Daily annual temperature variation. diurnal variation of temperature. Learning new material

The daily course of air temperature is the change in air temperature during the day - in general, it reflects the course of the temperature of the earth's surface, but the moments of the onset of maxima and minima are somewhat late, the maximum occurs at 2 pm, the minimum after sunrise.

The daily amplitude of air temperature (the difference between the maximum and minimum air temperatures during the day) is higher on land than over the ocean; decreases when moving to high latitudes (the greatest in tropical deserts - up to 400 C) and increases in places with bare soil. The magnitude of the daily amplitude of air temperature is one of the indicators of the continentality of the climate. In deserts, it is much greater than in areas with a maritime climate.

The annual course of air temperature (change in the average monthly temperature during the year) is determined, first of all, by the latitude of the place. The annual amplitude of air temperature is the difference between the maximum and minimum average monthly temperatures.

Theoretically, one would expect that the diurnal amplitude, i.e., the difference between the highest and lowest temperatures, would be greatest near the equator, because there the sun is much higher during the day than at higher latitudes, and even reaches the zenith at noon on the days of the equinox, i.e., it sends out vertical rays and therefore gives the greatest amount of heat. But this is not actually observed, since, in addition to latitude, many other factors also influence the daily amplitude, the totality of which determines the magnitude of the latter. In this regard, the position of the area relative to the sea is of great importance: whether the given area represents land, remote from the sea, or an area close to the sea, for example, an island. On the islands, due to the softening influence of the sea, the amplitude is insignificant, it is even less on the seas and oceans, but in the depths of the continents it is much greater, and the magnitude of the amplitude increases from the coast into the interior of the continent. At the same time, the amplitude also depends on the time of year: in summer it is larger, in winter it is smaller; the difference is explained by the fact that in summer the sun is higher than in winter, and the duration of the summer day is much longer than that of winter. Further, cloud cover influences the diurnal amplitude: it moderates the temperature difference between day and night, retaining the heat emitted by the earth at night, and at the same time moderating the action of the sun's rays.

The most significant daily amplitude is observed in deserts and high plateaus. Desert rocks, completely devoid of vegetation, become very hot during the day and quickly radiate all the heat received during the day during the night. In the Sahara, the daily air amplitude was observed at 20-25° and more. There were cases when, after a high daytime temperature, the water even froze at night, and the temperature on the surface of the earth fell below 0 °, and in the northern parts of the Sahara even to -6, -8 °, rising much higher than 30 ° during the day.

The daily amplitude is much less in areas covered with rich vegetation. Here, part of the heat received during the day is spent on the evaporation of moisture by plants, and, in addition, the vegetation cover protects the earth from direct heating, while at the same time delaying radiation at night. On high plateaus, where the air is considerably rarefied, the balance of heat inflow and outflow at night is sharply negative, and during the day it is sharply positive, so the daily amplitude here is sometimes greater than in deserts. For example, Przhevalsky, during his trip to Central Asia, observed in Tibet a daily fluctuation in air temperature, even up to 30 °, and on the high plateaus of the southern part of North America (in Colorado and Arizona), daily fluctuations, as observations showed, reached 40 °. Insignificant fluctuations in daily temperature are observed: in polar countries; for example, on Novaya Zemlya the amplitude does not exceed 1–2 on average even in summer. At the poles and in general in high latitudes, where the sun does not appear at all during the day or months, at this time there are absolutely no daily temperature fluctuations. It can be said that the daily course of temperature merges with the annual one at the poles, and winter represents night, and summer represents day. Of exceptional interest in this respect are the observations of the Soviet drifting station "North Pole".

