ENSO

1
ENSOS IMPACTS ON CLIMATE, WEATHER, EMVIRONMENT,
AND SOCIO-ECONOMIC DEVELOPMENT IN VIETNAM

Prof.
Dr. of Sciences Nguyen Duc Ngu Center for Hydro
Meteorological and Environment Science and
Technology (CHMEST)
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Strips of clouds in El Nino in December, 1997
and La Nina in December, 1998
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• INTRODUCTION
• Definitions of ENSO.
• El Nino
• La Nina
• ENSO
• Importance of research on ENSO.

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I. OVERVIEW OF PHYSICAL MECHANISM OF ENSO

• 1.1 Trade wind, Southern Oscillation and Walker
  circulation. (Figure 1.1)
• Pacific Oceans East and West air pressure
  gradient
• Lower and higher-layer wind in Pacific Equatorial
  region.
• Walker circulation.
• 1.2 Sea water's temperature, upward-water
  movement and thermo cline in Pacific Equatorial
  region. (Table 1.1)
• East - West temperature gradient
• Upward-water movement and thermo cline

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Cold, high pressure
Hot, low pressure
upward-water movement
cont.
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Table 1.1 Average monthly and yearly sea surface
water's temperature in NINO-affected Region (0C)
(period of 1961 1990)
Month Region D (Warm pool) 140N 00, 1300E-1500E Region A ( Nino.4) 40N 40S, 1500E-1500W Region B ( Nino.3) 40N 40S, 1500W-900W Region C ( Nino 12) 00 140S, 900W-800W
1 28.5 28.0 25.4 24.3
2 28.3 28.0 26.2 25.7
3 28.4 28.1 26.9 25.9
4 28.8 28.2 27.1 25.1
5 29.5 28.3 26.6 23.9
6 29.3 28.4 26.1 22.7
7 29.2 28.5 25.2 21.6
8 29.1 28.4 24.6 20.6
9 29.2 28.3 24.6 20.3
10 29.3 28.4 24.6 20.7
11 29.2 28.4 24.6 21.5
12 28.9 28.2 24.9 22.6
Year 29.0 28.3 25.6 22.9
Tr? v?
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I. OVERVIEW ABOUT ENSOS PHYSICAL MECHANISM

• 1.3 Ocean - atmosphere interaction
• Deep exchange and atmospheric cyclones are
  reflected through accumulation of directing winds
  and Outgoing Long wave Radiation (OLR).
• Ocean-atmosphere vertical exchange components of
  heat and moisture.

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I. OVERVIEW ABOUT ENSOS PHYSICAL MECHANISM
(cont.)

• 1.4 ENSOs operational mechanism
• Walker circulation in a normal condition (Figure
  1.1)
• Development process and roles of Kelvin and
  Rossby oceanic waves.
• Walker circulation in El Nino condition and
  operations of evaporative exchange in Pacific
  Ocean Equator region (Figure 1.2)
• Walker circulation in La Nina condition.
• Unstable factors that have impacts on Walker
  circulation and ENSO (Pacific sub-tropical high
  pressure, intensification of West-directing wind
  in the Western Pacific Equator region, MJO,
  tropical cyclones). (cont.)

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Cold, high pressure
Hot, low pressure
Decreased depth of thermo cline
Weak Upward-water movement
return
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I. OVERVIEW ABOUT ENSOS PHYSICAL MECHANISM
(cont.)

• 1.5 ENSOs indicators and El Nino and La Nina
  periods (1950 2005)
• Indicators Region NINO.3 (50N 50S, 1500W
  -900W)
• El Nino 5 Months 0,50C (Table 1.2)
• La Nina 5 Months - 0,50C (Table
  1.3)
• Duration 6 Months

