Statistical analysis of zonal wind component in the occurrence of sudden stratospheric warming

Document Type : Full length article


1 Department of Geography, Faculty of Literature and Humanities, Lorestan University, Khorramabad, Iran

2 Department of Meteorological, Meteorological and Joe Sciences Institute, Iran Atmospheric Science & Meteorogical Research Center, Tehran, Iran



In this study, the sudden heating of the Sunsphar, using NCEP/NCAR analysis data, was investigated in the statistical period of 1948-2020. The results of the analysis showed that the abundance of sudden heating events in February is 17 % more than other months. After calculating the intensity of the heating, it was found that in 2018-2017 heating, the average orbital component of the wind reached -48 m / s and the negative values of this quantity continued; This heating has been identified as the most severe sudden heating in the statistical period. The correlation between the changes of the orbital component of the wind is the time of the end of the final heating in all the years under the study of -0.6, which means that the higher the standard deviation of the wind orbital component data, the sooner the end of the cold season and the final warming. The correlation rate of the two winter heating and the final heating with the main heating intensity is -0.8 and indicates a strong and reverse relationship between the two parameters and indicates that the more intense (main) winter warming is more severe, the final heating occurs earlier and the distance The two main heating and the end are less
Extended abstract
In this research, sudden stratospheric warming has been investigated. The stratosphere and the troposphere play an active role in determining the climate of the Earth's surface. Sudden stratospheric warming refers to a large-scale winter disturbance that significantly affects the temperature and circulation in the middle atmosphere. One of the goals of this research is to investigate and discover the relationship between the changes in the speed of the zonal component of the wind and the occurrence of the two sudden winter significant warming and the final warming.
In order to further understand the phenomenon of sudden stratospheric warming, the average zonal wind component at the pressure level of 10 hPa on the longitude of 60° N was investigated for 73 years (1948-2020). NCEP/NCAR reanalysis data have been used to reveal this phenomenon. Moreover, from the zonal component of the wind at the level of 10 hPa on the 60° N, from zero to 360 degrees, which has 144 points with a spatial resolution of 2.5 degrees, a zonal average was taken; then in each month of the year for the number of years, the average zonal component of the wind has been averaged (measured) again. This study has been limited to the occurrence of this phenomenon only in the cold period of the year because it occurs only in cold seasons. The calculations were done by using Excel and MATLAB software. The criterion for detecting sudden stratospheric warming is the negative value of the average zonal component of the wind, and its intensity is considered based on the amount of this component going below zero and the number of consecutive days when this quantity has negative values. For the sudden warming of the stratosphere to occur, the speed of the zonal component of the wind must decrease, and as a result, the temperature must increase. Moreover, in the warming of March, the researcher did her best to allocate a time gap of at least 20 days with the final warming. Pearson's correlation test has been used to correlate the changes in the wind component with the final warming event.
Results and Discussion
Investigating and understanding the changes in the zonal wind speed will shed light on many factors. The speed of the zonal component of the wind is not the same throughout the year, but this component also changes due to the changes in the angle of the sun's rays. The highest speeds of this component are in January, with 44.05 m/s, and in December, with 39.94 m/s. The average speed of the zonal component of the wind is 21.29 m/s in October, 33.91 m/s in November, 36.31 m/s in February, and 23.34 m/s in March. In April, the speed of the currents is greatly reduced, and in some years, in the second half of the month, the wind currents blow eastward. The overall average wind speed in this month is 5.27. From May onwards, wind currents blow to the east; in other words, they become negative. Furthermore, this means the warm season and final warming have begun. The duration of the effect of wind speed changes on the amount of temperature changes was obtained by running Pearson correlation calculations between these two components. In addition to simultaneous correlation, the delayed correlation was also used. The degree of simultaneous correlation was measured to be -0.73 and has been the most related to the applied delays. These calculations show that reducing the speed and changing the direction of the wind simultaneously have the most significant effect on increasing the temperature. After examining and extracting the warming that occurred, the intensity of this phenomenon was also investigated by drawing a two-line graph for the two components of wind and temperature for all the years under investigation.
Identification of 36 sudden stratospheric warmings of the major type and determination of their intensity was carried out. The intensity of this phenomenon is different in each occurrence. The maximum drop in wind speed and the number of days below zero are the criteria for measuring the intensity of sudden stratospheric warming. In the year between 2017 and 2018, the most severe warming occurred with the negative direction of the zonal wind at the rate of -48.8 and remaining in a negative state for 20 days. The most likely occurrence of a sudden warming of the major type is related to February. The intensity of warming that occurred in each month shows a direct relationship with the amount of zonal wind speed. January ranks first in terms of warming intensity, with a rate of -20.5 m/s. Seemingly, March has had the slightest warming with a rate of -7.1 m/s. The annual fluctuation in the zonal component of the wind at the beginning of the final warming is a significant value. This relationship was explored by calculating the correlational strength between the zonal wind speed's standard deviation and the major warming's starting day. The degree of this correlation in all years under study (in years both with and without warming) is -0.6, which shows a moderately strong inverse relationship. Moreover, it means that the higher the standard deviation of the wind speed, the earlier ending of cold season and the occurrence of final warming. The commencement of the final warming, or in other words, the end of the cold season in years with sudden warming, was calculated as follows:
 The correlation between the intensity of sudden stratospheric warming and the interval time of the major warming and the final warming was measured; with a rate of -0.8, this correlation indicates a rather strong but inverse one between the two figures – it also states that the higher the intensity of the sudden warming, the sooner the final warming will occur, and the shorter the time interval of the two warmings will be.
Changes in the zonal wind speed at the level of 10 hPa on the longitude 60° have a relatively strong relationship with factors such as sudden stratospheric warming, the intensity of sudden warming, the percentage of sudden warming, and the time of final warming. The zonal wind speed in each month depends on the angle of the sun's rays. This has caused the possibility of sudden stratospheric warming to be different each month and also affects the intensity of the warming. With a zonal wind speed of 44.05 m/s, January has the most intense warming in terms of polar vortex destruction, which changes the direction of the wind orbit by 20.5 m/s. The degree of correlation between zonal wind changes and the occurrence of final warming indicates a strong but inverse relationship between the two. The higher the standard deviation of the zonal wind speed, the sooner the final warming will arrive. Finally, the relationship between the two major winter warmings and the final warming can be expressed as follows:
In years when sudden stratospheric warming occurs, the greater the warming intensity is, the earlier the final warming occurs.
There is no funding support.
Authors Contribution
All of the authors approved thecontent of the manuscript and agreed on all aspects of the work.
Conflict of Interest
Authors declared no conflict of interest.
We are grateful to all the scientific consultants of this paper.


Main Subjects

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