Thus, we observe the highest daily amplitude: not at the equator, where it is about 5 ° on land, but closer to the tropic of the northern hemisphere, since it is here that the continents have the greatest extent, and here the greatest deserts and plateaus are located. The annual temperature amplitude depends mainly on the latitude of the place, but, in contrast to the daily temperature, the annual amplitude increases with distance from the equator to the pole. At the same time, the annual amplitude is influenced by all the factors that we have already dealt with when considering daily amplitudes. In the same way, fluctuations increase with distance from the sea deep into the mainland, and the most significant amplitudes are observed, for example, in the Sahara and in Eastern Siberia, where the amplitudes are even greater, because both factors play a role here: continental climate and high latitude, while in Sahara amplitude depends mainly on the continentality of the country. In addition, fluctuations also depend on the topographic nature of the area. To see how much this last factor plays a significant role in the change in amplitude, it is sufficient to consider temperature fluctuations in the Jurassic and in the valleys. In summer, as you know, the temperature decreases with height rather quickly, therefore, on lonely peaks, surrounded on all sides by cold air, the temperature is much lower than in valleys, which are strongly heated in summer. In winter, on the contrary, cold and dense layers of air are located in the valleys, and the temperature of the air rises with height to a certain limit, so that individual small peaks are sometimes like heat islands in winter, while in summer they are colder points. Consequently, the annual amplitude, or the difference between winter and summer temperatures, is greater in the valleys than in the mountains. The outskirts of the plateaus are in the same conditions as individual mountains: surrounded by cold air, they at the same time receive less heat compared to flat, flat areas, so that their amplitude cannot be significant. The conditions for heating the central parts of the plateaus are already different. Strongly heated in summer due to rarefied air, they radiate much less heat compared to isolated mountains, because they are surrounded by heated parts of the plateau, and not by cold air. Therefore, in summer the temperature on the plateaus can be very high, while in winter the plateaus lose a lot of heat by radiation due to the rarefaction of the air above them, and it is natural that very strong temperature fluctuations are observed here.

The daily variation of air temperature near the earth's surface

1. The air temperature changes in the daily course following the temperature of the earth's surface. Since the air is heated and cooled from the earth's surface, the amplitude of the daily temperature variation in the meteorological booth is less than on the soil surface, on average by about one third. Above the sea surface, the conditions are more complicated, as will be discussed further.

The rise in air temperature begins with the rise in soil temperature (15 minutes later) in the morning, after sunrise. At 13-14 hours, the temperature of the soil, as we know, begins to drop. At 14-15 hours, the air temperature also begins to fall. Thus, the minimum in the daily course of air temperature near the earth's surface falls on the time shortly after sunrise, and the maximum - at 14-15 hours.

The diurnal variation of air temperature is quite correctly manifested only in conditions of stable clear weather. It seems even more regular on average from a large number of observations: long-term curves of the daily temperature variation are smooth curves similar to sinusoids.

But on some days, the daily course of air temperature can be very wrong. This depends on changes in cloudiness that change the radiation conditions on the earth's surface, as well as on advection, i.e., on the influx of air masses with a different temperature. As a result of these reasons, the minimum temperature can shift even to daytime hours, and the maximum - to the night. The diurnal variation of temperature may disappear altogether, or the diurnal change curve may take on a complex shape. In other words, the regular diurnal variation is blocked or masked by non-periodic temperature changes. For example, in Helsinki in January, with a probability of 24%, the daily maximum temperature falls between midnight and one in the morning, and only 13% of it falls on the time interval from 12 to 14 hours.

Even in the tropics, where non-periodic temperature changes are weaker than in temperate latitudes, the maximum temperature occurs in the afternoon only 50% of all cases.

In climatology, the daily course of air temperature, averaged over a long period, is usually considered. In such an averaged diurnal course, non-periodic temperature changes, which occur more or less uniformly for all hours of the day, cancel each other out. As a result, the long-term curve of the diurnal variation has a simple character, close to sinusoidal.
For example, we present in Fig. 22 daily course of air temperature in Moscow in January and July, calculated from long-term data. The long-term average temperature was calculated for each hour of a January or July day, and then, based on the obtained average hourly values, long-term curves of the daily variation for January and July were constructed.

Rice. 22. Daily variation of air temperature in January (1) and July (2). Moscow. The average monthly temperature is 18.5 °С for July, -10 "С for January.

