Typically 20-40 extreme cyclone events (sometimes called 'weather bombs') occur in the Arctic North Atlantic per winter season, with an increasing trend of 6 events/decade over 1979-2015, according ...to 6 hourly station data from Ny-Ålesund. This increased frequency of extreme cyclones is consistent with observed significant winter warming, indicating that the meridional heat and moisture transport they bring is a factor in rising temperatures in the region. The winter trend in extreme cyclones is dominated by a positive monthly trend of about 3-4 events/decade in November-December, due mainly to an increasing persistence of extreme cyclone events. A negative trend in January opposes this, while there is no significant trend in February. We relate the regional patterns of the trend in extreme cyclones to anomalously low sea-ice conditions in recent years, together with associated large-scale atmospheric circulation changes such as 'blockinglike' circulation patterns (e.g. Scandinavian blocking in December and Ural blocking during January-February).
In the Antarctic ozone hole, ozone mixing ratios have been decreasing to extremely low values of 0.01–0.1 ppm in nearly all spring seasons since the late 1980s, corresponding to 95–99% local chemical ...loss. In contrast, Arctic ozone loss has been much more limited and mixing ratios have never before fallen below 0.5 ppm. In Arctic spring 2020, however, ozonesonde measurements in the most depleted parts of the polar vortex show a highly depleted layer, with ozone loss averaged over sondes peaking at 93% at 18 km. Typical minimum mixing ratios of 0.2 ppm were observed, with individual profiles showing values as low as 0.13 ppm (96% loss). The reason for the unprecedented chemical loss was an unusually strong, long‐lasting, and cold polar vortex, showing that for individual winters the effect of the slow decline of ozone‐depleting substances on ozone depletion may be counteracted by low temperatures.
Plain Language Summary
The severe stratospheric chemical ozone loss in the Antarctic ozone hole and its impact on human health and climate have generated widespread public, political, and scientific interest. In contrast, Arctic stratospheric ozone reduction has been much more limited because of higher temperatures and higher transport variability in the Northern Hemisphere (lower temperatures lead to more chemical loss, and more transport can increase ozone values). In the Arctic spring 2020, however, observations of balloon sondes and satellites show that locally, absolute values of ozone (measured in mixing ratios, i.e., molecules of ozone per molecules of air) are significantly lower than in any previous year and are comparable to typical local values in the Antarctic ozone hole, albeit over a much narrower vertical layer. Locally, the chemical loss of ozone peaked at 93% in the Arctic spring of 2020, compared to values of 95–99% in the Antarctic in most winters since the late 1980s. The reason for the unprecedented loss was unusually cold and stable conditions in the Arctic stratosphere.
Key Points
Local minimum ozone mixing ratios of 0.1–0.2 ppm observed by sondes in Arctic spring 2020 are significantly lower than in any previous year
Local ozone loss (93%) and low mixing ratios are comparable to typical values in the Antarctic ozone hole (95–99%, 0.01–0.1 ppm)
The reason for the unprecedented chemical loss was an unusually strong, long‐lasting, and record cold polar vortex
Arctic trends of integrated water vapor were analyzed based on four reanalyses and radiosonde data over 1979–2016. Averaged over the region north of 70°N, the Arctic experiences a robust moistening ...trend that is smallest in March (0.07 ± 0.06 mm decade−1) and largest in August (0.33 ± 0.18 mm decade−1), according to the reanalyses’ median and over the 38 years. While the absolute trends are largest in summer, the relative ones are largest in winter. Superimposed on the trend is a pronounced interannual variability. Analyzing overlapping 30-yr subsets of the entire period, the maximum trend has shifted toward autumn (September–October), which is related to an accelerated trend over the Barents and Kara Seas. The spatial trend patterns suggest that the Arctic has become wetter overall, but the trends and their statistical significance vary depending on the region and season, and drying even occurs over a few regions. Although the reanalyses are consistent in their spatiotemporal trend patterns, they substantially disagree on the trend magnitudes. The summer and the Nordic and Barents Seas, the central Arctic Ocean, and north-central Siberia are the season and regions of greatest differences among the reanalyses. We discussed various factors that contribute to the differences, in particular, varying sea level pressure trends, which lead to regional differences in moisture transport, evaporation trends, and differences in data assimilation. The trends from the reanalyses show a close agreement with the radiosonde data in terms of spatiotemporal patterns. However, the scarce and nonuniform distribution of the stations hampers the assessment of central Arctic trends.