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Table 1.2 Hot ENSO period (El Nino) Underlined
periods are the strong El Nino
return
No. El Nino Month of commencement Month of disintegration Duration Maximal SSTA (0C) and occurring month Maximal SSTA (0C) and occurring month
1 1951/1952 6/1951 1/1952 8 1.3 10/1951
2 1953 3/1953 11/1953 9 1.1 9/1953
3 1957/1958 4/1957 5/1958 14 1.8 12/1957
4 1963/1964 6/1963 2/1964 9 1.2 12/0963
5 1965/1966 5/1965 2/1966 10 1.8 12/1965
6 1968/69/70 9/1968 2/1970 18 1.4 12/1969
7 1972/1973 4/1972 3/1973 12 2.6 12/1972
8 1976/1977 6/1976 2/1977 9 1.2 9,10/1976
9 1979 7/1979 12/1979 6 1.2 9/1979
10 1982/1983 4/1982 9/1983 18 3.6 1/1983
11 1986/87/88 9/1986 1/1988 17 2.0 9/1987
12 1991/1992 4/1991 6/1992 15 1.7 1/1992
13 1993 2/1993 8/1993 7 1.5 5/1993
14 1997/1998 4/1997 6/1998 15 3.9 12/1997
15 2002/2003 7/2002 1/2003 7 1.4 11,12/2002
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Table 1.3 Cold ENSO period (La Nina)
Underlined periods are the strong La Nina
No. La Nina Month of commencement Month of disintegration Duration Maximal SSTA (0C) and occurring month Maximal SSTA (0C) and occurring month
1 1949/1950 End 1949 4/1950 -1.7 2/1950
2 1954/55/1956 5/1954 2/1956 22 -2.0 11/1955
3 1964/1965 4/1964 1/1965 10 -1.2 12/1964
4 1967/1968 9/1967 4/1968 8 -1.3 2/1968
5 1970/1971 6/1970 12/1971 19 -1.5 12/1970
6 1973/1974 6/1973 3/1974 10 -1.4 1/1974
7 1975/1976 4/1975 3/1976 12 -1.5 12/1975, 1/1976
8 1984/1985 10/1984 12/1985 15 -1.2 12/1984
9 1988/1989 4/1988 3/1989 12 -1.7 11,12/18
10 1998/99/2000 10/1998 3/2000 18 -1.6 1/2000
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1.6 Characteristics of distribution and operation
of El Nino and La Nina1/ In 55 years (1951
2005), there were- 15 El Nino periods, of
which Longest period (1968 - 1970 and 1982 -
1983) 18 months. Shortest period (1979) 6
months. Average duration per period 12
months.- 10 La Nina periods, of which Longest
period (1954 - 1956) 22 months. Shortest
period (1967 - 1968) 8 months. Average
duration per period 13 months.- 6 times of 2
consecutive El Nino periods but only 1 time of 2
consecutive La Nina periods.
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1.6 Characteristics of distribution and operation
of El Nino and La Nina (cont.)2/ 8 strong El
Nino periods (average SSTA per month 1.50C)6
strong La Nina periods (maximal SSTA in a month
-1.50C)3/ Most of ENSO started in spring (March
- May), mostly in April, and ended in winter or
spring (December - April).No strong El Nino
period started in the middle of winter or
summer.No strong La Nina period started in the
middle of winter.
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1.6 Characteristics of distribution and operation
of El Nino and La Nina (cont.) 4/ Strongest
stage (maximum) of each ENSO period is the middle
of winter (December - January).5/ Each ENSO
period is clearly phased into 7 stages and each
stage lasts for 2 - 3 monthsstage of
pre-commencement.stage of commencement.stage of
development.stage of transition.stage of
maximum.stage of declination.stage of
disintegration.
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II. ENSO's impacts on weather AND climate IN
VIETNAM

• 2.1 ENSO's impacts on frequency of cold fronts in
  Vietnam
• Frequency of cold fronts in Hanoi (1956 - 2000)

Table 2.1 Frequency of cold fronts in Hanoi
(1956 - 2000)
Month 1 2 3 4 5 6 7 8 9 10 11 12 Year
Average 4.0 3.2 3.3 2.7 2.7 1.5 0.13 0.16 1.4 2.9 3.6 3.5 29.1
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• 2.1 ENSO's impacts on frequency of cold fronts in
  Vietnam
• Frequency of cold fronts in El Nino and La Nina
  conditions (Table 2.2)
• Generally, total Positive standard deviation of
  the whole year is always lower than total
  Negative standard deviation of the whole year,
  mainly decreasing at the end of winder and summer
  months

Table 2.2 Standard deviation of frequency of
cold fronts in Hanoi during El Nino and La Nina
months (1956 2000)
Standard deviation Standard deviation 1 2 3 4 5 6 7 8 9 10 11 12 Total Ratio
El Nino Positive 7 4 1 2 5 7 2 1 7 9 9 6 60 0.7
El Nino Negative 4 7 7 10 8 6 11 12 7 4 4 7 87 0.7
La Nina Positive 0 2 2 3 5 3 0 4 4 7 4 8 42 0.7
La Nina Negative 4 6 6 5 2 6 8 4 5 4 7 3 60 0.7
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2.2 ENSO's impacts on operations of storms in
Vietnam

