'Toxic Dew', a Below Freezing Phenomenon in Tropical Dieng Plateau

TheIndonesia.id - The Meteorology, Climatology and Geophysics Agency (BMKG) predicts the phenomenon of "upas dew" or literally means toxic dew that began to appear in the Dieng Plateau, Banjarnegara Regency, Central Java, on Thursday morning, will last for ten days. The air temperature in Dieng when the upas dew appeared on Thursday, June 30, 2022, morning was around minus 1 degree Celsius at 04.00 WIB to 05.00 western Indonesian time.

"Regarding the freezing dew phenomenon, it is still related to the existence of two low pressure areas (LPA) in the northern hemisphere, namely the 04W low pressure center in the South China Sea west of the Philippines and the 98W low pressure center in the northeastern Philippines," said Head of BMKG Banjarnegara Geophysics Station Setyoajie Prayoedie in Banjarnegara, Thursday, June 30, 2022.

According to him, this condition is coupled with the strong Australian Monsoon (eastern wind) which brings dry air that has an effect on reducing rainfall in Java, especially Central Java. So that in a few days, the weather conditions in Central Java tend to be sunny to cloudy.

However, this condition will last up to ten days in July 2022 (1-10 July) and after that it will tend to be wet again due to the influence of warm sea surface temperatures around Java and the weak intensity of La Nina climate anomaly with probability around 66 percent until the July-August 2022 period.

"So, it is still possible for this phenomenon to occur in the first basic period in July 2022," said Setyoajie.

Meanwhile, in a press release, Head of BMKG Class II Meteorological Station Ahmad Yani Semarang Sutikno said local residents call this dew as toxic dew. "This phenomenon occurs when the temperature cools down, then cold and frozen dew falls. This dew covers the potato plants and the Dieng people call it "upas dew" because it kills potatoes," he said.

According to him, several factors contributed to the formation of frost that was preceded by extreme cold temperatures in Dieng such the apparent motion of the sun, cold temperature intrusion, and the rate of temperature decrease with altitude. He said the occurrence of the upstream dew phenomenon in the Dieng Plateau on May 10, 2021, then next on July 7, 2021, and the last occurence was on July 15-16, 2021.

"In 2022, the toxic dew happened precisely on January 4, 2022. Then on June 30, 2022," said Sutikno.

Furthermore, he said the cold temperatures phenomena at night and frost on the slopes of the Dieng mountains was more due to meteorological conditions and the current dry season. According to him, the air temperature during the peak of the dry season is generally colder and the earth's surface is drier.

"In such conditions, more solar heat will be wasted and lost to space. That's what causes the dry season air temperature to be cooler than the rainy season air temperature," he said.

In addition, the water content in the soil is thinning and there is very little water vapor in the air as evidenced by the low humidity of the air. At the peak of the dry season in Java, some places that are at high altitudes, especially in mountainous areas, have the opportunity to experience surface air conditions of below freezing point of 0 (zero) degrees Celsius.

Due to the air molecules in mountainous areas being more tenuous than in lowlands, so it cools down very quickly, especially when the weather is sunny and not covered by clouds or rain. Water vapor in the air will condense at night and then condense to stick to the ground, leaves, or grass.

Dew water that sticks to the tops of leaves or grass will immediately freeze because the air temperature is very cold. "When it reaches minus or zero degrees, dew or frost occurs in the area. In Indonesia, several places have been reported to experience this phenomenon, namely the Dieng Plateau, Mount Semeru, and the Jayawijaya Mountains," said Sutikno.