2. The daily amplitude of air temperature depends on many influences. First of all, it is determined by the daily temperature amplitude on the soil surface: the greater the amplitude on the soil surface, the greater it is in the air. But the daily amplitude of temperature on the soil surface depends mainly on cloudiness. Consequently, the daily amplitude of air temperature is closely related to cloudiness: in clear weather it is much greater than in cloudy weather. This is clearly seen from Fig. 23, which shows the daily course of air temperature in Pavlovsk (near Leningrad), averaged for all days of the summer season and separately for clear and cloudy days.

The daily amplitude of air temperature also varies by season, by latitude, and also depending on the nature of the soil and terrain. In winter, it is smaller than in summer, as is the temperature amplitude of the underlying surface.

With increasing latitude, the daily amplitude of air temperature decreases, as the midday height of the sun above the horizon decreases. Under latitudes of 20-30° on land, the average daily temperature amplitude for the year is about 12°C, under latitude 60° about 6°C, under latitude 70° only 3°C. At the highest latitudes, where the sun does not rise or set for many days in a row, there is no regular diurnal temperature variation at all.

The nature of the soil and soil cover also matters. The greater the daily amplitude of the temperature of the soil surface itself, the greater the daily amplitude of the air temperature above it. In steppes and deserts, the average daily amplitude

There it reaches 15-20 °С, sometimes 30 °С. Above a dense vegetation cover, it is smaller. The proximity of water basins also affects the diurnal amplitude: it is less in coastal areas.

Rice. 23. Daily variation of air temperature in Pavlovsk depending on cloud cover. 1 - clear days, 2 - cloudy days, 3 - all days.

On convex landforms (on the tops and slopes of mountains and hills), the daily amplitude of air temperature is reduced in comparison with the flat terrain, and on concave landforms (in valleys, ravines and hollows) it is increased (Voyeikov's law). The reason is that on convex landforms, the air has a reduced area of contact with the underlying surface and is quickly removed from it, being replaced by new air masses. In concave landforms, the air heats up more strongly from the surface and stagnates more during the daytime, and at night it cools more strongly and flows down the slopes. But in narrow gorges, where both the influx of radiation and the effective radiation are reduced, the diurnal amplitudes are smaller than in wide valleys.

3. It is clear that small diurnal temperature amplitudes on the sea surface also result in small daily air temperature amplitudes above the sea. However, these latter are still higher than the daily amplitudes on the sea surface itself. Daily amplitudes on the surface of the open ocean are measured only in tenths of a degree, but in the lower layer of air above the ocean they reach 1 - 1.5 ° C (see Fig. 21), and even more over inland seas. The air temperature amplitudes are increased because they are influenced by the advection of air masses. The direct absorption of solar radiation by the lower layers of air during the day and their emission at night also play a role.

CHAPTERIIISHELLS OF THE EARTH

Topic 2 ATMOSPHERE

§thirty. DAILY CHANGE OF AIR TEMPERATURE

Remember what is the source of light and heat on Earth.

How is clear air heated?

HOW THE AIR HEATS. From the lessons of natural history, you know that transparent air transmits the sun's rays to the earth's surface and heats it up. It is the air that does not heat up with rays, but heats up from a heated surface. Therefore, the farther from the earth's surface, the colder it is. That is why when a plane is flying high above the ground, the air temperature is very low. At the upper boundary of the troposphere, it drops to -56 °C.

It has been established that after each kilometer of altitude, the air temperature drops by an average of 6 °C (Fig. 126). High in the mountains, the earth's surface receives more solar heat than at the foot. However, heat dissipates faster with height. Therefore, while climbing the mountains, you can notice that the air temperature gradually decreases. That is why snow and ice lie on the tops of high mountains.

HOW TO MEASURE THE AIR TEMPERATURE. Of course, everyone knows that air temperature is measured with a thermometer. However, it is worth remembering that a thermometer is incorrectly installed, for example, in the sun, it will show not the air temperature, but how many degrees the device itself has heated up. At meteorological stations, to obtain accurate data, the thermometer is placed in a special booth. Its walls are slatted. This allows air to freely enter the booth, together the grilles protect the thermometer of the wii. direct sunlight. The booth is installed at a height of 2 m from the ground. Thermometer readings are recorded every 3 hours.

