 |
||
|
Frequency
and Intensity of Sultriness in Istanbul Serdar
Bahad, M Zeki Karagülle
Istanbul Universitesi, Istanbul Tıp Fakültesi Tibbi Ekoloji ve Hidroklimatolojı ABD Millet Cad. 126, Fax : +90 212 531 89 04 e-mail : mzkaragulle@turk.net
Abstract: The combination of high air temperature and high humidity, calm or light wind and intensive radiation facilitate sultriness. The milieu is perceived as very hot or sultry by human beings depending on above meteorological conditions. This explains the appearance of heat stress affecting human beings, especially in highly sensitive individuals. Our purpose was to obtain the frequency and intensity of sultriness if it were to occur in Istanbul. Sultry index (S) was computed from hourly meteorological data, which were observed at Atatürk airport station. Based on the empirical boundary value for sultriness, i.e. S=30.0, all sultry hours were analysed from May to October for the years 1980-1989. Sultriness was most frequent between 12.00 h. and 15.00 h. in local time, and most intense during daytime especially in July and August. There were great differences in monthly and yearly number of sultry hours. These were related with the frequencies of tropical air masses affecting Istanbul Key words: Sultriness
∙Sultry index ∙Heat stress ∙Human comfort ∙Istanbul
Introduction: Human body perceives the ambient temperature in terms of the heat loss due to conduction, convection, radiation and evaporation. The apparent temperature depends on meteorological factors such as air temperature, mean radiant temperature, humidity and wind speed which all play an important role on heat loss. The heat loss is essentially regulated by the conditions of the surrounding atmosphere. Increase in air temperature, mean radiant temperature, and humidity and decreased wind speed all play a prominent role in the problems of sultriness. The human body cannot lose heat easily by sweating in sultry conditions because of the reduction of evaporation from the body surface. Sultry weather is always a problem on human health in tropical and sub-tropical regions, especially in the summer months. Human efficiency declines, both physically and intellectually, when the weather is perceived as sultry. Much
work has been devoted to study the human comfort, and a large number
of bio-meteorological indexes based on different combinations of the
above-mentioned variables have been introduced in this respect. The
perfect one of these combinations is the Predicted Mean Vote (PMV)
derived from human heat balance by Fanger (1982) and discussed in
detail by Jendritsky et.al. (1990), Höppe (1993, 1999) and Matzarakis
et.al. (1997, 1999). The application of PMV is rather more difficult
than the others because the radiation observations are not generally
available in practice. In
the literature, the indexes most widely used to study the sultriness
were the effective temperature (ET), water vapour pressure (℮)
and equivalent temperature (Teq). The frequencies of sultriness were
also determined with the empirical boundary values ET =24.0 ºC,
℮ =18.8 hPa and Teq =56.0 ºC between comfort and sultry
regions (Mayer 1975,1977;Mayer and Abele 1977;Dieterichs 1958,1980);
Olaniran (1982). King
(1955) had defined an empirical sultry index by using Teq, cooling
power and atmospheric counter radiation. Leistner (1964) had also
presented the relationship between wind speed and Teq. Dieterichs
(1980) had studied the sultriness by using sultry index (S) considering
wind speed and cloudiness in addition to air temperature and humidity.
The frequency of sultriness had also been determined with the empirical
boundaries ℮= 18.8 hPa and S= 25.0 in his study. Methods:
Sultry index (S) can be easily calculated by using the equation (1)
that was given by Dieterichs (1980). S = Td + 0.5 (T + N) – 0.15 [v (35–T)] ½
(1)
S:
Index value (dimensionless) Td:
Dew point temperature (˚C) T:
Dry bulb (air) temperature (˚C) N:
Total cloudiness (0-8 in eights) v
: Wind speed
(knots) The sultry index equation (1) considers wind-chill
and atmospheric counter radiation effects due to wind speed and cloudiness.
If N=0 and v=0 in Eq.(1), the curves of
S and Teq are closely similar in the temperature-humidity diagram.
For the sake of greater reliability, S is more preferable than Teq,
despite the fact that both are found to be approximately similar.
Under these conditions, sultry index value S=30.0 is a suitable
value compared to the boundary value Teq =56.0 ˚C for sultriness.
Therefore in this study, sultriness had been investigated by using
sultry index Eq. (1) and S≥ 30.0 is considered ‛sultry
’ while S< 30.0 ‛not sultry’. On
hourly basis, S was computed from meteorological data, which were
recorded between May and October for the years 1980-1989 at the Atatürk
airport meteorological station. The station is located at the southwest
coastal area nearby Istanbul city center (h=19 m. above sea level,
latitude 40º 58′ and longitude 28º 49′ ). To
determine the frequency of sultriness,
all sultry hours with S ≥ 30.0 were counted. Hourly
and monthly numbers of sultry hours were recorded and the intensity
of sultriness was analysed in detail by using the classified index
values. Meteorological parameters accompanied by sultriness were also
examined. Results:
Table 1 indicates that sultriness with S ≥30.0 never occurred
in the months of May and October for the years 1980-1989. The numbers
of sultry hours varied significantly from year to year. The last four-years
(1986-1989) were significant because the cumultative hours of sultriness
were calculated to be 2320 hours (78.9%) out of a total of 2940 sultry
hours for ten years. Monthly
sultry hours with S ≥ 30.0 were most frequent in August with
1255 hours (42.7 %) and in July with 1202 hours (40.9%) out of a total
of 2940 sultry hours.
