Horizontal baric gradient. Changes in pressure with height. Standard atmosphere. Horizontal baric gradient Vertical and horizontal gradient

Looking at the isobars on the synoptic map, we notice that in some places the isobars are thicker, in others - less often.

It is obvious that in the first places the atmospheric pressure changes in the horizontal direction more strongly, in the second - weaker. They also say: "faster" and "slower", but one should not confuse the changes in space in question with changes in time.

To accurately express how atmospheric pressure changes in the horizontal direction, you can use the so-called horizontal baric gradient, or horizontal pressure gradient. Chapter 4 discussed the horizontal temperature gradient. Similarly, the change in pressure per unit distance in a horizontal plane (more precisely, on a level surface) is called a horizontal pressure gradient; in this case, the distance is taken in the direction in which the pressure decreases most strongly. And such a direction of the strongest change in pressure at each point is the direction along the normal to the isobar at this point.

Thus, the horizontal baric gradient is a vector whose direction coincides with the direction of the normal to the isobar in the direction of decreasing pressure, and the numerical value is equal to the derivative of pressure along this direction. Let's denote this vector by the symbol - С R, and its numerical value - dp / dn , where P is the direction of the normal to the isobar.

Like any vector, the horizontal baric gradient can be represented graphically by an arrow; in this case, an arrow directed along the normal to the isobar in the direction of decreasing pressure. In this case, the length of the arrow should be proportional to the numerical value of the gradient.

At different points in the baric field, the direction and magnitude of the baric gradient will, of course, be different. Where the isobars are condensed, the change in pressure per unit distance along the normal to the isobar is greater; where the isobars are moved apart, it is smaller. In other words, the magnitude of the horizontal baric gradient is inversely proportional to the distance between the isobars.

If there is a horizontal baric gradient in the atmosphere, this means that the isobaric surfaces in a given section of the atmosphere are inclined to the level surface and, therefore, intersect with it, forming isobars. Isobaric surfaces are always inclined in the direction of the gradient, i.e., where the pressure decreases.

The horizontal baric gradient is the horizontal component of the total baric gradient. The latter is represented by a spatial vector, which at each point of the isobaric surface is directed along the normal to this surface towards the surface with a lower pressure value. The numerical value of this vector is – dp/dn; but here n- the direction of the normal to the isobaric surface. The total baric gradient can be decomposed into vertical and horizontal components, or into vertical and horizontal gradients. You can also decompose it into three components along the axes of rectangular coordinates X, Y, Z. The pressure changes with height much more strongly than in the horizontal direction. Therefore, the vertical baric gradient is tens of thousands of times greater than the horizontal one. It is balanced or almost balanced by the force of gravity directed opposite to it, as follows from the basic equation of atmospheric statics. The vertical baric gradient does not affect the horizontal movement of air. Later in this chapter, we will only talk about the horizontal baric gradient, simply calling it the baric gradient.

Wind speed

As we already know from Chapter Two, the wind is the movement of air relative to the earth's surface, and, as a rule, the horizontal component of this movement is meant. However, sometimes one speaks of an upwind or a downwind, taking into account the vertical component as well. The wind is characterized by a velocity vector. In practice, wind speed refers only to the numerical value of the speed; this is what we will call the wind speed in the future, and the direction of the velocity vector - the direction of the wind.

Wind speed is expressed in meters per second, in kilometers per hour (especially for aviation services) and in knots (in nautical miles per hour). To convert the speed from meters per second to knots, it is enough to multiply the number of meters per second by 2.

There is also an estimate of the speed (or, as they say in this case, strength) of the wind in points, the so-called Beaufort scale , according to which the entire interval of possible wind speeds is divided into 12 gradations. This scale relates the strength of the wind to its various effects, such as the degree of sea waves, the swaying of branches and trees, the spread of smoke from chimneys, etc. Each gradation on the Beaufort scale has a specific name. So, zero of the Beaufort scale corresponds to calm, i.e., the complete absence of wind. wind at 4 points, according to Beaufort is called moderate and corresponds to a speed of 5-7 m/s; in 7 points - strong, with a speed of 12-15 m/s; at 9 points - by a storm, at a speed of 18-21 m/s; finally, a wind of 12 Beaufort is already a hurricane, with a speed of over 29 m/sec.

