Researchers from KU aim to characterize the weather features over the Arabian Peninsula and establish knowledge on their seasonal and annual variability.

Khalifa University researchers are gaining a deeper scientific understanding of the processes that affect the climate in the Arabian Peninsula. And with this new insight, they will be better equipped to simulate and project future changes in the region’s climate.

Dr. Ricardo Fonseca, Postdoctoral Fellow, Dr. Diana Francis, Senior Research Scientist and Head of the KU Environmental and Geophysical Sciences (ENGEOS) Laboratory, and Dr. Narendra Nelli, Postdoctoral Fellow, with Dr. Mohan Thota from the Indian National Centre for Medium Range Weather Forecasting, investigated two of the weather systems that are responsible for determining the climate of the Arabian Region: The Arabian Heat Low (AHL) and the Intertropical Discontinuity (ITD). The researchers published their findings in the.

The AHL is an area of warm air close to the ground that develops inland as a result of strong surface heating by the sun, while the ITD is the boundary between the hot and dry winds from the desert and the cooler, moist winds from the Arabian Sea. Together, these systems play an important role in triggering summertime�� moist convection in one of the driest places on Earth.

“Thermal heat lows and convergence zones between moist and dry air masses are ubiquitous features of tropical and subtropical regions,” explained Dr. Francis. “They impact the meteorological features in these regions, and cause the regions’ dust storms, convection, and rainfall.”

“Like other desert regions, the Arabian Peninsula sees a thermal heat low develop during the summer season, and with this, the movement of the intertropical front from the Arabian Sea to the inland areas.”����

The ITD is a well-known convergence line, marking the leading edge of the monsoon flow. It separates the moist monsoon layer to the south from the dry boundary layer to the north. The convergence along this front plays a key role in favoring the development of moist air over the UAE during summer.

“Several studies have been conducted over Africa on the variability and dynamic role of the ITD,” said Dr. Francis. “But despite being key elements of the regional climate and weather patterns, the characteristics of the AHL and the ITD over the Arabian Peninsula have not been established yet. This is what we aimed to do: investigate the variability of the AHL and ITD over different periods of time.”

With more data on how these weather systems interact in the region, scientists will be able to develop more accurate climate models, enabling them to better predict future changes in the region’s climate systems, which is critical information in light of a rapidly changing climate due to human-induced climate change.

The AHL is a deep thermal low that develops in response to strong surface heating, mostly occurring as a summertime feature. The researchers found, however, that the AHL coincides directly with the active and break periods of the Indian Summer Monsoon: increased levels of rain over the Arabian Sea and the Indian subcontinent cause greater warming over the Arabian Peninsula.

Like the heat lows studied over the Sahara Desert, the Arabian Heat Low presents a cycle as it moves across the desert. The AHL moves northwest towards the core of the Arabian desert over the course of five to 15 days, where it intensifies, before moving southeast and weakening near the Arabian Sea.

“We also noticed that the build up and subsequent decline over the summer months is rapid and sudden at both ends of the season,” said Dr. Francis. “Besides the annual march of the sun, this may arise from the fact that the majority of the rainfall in the region occurs in winter and early spring. Once the soil and the atmosphere are bone dry, the heat low can develop very quickly, and collapse just as quickly once the rains return.”

Linked to the seasonal variability of the AHL is the ITD, as the stronger the heat low becomes, the further the ITD is pushed northwards.

The ITD is located along the Arabian Peninsula coastline during the winter, but migrates northwards as the summer months approach. In the warm season, its position can fluctuate by as much as 10 degrees, reaching the Arabian Gulf and southern Iranian coastline at night. These daily fluctuations are roughly five to ten times larger than those seen over Africa, with the researchers determining that this is due to the location of the AHL, which is closer to the nearby seas than its equivalent over Africa.

The researchers also noticed the link between the daily cycle of the ITD and the daytime expansion of the AHL. As the AHL intensified, increased moisture would move inland and the ITD would move northwards. As the cooler moist air moves with the ITD, the heat low weakens, and the ITD shifts southwards again.

The researchers also considered the variability of the AHL over a period of 41 years. They found that the AHL exhibits a clear positive trend linked to the increase in surface and air temperatures in the region over the last few decades associated with global warming. Interestingly, they found that while the surface temperatures have been increasing throughout the region, the increase in temperature is more pronounced in the heat low region, and roughly 35 percent lower in the areas outside the AHL region.

“Both features play a crucial role in weather conditions in the Arabian Peninsula by modulating the atmospheric circulation at different altitudes,” explained Dr. Francis.

