) seasons in the period 1950-2000.
Spring (III-V)
Summer (VI-VIII)
Autumn (IX-XI)
Winter (XII-II)
E
L
N
E
L
N
E
L
N
E
L
N
1953
1950
1951
1951
1954
1950
1951
1954
1950
51/52
49/50
50/51
1957
1954
1952
1953
1955
1952
1953
1955
1952
57/58
64/65
52/53
1958
1955
1956
1957
1964
1956
1957
1964
1956
63/64
67/68
53/54
1969
1964
1959
1963
1970
1958
1963
1967
1958
65/66
70/71
54/55
1972
1968
1960
1965
1971
1959
1965
1970
1959
68/69
73/74
55/56
1982
1971
1961
1969
1973
1960
1968
1971
1960
69/70
75/76
56/57
1983
1985
1962
1972
1975
1961
1969
1973
1961
72/73
84/85
58/59
1987
1988
1963
1976
1985
1962
1972
1975
1962
76/77
85/86
59/60
1991
1999
1965
1979
1988
1966
1976
1984
1966
79/80
88/89
60/61
1992
1966
1982
1999
1967
1979
1985
1974
82/83
98/99
61/62
1993
1967
1983
1968
1982
1988
1977
86/87
99/00
62/63
1997
1970
1987
1974
1986
1998
1978
87/88
66/67
1998
1973
1991
1977
1987
1999
1980
91/92
71/72
1974
1993
1978
1991
1981
97/98
74/75
1975
1997
1980
1997
1983
77/78
1976
1981
1989
78/79
1977
1984
1990
80/81
1978
1986
1992
81/82
1979
1989
1993
83/84
1980
1990
1994
89/90
1981
1992
1995
90/91
1984
1994
1996
92/93
1986
1995
2000
93/94
1989
1996
94/95
1990
1998
95/96
1994
2000
96/97
1995
00/01
1996
2000
e: el Niño, l: la Nina, N: non-eNSo.
December 2017 Vol.59 Number 4
Vietnam Journal of Science,
Technology and Engineering
91
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Impact of ENSO on extreme temperatures in Vietnam. This paper presents the results of research on the effects of ENSO to extreme temperature in Vietnam [1] through the frequency deviation of the occurrence extreme temperatures during ENSO and non-ENSO seasons. The results demonstrate that in an El Niño winter, the frequency of absolute maximum temperature decreased over mountainous areas of the temperature in comparison to those under the influence of a non-ENSO winter. In summer, the effects of El Niño and La Nina generally led to a reduction in the frequency of maximum temperatures in comparison to the non-ENSO condition. For minimum temperatures, the effect of El Niño winter led to a decrease in the appearance of the temperatures, while the effect of La Nina led to an increase in the appearance of this characteristic. In contrast, the effects of El Niño and La Nina led to a reduction in the frequency of minimum temperatures during summer. Generally, in both El Niño and La Nina conditions, significant changes were observed in the distribution of frequency deviation with regard to both patterns and values of seasons, in which the South obviously exhibited more changes than the North..

