and Intensity of Sultriness in Istanbul
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 : firstname.lastname@example.org
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.
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.
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);
(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.
(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.
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
Index value (dimensionless)
Dew point temperature (˚C)
Dry bulb (air) temperature (˚C)
Total cloudiness (0-8 in eights)
: Wind speed
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’.
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′ ).
determine the frequency of sultriness,
all sultry hours with S ≥ 30.0 were counted.
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
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
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).
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
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
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.
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1. Monthly numbers of
sultry hours with S ≥ 30.0 for the years 1980-1989.
2. Average monthly frequencies
of sultry hours with S ≥ 30.0 for ten-year.
hours / Total hours
343 h / 7200 h
1202 h / 7440 h
h / 7440 h
h / 7200 h
2940 h / 29280 h
3. Monthly total numbers of sultry hours with the classified values
of sultry index S.
S = 30.0-30.9
4. The monthly numbers of sultry hours with S ≥ 30.0 according
to the wind directions accompanied with sultriness (Vrb..=Variable).
1: Hourly numbers of
sultry hours with S ³ 30.0 for the years 1980-1989.
2: Hourly numbers of
sultry hours with classified S ³
30.0 values for the years 1980-