Rice. 126. Air temperature change with height

Flying above the clouds

In 1862, two Englishmen flew in a balloon. At an altitude of 3 km, bypassing the clouds, the researchers were shivering from the cold. When the clouds disappeared and the sun came out, it got even colder. At the height of these 5 km, the water froze. It became difficult for people to breathe, it was noisy in their ears, and with a lack of strength, it was actually the axis. So slam the rarefied air on the body. At an altitude of 3 km, one of the survivors lost consciousness. At altitudes and 11 km it was -24°C (on Earth at that time the grass was green and flowers were blooming). Both daredevils were threatened with death. Therefore, they descended to Earth as quickly as possible.

Rice. 127. Graph of the daily course of air temperature

DAILY CHANGE OF TEMPERATURE. The sun's rays during the day heat the Earth unevenly (Fig. 128). At noon, when the sun is high above the horizon, the earth's surface heats up the most. However, high air temperatures are observed not at noon (at 12 o'clock), but two or three hours after noon (at 14-15 o'clock). This is because it takes time to transfer heat from the earth's surface. In the afternoon, despite the fact that the Sun is already descending to the horizon, the air continues to receive heat from the heated surface for another two hours. Then the surface gradually cools down, the air temperature decreases accordingly. The lowest temperatures are before sunrise. True, on some days such a daily temperature pattern may be disturbed.

Consequently, the reason for the change in air temperature during the day is a change in the illumination of the Earth's surface due to its rotation around its axis. A more visual representation of the change in temperature is given by the graphs of the daily course of air temperature (Fig. 127).

WHAT IS THE AMPLITUDE OF AIR TEMPERATURE VARIATION. The difference between the highest and lowest air temperatures is called the amplitude of the temperature fluctuation (A). There are daily, monthly, annual amplitudes.

For example, if the highest air temperature during the day was +25 °C, and +9 °C, then the amplitude of the fluctuations will be 16 °C (25 - 9 = 16) (Mat. 129). The nature of the earth's surface (it is called the underlying) affects the daily amplitudes of temperature fluctuations. For example, over the oceans, the amplitude is only 1-2 °C, over the steppes 15-0 °C, and in deserts it reaches 30 °C.

Rice. 129. Determination of the daily amplitude of fluctuations in air temperature

REMEMBER

The air is heated from the earth's surface; With altitude, its temperature drops by about 6 ° C for every kilometer of altitude.

The air temperature during the day changes due to changes in surface illumination (change of day and night).

The amplitude of temperature fluctuation is the difference between the highest and lowest air temperatures.

QUESTIONS AND TASKS

1. The air temperature at the earth's surface is +17 °C. Determine the temperature outside an aircraft flying at an altitude of 10 km.

2. Why is a thermometer installed in a special booth at meteorological stations?

3. Tell us how the air temperature changes during the day.

4. Calculate the daily amplitude of air fluctuations according to the following data (in ° C): -1.0, + 4, +5, +3, -2.

5. Think about why the highest daily air temperature is not observed at noon, when the Sun is high above the horizon.

PRACTICE 5 (Beginning. See pp. 133, 141.)

Topic: Solving problems on the change in air temperature with height.

1. The air temperature at the earth's surface is +25 °C. Determine the air temperature at the top of a mountain whose height is 1500 m.

2. The thermometer on the meteorological station, located on the top of the mountain, shows 16 ° C above zero. At the same time, the air temperature at its foot is +23.2 °C. Calculate the relative height of the mountain.

Another feature of the daily temperature variation can be considered the absence of seasonal variability at the daily temperature maximum. The whole year it is observed at 13-15 hours. And the presence of a daily variation in the daily temperature minimum. In the cold part of the year, it is observed at 5-8 o'clock, in the warm half of the year - at 3-5 o'clock. An essential characteristic of the daily course of air temperature is the temperature difference between the warmest and coldest hours - the amplitude. This difference gradually increases from 2.6° in December to 6.3° in September, when the nights are already cool in autumn and the days are hot in summer.

