Search

Fire activity in 288 areas (2.5° N × 10° E) in the Arctic region (50°–70° N, 0°–360° E) was analyzed using about 4.4 million satellite hotspot (HS) data from 2002 to 2021. A total of 21 high fire density areas from eastern Europe to western Canada were selected, and their fire–weather conditions during each active fire period were analyzed using about 1820 various weather maps at the upper and the lower air level. Analysis results showed that the active fires in the Arctic region occurred under the fire–weather conditions associated with the northward movement of cut-off high (COH) and warm air masses detached from the south caused by large westerly meandering (LWM). LWM is a sign of the beginning of an active fire period. Very active fires on HS peak days occurred several days after the start of the northward movement of COHs and under mainly high-pressure conditions in the upper air and strong wind conditions in the lower air. The time lag of these several days suggests that we may be prepared for very active fires. The fire–weather analysis approach described in this paper has shown that future large-scale fire outbreaks are predictable. [ABSTRACT FROM AUTHOR]

Climate changes over the past two millennia in the central part of the Gulf of St. Lawrence are documented in this paper with the aim of determining and understanding the natural climate variability and the impact of anthropogenic forcing at a regional scale. The palynological content (dinocysts, pollen, and spores) of the composite marine sediment core MSM46-03 collected in the Laurentian Channel was used to reconstruct oceanographic and climatic changes with a multidecadal temporal resolution. Sea-surface conditions, including summer salinity and temperature, sea-ice cover, and primary productivity, were reconstructed from dinocyst assemblages. Results revealed a remarkable cooling trend of about 4°C after 1230 cal yr BP (720 CE) and a culmination with a cold pulse dated to 170-40 cal yr BP (1780-1910 CE), which likely corresponds to the regional signal of the Little Ice Age. This cold interval was followed by a rapid warming of about 3°C. In the pollen assemblages, the decrease of Pinus abundance over the past 1700 yr suggests changes in wind regimes, likely resulting from increased southerly incursions of cold and dry Arctic air masses into southeastern Canada. [ABSTRACT FROM AUTHOR]

The TROPOspheric Monitoring Instrument (TROPOMI) aboard the Sentinel-5 Precursor satellite (launched on 13 October 2017) is a nadir-viewing spectrometer measuring reflected sunlight in the ultraviolet, visible, near-infrared, and shortwave infrared spectral ranges. The measured spectra are used to retrieve total columns of trace gases, including nitrogen dioxide (NO2). For ground validation of these satellite measurements, Pandora spectrometers, which retrieve high-quality NO2 total columns via direct-sun measurements, are widely used. In this study, Pandora NO2 measurements made at three sites located in or north of the Greater Toronto Area (GTA) are used to evaluate the TROPOMI NO2 data products, including a standard Royal Netherlands Meteorological Institute (KNMI) tropospheric and stratospheric NO2 data product and a TROPOMI research data product developed by Environment and Climate Change Canada (ECCC) using a high-resolution regional air quality forecast model (in the air mass factor calculation). It is found that these current TROPOMI tropospheric NO2 data products (standard and ECCC) met the TROPOMI design bias requirement (< 10 %). Using the statistical uncertainty estimation method, the estimated TROPOMI upper-limit precision falls below the design requirement at a rural site but above in the other two urban and suburban sites. The Pandora instruments are found to have sufficient precision (< 0.02 DU) to perform TROPOMI validation work. In addition to the traditional satellite validation method (i.e., pairing ground-based measurements with satellite measurements closest in time and space), we analyzed TROPOMI pixels located upwind and downwind from the Pandora site. This makes it possible to improve the statistics and better interpret the high-spatial-resolution measurements made by TROPOMI. By using this wind-based validation technique, the number of coincident measurements can be increased by about a factor of 5. With this larger number of coincident measurements, this work shows that both TROPOMI and Pandora instruments can reveal detailed spatial patterns (i.e., horizontal distributions) of local and transported NO2 emissions, which can be used to evaluate regional air quality changes. The TROPOMI ECCC NO2 research data product shows improved agreement with Pandora measurements compared to the TROPOMI standard tropospheric NO2 data product (e.g., lower multiplicative bias at the suburban and urban sites by about 10 %), demonstrating benefits from the high-resolution regional air quality forecast model. [ABSTRACT FROM AUTHOR]

