scholarly journals Satellite-Derived Spatio-Temporal Distribution and Parameters of North Atlantic Polar Lows for 2015–2017

Atmosphere ◽  
2021 ◽  
Vol 12 (2) ◽  
pp. 224
Author(s):  
Pavel Golubkin ◽  
Julia Smirnova ◽  
Leonid Bobylev
Keyword(s):  
North Atlantic ◽  
Barents Sea ◽  
Auxiliary Information ◽  
Low Frequency ◽  
Temporal Distribution ◽  
Study Region ◽  
Polar Lows ◽  
Mean Values ◽  
Polar Low ◽  
Spatio Temporal

A list of North Atlantic polar lows was compiled for 2015–2017. A total of 131 polar lows were found by analyzing the Moderate Resolution Imaging Spectroradiometer (MODIS) infrared imagery and auxiliary information. The study region was additionally divided by the 20° W meridian to assess possible differences in the polar lows occurring in the western and eastern parts of the region. The highest polar low activity was found over the Barents Sea and the northern Norwegian Sea. A large number of polar lows over this region were dual or multiple. When considering such systems as a single event, more polar lows were found in 2015 over the Labrador Sea and southern Davis Strait, which is the region with the second highest number of polar lows. High interannual variability of polar low frequency was noted, which was more pronounced in the western part of the region. During the analyzed period, the largest number of polar lows occurred in January for the western part of the region and in February for the eastern part. The main polar low parameters were similar within the region, with the mean values slightly higher in the western part of the region, but all extreme high values were observed in the eastern part.

scholarly journals Estimation of harp seal (Pagophilus groenlandicus) pup production in the North Atlantic completed: results from surveys in the Greenland Sea in 2002

2006 ◽  
Vol 63 (1) ◽  
pp. 95-104 ◽  
Author(s):  
Tore Haug ◽  
Garry B. Stenson ◽  
Peter J. Corkeron ◽  
Kjell T. Nilssen
Keyword(s):  
North Atlantic ◽  
Barents Sea ◽  
Temporal Distribution ◽  
Harp Seal ◽  
Greenland Sea ◽  
The North ◽  
Pagophilus Groenlandicus ◽  
Pack Ice ◽  
Photographic Survey ◽  
Strip Transect

Abstract From 14 March to 6 April 2002 aerial surveys were carried out in the Greenland Sea pack ice (referred to as the “West Ice”), to assess the pup production of the Greenland Sea population of harp seals, Pagophilus groenlandicus. One fixed-wing twin-engined aircraft was used for reconnaissance flights and photographic strip transect surveys of the whelping patches once they had been located and identified. A helicopter assisted in the reconnaissance flights, and was used subsequently to fly visual strip transect surveys over the whelping patches. The helicopter was also used to collect data for estimating the distribution of births over time. Three harp seal breeding patches (A, B, and C) were located and surveyed either visually or photographically. Results from the staging flights suggest that the majority of harp seal females in the Greenland Sea whelped between 16 and 21 March. The calculated temporal distribution of births were used to correct the estimates obtained for Patch B. No correction was considered necessary for Patch A. No staging was performed in Patch C; the estimate obtained for this patch may, therefore, be slightly negatively biased. The total estimate of pup production, including the visual survey of Patch A, both visual and photographic surveys of Patch B, and photographic survey of Patch C, was 98 500 (s.e. = 16 800), giving a coefficient of variation of 17.9% for the survey. Adding the obtained Greenland Sea pup production estimate to recent estimates obtained using similar methods in the Northwest Atlantic (in 1999) and in the Barents Sea/White Sea (in 2002), it appears that the entire North Atlantic harp seal pup production, as determined at the turn of the century, is at least 1.4 million animals per year.

NUMERICAL MODELING OF POLAR LOWS OVER THE BARENTS SEA: IMPACT OF WRF PARAMETRIZATIONS ON THE QUALITY OF FORECAST.

2017 ◽  
Author(s):  
Antonina Polezhayeva ◽  
Antonina Polezhayeva
Keyword(s):  
Boundary Layer ◽  
Numerical Experiments ◽  
Barents Sea ◽  
Wrf Model ◽  
Polar Lows ◽  
The Barents Sea ◽  
Polar Low ◽  
Planetary Boundary Layer Parameterization ◽  
The Impact