The range of average daily air temperatures throughout the year ranged from -12.9° to +32°. Analyzing (Table 2.6), we see the coldest month of the year - January, the warmest - August.

Negative average daily air temperature is observed in the Tuapse region in January, February, March, November and December. During the study period, 413 days were observed with a negative average daily temperature, including 159 in January, 127 in February, 44 in March, 15 in November and 68 in December. The average daily air temperature in the range of 16.1-17 ° is observed in the Tuapse region, with the exception of January. The average daily temperature of 15.1°-16°, except for January, is not observed even in July. And more interestingly, the average daily temperature in the range of 11.1 ° -15 ° is observed all year round, with the exception of July and August.

The average daily air temperature above 25 ° is observed in the Tuapse region from May to September. In total, during the study period, 454 days were noted with an average daily temperature above 25°, including 1 day in May, 16 days in June, 191 days in July, 231 days in August and 15 days in September. The air temperature does not remain unchanged, but it experiences large fluctuations from year to year, so the dates of its steady transition through various limits deviate significantly from the long-term average date. So, in some warm springs, there may not be a stable transition of the average daily air temperature through 20 °, and the transition through 15 and 20 ° occurs a month earlier. In other years, on the contrary, spring is cold and only by the end of June does the average daily temperature reach 15 °.

Thus, in the Tuapse region, on average, there are 131 days with an average daily air temperature below 10°, 74 days with an average daily temperature of 10-15°, 74 days with an average daily temperature of 15-20° and 66 days with an average daily temperature above 20 °.

In the period when the average daily air temperature is below 10 °, days of frost can be observed.

And, although there is no stable frosty period in the described area, when cold air masses invade the coast, the temperature drops to negative values every year.

Table 2.6 Daily variation of air temperature

Daily amplitude.

Usually frosts begin in the second or third decade of November, and stop in the first or second decade of March. A day with frost is considered to be one in which, at least in one of the periods of observation, the temperature according to the minimum thermometer was 0 ° and below 11, s. 115 - 125.

A characteristic feature of the cold period is that even on relatively cold days, when the average daily air temperature is negative, thaws are often observed in the daytime and the maximum air temperature is positive. The continuity of frost periods is constantly interrupted by thaws.

Let us also dwell in more detail on the nature of the distribution of hot days in the Tuapse region (Table 2.7). Days with an average daily temperature of 20.1 to 25° can be classified as moderately hot, and with an average daily temperature above 25° - hot. Note that on days when the average daily air temperature is 20° and above, the temperature observed during the day reaches 30-35°, and sometimes even higher.

Table 2. 7 Frequency of periods with hot days of various lengths

Hot days are observed from May to September, but mainly in July and August. So, for 35 years, 2741 days with moderately hot weather and 454 hot days were observed in the Tuapse region, including 422 hot days were observed in July and August. For the entire observation period, only three times the average daily air temperature was above 30°.

Days on which the air temperature is above 19°C, and the water vapor pressure is above 18.8 mb, can be classified as days with sweltering weather. In (Table 2.8), cases with stuffy weather are highlighted. Stuffy weather in the Tuapse region is observed in the warm part of the year both at night and during the day, with 38% of cases at night and 60% of cases during the day. The greatest probability of stuffy weather at night is about reaching an air temperature of 21-23 ° at a relative humidity of 81-90%. During the day, the weather is usually stuffy at an air temperature of 25-27 ° and air humidity of 61-80%.

Table 2.8 Repeatability (%) of various values of air temperature at certain values of relative humidity in July (1969-1978).


Air temperature, °С

It should be noted that in the Tuapse region, high air humidity can also be observed in the cold season. And the combination of low temperature and high humidity is perceived by the human body very hard. At the same time, the cold is very acutely felt, it is difficult to warm up. In addition, cold weather is perceived by the human body differently in calm and windy weather. The combination of negative air temperature with a strong wind, as it were, doubles the feeling of cold. In the Tuapse region, this combination occurs during the cold season with strong northeast winds.

On average, for the period from April to November, about 91 days of moderately hot and hot weather were observed in the Tuapse region, including 56 days of them in July and August.