• Average frequency of storms (1956 2000)
• Average per year 6.9 storms
• Average per storm season (June December) 6.6
  storms
• Average per storm month 0.95 storms

Table 2.3 Frequency of storms per month and year
that have direct impacts on Vietnam (1956-2000)
Month 1 2 3 4 5 6 7 8 9 10 11 12 Year storm season storm month
frequency 0 0 0.1 0.1 0.1 0.7 0.7 1.2 1.4 1.3 1.0 0.3 6.9 6.6 0.95
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2.2 ENSO's impacts on operations of storms in
Vietnam

• Operations of storms in El Nino condition
  (Table 2.4)
• Average per El Nino months 0,4 storms (less
  than in a normal condition 28)
• Average per the whole storm season of El Nino
  period 4.8 storms (less than in a normal
  condition 28)
• Average in 1 storm month of El Nino period 0.69
  storms (less than in a normal condition 27)

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Table 2.4 Storms that have direct impacts on
Vietnam during El Nino period
El Nino period El Nino period El Nino period IV V VI VII VIII IX X XI XII No. of storms Ratio (No. of storms per month E)
From Until Duration (Month) IV V VI VII VIII IX X XI XII No. of storms Ratio (No. of storms per month E)
IV/57 IV/58 14 1 1 2 2/14
VI/63 II/64 9 1 4 2 7 7/9
V/65 II/66 10 1 2 1 1 5 5/10
IX/68 II/70 18 2 1 3 2 8 8/18
IV/72 III/73 12 1 1 3 2 7 7/12
VI/76 II/77 9 0 0/9
VII/79 XII/79 6 2 1 1 4 4/6
IV/82 IX/83 17 1 1 2 1 5 5/18
IX/86 I/88 18 2 3 3 2 2 12 12/17
IV/91 VI/92 15 1 1 1 1 2 6 6/15
II/93 VIII/93 7 1 1 2 4 4/7
IV/97 VI/98 15 1 1 1 3 3/15
Total Total 150 1 5 9 16 16 5 5 6 63 63/150
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2.2 ENSO's impacts on operations of storms in
Vietnam

• Operations of storms in La Nina condition
  (Table 2.5)
• Average per La Nina Month 0.8 storms (higher
  than in a normal condition 38, double in 1 El
  Nino month)
• Average per the whole storm season in La Nina
  period 9.17 storms (higher than in a normal
  condition 27, higher than in a storm season of
  a El Nino period 91)
• Average per 1 storm of La Nina month 1.31
  storms (higher than in a normal condition 27,
  higher than in 1 storm month of El Nino period
  90)

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Table 2.5 No. of storms affecting on in Vietnam
during La Nina period
La Nina period La Nina period La Nina period V VI VII VIII IX X XI XII No. of storms Ratio (No. of storms per Month L)
From Until Duration (Month) V VI VII VIII IX X XI XII No. of storms Ratio (No. of storms per Month L)
IV/64 I/65 10 1 1 3 3 3 11 11/10
IX/67 IV/68 8 1 2 1 4 4/8
VI/70 XII/71 19 1 2 3 1 2 4 5 18 18/19
VI/73 III/74 10 1 2 5 2 2 12 12/10
IV/75 III/76 15 1 2 2 3 1 9 9/15
X/84 XII/85 15 1 2 3 5 1 12 12/15
IV/88 III/89 12 3 2 5 5/12
X/98 III/2000 18 1 1 1 1 2 3 3 3 15 15/18
Total Total 107 2 5 6 9 18 25 16 5 86 86/107
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2.3 ENSO's impacts on temperature

• During most of El Nino months all regions have
  positive standard deviation, which is higher than
  negative standard deviation (Ratio ranging from
  1.2 to 2.0).
• During most of La Nina months all regions have
  positive standard deviation, which is lower than
  negative standard deviation (Ratio ranging from
  0.5 to .7)
• However, besides during some El Nino periods,
  the absolute lowest temperature was recorded, and
  during some La Nina periods, the absolute highest
  temperature was recorded

