Researchers from KU’s ENGEOS Lab carried out the first fog microphysics measurements over the UAE, filling a gap in the existing studies of fog microphysics and contributing to region-specific prediction models that can help mitigate the impact that fog can have on society

Despite being a desert country, the UAE has all the necessary ingredients for fog, seeing up to 50 foggy nights per year. Dry desert conditions exist next to the warm seas of the Gulf, with moist air carried inland by the afternoon sea breeze cooled by the desert surface at night. This type of fog is known as radiation fog.

Fog can be considered a low-lying cloud; it’s a visible aerosol of miniscule water droplets hovering above the ground. This aerosol impacts visibility and can have a major impact on societal activities, particularly transportation, where low visibility can result in flight delays or create hazardous driving conditions.

Dr. Michael Weston, Dr. Diana Francis, Dr. Narendra Nelli, Dr. Ricardo Fonseca, Dr. Marouane Temimi and Dr. Yacine Addad published their results in the

“Fog microphysics characteristics play a key role in fog life cycle, radiation and visibility,” Dr. Francis said. “Measurements of fog microphysics are important to understand and improve existing model parameter schemes for more accurate fog forecasting. We carried out the first fog microphysics measurements over the UAE, where fog is a frequent occurrence in the winter months. The results from this study are the first of their kind in the region, and expected to advance our current knowledge on fog dynamics and characteristics.”

Once fog develops, it will persist for as long as moisture can continue to condense out of the air. When the condensation process is slowed by rising temperatures or other factors, the fog will begin to dissipate. Much of the fog seen in the UAE is radiation fog, but some develops via a different mechanism known as advection fog. This type of fog forms over the surrounding seas and moves over the UAE. Regardless of the type of fog, when the sun rises and warms the country in the morning, the fog dissipates.

“The stages of fog from onset, to maturation, and finally dissipation, are dependent on the complex interactions of droplet microphysics, aerosol chemistry, radiation, turbulence, and surface conditions,” Dr. Francis said. “For example, the number of fog droplets gives an indication of the number of activated cloud condensation nuclei, which is an important interaction in understanding fog onset and persistence.”

The research team collected the microphysical measurements of fog in the UAE from 28 January to 17 February 2021. These measurements are novel as they were collected at a site next to a warm water body and in an arid subtropical region. While fog microphysics have been reported for arid regions, they are normally associated with cold oceans located on the western coast of continents. The team’s results fill a gap in the existing studies of fog microphysics.

“Knowing the microphysical properties of fog helps in developing a more accurate forecast of the fog life cycle,” Dr. Francis said. “Previously, we were applying the generally known properties of fog because we didn’t have information on fog microphysics in the UAE available to us.”

To understand what’s happening during foggy periods, forecasters need to know the aerosol content and quantity in the atmosphere to determine the number of cloud droplets that will form around the aerosols.

The depth of the fog and the resulting reduction in visibility depends on the number of droplets that form, but research has shown that neither the number of fog droplets nor their shape remains constant during the different stages of the fog lifecycle.

For numerical prediction models to reflect these processes, the fundamental properties of the single droplets and aerosol particles must be considered.

The team’s results are useful for future work on fog harvesting as knowing the microphysical properties of fog droplets helps in the design of fog harvesting systems.  The current observations are the first part of a long-term data set on fog microphysics for this region and future measurements are planned for the next winter season in the UAE.

Jade Sterling
Science Writer
22 March 2022

The post KU Researchers Making Fog Forecasting Models More Precise in the UAE appeared first on Khalifa University.

Despite being a desert country, the UAE has all the necessary ingredients for fog, seeing up to 50 foggy nights per year. 

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Why is there so much fog in a desert country? On Dr. Diana Francis, Head of the ENGEOS Lab , explains why the , despite being a desert country, has all the necessary ingredients for fog, seeing up to 50 foggy nights per year

— جامعة خليفة للعلوم والتكنولوجيا (@KhalifaUni)

Winter in the UAE brings respite from the scorching summer temperatures for which this region is famed. It also brings foggy mornings, enveloping the country from the skyscrapers in Dubai to the dunes in Liwa.

Despite being a desert country, the UAE has all the necessary ingredients for fog, seeing up to 50 foggy nights per year. Dry desert conditions exist next to the warm seas of the Gulf, with moist air carried inland by the afternoon sea breeze cooled by the night desert surface.

“The fog that forms over the UAE is known as radiation fog and is caused by the rapid cooling of the desert surface at night during the winter,” explained Dr. Diana Francis, Head of the Environmental and Geophysical Sciences (ENGEOS) Lab at Khalifa University. “This cooling leads to cool air in the lower layers of the atmosphere, which condenses the water vapor present there. The UAE has an atmosphere rich in water vapor since it’s surrounded by water bodies, where sea breeze circulation brings large amounts of water vapor inland during the day, which is trapped and forms fog during the night.”

Fog can be considered as a low-lying cloud; it’s a visible aerosol of miniscule water droplets hovering above the ground. About 95 percent of the fog seen in the UAE is radiation fog, which is why it is so prevalent in the winter and not the summer. The other 5 percent is advection fog, meaning it forms over the surrounding seas and moves over the UAE. Regardless of the type of fog, when the sun rises and warms the country in the morning, the fog dissipates.

The desert part of the country also plays a vital role in the weather over the UAE. When the winds over the country are calm, the moist air blown in from the sea earlier in the day mixes with the dust and sand in the air from the desert. This dust acts as the catalyst for fog development.

“Dust is the main component in the aerosol load present in the atmosphere over the UAE,” explained Dr. Francis. “Aerosols act as condensation nuclei for water vapor, causing the water to condense around the dust particles in the air. This is the same principle that leads to the condensation of water vapor on the mirror when you shower—the mirror is the aerosol particle. Given how much of the atmosphere is sand from the desert and the large capacity of the desert to cool down quickly at night, it makes sense that two of the hot spots for fog formation in the UAE are the Sweihan desert and the South West of Abu Dhabi. Both  are desert areas, with fog forming over these places, expanding, and then merging together, particularly over Abu Dhabi airport.”

ENGEOS lab research work shows that Abu Dhabi airport experiences more low visibility events than Dubai or Al Ain due to the fog that starts nearby. The fog is most frequent between 20 and 100 kilometers inland but can extend up to 200 kilometers inland over the desert, and tends to occur the most in December and January, even though the fog season lasts between September and March.

“At ENGEOS we perform now-casting of fog formation, spatial cover and duration using satellite observations and artificial intelligence techniques,” said Dr. Francis. “We also forecast fog formation, time of occurrence, intensity and duration one day in advance using modelling. We found that fog can occur any time between 7pm and 11am local time, but the highest number of events occur between 3am and 7am. This information is critical for operations at Abu Dhabi airport and the transport sector in general to reduce the risks related to fog and low visibility.”

Jade Sterling
Science Writer
28 March 2021

The post KU Researcher Explains What Makes the UAE So Foggy in the Winter appeared first on Khalifa University.