Distinguish hot sun concepts

Hanoi is experiencing intense hot days, the highest temperature is 42 degrees Celsius. Many people just feel, or hear the reporters notice, not understand the related concepts.

Question 1: How is the weather called hot weather?

Hot weather is a special type of weather that usually occurs during the summer months. One day, in a locality, it is considered to be hot weather when the highest temperature (symbolized Tx) reaches 35 degrees C

In a forecasted area (eg Northern Delta), if at least half of the monitoring stations are observed, the highest temperature in Tx ≥ 35 degrees C is called a hot day. widespread. When only observing less than half of the stations in the region with the highest temperature in Tx ≥ 35 degrees C, it is called the local heat.

One day is considered to be a fierce heat on a large scale when at least 2/3 of the monitoring stations in the region have the highest temperature Tx ≥ 35 degrees C, of ​​which at least half of the monitoring stations in the region forecast the highest temperature Tx ≥ 37 degrees C.

When wide-area sunshine appears continuously for 2 days or more in a forecasted area, it is called a heat wave.

In hot sunny days, the outdoor temperature is usually 4-6 degrees higher than the temperature measured in meteorological stations. (Photo: Ngoc Thanh).

Question 2: What is the phantom effect (or hot dry wind)?

In meteorology, the phenomenon of wind passing the mountain is called foehn . From the side of the mountain to receive the wind, the air moves up, the higher the air, the more cold it becomes and the agglomeration creates clouds for the rain on the side to receive the wind, and to collect more heat from the condensation emitted.

Mechanism to form wind.(Photo: National Hydrometeorological Center).

After crossing the mountain pass, the wind blew down this mountain. At that time the air has become drier, the temperature has increased due to the process of air being compressed, so to the foot of this mountain side the air becomes hotter and hotter than the air on the flank of the wind.

This phenomenon is known as phlegm and hyperthermia, a so-called damping effect. The stronger the effect, if the air reaches the side, the more humid the wind is and the higher the mountain peak. For example, with a mountain range of 3,000m high, the air temperature across the mountain is 10 degrees Celsius, to the foot of this mountain side the temperature is up to 18 degrees C.

Question 3: What is Lao wind?

Every year, in the summer months, Central Vietnam is often influenced by the summer monsoon winds blowing from the Bay of Bengan in the southwest direction. After crossing the territory of Cambodia and Laos, the wind has lost some moisture, encountered the Truong Son mountain range, the air has been pushed up high and cold, so most of the condensed water vapor has formed rain and falls down. west side of Truong Son range. When blowing to the east side, the wind becomes dry and hot. People often call this wind Lao wind. Thus, the Laos wind is also a hot dry wind due to the phlegm effect.

Vinh City, Nghe An, where often affected by Laos wind.(Photo: Nguyen Hai).

The main driving force behind the Lao wind is the hot low pressure area that often forms in China and China, sometimes the low pressure center is located in the North Delta. The low pressure area has the effect of drawing wind through the Truong Son range. The deeper this low pressure area (meaning that the lower the central pressure in the low pressure area), the stronger the wind blows, and there is a case spreading to the North, up to the Viet Bac area.

Question 4: When does the Lao wind appear?

Every year, in the coastal provinces of Central Vietnam, the Lao wind season usually starts from April to mid-September, blowing the most in June and July. According to statistics, each month this average has 7 -10 days, of which 2-4 days the wind blows strongly in Laos. Lao wind often blows in waves, short-term 2-3 days, 10-15 days long, lasting 20-21 days.

In one day, Lao wind often starts to blow from 8-9 am until evening, blowing the most from near noon to late afternoon, sometimes blowing continuously throughout the day and night, there is a 10-day-long night.

In order to cope with the burning Lao wind, farmers go to the fields to wear robes made of palm leaves.(Photo: Duc Hung).

When Lao winds blow, the highest temperature during the day often exceeds 37 degrees Celsius and the relative humidity of the day often drops very low, sometimes down to 30%. The sky was not cloudy, the sun was shining, the wind blew evenly like a fan of fire, the trees withered, the ponds dried up, the people and the animals were suffocating, it was easy to fire.

Other places also have hot dry winds, but the level is lighter than the Central. To quantify the phenomenon of hot and dry wind, meteorologists give the target: the day has a temperature of> 35 degrees C, the relative humidity có 55% is considered a hot and dry wind.

Question 5: What is the sign of the Lao wind coming?

Before the phenomenon of Lao wind blowing, the sky is often blue, the wind is weak or calm. In the sky there are only a few tiny clouds. The western horizon often has orange-yellow dry blinds, a very clear atmosphere that can sense a hot thing makes the skin look like it is in a mild fever. It is a warning sign that there will be Lao wind after a short time.

The hot season is also the exam season so both parents and students struggle.(Photo: Giang Huy).

At the same time, if you watch the evolution of meteorological factors in the day, you will see the following:

1. The wind changed direction, weakened, then turned counterclockwise, indicating a low pressure area was dominating.
2. The pressure is continuously reduced, when the largest reduction is made, the Lao wind will blow the most.
3. Very good foresight.

Of course, to forecast the weather with Laos wind, it is necessary to rely on the evolution of the weather systems in the region.