Table 2.6 Ratio between total Positive and
Negative standard deviations of average
temperature per month duringEl Nino and La Nina
periods in some locations (1960-2000)
Station Lang Son Son La Hanoi Vinh Da Nang Pleiku Can Tho Tan Son Nhat Average
El Nino 1.4 1.5 1.2 1.2 1.8 1.3 1.6 2.0 1.5
La Nina 0.7 0.5 0.7 0.7 0.6 0.6 0.6 0.7 0.6
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Table 2.7 Some absolute maximum (Tx) and minimum
(Tm) record temperatures duringEl Nino and La
Nina period (0C)
Station Station Lang Son Son La Hanoi Vinh Da Nang Pleiku Can Tho Tan Son Nhat
El Nino TX (Month/Year) 37.6 (7/83) 36.3 (3/98) 39.4 (6/83) 39.6 (6/98) 40.0 (5/98) 40.1 (6/98) 38.9 (5/98) 36.0 (4/98) 39.3 (5/98)
El Nino Tm (Month/Year) 5.4 (1/77) 10.6 (11/79) 13.1 (2/77) 8.6 (2/77) 16.5 (12/63)
La Nina TX (Month/Year) 39.5 (6/99) 40.0 (5/88) 37.3 (3/99) 39.7 (1/99)
La Nina Tm (Month/Year) -1.7 (2/68) -1.5 (12/75) -0.2 (12/75) 5.0 (2/68) 5.9 (1/74) 5.1 (12/99) 9.4 (12/99) 10.2 (1/74) 6.1 (12/75) 14.8 (1/63)
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2.4 ENSO's impacts on rainfall

• Criteria for evaluation
• A reduction of rainfall in 1 ENSO period is
  defined as a subtraction between the actual
  rainfall in each period of El Nino (La Nina) and
  the total of average rainfall of many years
  within the same period, same point of time. The
  reduction is represented by .

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• Results
• Most of El Nino periods caused a reduction in
  rainfall in most of areas of the country, average
  reduction per period 20 50. The higher
  reduction in 1 El Nino period 69 in Buon Ma
  Thuot
• About a half of La Nina period caused a
  reduction in rainfall in areas, mostly in
  Northern and Central Highland Regions, average
  reduction per period15 20. The higher
  reduction in 1 La Nina period 47.2 in Nha
  Trang. However, total La Nina periods that cause
  a reduction in rainfall is as many as total La
  Nina periods that cause a surplus in rainfall,
  mainly in Coastal Central and South Western
  regions (Table 2.8)

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Table 2.8 Reduction in rainfall during ENSO
months in some locations
Characteristics Vinh Da Nang Nha Trang Phan Thiet Plei Ku Buon Ma Thuot Da Lat Remarks
Number of El Nino periods causing a reduction in rainfall out of 11 periods under review 6/11 8/11 9/11 10/11 7/11 10/11 8/11
Average reduction in rainfall per El Nino period () 22.6 (12.4) 17.6 (12.8) 24.1 (19.7) 13.4 (12.2) 17.4 (11.1) 21.7 (19.7) 19.0 (13.8) the figure in ( ) is the average figure of total 11 El Nino periods under review
Number of La Nina periods causing a reduction in rainfall out of 8 periods under review 3/8 3/8 1/7 5/8 5/8 3/7 3/7
Average reduction in rainfall per La Nina period () 15.0 (5.6) 19.2 (7.2) 47.2 (5.9) 17.0 (10.6) 18.0 (11.3) 20.9 (8.9) 9.7 (5.5) the figure in ( ) is the average figure of total 8 La Nina periods under review
The figure in ( ) is the average of total El
Nino and La Nina periods under review
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Table 2.9 Some maximum records in rainfall (Rx)
occurring during El Nino and La Nina periods (mm)
Station Station Lang Son Son La Hanoi Vinh Da Nang Can Tho Tan Son Nhat
El Nino Rx (Month/Year) 162 (5/82) 128(9/86) 161 (7/91) 126 (9/69) 81 (5/73) 206 (8/72) 118 (9/83) 116 (11/86) 131 (8/83) 113 (10/91)
La Nina Rx (Month/Year) 202 (7/71) 123 (3/98) 135 (8/99) 395 (11/84) 388 (9/85) 393 (11/99) 105 (10/98) 134 (11/98)
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2.5 ENSO's impacts on salinity in coastal areas
and islands of Vietnam.In general, El Nino
increased the salinity in contrast, La Nina
reduced the salinity of Sea water in the coastal
areas and islands of Viet Nam.
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• 2.6 ENSO's impacts on the flow of rivers in
  Vietnam.
• In the years under the impact of El Nino, the
  annual flow of rivers was lower by over 10 than
  the average of many years.
• In the years under the impact of La Nina, the
  annual flow of rivers was usually higher by 80
  100 than the average of many years
• In the years under the impact of El Nino, the
  flow was lower than the average flow of many
  years, the ratio () between the flow of flood
  season and the average flow of many years reached
  by 65 95
• In the years under the impact of La Nina, this
  ratio reached by 101 110 and even by 130
  140 in some regions.
• In the years under the impact of El Nino, the
  minimum flow of rivers in 3 consecutive months is
  as much as 80-90 of the average flow of many
  years
• In contrast, in the years under the impact of La
  Nina, the flow was higher by 101 140 than the
  average value of many years.