Nội dung

EnvironmEntal SciEncES | Climatology Impact of ENSO on extreme temperatures in Vietnam Duc Ngu Nguyen* Centre for Hydro-Meteorological and Environmental Sciences and Technologies Received 25 May 2017; accepted 30 October 2017 Abstract: in the frequency distribution and This paper presents the results of research on the effects of ENSO to extreme temperature in Vietnam [1] through the frequency deviation of the occurrence extreme temperatures during ENSO and non-ENSO seasons. The results demonstrate that in an El Niño winter, the frequency of absolute maximum temperature decreased over mountainous areas of the temperature in comparison to those under the influence of a non-ENSO winter. In summer, the effects of El Niño and La Nina generally led to a reduction in the frequency of maximum temperatures in comparison to the non-ENSO condition. For minimum temperatures, the effect of El Niño winter led to a decrease in the appearance of the temperatures, while the effect of La Nina led to an increase in the appearance of this characteristic. In contrast, the effects of El Niño and La Nina led to a reduction in the frequency of minimum temperatures during summer. Generally, in both El Niño and La Nina conditions, significant changes were observed in the distribution of frequency deviation with regard to both patterns and values of seasons, in which the South obviously exhibited more changes than the North. Keywords: effects of ENSO, extremes temperature, winter. Classification number: 6.2 intensity of climatic extremes that affect production, and more importantly, can cause severe natural disasters such as heat waves, cold weather, floods, prolonged droughts, unusually strong typhoons, among others. This study investigates the distribution of extreme temperature in the seasons of El Niño (E), La Nina (L), and non-ENSO (N) during winter and summer across regions spread throughout the country. The impacts of ENSO on extreme temperatures in Vietnam have been assessed, an evaluation that facilitates the creation of forecasting and early warning methods that can contribute to the prevention and reduction of damage caused by natural disasters. Data and methods Data Introduction Research on weather and climate extremes is of particular importance for both scientific and practical purposes. Most climate extremes occur under conditions of abnormal variability in terms of atmospheric circulation or solar radiation. In the context of global climate change, some of the weather and climate extreme events are likely to occur more frequently in the 21st century [2]. In fact, the variation in extreme weather and climate has been exhibited in many places; further, even the moderating climate of local climate conditions also causes to extreme changes [3]. The climate extreme has occurred increasingly more, especially the El Niño and La Nina (ENSO) phenomenon [4] that effects a change To investigate the distribution of extreme temperature, we have utilized the average maximum and minimum temperature and monthly absolute maximum and minimum temperature data from 38 meteorological stations from the period 1961-2000 and ENSO data from the period 1951-2000. Methods The periods of ENSO (El Niño and *Email: nguyenducngu@yahoo.com. December 2017 • Vol.59 Number 4 Vietnam Journal of Science, Technology and Engineering 89 EnvironmEntal SciEncES | Climatology La Nina) that occurred during the period 1951-2010 are determined with red to the following regulations: temperature in non-ENSO seasons). Determine the extreme temperature values for the 95th, 90th, 5th, and 10th Results and discussions For the above definition, the years and seasons of El Niño (N), La Nina - El Niño (La Nina) forms a percentile utilized as the “threshold” (L), and non-ENSO (N) are presented continuous period of no less than 6 months with a 5-month moving average of the monthly mean sea surface temperature anomalies in NINO.3 (5oN-5oS, 150oW-90oW) that is greater than or equal to 0.5oC (less than or equal to - 0.5oC) [3]. - Define months and seasons as (3 months) El Niño (E), La Nina (L), and non-ENSO (N): From the El Niño and La Nina periods defined as above, the months E, L, and N are determined. To determine the ENSO seasons (El Niño and La Nina), each season is defined as constituting 3 months, wherein the spring stretches from March to May, summer from June to August, Autumn from September to November, and winter from December to February, while the average sea surface temperature anomaly (SSTA) in the NINO.3 area is in