Conclusion

1. Weather forecast using wrf model

According to the typhoon simulation we studied, the expected forecast is as follows :

BAVI is expected to land on the Korean Peninsula at 12 p.m. on the 26th. At this time, the typhoon is at a very strong level of about 42m/s to 51m/s , allowing humans and large stones to fly away. Therefore, it is necessary to refrain from going out.

Typhoon warnings will be issued because strong winds and storms have reached the watch standards. It is expected to rain nationwide, especially from 2 a.m. on August 26.

2. Path+SST

In conclusion, we would like to compare numerical forecasts and real-world path.

First, the actual path is as above. (The date and time of the image above follow KST.)

It can be seen that the numerical forecasts and the real path are different. Especially in the actual path, we could see a lot of western bias. As the BAVI moved northward quickly, it came up to Korea before North Pacific anticyclone escaped. Thus it moved westward along the edge of the anticyclne.

BAVI originated at a high altitude near Taiwan and turned into a very strong typhoon near Jeju Island. The reason can be found at sea level temperatures. When Typhoon BAVI moved northward, the sea temperature near Jeju Island was 303K. Since it was about 0.5K higher than the average year, BAVI received a lot of energy from this high-temperature sea.

Although Korea's West Sea water temperature is slightly lower than the sea near Jeju Island, it can be the high temperature area of 299K-300K, so the power of typhoon BAVI did not weaken sharply even as it passed the West Coast. In other words, BAVI is a typhoon that quickly expanded and maintained its power despite the unusual occurrence process. We saw the cause of this rise in sea level temperature as the effect of global warming. It was determined that the occurrence of unusual typhoons, such as typhoon BAVI, could increase further due to climate change in the future. The increase in these unusual typhoons will make typhoon forecast more difficult to predict, so we felt the need for development of numerical forecasting technology again.

Our team identified the association with sea surface temperature in the progress of real BAVI and analyzed Surface Sea Temperature (SST) through numerical forecasts. It was confirmed that the sea level temperature was high near Jeju Island, and SST in the West Sea was also 297-299K, which was included in the high temperature zone.

This additional analysis allowed us to deepen our understanding of the progress of BAVI.

3. Weather Analysis

(1) In particular, precipitation was observed up to 45mm near the eye of the typhoon, and considering the size and extent of the typhoon's impact, heavy precipitation is expected throughout the Korean Peninsula. Furthermore, the maximum wind speed outside the center is expected to be more than 12 m/s, so much higher wind speeds are expected near the center.

(2) As the typhoon developed, it rained the most on the Korean Peninsula around the afternoon of August 26th, and the SLP became narrower as it became the center of the typhoon.

(3) From August 22. we identified the center of the typhoon and its shape, and there were active temperature changes during the day time than in the early morning hours.

(4) the precipitation increased sharply as the typhoon approached, and decreased sharply as the typhoon passed. This seems to be because the typhoon was accompanied by precipitation.

To compare with real-world precipitation changes, we further narrowed the index to draw a graph of cumulative precipitation. The results show similar values (average cumulative precipitation of 36 mm) compared to data presented by the Korea Meteorological Administration.

(5) Wind speeds increased as the typhoon approached, and air pressure decreased. However, the change in direction of wind speed was not perfectly consistent with the change in the normal wind blowing in the actual danger zone. This is presumably due to the use of rectangular index averages covering the Korean Peninsula.

(6) The temperature at the center of the typhoon BAVI gradually increased, and decreased as the typhoon landed on the Korean Peninsula. The SLP at the center of the typhoon BAVI gradually decreased and then increased as it landed on the Korean Peninsula.

(7) As the typhoon developed, the area with low water vapor distribution appeared in the form of funnels at the center of the typhoon BAVI, and this form was maintained during the typhoon.

(8) Winds were initially weak, but over time they developed at their peak from 08/24 03:00:00 to 08/26 03:00:00, with maximum values of 58.7 m/s and 63.4 m/s in the u and v directions, respectively. The wind speed was at least 10 m/s faster than the actual observed wind speed, which could be seen as a difference between the modeling and real values, or as a result of decomposing them in the u and v directions.

(9) Anomalies have been observed in the west-east section, but overall, the temperature near the center is the highest and the variation is the highest. The high temperature in the center seems to be due to weak high pressure at the center of the typhoon. At the time of the typhoon's extinction, the stable temperature layer collapses and shows a fairly unstable state.

4. Limitations of numerical forecasts

Several climatic value predictions and analyses were possible while conducting numerical forecasting studies using wrf modeling, but the climatic values predicted through modeling, such as those shown in path prediction, appear to some extent similar to the true value, but have not been fully predicted. In other words, numerical forecasts have a limitation that there is a significant difference between model values and real values. Given the feature of numerical forecasts predicting weather through calculations using initial values and boundary conditions, we could guess that this limitation is due to the effects of unconsidered momentary changes or variables in the modeling process.

5. What was disappointing?

The second was that the correlation analysis could not clearly show the correlation between sea level temperature and SLP that experts analyzed. Although correlation is difficult to determine the relation between the two climate values, comparing the time series graphs of temperature and SLP change at the center of the typhoon BAVI together shows that the SLP increases as the temperature at the center of the typhoon decreases rapidly. In other words, it was indirectly guessed that a decrease in temperature in the area around the typhoon would reduce the intensity of the typhoon.

Finally, the last part was the limitation of accurate path analysis. The path prediction in the numerical forecasting model was one of the most important things for our team project. Comparing the path of the actual observed typhoon with the path we predicted, we could see that the path of real typhoon BAVI was generally located west of the predicted path. However, since there were so many factors affecting the path prediction of typhoons, it was difficult to analyze the obvious reasons of the result with just one wrf model.

6. Significance of this Research

Although there was a difference between the actual typhoon's route and the predicted route, the WRF model showed that Jeju Island was the most affected by BAVIi’s on the 26th.

In addition, BAVI moved westward rather than the Korea Meteorological Administration's forecast, so the path forecast was somewhat disappointing. But the excellent intensity forecast was able to prepare in advance. A numerical model with 100 percent accuracy may not exist, and it seems necessary to develop technologies to maximize accuracy.

Currently, the Korean Integrated Model(KIM) is actually being used, and the next-generation numerical forecast model project is in progress. If completed successfully, it will be possible to enter advanced weather countries as well as leap from beneficiary countries in the weather sector to support countries. It is also expected that high-accuracy weather forecasts will greatly contribute to protecting the property and lives of the people and improving the quality of life.