The Changma


Atmospheric setup that produces this event?

The upper-level winds 300mb are very zonal, and will generally only have a few jet fingers that will migrate through the area. This will end up enhancing the lifting ability of the boundary. There will be 500mb and 700mb troughs, that run from the China area, and perpendicular to the Korean Peninsula. These little disturbances aid in lift, cloud development, and enhance showers over the area. The 850 to the surface are effected with a high that is to the south or southeast of Japan, feeding a continuous flow of warm air advection and moisture into the Korean Peninsula. This is also antagonized by mountains that run from north to the south, fueling the fire of the Changma and pooling the moisture in the low laying area aiding in the instability. A boundary, develops from ranging from the surface to the 850, that instigates the rain, between the high to the southeast and the high that is over Mongolia, with cool, dry air.

How often does this particular forecast problem occur?

Every year in late June to early August

What are consequences of the forecast problem?

Flash flooding being the largest of the consequences with many side effects. Flooding often up roots the crops and flush this valuable product into the sea. One of the largest agricultural products that South Korea produces is its rice, which isn't only to feed their people but for export. So this effects price for the food, imports, and exports of their crops. With Seoul being between the north and south branches of the Han River it also presents a danger to their capital city, and half of the country's population. Some of the countries national treasures are also at risk of destruction, much of their history with the Shilla Kingdom's treasures are in the higher elevation. Land Slides in the higher elevations, where they have a variety of other crops and destroying property. (1)"Annual precipitation is around 1500 mm in the southern part of Korea, and 1300 mm in the central part. The precipitation that fall over the peninsula during the Changma accounts for more 1/2 the annual rainfall." Other side effects will be the reduction of visibility due to fog or low clouds, leaving a cloud depth from the surface up to 5,000' or more. Precipitation can vary from a light drizzle to a heavy rain delivering almost an inch an hour if not more.

Why is this particular event difficult to forecast for?

While this would seem to be an easy forecast, knowing how long the season, and when it will develop. What is most challenging is where the boundary will move over the area. While some diurnal effect reveal clues, portions of the boundary often move in different directions. Orientation can vary from northwest to southeast or from southwest to northeast and sometimes in different segments. The variant topography of Korea, deep valleys and mountains that range from the north to the south, while by Changma boundary oriented from west to east. The developing landscape of this land is amazing, in its resilience, but the older farming communities are often challenged if not devastated. Most of their farmland is generally just above or no more than 3 feet above sea level. One of the side effects is visibility decreases down to nothing if a soupy fog that coats not just the areas receiving the rain. This becomes a problem with aviation and landing. Effecting Inchon and Seoul. Another challenge is and extremely thick cloud deck from the surface all the way to 25,000 feet+; in the areas where the Changma is raining and drizzling. As this is related during the periods when more lift associated with the mid and upper level troughs aiding in more cloud development and rain showers through the column. In addition,that adds to the difficulty is, the development of the country, exploding with development. Through out, the country new communities are developing and new road ways over the land scape, this isn't over just a small area but the whole country. While most of the areas that once were rice paddies, and the differential between the land was fairly uniform. That is changing, and as such the puzzle that is the Changma becoming even more complex. This also adds more heat island effect, giving the environment more differential thermal and moisture over the entire spectrum.

What research or expert opinion is out there about this forecast problem?

Our local experts are the Korean Meteorological Association and USAF Meteorologist that tackle this issue every year. Climotological Analysis indicate that Central Korea receives on an annual account and where does it strike the most consistently. USAF installations in the Republic of Korea are required to observe weather elements, forecast and record climotological data and trends. This often gives indication of the past 50+ years of data, indicating potential climotological trends, long range models, and identifying trends with in the atmosphere. To add to analysis of the atmosphere, the USAF, utilize Doppler radar, which is unique to the area, and fairly new to the area. Working together, in a study to see a correlation of the radar products of Vertical Integrated Liquid, and Reflectivity to what potential rain fall could occur over the area. KMA typically issue 1, 3, and 6 month forecast for the Changma, Yellow wind and Typhoons which more traditionally occur around the same half of the year. (2) " The 3 month forecasts which are produced at monthly basis include trends of temperature, precipitation including special seasonal events. " KMA also utilize extended range forecast models based on global climate and water temperatures. They even ensure to review over data of global temperatures in the Pacific theater, to ensure to consider El Nino and La Nina, which could either enhance the Changma or retard its development. They take into the effect of temperature flux and vertical mixing with in the lowest five thousand feet ensuring a more effective forecasting model.

What can be done to better forecast this forecasting problem?

Continue to work on climotological study on the movements of the boundary and the highs that may be influencing the boundary. Determining the study in the Doppler data and identification of a way of tracking potential rain fall over the areas. Also upper air analysis, looking for upper-level waves that will move over the areas that will enhance the lift and also enhance the rain fall. Meteorological watch over the conditions as they develop. To contend with this challenging phenomena, the USAF and the Korean Meteorological Association have been working in unison to understand the demeanor of the Changma and its movements. Lastly, interrogation of local forecast products, extended forecasting numerological models, and sea surface data; my experience is that, forecast products that are indigenous seem to be far more reliable.



"Annual precipitation is around 1500mm in the southern part of Korea, and 1300mm in the central part. Precipitation during the winter accounts for less than 10% of total. More than half the annual rainfall occurs during changma season (monsoon season) when a stationary front hangs over the penninsula for about a month in the summer."


" The 3-month forecasts which are produced at monthly basis include the trends of temperature, precipitation including special seasonal events such as Asian dust, Typhoon and Changma for the next 3 months. "