A distinction is made between the smoothed wind speed for a certain short period of time during which observations are made, and the instantaneous wind speed, which generally fluctuates strongly and at times can be significantly lower or higher than the smoothed speed. Anemometers usually give values ​​of the smoothed wind speed, and in the future we will talk about it.

Near the earth's surface, most often you have to deal with winds with speeds of the order of 4-8 m/s and rarely exceed 12-15 m/sec. But still, in storms and hurricanes of temperate latitudes, speeds can exceed 30 m/s, and in some gusts reach 60 m/sec. In tropical hurricanes, wind speeds reach up to 65 m/s, and individual gusts - up to 100 m/sec. In small-scale eddies (tornadoes, blood clots), velocities of more than 100 m/sec. In the so-called jet streams in the upper troposphere and lower stratosphere, the average wind speed over a long time and over a large area can reach up to 70-100 m/sec.

The wind speed near the earth's surface is measured by anemometers of various designs. Most often they are based on the fact that wind pressure causes the receiving part of the device to rotate (cup anemometer, mill anemometer, etc.) or deviates it from the equilibrium position (Wild board). Wind speed can be determined from the rotation speed or deviation. There are designs based on the manometric principle (Pitot tube). There are a number of designs of self-recording instruments - anemographs and (if the wind direction is also measured) anemorumbographs. Instruments for measuring wind at ground stations are installed at a height of 10-15 m above the earth's surface. The wind measured by them is called the wind near the earth's surface.

Direction of the wind

It must be well remembered that when speaking of the direction of the wind, they mean the direction from which it blows. You can indicate this direction by naming either the point on the horizon from where the wind blows, or the angle formed by the direction of the wind with the meridian of the place, that is, its azimuth. In the first case, 8 main points of the horizon are distinguished: north, northeast, east, southeast, south, southwest, west, northwest - and 8 intermediate points between them: north-northeast, east-north- east, east-southeast, south-southeast, south-southwest, west-southwest, west-northwest, north-northwest (Fig. 68). The 16 points indicating the direction from which the wind is blowing have the following abbreviations, Russian and international:

If the direction of the wind is characterized by its angle with the meridian, then the countdown is from the north clockwise. So north would be 0° (360°), northeast 45°, east 90°, south 180°, west 270°. When observing the wind in high layers of the atmosphere, its direction is usually indicated in degrees, and when observing at ground meteorological stations, in horizon points.

Wind direction is determined by a weather vane rotating about a vertical axis. Under the influence of the wind, the weather vane assumes a position in the direction of the wind. The weather vane is usually connected to the Wild board.

Just as for speed, one distinguishes between instantaneous and smoothed wind direction. The instantaneous wind directions fluctuate significantly around some average (smoothed) direction, which is determined by weather vane observations.

However, the smoothed direction of the wind in each given place on the Earth is constantly changing, and in different places at the same time it is also different. In some places, winds of different directions have almost equal frequency for a long time, in others - a well-pronounced predominance of some wind directions over others throughout the season or year. It depends on the conditions of the general circulation of the atmosphere and partly on the local topographical conditions.

With climatological processing of observations over the wind, it is possible to construct a diagram for each given point, which is the distribution of the frequency of occurrence of wind directions along the main points, in the form of the so-called wind rose (Fig. 69). From the origin of polar coordinates, directions are plotted along the horizon points (8 or 16) in segments, the lengths of which are proportional to the frequency of winds of a given direction. The ends of the segments can be connected by a broken line. Calm repeatability is indicated by a number in the center of the diagram (at the origin). When constructing a wind rose, one can also take into account the average wind speed in each direction, multiplying the frequency of this direction by it. Then the graph will show in arbitrary units the amount of air carried by the winds of each direction.

For presentation on climate maps, wind direction is summarized different ways. You can put wind roses on the map in different places. It is possible to determine the resultant of all wind speeds (considered as vectors) at a given location for a given calendar month over a multi-year period and then take the direction of this resultant as the mean wind direction. But more often the prevailing wind direction is determined. Namely, the quadrant with the greatest repeatability is determined. The midline of this quadrant is taken as the dominant direction.