The sizes and shapes of ice crystals influence the radiative properties of clouds, as well as precipitation initiation and aerosol scavenging. However, ice crystal growth mechanisms remain only ...partially characterized. We present the growth processes of two complex ice crystal habits observed in Arctic mixed‐phase clouds during the Ny‐Ålesund AeroSol Cloud ExperimeNT campaign. First, are capped‐columns with multiple columns growing out of the plates' corners that we define as columns on capped‐columns. These ice crystals originated from cycling through the columnar and plate temperature growth regimes, during their vertical transport by in‐cloud circulation. Second, is aged rime on the surface of ice crystals having grown into faceted columns or plates depending on the environmental conditions. Despite their complexity, the shapes of these ice crystals allow to infer their growth history and provide information about the in‐cloud conditions. Additionally, these ice crystals exhibit complex shapes and could enhance aggregation and secondary ice production.
Plain Language Summary
Snowflakes formed in the atmosphere have a wide variety of shapes and sizes and no two snowflakes are identical. The reason for this infinite number of shapes is that the environmental temperature and relative humidity prevailing during the snowflakes' growth determine their exact aspects. Thus, the prevailing environmental conditions can be determined from the shape of snowflakes, and become more complicated with increased shape complexity. During a measurement campaign in the Arctic, we identified two complex snowflake types and the history of environmental conditions in which they grew in. We inferred that some snowflakes were recirculating to higher or lower parts of the clouds and that others had collided with cloud droplets that froze on their surface at the early stage of their growth. These snowflakes may enhance the formation of new snowflakes and the initiation of precipitation.
Key Points
A large variety of ice crystal sizes and shapes were observed in Arctic mixed‐phase clouds with a holographic imager
The growth history of two types of complex ice crystals was inferred from their shapes
These ice crystals could enhance aggregation and secondary ice production
A consistent meteorological dataset of the Arctic site Ny-Ålesund (11.9° E, 78.9° N) spanning the 18 yr-period 1 August 1993 to 31 July 2011 is presented. Instrumentation and data handling of ...temperature, humidity, wind and pressure measurements are described in detail. Monthly mean values are shown for all years to illustrate the interannual variability of the different parameters. Climatological mean values are given for temperature, humidity and pressure. From the climatological dataset, we also present the time series of annual mean temperature and humidity, revealing a temperature increase of +1.35 K per decade and an increase in water vapor mixing ratio of +0.22 g kg−1 per decade for the given time period, respectively. With the continuation of the presented measurements, the Ny-Ålesund high resolution time series will provide a reliable source to monitor Arctic change and retrieve trends in the future. The relevant data are provided in high temporal resolution as averages over 5 (1) min before (after) 14 July 1998, respectively, placed on the PANGAEA repository (doi:10.1594/PANGAEA.793046). While 6 hourly synoptic observations in Ny-Ålesund by the Norwegian Meteorological Institute reach back to 1974 (Førland et al., 2011), the meteorological data presented here cover a shorter time period, but their high temporal resolution will be of value for atmospheric process studies on shorter time scales.
In this work, an evaluation of an intense biomass burning event observed over Ny-Ålesund (Spitsbergen, European Arctic) in July 2015 is presented. Data from the multi-wavelengths Raman-lidar KARL, a ...sun photometer and radiosonde measurements are used to derive some microphysical properties of the biomass burning aerosol as size distribution, refractive index and single scattering albedo at different relative humidities. Predominantly particles in the accumulation mode have been found with a bi-modal distribution and dominance of the smaller mode. Above 80% relative humidity, hygroscopic growth in terms of an increase of particle diameter and a slight decrease of the index of refraction (real and imaginary part) has been found. Values of the single scattering albedo around 0.9 both at 355 nm and 532 nm indicate some absorption by the aerosol. Values of the lidar ratio are around 26 sr for 355 nm and around 50 sr for 532 nm, almost independent of the relative humidity. Further, data from the photometer and surface radiation values from the local baseline surface radiation network (BSRN) have been applied to derive the radiative impact of the biomass burning event purely from observational data by comparison with a clear background day. We found a strong cooling for the visible radiation and a slight warming in the infra-red. The net aerosol forcing, derived by comparison with a clear background day purely from observational data, obtained a value of -95 W/m
2
per unit AOD500.
REFERENCE UPPER-AIR OBSERVATIONS FOR CLIMATE Bodeker, G. E.; Bojinski, S.; Cimini, D. ...
Bulletin of the American Meteorological Society,
01/2016, Letnik:
97, Številka:
1
Journal Article
Recenzirano
Odprti dostop
The three main objectives of the Global Climate Observing System (GCOS) Reference Upper-Air Network (GRUAN) are to provide long-term high-quality climate records of vertical profiles of selected ...essential climate variables (ECVs), to constrain and calibrate data from more spatially comprehensive global networks, and to provide measurements for process studies that permit an in-depth understanding of the properties of the atmospheric column. In the five years since the first GRUAN implementation and coordination meeting and the printing of an article (Seidel et al.) in this publication, GRUAN has matured to become a functioning network that provides reference-quality observations to a community of users.
