IPB Lecturer Explains Why Nights Feel Colder During the Dry Season

Dr Givo Alsepan, a lecturer in the Department of Geophysics and Meteorology at IPB University’s Faculty of Mathematics and Natural Sciences, explained that the colder air temperatures felt at night and in the early morning during the dry season are a natural phenomenon known as bediding. In a statement from Bogor on Wednesday, Givo said the bediding phenomenon is not a direct impact of climate change, but rather part of seasonal climate dynamics that almost always occur from June to September. “Bediding is a normal atmospheric phenomenon that occurs during the dry season. It does not stand alone, but is a manifestation of physical atmospheric processes. This condition occurs when the daily minimum temperature drops quite significantly due to very effective radiative cooling,” he said. He explained that the phenomenon is triggered by a combination of atmospheric conditions common during the dry season. One of the main causes is the tendency for clear skies at night, which allows heat absorbed by the earth’s surface during the day to be more easily radiated back into the atmosphere and outer space. Furthermore, the air during the dry season is generally drier than during the rainy season. The reduced water vapour content in the atmosphere means less heat is trapped, making the cooling process more effective. “When the air is drier, the release of heat from the earth’s surface takes place more effectively. As a result, the air at night and into the morning feels much colder,” he stated. According to Givo, this condition is more pronounced in mountainous and highland areas, influenced by higher elevation and the tendency of cold air to accumulate in valleys. In areas such as the Dieng Plateau, this condition can even trigger the formation of frost or ‘embun upas’. He added that the Australian monsoon wind also strengthens the bediding phenomenon. During the dry season, Australia is experiencing winter, so the air mass moving towards Indonesia carries cooler and drier air characteristics, especially to areas south of the equator such as Java, Bali, and Nusa Tenggara. According to him, the developing El Niño phenomenon also has the potential to strengthen dry season conditions through reduced rainfall, lower air humidity, and more frequent clear skies at night, making the radiative cooling process more optimal. Givo urged the public to maintain their health during this phenomenon, especially children, the elderly, and those with respiratory illnesses, as the cold and dry air can worsen symptoms of influenza, asthma, and respiratory infections. He also reminded the public to maintain adequate fluid intake despite the cold weather and to increase vigilance against forest and land fires, which tend to increase during the dry season. He estimates that the bediding phenomenon will continue until the peak of the dry season in late July to August, and in some areas may persist until early September depending on atmospheric conditions. “The public does not need to worry excessively because bediding is part of the seasonal climate cycle. The most important thing is to continue to follow weather and climate forecast information from the BMKG in order to better anticipate changes in weather conditions,” he said.