In everyday life, daily temperatures are of particular importance for a person.

The lowest average daily air temperature in Tuapse is observed from January 14 to February 10. In January 1972, the most severe for the study period, on the 14th and 15th, the average daily air temperature was below -11°, and on January 13, 1964, the lowest average daily temperature was observed and amounted to -12.6°. Such a decrease in air temperature with the emergence of bora - a strong northeast wind. Negative average daily air temperature can be observed in the study area in January, February, March and December.

Due to the active winter cyclonic activity, warm air masses from the south often enter the Black Sea. Note that the average daily air temperature, for example, in January, can vary from -12.6° to 14.4°, and in February - from -10.3° to 15.3°. Those. and warm sunny days can be observed in the Tuapse region during the winter months.

A steady and at first slow increase in the average daily air temperature begins from the end of March and continues until July. The spring months are characterized by a change from relatively hot days to relatively cold ones. So, from April 29 to May 1, 1986, the average daily temperature was 7-9 ° above the long-term average temperature, and from May 5 to May 9 of the same year it fell 6-7 ° below the long-term average. Such sudden changes in temperature are usually accompanied by various natural phenomena (showers, snowfalls in the mountains, floods on rivers) and adversely affect people's health.

The warm period of the year in the Tuapse region begins on June 17 and lasts until September 10. The highest average long-term temperature of each day is from July 14 to August 24 and it is kept within 23.0-24.1 °. This period of the year can be considered hot and in some years and days of this period the average daily temperature reaches and exceeds 25 °.

In some years and this warm period, the average daily air temperature is below 20 °. In the last ten days of August, there is often a sharp drop in temperature, accompanied by intense showers. So it was in 1960, 1966, 1978 and 1980, and in 1980 the minimum temperature was 10.2 °.

There are cases when it is important to know the patterns of distribution not only of individual meteorological elements, but also of their complexes. An important role in the formation of the thermal regime is played by the advection of warm or cold air masses. The nature of advection depends on the direction of air masses. Complex processing of air and wind temperature - thermal roses - makes it possible to trace the influence of wind on air temperature.

In the winter months (January, February and December), the air masses that came from the northern half of the horizon are cold, and from the southern half of the horizon they are warm. March and November roses are almost the same. In both months, cold air masses come from the northeastern half of the horizon, and warm air masses come from the south and southwest. Only in November, the decrease and increase in temperature is more pronounced than in March. An interesting April rose. Some increase in temperature occurs only during easterly and western transport. The winds of the other points bring cold air to the Tuapse region. Note that in April the water in the sea has not yet warmed up, so the air masses over the sea are colder. Little different from the April rose of May. True, in May, in addition to the western and eastern winds, warm air is brought by northwestern and northern winds. Interesting rose of June. In June, the north, northeast and southeast winds bring cold air masses, the east and south winds are neutral, and the southwest, west and northwest winds come with warm air masses. In summer, when the winds are weaker than in the winter months, their influence on the temperature regime is less pronounced. The roses of July, August and September differ little from each other. In the summer months, winds from north to southeast come with relatively cold air masses, and winds from south to west, on the contrary, with warm air masses. The rose of October differs little from the roses of the winter months, but is somewhat differently oriented. 11, p. 125 - 131.

The comprehensive study of air temperature and humidity is of great practical importance. A complex characteristic for July separately for two periods of the day: from 9 to 18 hours - day and from 21 to 06 hours - night. Data processing was carried out according to gradations of air temperature through 2 °, and relative air humidity - through 10%. Materials are taken for 10 years (1969-1978).

In the Tuapse region, anomalous years, seasons, and months can be observed in terms of temperature. Years with all four normal seasons account for only about 3% of all years of the study period, years with one anomalous season - 21%, with two anomalous seasons - 35%, with three anomalous seasons - 28% and with all four anomalous seasons - 10 %. Such completely anomalous years are: 1924, 1938, 1948, 1953, 1962, 1963, 1966, 1972, 1981 and 1984.

atmosphere turbulent circulation air