Wind gust

The wind is constantly and rapidly changing in speed and direction, fluctuating around some average values. The reason for these fluctuations (pulsations or fluctuations) of the wind is turbulence, which was discussed in Chapter Two. These fluctuations can be registered by sensitive self-recording instruments. The wind, which has sharply pronounced fluctuations in speed and direction, is called gusty. With especially strong gustiness, they speak of a squally wind.

During conventional station observations over the wind, the average (smoothed) direction and its average speed are determined over a period of time of the order of several minutes. When observing using the Wild vane, the observer must follow the fluctuations of the wind vane for two minutes and the fluctuations of the Wild board for two minutes, and as a result determine the average (smoothed) direction and average (smoothed) speed for this time. A cup anemometer makes it possible to determine the average wind speed for any finite period of time.

However, it is also of interest to study the gustiness of the wind. The gustiness can be characterized by the ratio of the amplitude of wind speed fluctuations over a certain period of time to the average speed over the same time; in this case, either the average or the most frequently occurring amplitude is taken. Amplitude is the difference between successive maximum and minimum instantaneous speed. There are other characteristics of variability, including the direction of the wind.

Impulsiveness is greater, the greater the turbulence. Consequently, it is more pronounced over land than over sea; especially large in areas with complex terrain; more in summer than in winter; has an afternoon maximum in the diurnal variation.

In a free atmosphere, turbulence can cause aircraft to wobble. The turbulence is especially great in highly developed convection clouds. But it also increases sharply in the absence of clouds in the zones of the so-called jet streams.

CSS gradient represents the transition from one color to another.

Gradients are created using the linear-gradient() and radial-gradient() functions.

A gradient background can be set in the background , background-image , border-image , and list-style-image properties.

How to make a gradient in CSS

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1. linear-gradient()

linear gradient created using two or more colors that have a direction, or gradient line.

If no direction is specified, the default value is used − top down.

The default gradient colors are distributed evenly in a direction perpendicular to the gradient line.

Background: linear-gradient(angle/side or slope angle via keyword (keyword pairs), first color, second color, etc.);

Direction The gradient can be specified in two ways:
with tilt angle in degrees deg , whose value determines the angle of the line inside the element.

Div ( height: 200px; background: linear-gradient(45deg, #EECFBA, #C5DDE8); )

using keywords to top , to right , to bottom , to left , which correspond to the gradient angle of 0deg , 90deg , 180deg and 270deg respectively.

Div ( height: 200px; background: linear-gradient(to right, #F6EFD2, #CEAD78); )

If the direction is given by a pair of keywords, such as to top left , then the starting point of the gradient will be in the opposite direction, in this case, bottom right.

Div ( height: 200px; background: linear-gradient(to top left, powderblue, pink); )

For uneven distribution of colors, the starting position of each color is specified through the gradient stop points, the so-called color stops. Breakpoints are specified in % , where 0% is the start point, 100% is the end point, for example:

Div ( height: 200px; background: linear-gradient(to top, #E4AF9D 20%, #E4E4D8 50%, #A19887 80%); )

For a clear distribution of color bands, each subsequent color must be started from the stop point of the previous color:

Div ( height: 200px; background: linear-gradient(to right, #FFDDD6 20%, #FFF9ED 20%, #FFF9ED 80%, #DBDBDB 80%); )

2. radial-gradient()

radial gradient differs from linear in that the colors come out from one point (the center of the gradient) and evenly spread outward, drawing the shape of a circle or ellipse.

Background: radial-gradient(gradient shape/size/center position, first color, second color, etc.);

gradient shape defined by the keywords circle or ellipse . If no shape is specified, the radial gradient defaults to an ellipse.

Div ( height: 200px; background: radial-gradient(white, #FFA9A1); )

Center position set using the keywords used in the background-position property, with the at prefix added. If no center position is specified, the default at center is used.

Div ( height: 200px; background: radial-gradient(at top, #FEFFFF, #A7CECC); )

A pair of values, specified in length units % , em , or px , controls the size of the elliptical gradient. The first value specifies the width of the ellipse, the second value specifies the height.

Div ( height: 200px; background: radial-gradient(40% 50%, #FAECD5, #CAE4D8); )

Gradient size set using keywords. The default is farthest-corner.

With a radial gradient, you can create realistic three-dimensional figures such as balls, buttons.

Ball

Button

Postage Stamp

Using a transparent color in gradients, you can create such effects.

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