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3.1 ENSO's impacts on output of
hydroelectricity.The relationship between the
average water flow per year with the annual
output of four hydro power plants including Hoa
Binh, Thac Ba, Tri An, Da Nhim was in the direct
proposition with the correlation rate of 0.5
0.8. Therefore, it is notable that ENSO had the
impact on the reduction of the output for the
hydroelectricity. Meanwhile, the impact of La
Nina facilitated the increase in output of the
above-mentioned hydro power plants.
III. ENSO's impacts on SOME ECONOMIC SECTORS
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3.2 ENSO's impacts on agricultural production.-
In the condition of El Nino, the average turnover
of the spring harvest reduced comparing with the
previous harvest, especially for the Midland in
Northern Viet Nam in contrast, the output of the
autumn harvest increased, especially for the
Northern Central region.- In the condition of La
Nina, the average output of the spring and the
autumn harvest also increased than the previous
harvests.- In the condition of ENSO, the area of
coffee plant that could be harvested and the
output of coffee bean also increased comparing
with the previous harvest in the years under the
impact of La Nina, the area of coffee plant was
higher than in the years under the impact of El
Nino, but the output of coffee bean in the years
under the impact of El Nino was higher in the
years under the impact of La Nina.
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3.3 ENSO's impacts on life and health of human
being.- Since 1977 until 2000, the total number
of dead and missing people caused by the natural
disaster was 14,962 people of which 64 of
cases occurred in the years under the impact of
ENSO (El Nino 43, La Nina 21).- The prevalence
of petechial fever reached 100,000 cases in the
period of 1976 1998 in relation to El Nino
phenomenon with the correlation rate from 0.4
0.6. Only within a period of El Nino from 1997
1998, the petechial fever occurred in 51
provinces and cities of Viet Nam with the average
rate of 306 cases/100,000 people.
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Some statistics-based forecast models for seasons
(3 months) are developed based on information and
data of ENSO applicable to some factors and
hydrological phenomenon as follows- Frequency
of tropical cyclones in South China Sea and
Vietnam.- Average and maximum air temperature.-
(Total and maximum) Rainfall.- Flows of running
water in some locations in the Red River basin.-
Draughts.
IV. CAPACITY FOR PREDICTION OF ENSO's impacts
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Besides measures for irrigation, protection
forests, coastal protection, etc.,
non-infrastructure-based measures are as
follows1. Integrated planning and management
for water basin and water reservoirs.2.
Transformation of cropping patterns and
structures in some regions to adapt to ENSO's
impacts.
V. SOME MEASURES TO MITIGATE ADVERSE IMPACTS AND
DAMAGES CAUSED BY ENSO
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3. Develop and finalize measures to monitor,
predict, and warn about ENSO's impacts.4.
Intensify disaster management of the Government
and agencies for ENSO's impacts as a part of the
National Strategy on Sustainable Development.5.
Continue to intensify propaganda and awareness
raising for the public on ENSO and mitigation
measures.
V. SOME MEASURES TO MITIGATE ADVERSE IMPACTS AND
DAMAGES CAUSED BY ENSO (cont.)
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VI. CONCLUSION

• ENSO (El Nino, La Nina) has had discernible
  impacts on weather and climate of our country,
  and sometimes caused abnormal climate phenomenon,
  especially for the last 2 decades
• ENSO's impacts on weather and climate of our
  country are very complicated, various but it is
  possible to identify a general trend of impacts
  in El Nino or La Nina.
• Based on understanding on mechanisms and rules of
  ENSO's impacts and its consequences on weather
  and climate, we are able to provide early warning
  so that effective mitigation measures are
  developed to encounter with negative impacts
  caused by ENSO as well as develop long-term,
  strategic planning for sustainable socio-economic
  development.

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THANK YOU.