Polar lows are generally characterized by severe weather in the form of strong winds, showers and occasionally heavy snow, which have sometimes resulted in the loss of life, especially at sea. Numerical simulations with mesoscale atmospheric models is a good alternative to investigate polar low phenomenon, because they produce temporally and spatially regular-spaced fields of atmospheric variables with high resolution. To describe the evolution of atmospheric processes the Advanced Weather Research and Forecasting (WRF-ARW) model was used. The principal objectives of this study were 1) the understanding of mesoscale WRF model and adapting the model for the Barents Sea region; 2) to conduct numerical experiments using WRF model with different Planetary Boundary Layer parameterization (PBLs) schemes and investigate the impact of each scheme on the quality of forecast; and 3) the investigation of the capability of WRF model to successfully simulate evolution of polar lows. The impact on the quality of forecast was investigated. The results of the study, obtained by numerical modeling of polar mesoscale low over the Barents Sea. One polar low, near Spitsbergen, from 24 of March to 26 of March 2014 were targeted. The results of numerical experiments showed that each of Planetary Boundary Layer parameterization scheme isn't successful for simulation of polar low.

scholarly journals Polar Lows over the Nordic Seas: Improved Representation in ERA-Interim Compared to ERA-40 and the Impact on Downscaled Simulations

2014 ◽  
Vol 142 (6) ◽  
pp. 2271-2289 ◽  
Author(s):  
Thibaut Laffineur ◽  
Chantal Claud ◽  
Jean-Pierre Chaboureau ◽  
Gunnar Noer
Keyword(s):  
Barents Sea ◽  
Mesoscale Model ◽  
Cold Season ◽  
Small Scale ◽  
Polar Lows ◽  
Wind Speeds ◽  
Short Life Span ◽  
Synoptic Conditions ◽  
Polar Low ◽  
The Impact

Abstract Polar lows are intense high-latitude mesocyclones that form during the cold season over open sea. Their relatively small-scale and short life span lead to a rather poor representation in model outputs and meteorological reanalyses. In this paper, the ability of the Interim European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-Interim) to represent polar lows over the Norwegian and Barents Sea is assessed, and a comparison with the 40-yr ECMWF Re-Analysis (ERA-40) is provided for three cold seasons (1999–2000 until 2001–02). A better representation in ERA-Interim is found, with 13 systems captured out of the 29 observed, against 6 in the case of ERA-40. Reasons for the lack of representation are identified. Unexpectedly, the representation of different polar low sizes does not appear to be linked to the resolution. Rather, it is the representation of synoptic conditions that appears to be essential. In a second part, a downscaling is conducted using the mesoscale model Méso-NH. For each observed polar low, a pair of simulations is performed: one initialized by ERA-Interim and the other one by ERA-40. An improvement is noted with 22 polar lows represented when ERA-Interim is used. Through a model-to-satellite approach, it is shown that even if polar lows are simulated, convective processes remain insufficiently represented. Wind speeds, which were underestimated in reanalyses, are nevertheless more realistic in the Méso-NH simulations. These results are supported by a spectral analysis of reanalyses and Méso-NH fields.

scholarly journals Harmattan, Saharan heat low and West African Monsoon circulation: Modulations on the Saharan dust outflow towards the north Atlantic

2017 ◽  
Author(s):  
Kerstin Schepanski ◽  
Bernd Heinold ◽  
Ina Tegen
Keyword(s):  
North Atlantic ◽  
Dust Emission ◽  
Temporal Distribution ◽  
Saharan Dust ◽  
Monsoon Circulation ◽  
North African ◽  
Dust Source ◽  
The North ◽  
The North Atlantic ◽  
Spatio Temporal

Abstract. The outflow of dust from the North African continent towards the north Atlantic is stimulated by the atmospheric circulation over North Africa, which modulates the spatio-temporal distribution of dust source activation and consequently the entrainment of mineral dust into the boundary layer, as well as the transport of dust out of the source regions. The atmospheric circulation over the North African dust source regions, predominantly the Sahara and the Sahel, is characterised by three major circulation regimes: (1) the Harmattan (trade winds), (2) the Saharan heat low (SHL), and (3) the West African Monsoon circulation. The strength of the individual regimes controls the Saharan dust outflow by affecting the spatio-temporal distribution of dust emission, transport pathways, and deposition fluxes. This study aims at investigating the atmospheric circulation pattern over North Africa with regard to its role favouring dust emission and dust export towards the tropical North Atlantic. The focus of the study is on summer 2013 (June to August), during which also the SALTRACE (Saharan Aerosol Long-range TRansport and Aerosol-Cloud interaction Experiment) field campaign took place. It involves satellite observations by the Spinning Enhanced Visible and InfraRed Imager (SEVIRI) flying on-board the geostationary Meteosat Second Generation (MSG) satellite, which are analysed and used to infer a data set of active dust sources. The spatio-temporal distribution of dust source activation frequencies (DSAF) allows for linking the diurnal cycle of dust source activations to dominant meteorological controls on dust emission. In summer, Saharan dust source activations clearly differ from dust source activations over the Sahel regarding the time-of-day when dust emission begins. The Sahara is dominated by morning dust source activations predominantly driven by the break-down of the nocturnal low-level jet. In contrast, dust source activations in the Sahel are predominantly activated during the second half of the day when down-drafts associated with deep moist convection are the major atmospheric driver. Complementary to the satellite-based analysis on dust source activations and implications from their diurnal cycle, simulations on atmosphere and dust life-cycle were performed using the meso-scale atmosphere-dust model system COSMO-MUSCAT (COSMO: COnsortium for Small-scale MOdelling; MUSCAT: MUltiScale Chemistry Aerosol Transport Model). Fields from this simulation were analysed regarding the variability of the Harmattan, the Saharan heat low, and the Monsoon circulation as well as their impact on the variability of the Saharan dust outflow towards the north Atlantic. This study illustrates the complexity of the interaction among the three major circulation regimes and their modulation of the North African dust outflow. Enhanced westward dust fluxes frequently appear following a phase characterised by a deep SHL. Ultimately, findings from this study contribute to the quantification of the interannual variability of the atmospheric dust burden.

