Assessing Heatwaves and Their Association with North African Dust Intrusions in the Algarve (Portugal)

Heatwaves are an extreme meteorological event in which affected populations may also be exposed to deteriorated air quality conditions due to the increase in air pollutant concentrations, such as PM10 (particulate matter < 10 µg/m3). In order to identify heatwaves (1973–2019) in the region of Faro (Algarve) during the hot season (April–September), the Excess Heat Factor (EHF) index was applied. The Mann–Kendall test revealed an upward trend in three heatwave metrics in Faro, and the trend of accumulated heat load (EHF load) was also positive as would be expected, but its signal was not statistically significant. An inventory of North African dust events (2006–2019) was made, and their simultaneous occurrence with heatwaves was assessed, pointing to only 20% of dust events of the Sahara occurring simultaneously with heatwave days. A cluster analysis was conducted on daily geopotential height fields at 850 hPa level over the 2006–2019 period, and four distinct patterns were identified as the most prominent synoptic circulations promoting both heatwave conditions and North African dust over the Algarve.

Observation and modeling of the historic “Godzilla” African dust intrusion into the Caribbean Basin and the southern US in June 2020

This study characterizes a massive African dust intrusion into the Caribbean Basin and southern US in June 2020, which is nicknamed the “Godzilla” dust plume, using a comprehensive set of satellite and ground-based observations (including MODIS, CALIOP, SEVIRI, AERONET, and EPA Air Quality network) and the NASA GEOS global aerosol transport model. The MODIS data record registered this massive dust intrusion event as the most intense episode over the past 2 decades. During this event, the aerosol optical depth (AOD) observed by AERONET and MODIS peaked at 3.5 off the coast of West Africa and 1.8 in the Caribbean Basin. CALIOP observations show that the top of the dust plume reached altitudes of 6–8 km in West Africa and descended to about 4 km altitude over the Caribbean Basin and 2 km over the US Gulf of Mexico coast. The dust intrusion event degraded the air quality in Puerto Rico to a hazardous level, with maximum daily PM10 concentration of 453 µg m−3 recorded on 23 June. The dust intrusion into the US raised the PM2.5 concentration on 27 June to a level exceeding the EPA air quality standard in about 40 % of the stations in the southern US. Satellite observations reveal that dust emissions from convection-generated haboobs and other sources in West Africa were large albeit not extreme on a daily basis. However, the anomalous strength and northern shift of the North Atlantic Subtropical High (NASH) together with the Azores low formed a closed circulation pattern that allowed for accumulation of the dust near the African coast for about 4 d. When the NASH was weakened and wandered back to the south, the dust outflow region was dominated by a strong African easterly jet that rapidly transported the accumulated dust from the coastal region toward the Caribbean Basin, resulting in the record-breaking African dust intrusion. In comparison to satellite observations, the GEOS model reproduced the MODIS observed tracks of the meandering dust plume well as it was carried by the wind systems. However, the model substantially underestimated dust emissions from haboobs and did not lift up enough dust to the middle troposphere for ensuing long-range transport. Consequently, the model largely missed the satellite-observed elevated dust plume along the cross-ocean track and underestimated the dust intrusion into the Caribbean Basin by a factor of more than 4. Modeling improvements need to focus on developing more realistic representations of moist convection, haboobs, and the vertical transport of dust.

Characterization of dynamic and thermodynamic features of African dust outbreaks over the western Mediterranean basin: trend analysis for the 1948-2020 period

&lt;p&gt;All African dust outbreaks (ADO) that increased the regional-background levels of PM at the SE, SW, E, Central, NW, N and NE regions of the Iberian Peninsula and the Balearic Islands have been identified from 2001 to 2020 using a well-known procedure (https://www.miteco.gob.es/images/es/metodologiaparaepisodiosnaturales-revabril2013_tcm30-186522.pdf). However, the meteorological tools (air mass back-trajectories, satellite imagery and numerical models for prediction of dust levels) and data bases (time series of PM levels registered at air quality monitoring stations) needed to perform the identification procedure are scarce before the year 2000. For this reason the occurrence of ADO in the western Mediterranean basin during the former decades has not been well addressed so far.&lt;/p&gt;&lt;p&gt;In this study we have used the NCEP/NCAR global reanalysis dataset fields of meteorological parameters to characterize the main distinctive synoptic dynamic and thermodynamic features that were associated to the development of ADO and analyze their time evolution in the 1948-2020 period.&lt;/p&gt;&lt;p&gt;First, the main synoptic circulation types that favored the occurrence of the ADO identified in 2001-2020 were obtained. With this aim, a circulation classification methodology was applied for classifying the daily fields of geopotential height at the 850 hPa level at 12 UTC into prevalent atmospheric circulation types for SW Europe and NW Africa.&lt;/p&gt;&lt;p&gt;Next, the daily mean values of the 1000-500 hPa layer geopotential thickness (GT), the mean 925-700 layer potential temperature (TPOT) and the anomalies of temperature at 850 hPa (TANOM) were computed over all the regions of study. High values of these thermodynamic variables are associated with the presence of warm, stable and dry air masses. In fact, significantly higher values of GT, TPOT and TANOM were obtained in all regions during days under ADO circulation types than during other days in 2001-2020.&lt;/p&gt;&lt;p&gt;Finally, we analyzed the time evolution of all the days under ADO circulation types and their associated daily mean values of GT, TPOT and TANOM over the regions of study using the Theil-Sen method from 1948 to 2020.&lt;/p&gt;&lt;p&gt;Our results show that the monthly number of days under ADO circulation types display an upward trend of 0.06 monthly days per year at the 99.9% confidence level. Statistically significant upward trends for the monthly mean values of GT, TPOT and TANOM were also obtained over all the regions during days under prevailing ADO circulation types in summer, spring and winter.&lt;/p&gt;&lt;p&gt;In summary, the frequency of the dynamic and thermodynamic synoptic conditions favouring the development of ADO over the western Mediterranean basin has increased over the last 70 years. These results are in line with the exacerbation of warm conditions registered in southern Europe during the last decades.&lt;/p&gt;&lt;p&gt;Acknowledgements:&lt;/p&gt;&lt;p&gt;This study was funded by research project POSAHPI (Agencia Estatal de Investigaci&amp;#243;n, PID2019-108101RB-I00).&lt;/p&gt;

North African dust intrusions and increased risk of respiratory diseases in Southern Portugal

The study of dust intrusions in Portugal is still a subject on which little investigation has been made, especially in terms of their effects. Thus, this work aims to achieve two goals: firstly, to characterize the dust intrusions in the study area; and secondly, to evaluate the possible statistical association between the dust intrusion days and hospital admissions due to respiratory diseases. Dust intrusions in Portugal are prevalent during the summer season. During this season, the dust plumes tend to cover broader areas than in the other seasons and they have origin in the North African countries. In the study area for the period between 2005 and 2015, the relative risk of urgent hospitalizations due to respiratory diseases was 12.6% higher during dust intrusion days. In order to obtain this statistical association, a Distributed Lag Nonlinear Model was developed. With this work, we expect to help the development of further studies regarding North African dust intrusions in Portugal, more precisely their effects on human health.