Tropical air masses affecting Istanbul occurred almost regularly in
July and August, but irregularly in June and September. Therefore,
the sultriness was found to be infrequent in June with 343 sultry
hours (11.7 %) and especially in September with 140 sultry hours (4.8
%) out of a total of 2940 sultry hours for ten years (Table 1).
The sultry hours with S ≥ 30.0 displayed dispersion during
the months of June, July and August but only at the first ten days
of September for the years 1980-1989. The rates of sultry hours to the total time showed that sultriness
occurred most often in July (16.13%) and August (16.87%), occasionally
in June (4.74%) and September (1.94%) (Table 2). Hourly frequencies of sultriness with S ≥30.0
were also analysed for ten years. In Figure 1,
sultriness for all months occurred frequently during the daytime
between 0800 h. and 1900 h. and infrequently between 2000 h. and 0700
h. in local time. Especially at night in June and September,
relatively few sultry hours with S ≥ 30.0 were recorded
for the years 1980-1989, as depicted in Figure 1.
In Table 3, monthly numbers of sultry hours were categorized
according to various levels of
classified S values
for ten years. Intensive sultriness with the value of S ≥ 34.0
occurred in July and August with few sultry hours in June but none
in September. The hourly numbers of sultry hours with classified S
values are depicted in Figure 2.
It showed that
all of the intensive sultriness ( S ≥ 34.0) occurred between
0800h. and 2300h. in local time, especially during daytime at high
air temperatures.
The important meteorological parameters accompanied
by sultriness were examined in detail and
summarized in Table 4. The data indirectly suggested that the
sultriness observed in Istanbul was mainly dependent on a higher values
of water vapour pressure, i.e. ℮≥18.8hPa. The activity
of the cumulus clouds was increased by convection and humid air due
to intensive solar radiation especially at noon. Therefore, the sultriness
could often occur even if the sky were partly covered by cumulus clouds
at low level, although the maximum frequency of sultry hours with
S ≥30.0 was in clear sky conditions.
Total number of sultry hours with S≥ 30.0
was reduced approximately half by wind chill effect due to wind speed
in Equation 1. In other words, sultry index values closed to 30.0
were eliminated by wind chill, especially in air temperature less
than 25.0 ºC. But sultriness
could occur even in windy (v≥10 knots) conditions at higher
temperatures (Table 4).
Discussion:
The results of this study are valid for shady areas by appropriating
air temperature as equal
to mean radiant temperature (Tmrt). On the other hand, the meteorological
data in this study are related to rural site of Istanbul. Asphalt
and buildings in the urban cause an increase in the value of Tmrt
by long-wave irradiation, compared to the rural site. The wind chill
effect due to wind speed is also decreased by irregular, building
structure in the urban. The number of sultry hours in the urban must
be more than that observed in this
study because of the increased heat load on human beings.
Dieterichs (1980) has found only 190 sultry hours
with S≥30.0 at North Sea coast in Germany for the years 1966-1976.
During the ten-year period (1980-1989), 2940 sultry hours with S≥30.0
had been realized in Istanbul. This great difference in the number
of sultry hours between Istanbul and northern coast of Germany shows
that the sultriness increases toward the low latitudes. Harlfinger
(1975) has indicated that the sultriness chanced in accordance with
altitude and latitude. In both studies, sultry index S showed
similar diurnal variation.
The frequency of tropical air masses affecting
Istanbul is very high especially in the summer, but this can vary
year by year due to synoptic pattern related to the vicinity of Istanbul.
Because of this, frequency of sultriness varies year by year with
great differences.
The sultry period (June-September) included 830 summer
days with Tmax ≥ 25.0 ºC and 142 tropical days with Tmax ≥
30.0 ºC. This can be taken as indicators of the high air temperatures
realized in Istanbul. There are two big water masses such as the Black
Sea and Marmara Sea, which are situated in the north and south of
Istanbul respectively. In high sun season, the intensive solar radiation
causes humid air by evaporation over the seas and a heated atmosphere
by irradiation over the artificial structure in the city center of
Istanbul. The humid air occurring over the Black Sea and Marmara Sea
is continually injected to the heated city atmosphere by the north,
northeast and southwest winds (Table 5).
Matzarakis and Mayer (1997) calculated the values of
PMV in Greece for the years 1980-1989, as in the same period of our
study. But it is impossible to compare because
the results were computed by different methods in our and their
studies. For the sake of comparison, the values of PMV in Istanbul
for same period (1980-1989) will be examined in detail in our next
study.
Acknowledgements:
This study is a part of Doctoral Thesis. “ Frequency and Intensity
of Sultriness in Istanbul “ by S. Bahadır at Istanbul University.