scholarly journals Spatio-temporal distribution of shallow very-low-frequency earthquakes between December 2020 and January 2021 in Kumano-nada, Nankai subduction zone, detected by a permanent seafloor seismic network

2022 ◽  
Vol 74 (1) ◽  
Author(s):  
Yojiro Yamamoto ◽  
Keisuke Ariyoshi ◽  
Shuichiro Yada ◽  
Masaru Nakano ◽  
Takane Hori
Keyword(s):  
Fluid Pressure ◽  
Low Frequency ◽  
Temporal Distribution ◽  
Active Area ◽  
Small Scale ◽  
Very Low Frequency ◽  
Eastern Side ◽  
Activity Area ◽  
Spatio Temporal ◽  
Western Side

AbstractWe estimate the hypocenter locations and the centroid moment tensor solutions of the shallow very-low-frequency earthquake (sVLFE) activity that occurred in the Kumano-nada region of the Nankai Trough megathrust zone in central Japan from December 2020 to January 2021. Using seafloor observation data, we examined the detailed spatio-temporal distribution of the sVLFE activity. During this episode, the activity area was within the vicinity in which the sVLFE activity has been observed in the past and can be divided into two major parts. The sVLFE activity started from the eastern side and remained there for the first 5 days and then migrated to the western side via secondary expansion. The eastern active area is located just below the outer ridge and coincides with the location where the paleo-Zenith Ridge subducted. The western activity area is centered between the outer wedge and the outer ridge with the primary active area being at the outer wedge. Comparing the activity in the eastern and western areas, the eastern side is more active, but the individual moment releases on this side are smaller than those on the western side. This may indicate a difference in the fluid pressure along the plate boundary between the eastern and western areas. After the second expansion of the active area, we observed several migration patterns within the expanded area with a faster velocity than those of the initial and second expansions. The direction of these migrations is opposite to that of the first and second expansions. This indicates that the fluid pressure and/or stress level in the sVLFE generation region changed with time within this episode. Furthermore, many waveforms with sVLFE characteristics were observed at only one or a few observation points near the trough axis in the middle to latter half of January 2021. This indicates the occurrence of small-scale sVLFEs in the vicinity of the trough axis at the end of this sVLFE episode. Graphical Abstract

Comprehensive palaeomagnetic study of San Borja and Jaraguay monogenetic volcanic fields, Baja California (28–30°N): considerations on latitudinal corrections

2021 ◽  
Author(s):  
Ahmed Nasser Mahgoub ◽  
Bernardo Ignacio García-Amador ◽  
Luis Manuel Alva-Valdivia
Keyword(s):  
Dipole Moment ◽  
Late Miocene ◽  
Baja California ◽  
Temporal Distribution ◽  
Magnetic Minerals ◽  
Mean Values ◽  
Kinematic Evolution ◽  
Volcanic Fields ◽  
Spatio Temporal ◽  
Northwestern Mexico