This article describes the achievements within GRUAN over the past five years toward making reference-quality observations of upper-air ECVs. Milestones in the evolution of GRUAN are emphasized, including development of rigorous criteria for site certification and assessment, the formal certification of the first GRUAN sites, salient aspects of the GRUAN manual and guide to operations, public availability of GRUAN’s first data product, outcomes of a network expansion workshop, and key results of scientific studies designed to provide a sound scientific foundation for GRUAN operations.
Two defining attributes of GRUAN are 1) that every measurement is accompanied by a traceable estimate of the measurement uncertainty and 2) that data quality and continuity are maximized because network changes are minimized and managed. This article summarizes how these imperatives are being achieved for existing and planned data products and provides an outlook for the future, including expected new data streams, network expansion, and critical needs for the ongoing success of GRUAN.
Sunlit snow is highly photochemically active and plays a key role in the
exchange of gas phase species between the cryosphere and the atmosphere.
Here, we investigate the behaviour of two selected ...species in surface snow:
mercury (Hg) and iodine (I). Hg can deposit year-round and accumulate in the
snowpack. However, photo-induced re-emission of gas phase Hg from the
surface has been widely reported. Iodine is active in atmospheric new
particle formation, especially in the marine boundary layer, and in the
destruction of atmospheric ozone. It can also undergo photochemical
re-emission. Although previous studies indicate possible post-depositional
processes, little is known about the diurnal behaviour of these two species
and their interaction in surface snow. The mechanisms are still poorly
constrained, and no field experiments have been performed in different
seasons to investigate the magnitude of re-emission processes Three sampling
campaigns conducted at an hourly resolution for 3 d each were carried out
near Ny-Ålesund (Svalbard) to study the behaviour of mercury and iodine
in surface snow under different sunlight and environmental conditions
(24 h darkness, 24 h sunlight and day–night cycles). Our results indicate a
different behaviour of mercury and iodine in surface snow during the
different campaigns. The day–night experiments demonstrate the existence of a
diurnal cycle in surface snow for Hg and iodine, indicating that these
species are indeed influenced by the daily solar radiation cycle.
Differently, bromine did not show any diurnal cycle. The diurnal cycle also
disappeared for Hg and iodine during the 24 h sunlight period and during
24 h darkness experiments supporting the idea of the occurrence (absence) of
a continuous recycling or exchange at the snow–air interface. These results
demonstrate that this surface snow recycling is seasonally dependent,
through sunlight. They also highlight the non-negligible role that snowpack
emissions have on ambient air concentrations and potentially on
iodine-induced atmospheric nucleation processes.
The Arctic climate is modulated, in part, by atmospheric aerosols that affect the distribution of radiant energy passing through the atmosphere. Aerosols affect the surface‐atmosphere radiation ...balance directly through interactions with solar and terrestrial radiation and indirectly through interactions with cloud particles. Better quantification of the radiative forcing by different types of aerosol is needed to improve predictions of future climate. During April 2009, the airborne campaign Pan‐Arctic Measurements and Arctic Regional Climate Model Inter‐comparison Project (PAM‐ARCMIP) was conducted. The mission was organized by Alfred Wegener Institute for Polar and Marine Research of Germany and utilized their research aircraft, Polar‐5. The goal was to obtain a snapshot of surface and atmospheric conditions over the central Arctic prior to the onset of the melt season. Characterizing aerosols was one objective of the campaign. Standard Sun photometric procedures were adopted to quantify aerosol optical depth AOD, providing a three‐dimensional view of the aerosol, which was primarily haze from anthropogenic sources. Independent, in situ measurements of particle size distribution and light extinction, derived from airborne lidar, are used to corroborate inferences made using the AOD results. During April 2009, from the European to the Alaskan Arctic, from sub‐Arctic latitudes to near the pole, the atmosphere was variably hazy with total column AOD at 500 nm ranging from ∼0.12 to >0.35, values that are anomalously high compared with previous years. The haze, transported primarily from Eurasian industrial regions, was concentrated within and just above the surface‐based temperature inversion layer. Extinction, as measured using an onboard lidar system, was also greatest at low levels, where particles tended to be slightly larger than at upper levels. Black carbon (BC) (soot) was observed at all levels sampled, but at moderate to low concentrations compared with historical records. BC was highest near the North Pole, suggesting there had been an accumulation of soot within the Arctic vortex. Few, optically thick elevated aerosol layers were observed along the flight track, although independent lidar observations reveal evidence of the passage of volcanic plumes, which may have contributed to abnormally high values of AOD above 4 km. Enhanced opacity at higher altitudes during the campaign is attributed to an accumulation of industrial pollutants in the upper troposphere in combination with volcanic aerosol resulting from the March–April 2009 eruptions of Mount Redoubt in Alaska. The presence of Arctic haze during April 2009 is estimated to have reduced the net shortwave irradiance by ∼2–5 W m−2, resulting in a slight cooling of the surface.
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