accordance to the following criteria: SSTA ≥ 0.5oC El Niño (E) - 0.5oC ≤ SSTA< 0.5oC neutral or non-ENSO (N) SSTA < - 0.5oC La Nina (L) Each season must comprise at least two consecutive months to satisfy one of the above provided criteria. In the case where there are no two consecutive months that fulfill the above criteria, the average SSTA of 3 months must meet that criterion. The frequency and frequency deviation of temperature extremes in ENSO (El Niño, La Nina), and non-ENSO seasons are calculated as follows: values of the “warm” (“cold”) events with the following rules: The “extreme” events occur when maximum/minimum temperature in the ENSO seasons are higher (lower) than the “threshold” values that correspond to the 90th, 95th (5th, 10th) percentile for the non-ENSO (normal) seasons. - Calculate the frequency of occurrence of extreme temperatures in ENSO seasons, with the extreme temperature as higher (lower) than the “threshold” of extreme temperatures with percentiles 90th, 95th (5th, 10th) in non-ENSO seasons of the corresponding seasons. - Calculate the frequency deviation (Panom) of extreme temperatures in ENSO seasons that correspond to the percentiles 90th, 95th (5th, 10th) (“threshold”) in non-ENSO seasons of the corresponding seasons through the application of by the formula given below [5]: Panom = 100(100− m −1) where: p forms the frequency of extremes for ENSO seasons higher (lower) than the “threshold” values for the m percentile in the non-ENSO seasons (base seasons) of the corresponding seasons; m represents the number of percentiles. Thus, the frequency anomaly reflects the increase or decrease in the frequency of extremes during ENSO seasons in comparison to their occurrences in Table 1 Mean winter, summer of E, L, N seasons’ extreme temperature distribution (spring and autumn cases are omitted) Monthly average maximum temperature (Tx ): - Winter: In the North-West, the values of monthly Tx in E seasons were found to be higher in N and L seasons with 0.5-2oC. The difference between the highest value and the lowest value of the average monthly maximum temperature (∆x) in E and L seasons was determined to be nearly 8-10oC, values that are comparatively lesser than that in N seasons (about 12oC). In the North-East, monthly Tx in E seasons was found to be greater than that in L seasons, but at the same level as that of N seasons. In contrast, the maximum value of monthly Tx in E seasons was found to be greater than L and N seasons of 2-3oC, while the minimum value for the monthly Tx in E seasons was determined as being greater than that in L seasons and less than that in N seasons of about 1-2oC. ∆x in E seasons is 10-11oC higher than that in L seasons (9-10oC) and N seasons (7-9oC). In North central and South central regions, monthly Tx in E seasons was found to be higher in N and L seasons, especially in the North central region (2-5oC) (in the South central, it was only 0.5-1oC). ∆x in E seasons in the North central reached 9-10oC, while for N and - Calculates the 5th, 10th, 25th, 50th, 75th, 90th, 95th percentile of the extreme during non-ENSO seasons for the corresponding seasons. L seasons it was only 7-8oC. In the South central region, the value of this 90 Vietnam Journal of Science, Technology and Engineering December 2017 • Vol.59 Number 4 EnvironmEntal SciEncES | Climatology Table 1. ENSO (E, L) and non-ENSO (N) seasons in the period 1950-2000. Spring (III-V) Summer (VI-VIII) Autumn (IX-XI) Winter (XII-II) E L 1953 1950 1957 1954 1958 1955 1969 1964 1972 1968 1982 1971 1983 1985 1987 1988 1991 1999 1992 1993 1997 1998 N E L 1951 1951 1954 1952 1953 1955 1956 1957 1964 1959 1963 1970 1960 1965 1971 1961 1969 1973 1962 1972 1975 1963 1976 1985 1965 1979 1988 1966 1982 1999 1967 1983 1970 1987 1973 1991 1974 1993 1975 1997 1976 1977 1978 1979 1980 1981 1984 1986 1989 1990 1994 1995 1996 2000 N E L 1950 1951 1954 1952 1953 1955 1956 1957 1964 1958 1963 1967 1959 1965 1970 1960 1968 1971 1961 1969 1973 1962 1972 1975 1966 1976 1984 1967 1979 1985 1968 1982 1988 1974 1986 1998 1977 1987 1999 1978 1991 1980 1997 1981 1984 1986 1989 1990 1992 1994 1995 1996 1998 2000 N E L N 1950 51/52 49/50 50/51 1952 57/58 64/65 52/53 1956 63/64 67/68 53/54 1958 65/66 70/71 54/55 1959 68/69 73/74 55/56 1960 69/70 75/76 56/57 1961 72/73 84/85 58/59 1962 76/77 85/86 59/60 1966 79/80 88/89 60/61 1974 82/83 98/99 61/62 1977 86/87 99/00 62/63 1978 87/88 66/67 1980 91/92 71/72 1981 97/98 74/75 1983 77/78 1989 78/79 1990 80/81

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