<p>We report 24 palaeomagnetic directions and 10 high-quality Thellier-derived palaeointensity (PI) values, obtained from 27 sites located in Baja California Peninsula, northwestern Mexico. Sampling was done in four rock units (magnesian andesites, calc-alkaline lavas, ignimbrites, adakites) belonging to San Borja and Jaraguay monogenetic volcanic fields. These units were erupted between ~ 15 and 2.6 Ma (previous K-Ar and <sup>40</sup>Ar/<sup>39</sup>Ar data), hence results are presented in two consecutive periods: middle-late Miocene and Pliocene. Based on previous geological and geophysical records, the kinematic evolution of the region was carefully considered, allowing for the independent restoration of the palaeoposition of each sampled site. The identified main magnetic minerals are titanomagnetite, magnetite, and minor hematite, of variable grain size, present as intergrowths, which reflect varying oxidation/reduction conditions during emplacement of high-temperature magmas. We did not observe a clear relationship between the magnetic properties of the different sites and their success rate for PI experiments. This is with the exception of the FORC analysis which showed a fairly good correlation with PI success. Pliocene (Dec=359.2°; Inc= 47.4°; α<sub>95</sub>=7.6°; and k= 41.43) and Middle-late Miocene (Dec=353.9°; Inc= 38.5°; α<sub>95</sub>=9.2°; and k= 28.56) mean directions were calculated from 20 sites (10 sites per period), and PI mean values of 29.2 ± 9.1 μT and 23.2 ± 6.3 μT were determined for the two periods, respectively. Compiling global filtered PI data, together with our results, indicates that the strength of the geomagnetic field during middle-late Miocene was weak (virtual dipole moment = 5.0±2.2×10<sup>22</sup> Am<sup>2</sup>) compared to Pliocene (6.4±2.8× 10<sup>22</sup> Am<sup>2</sup>), and also relative to the present-day value (7.6 × 10<sup>22</sup> Am<sup>2</sup>). This indicates the global nature of the low dipole moment during the middle-late Miocene, which is consistent with what was previously concluded that from the past 30 Ma to the present time the magnetic field strength has increased. However, issues related to the Spatio-temporal distribution of PI data still present an obstacle to validating these suggestions; therefore, more reliable data are still needed.</p>

NUMERICAL MODELING OF POLAR LOWS OVER THE BARENTS SEA: IMPACT OF WRF PARAMETRIZATIONS ON THE QUALITY OF FORECAST.

2017 ◽  
Author(s):  
Antonina Polezhayeva ◽  
Antonina Polezhayeva
Keyword(s):  
Boundary Layer ◽  
Numerical Experiments ◽  
Barents Sea ◽  
Wrf Model ◽  
Polar Lows ◽  
The Barents Sea ◽  
Polar Low ◽  
Planetary Boundary Layer Parameterization ◽  
The Impact

Polar lows are generally characterized by severe weather in the form of strong winds, showers and occasionally heavy snow, which have sometimes resulted in the loss of life, especially at sea. Numerical simulations with mesoscale atmospheric models is a good alternative to investigate polar low phenomenon, because they produce temporally and spatially regular-spaced fields of atmospheric variables with high resolution. To describe the evolution of atmospheric processes the Advanced Weather Research and Forecasting (WRF-ARW) model was used. The principal objectives of this study were 1) the understanding of mesoscale WRF model and adapting the model for the Barents Sea region; 2) to conduct numerical experiments using WRF model with different Planetary Boundary Layer parameterization (PBLs) schemes and investigate the impact of each scheme on the quality of forecast; and 3) the investigation of the capability of WRF model to successfully simulate evolution of polar lows. The impact on the quality of forecast was investigated. The results of the study, obtained by numerical modeling of polar mesoscale low over the Barents Sea. One polar low, near Spitsbergen, from 24 of March to 26 of March 2014 were targeted. The results of numerical experiments showed that each of Planetary Boundary Layer parameterization scheme isn't successful for simulation of polar low.

Variability in atmospheric circulation and moisture flux over the Arctic

1995 ◽  
Vol 352 (1699) ◽  
pp. 215-225 ◽  
Keyword(s):  
Water Vapour ◽  
North Atlantic ◽  
Temporal Distribution ◽  
Local Maximum ◽  
Precipitable Water ◽  
Moisture Flux ◽  
The Arctic ◽  
Polar Cap ◽  
Arctic Water ◽  
Spatio Temporal

Mean characteristics and variability in the spatio-temporal distribution of Arctic water vapour and vapour fluxes are examined using several different rawinsondederived databases. Precipitable water averaged over the polar cap, 70-90° N, peaks in July at 14.0 mm. Large poleward fluxes near the prime meridian reflect transport associated with north Atlantic cyclones and, for most months, a local maximum in available water vapour. The mean vapour flux convergence averaged for the polar cap peaks in September. There is a mean annual excess of precipitation minus evaporation ( P — E ) of 163 mm, with a 78 mm range between extreme years. High P — E is favoured by a meridional circulation accompanied by a more dominant North Atlantic cyclone track. No trend in annual P — E is apparent over the 1974-1991 period.

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