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Michael Weston
,
Marouane Temimi
,
Roelof Burger
, and
Stuart Piketh

Abstract

Fog has a significant effect on aviation and road transport networks around the world. The International Airport in Abu Dhabi, United Arab Emirates, experiences dense fog during winter months that affect operations at the airport. We describe the fog climatology at the airport using 36 years of aviation routine weather reports (METAR), an important long-term data source, and report on the number of fog days per year, the seasonal cycle, the diurnal cycle, and the duration of fog events. Fog days per year vary from 8 to 51, with a mean of ~23.91 days (standard deviation of 9.83). Events are most frequent from September until March, with December and January being the most active months. November, unexpectedly, has a low number of fog days, which appears to be due to a decrease in aerosol loading in the atmosphere. The most fog days experienced in one month is 13 (March 2004). Fog occurs any time from 1900 to 1100 local time, and the frequency increases as night progresses, peaking around sunrise. Fog events most frequently last 1 h or less. Events of 9 h or more were recorded in January and December, with the longest event lasting 16 h. Events are strongly dependent on the land–sea breeze and seldom form when the wind is blowing from the Arabian Gulf. The thickness of the nocturnal inversion layer increases up to about 500 m AGL on fog days as compared with 273 m AGL on clear-sky days. This study is the first to use the 36-yr dataset to characterize fog climatology at Abu Dhabi Airport.

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Paquita Zuidema
,
Jens Redemann
,
James Haywood
,
Robert Wood
,
Stuart Piketh
,
Martin Hipondoka
, and
Paola Formenti
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Paola Formenti
,
Barbara D’Anna
,
Cyrille Flamant
,
Marc Mallet
,
Stuart John Piketh
,
Kerstin Schepanski
,
Fabien Waquet
,
Frédérique Auriol
,
Gerard Brogniez
,
Frédéric Burnet
,
Jean-Pierre Chaboureau
,
Aurélien Chauvigné
,
Patrick Chazette
,
Cyrielle Denjean
,
Karine Desboeufs
,
Jean-François Doussin
,
Nellie Elguindi
,
Stefanie Feuerstein
,
Marco Gaetani
,
Chiara Giorio
,
Danitza Klopper
,
Marc Daniel Mallet
,
Pierre Nabat
,
Anne Monod
,
Fabien Solmon
,
Andreas Namwoonde
,
Chibo Chikwililwa
,
Roland Mushi
,
Ellsworth Judd Welton
, and
Brent Holben

Abstract

The Aerosol, Radiation and Clouds in southern Africa (AEROCLO-sA) project investigates the role of aerosols on the regional climate of southern Africa. This is a unique environment where natural and anthropogenic aerosols and a semipermanent and widespread stratocumulus (Sc) cloud deck are found. The project aims to understand the dynamical, chemical, and radiative processes involved in aerosol–cloud–radiation interactions over land and ocean and under various meteorological conditions. The AEROCLO-sA field campaign was conducted in August and September of 2017 over Namibia. An aircraft equipped with active and passive remote sensors and aerosol in situ probes performed a total of 30 research flight hours. In parallel, a ground-based mobile station with state-of-the-art in situ aerosol probes and remote sensing instrumentation was implemented over coastal Namibia, and complemented by ground-based and balloonborne observations of the dynamical, thermodynamical, and physical properties of the lower troposphere. The focus laid on mineral dust emitted from salty pans and ephemeral riverbeds in northern Namibia, the advection of biomass-burning aerosol plumes from Angola subsequently transported over the Atlantic Ocean, and aerosols in the marine boundary layer at the ocean–atmosphere interface. This article presents an overview of the AEROCLO-sA field campaign with results from the airborne and surface measurements. These observations provide new knowledge of the interactions of aerosols and radiation in cloudy and clear skies in connection with the atmospheric dynamics over southern Africa. They will foster new advanced climate simulations and enhance the capability of spaceborne sensors, ultimately allowing a better prediction of future climate and weather in southern Africa.

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Sarah A. Tessendorf
,
Roelof T. Bruintjes
,
Courtney Weeks
,
James W. Wilson
,
Charles A. Knight
,
Rita D. Roberts
,
Justin R. Peter
,
Scott Collis
,
Peter R. Buseck
,
Evelyn Freney
,
Michael Dixon
,
Matthew Pocernich
,
Kyoko Ikeda
,
Duncan Axisa
,
Eric Nelson
,
Peter T. May
,
Harald Richter
,
Stuart Piketh
,
Roelof P. Burger
,
Louise Wilson
,
Steven T. Siems
,
Michael Manton
,
Roger C. Stone
,
Acacia Pepler
,
Don R. Collins
,
V. N. Bringi
,
M. Thurai
,
Lynne Turner
, and
David McRae

As a response to extreme water shortages in southeast Queensland, Australia, brought about by reduced rainfall and increasing population, the Queensland government decided to explore the potential for cloud seeding to enhance rainfall. The Queensland Cloud Seeding Research Program (QCSRP) was conducted in the southeast Queensland region near Brisbane during the 2008/09 wet seasons. In addition to conducting an initial exploratory, randomized (statistical) cloud seeding study, multiparameter radar measurements and in situ aircraft microphysical data were collected. This comprehensive set of observational platforms was designed to improve the physical understanding of the effects of both ambient aerosols and seeding material on precipitation formation in southeast Queensland clouds. This focus on gaining physical understanding, along with the unique combination of modern observational platforms utilized in the program, set it apart from previous cloud seeding research programs. The overarching goals of the QCSRP were to 1) determine the characteristics of local cloud systems (i.e., weather and climate), 2) document the properties of atmospheric aerosol and their microphysical effects on precipitation formation, and 3) assess the impact of cloud seeding on cloud microphysical and dynamical processes to enhance rainfall. During the course of the program, it became clear that there is great variability in the natural cloud systems in the southeast Queensland region, and understanding that variability would be necessary before any conclusions could be made regarding the impact of cloud seeding. This article presents research highlights and progress toward achieving the goals of the program, along with the challenges associated with conducting cloud seeding research experiments

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