We are thankful to Msc.
Eng. E. Başak for his kindly help in preparing this article.
References:
Dieterichs H (1958) Dauer und Haeufigkeit schwüler
stunden in San Salvador. Arch Met Geoph Biokl B 8:369-377. Dieterichs H (1980) Haeufigkeit und intensitaet
der schwüle im hinterland der Ostfriesischen Nordseeküste.Arch Met
Geoph Biokl B 28:149-164. Fanger PO (1982) Thermal comfort. Robert E.Krieger,Florida. Harlfinger O (1975) Vergleichende untersuchung der
physiologischen waermebelastung zwischen mitteleuropa und den mittelmeerlaendern.Arch
Met Geoph Biokl B 24:361-372. Höppe
PR (1993) Heat balance modeling. Experientia 49; 741-746. Höppe
PR (1999) The physiologischen equivalent temperature-a universal index
for the biometeorological assessment of the thermal environment.Int
J Biometeorol 43:71-75. Jendritzky
G,Menz H,Schmidt-Kessen W,Schirmer H (1990) Methodik zur raumbezogenen
Bewertung der thermischen Komponente im Bioklima des Menschen.Beitr
Akad Raumforsch Landesplan 114. King E (1955) Ein empirisches schwülemass.Med Met
Hefte 10:5-8. Leistner W (1964) Die praktische bedeutung eines
geeigneten schwülemasses.Arch Physik Ther,Heft 1:67-76. Mayer H (1975) Die effektive temperatur unter dem aspekt schwüle in 2m.
und 175m. über grund.Arch Met Geoph Biokl B 23:147-155. Mayer H (1977) Schwüleverhaeltnisse an der deutschen
Nordseeküste.Arch Met Geoph Biokl B 24:361-372. Mayer H, Abele J (1977) Bioklimatische verhaeltnisse
im Südwestafrikanischen
Steppen gebiet.Arch Met Geoph Biokl B 24: 337-347. Matzarakis
A,Mayer H (1997) Heat stress in Greece. Int J Biometeorol 41:34-39. Matzarakis
A,Mayer H,Iziomon MG (1999) Applications of a universal thermal index:
physiological equivalent temperature.Int J Biometeorol 43:76-84. Olaniran
OJ (1982) The physiological climate of Ilorin,Nigeria.Arch Met Geoph
Biokl B 31:287-299. Table
1. Monthly numbers of
sultry hours with S ≥ 30.0 for the years 1980-1989.
June July
Aug Sept
Total
Hours %
1980 4
36
29 5
74
2.5
1981 2
54
54
1
111 3.8
1982 19
3
18
35
75
2.6
1983 3
146
40
1
190
6.5
1984 10
27
15
2
54
1.8
1985 2
15
87
12
116
3.9
1986 148
150 274
5
577 19.5
1987 48
198
61
12
319 10.9
1988 82
454 330
44
910 31.0
1989 25
119 347
23
514 17.5
Hours 343
1202 1255
140 2940
100.0 Total
% 11.7
40.9 42.7
4.8 100.1
Table
2. Average monthly frequencies
of sultry hours with S ≥ 30.0 for ten-year.
Sultry
hours / Total hours
%
JUNE
343 h / 7200 h
4.74
JULY
1202 h / 7440 h
16.13 AUGUST 1255
h / 7440 h
16.87 SEPTEMBER 140
h / 7200 h
1.94 TOTAL
2940 h / 29280 h
10.04 Table
3. Monthly total numbers of sultry hours with the classified values
of sultry index S.
Sultry index
JUNE JULY
AUG .
SEPT. TOTAL
%
S = 30.0-30.9
181
487 539
81
1288 43.8
31.0-31.9
101 297
333
43 774
26.3
32.0-32.9
39 202
214
11 466
15.9
33.0-33.9
14 115
89
5 223
7.6
34.0-34.9
3 50
46
-
99
3.4
35.0-35.9
3 29
24
-
56
1.9
36.0-36.9
1 15
7
-
23
0.8
37.0-37.9
1 5
1
-
7 0.2
38.0-38.9
- 2
2
-
4 0.1
TOTAL
343 1202
1255
140 2940
100.0
Table
4. The monthly numbers of sultry hours with S ≥ 30.0 according
to the wind directions accompanied with sultriness (Vrb..=Variable).
JUNE JULY
AUG. SEPT.
TOTAL %
NW 3
7
11
-
21 0.7
N
65 157
126
6 354
12.0
NE 62
608
641 54
1365
46.4
E 20
95
145 10
270
9.2
SE
9 22
36
5 72
2.4
S 14
34
50 7
105
3.6 SW 89
154
128 23
394
13.4
W
36 57
56
17 166
5.6
Calm 44
67
60 16
187
6.4
Vrb. 1
1 2
2
6 0.2
TOTAL 343
1202
1255
140
2940
99.9
Figure
1: Hourly numbers of
sultry hours with S ³ 30.0 for the years 1980-1989.
Figure
2: Hourly numbers of
sultry hours with classified S ³
30.0 values for the years 1980-
1989. |
|