A chemistry box model containing a comprehensive suite of mercury (Hg) oxidation mechanisms involving O3, OH, H2O2, Br, BrO, NO2, HO2, and other oxidants was used to simulate the formation of gaseous oxidized mercury (GOM) and understand the chemical processes driving the observed trends in GOM at Kejimkujik, Nova Scotia, Canada. Simulations were conducted using chemical schemes with and without oxidation by O3 and OH. The major oxidants of Hg are O3 and OH (79%), H2O2 (10%), Br with second-stage HgBr oxidation by NO2 (7%), and BrO (3%) in simulations where all GEM oxidation reactions were considered simultaneously. In an alternative chemical scheme without gas-phase oxidation by O3 and OH, the dominant GOM species were HgBrNO2 (58%) and HgBrO (23.5%). Using this chemical scheme, the model reproduced the observed GOM at sub-ppqv Br2 mixing ratios. In the scheme with O3 and OH, the variability in GOM between seasons and between continental and marine air masses was mainly due to the variability in gaseous elemental Hg, O3, OH, and aerosol liquid water content (LWC). LWC governs the partitioning of GOM to the aerosol aqueous phase in the model. In the scheme without O3 and OH, the variability in GOM by season and airmass origin strongly depends on Br and BrO, suggesting that rigorous validation of modeled Br and BrO data are essential for improving the model predictions of GOM in coastal environments. [ABSTRACT FROM AUTHOR]

The linkage between changes in air mass distribution and temperature trends from 1971 to 2010 is explored in the Hudson Bay/Foxe Basin region. Statistically significant temperature increases were found of varying spatial and temporal magnitude. Concurrent statistically significant changes in air mass frequency at the same locations were also detected, particularly in the declining frequency of dry polar (DP) air. These two sets of changes were found to be linked, and we thus conclude that the heterogeneity of the climatic warming signal in the region is at least partially the result of a fundamental shift in the concurrent air mass frequency in addition to global and regional changes in radiative forcing due to increases in long-lived greenhouse gases. [ABSTRACT FROM AUTHOR]

Surface observations, soundings, and a thermodynamic budget are used to investigate the formation process of 93 arctic airmass events. The events involve very cold surface temperatures-an average of −42.8°C at Norman Wells, a centrally located station in the formation region-and cooling in the 1000-500-hPa layer. A multistage process for their formation in northwestern Canada is proposed. This process is contrary to the classical conceptualization of extremely shallow, surface formations. In the first stage of formation, snow falls into a layer of unsaturated air in the lee of the Rocky Mountains, causing sublimational cooling and moistening the subcloud layer. Simultaneously, the midtroposphere is cooled by cloud-top radiation emissions. In the second stage, snowfall abates, the air column dries, and clear-sky surface radiational cooling predominates, augmented by the high emissivity of fresh snow cover. The surface temperature falls very rapidly, up to a maximum of 18°C day−1 in one event. In the final stage, after near-surface temperatures fall below the frost point, ice crystals and, nearer the surface, ice fog form. At the end of formation, there is cold-air damming, with a cold pool and anticyclone in the lee of the Rockies, lower pressure in the Gulf of Alaska, and an intense baroclinic zone oriented northwest to southeast along the mountains. There have been secular changes in the characteristics of the arctic air masses over the period 1948-2008. The surface temperature during the events has become warmer, and the air masses are deeper and moister. The 1000-hPa diabatic cooling during events, which includes latent heat and radiative processes, has decreased by 2.2°C day−1. [ABSTRACT FROM AUTHOR]

Fresh snow samples were collected following seven snow accumulation events along an altitudinal transect of the Robertson Valley. This glacierized valley is on the eastern slopes of the Canadian Rockies at the Continental Divide and receives precipitation from both westerly (Pacific) air masses and from easterly (upslope) systems. Snow samples were collected over two winter seasons and were analyzed for δ18O, revealing altitudinal gradients that ranged from -0.3%/100 m to +1.8‰/100 m. Five of seven snow events had positive (inverse) isotopic gradients with altitude: 18O enrichment at higher altitudes. Surface and upper-air meteorological data were analyzed to classify the type of weather systems bringing precipitation to the area for each accumulation event. Three storm classifications were developed: westerly, upslope, and mixed/ northwesterly systems. Positive δ18O-elevation gradients were found under strong westerly and northwesterly flow, when the Robertson Valley acts as a leeward slope, while more conventional negative gradients correspond with upslope flow, when easterly winds make the Robertson Valley a windward snow deposition environment. We interpret the inverse isotopic gradients as evidence of ongoing Rayleigh distillation as westerly systems cross the Continental Divide. Position on the Rayleigh distillation curve had a strong influence on the magnitude of δ18O-elevation gradients. [ABSTRACT FROM AUTHOR]