“The ITD helps in triggering dust storms and rainfall as convergence between the systems promote cloud development while also increasing turbulence near the ground, which helps lift dust into the air. Investigating how processes such as dust storms are modulated by the AHL and ITD is an area we’d like to research in the future.”

Jade Sterling
Science Writer
24 August 2021

The post Khalifa University Research Shows Increasing Trends in Summertime Temperatures over the UAE appeared first on Khalifa University.

A new study from Khalifa University ��ݮ��Ƶ just how much dust contributes to the total aerosol load over the UAE, and how the atmospheric conditions have been changing since 2009.

Read Arabic story��.

By analyzing the atmospheric conditions over the United Arab Emirates using data from satellites and a ground-based robotic network, researchers at Khalifa University have determined the composition and variability of the atmospheric aerosols over the UAE.

Dr. Narendra Nelli, Postdoctoral Fellow, Samson Fissehaye, Graduate Student, Dr. Diana Francis, Senior Research Scientist and Head of the Environmental and Geophysical Sciences (ENGEOS) Lab, Dr. Ricardo Fonseca, Postdoctoral Fellow, Michael Weston, Research Engineer, Dr. Rachid Abida, Research Scientist, and Dr. Oleksander Nesterov, Postdoctoral Fellow, published in the. Chief among their insights is the large contribution of dust aerosols to the total aerosol load over the UAE and the need to account for these dust particles in weather and air quality forecasts.

While the UAE is famed for its year-round sunshine, it’s also well known that the air across the country tends to be dusty, thanks to the country’s desert geography. Particles in the atmosphere, including dust and pollution, can block the sunlight by absorbing or scattering light, preventing it from reaching the ground. This is known as aerosol optical depth.

“On a climatological time scale, we found that the aerosol optical depth (AOD) over the UAE has been decreasing since 2009, possibly due to the increasing trend in precipitation and changes in land use,” explained Dr. Francis. “Atmospheric aerosols have a wide range of impacts on the climate system but quantifying these effects is a challenge, primarily due to their sporadic nature. There’s still considerable uncertainty as to their net effect on the climate.”

Given that the areas needing to be investigated are so large, researchers use satellite-based observations to determine the variability of atmospheric aerosols over large regions. The KU researchers used data from the Cloud Aerosol Lidar and Infrared Pathfinder Satellite Observation satellite (CALIPSO) collected over a 14-year period.

“Long-term and global aerosol measurements with space-borne instruments are crucial for a better understanding of aerosol distribution and their effects on the environment,” said Dr. Francis. “But we also need to evaluate the accuracy of satellite observations against ground-based measurements, especially near source regions.”

The Aerosol Robotic Network (AERONET) is a collection of sun photometers distributed across the planet and used in a number of studies to validate satellite observations of atmospheric aerosols. The team compared the data from a seven-year period collected by AERONET against the data from CALIPSO.

“While there are aerosol-related studies in the UAE, they generally focus on individual events,” explained Dr. Francis. “We wanted to investigate the characteristics of the aerosols in the Arab region over a longer term and look at variability across the seasons and years.”

Understandably, dust is the predominant aerosol subtype in the region, in particular in the summer season when dust storms occur more frequently in the UAE. Combined with the dust particles in the atmosphere are what is known as “polluted dust”, which is a mixture of dust with particles from biomass burning and urban pollution, and “polluted continental”, which refers to aerosols that have originated from industrialized countries from both human and natural sources. Polluted continental is only seen in the colder months of the year due to the background northwesterly winds and weather systems that affect the region during the winter, blowing these fine aerosol particles in from other industrialized nations.

Over the longer term, the researchers noticed a “clear, albeit small, decreasing trend from 2009 onwards” in the AOD, particularly during the day time, indicating that there is a decreasing amount of dust in the atmosphere during the day now as compared to the years before 2009.

“A possible explanation is the increasing trend in precipitation in the same period, as rainfall is known to wash out aerosols leaving the atmosphere cleaner,” explained Dr. Francis. “Cloud seeding plays a potential role in this increase in precipitation as these operations have been conducted in the UAE since 2010. In addition, changes in land use and land cover in the UAE can also explain this decreasing trend in AOD. While urbanization may lead to an increase in pollution, it will also reduce the potential for dust emission, so providing the increase in AOD from pollution does not outweigh the decrease in amounts of dust, we’ll see a decrease in AOD overall.”

The researchers found that dust is a quasi-permanent component of the atmosphere over the UAE and so its presence needs to be accounted for in climate projections as well as in meteorological and air-quality forecasts.

The team plans to continue their research by extending the geographic area in question to cover the entire Arabian Peninsula, including Iran, to assess the regional atmospheric composition and links to patterns in atmospheric circulation.��

Jade Sterling
Science Writer
1 June 2021

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