scholarly journals Large-Scale Synoptic Systems and Fog During the C-FOG Field Experiment

2021 ◽  
Author(s):  
Clive E. Dorman ◽  
Sebastian W. Hoch ◽  
Ismail Gultepe ◽  
Qing Wang ◽  
Ryan T. Yamaguchi ◽  
...  
Keyword(s):  
Large Scale ◽  
Longwave Radiation ◽  
Meteorological Conditions ◽  
Cloud Base ◽  
Atlantic Canada ◽  
The North ◽  
Coastal Fog ◽  
Surface Measurements ◽  
Avalon Peninsula ◽  
Cloud Base Height

AbstractThe goal of this work is to summarize synoptic meteorological conditions during the Coastal Fog (C-FOG) field project that took place onshore and offshore of the Avalon Peninsula, Newfoundland, from 25 August until 8 October 2018. Visibility was measured at three locations at the Ferryland supersite that are about 1 km from each other, and at two additional sites 66 and 76 km to the north. Supporting meteorological measurements included surface winds, air temperature, humidity, pressure, radiation, cloud-base height, and atmospheric thermodynamic profiles from radiosonde soundings. Statistics are presented for surface measurements during fog events including turbulence kinetic energy, net longwave radiation, visibility, and precipitation. Eleven fog events are observed at Ferryland. Each significant fog event is related to a large-scale cyclonic system. The longest fog event is due to interaction of a northern deep low and a tropical cyclone. Fog occurrence is also examined across Atlantic Canada by including Sable Island, Yarmouth, Halifax, and Sydney. It is concluded that at Ferryland, all significant fog events occur under a cyclonic system while at Sable Island all significant fog events occur under both cyclonic and anticyclonic systems. The fog-formation mechanism involves cloud lowering and stratus broadening or only stratus broadening for the cyclonic systems while for the anticyclonic systems it is stratus broadening or radiation. Although widely cited as the main cause of fog in Atlantic Canada, advection fog is not found to be the primary or sole fog type in the events examined.

scholarly journals Characterisation and surface radiative impact of Arctic low clouds from the IAOOS field experiment

2021 ◽  
Vol 21 (5) ◽  
pp. 4079-4101
Author(s):  
Julia Maillard ◽  
François Ravetta ◽  
Jean-Christophe Raut ◽  
Vincent Mariage ◽  
Jacques Pelon
Keyword(s):  
Field Experiment ◽  
Cloud Cover ◽  
Great Majority ◽  
Cloud Base ◽  
The North ◽  
Low Clouds ◽  
Radiative Impact ◽  
Low Cloud ◽  
Ocean Observing ◽  
Cloud Base Height

Abstract. The Ice, Atmosphere, Arctic Ocean Observing System (IAOOS) field experiment took place from 2014 to 2019. Over this period, more than 20 instrumented buoys were deployed at the North Pole. Once locked into the ice, the buoys drifted for periods of a month to more than a year. Some of these buoys were equipped with 808 nm wavelength lidars which acquired a total of 1777 profiles over the course of the campaign. This IAOOS lidar dataset is exploited to establish a novel statistic of cloud cover and of the geometrical and optical characteristics of the lowest cloud layer. The average cloud frequency from April to December over the course of the campaign was 75 %. Cloud occurrence frequencies were above 85 % from May to October. Single layers are thickest in October/November and thinnest in the summer. Meanwhile, their optical depth is maximum in October. On the whole, the cloud base height is very low, with the great majority of first layer bases beneath 120 m. In April and October, surface temperatures are markedly warmer when the IAOOS profile contains at least one low cloud than when it does not. This temperature difference is statistically insignificant in the summer months. Indeed, summer clouds have a shortwave cooling effect which can reach −60 W m−2 and balance out their longwave warming effect.

Linking marine fog variability in Atlantic Canada to changes in large-scale atmospheric and marine features

2020 ◽  
Author(s):  
Patrick Duplessis ◽  
Minghong Zhang ◽  
William Perrie ◽  
George A Isaac ◽  
Rachel Y W Chang
Keyword(s):  
Large Scale ◽  
Climate Model ◽  
Internal Variability ◽  
Reanalysis Data ◽  
Sea Surface ◽  
Atlantic Canada ◽  
Climate Projections ◽  
The North ◽  
Marine Traffic ◽  
Highly Correlated

<p>Marine and coastal fog forms mainly from the cooling of warm and moist air advected over a colder sea surface. Atlantic Canada is one of the foggiest regions of the world due to the strong temperature contrast between the two oceanic currents in the vicinity. Recurring periods of low visibility notably disrupt off-shore operations and marine traffic, but also land and air transportation. On longer time-scales, marine fog variability also has a significant impact on the global radiative budget. Clouds, including fog, are the greatest source of uncertainty in the current climate projections because of their complex feedback mechanisms. Meteorological records indicate a significant negative trend in the occurrence of foggy conditions over the past six decades at most airports in Atlantic Canada, with large internal variability, including interannual and interdecadal variations. Using the airport observations, reanalysis data and climate model outputs, we investigated the various variabilities on the trend, at interannual and interdecadal scales, and attempted to address what caused these changes in fog frequency. Our results show that the strength and position of the North Atlantic Subtropical High as well as the sea-surface temperature of the cold and warm waters near Atlantic Canada were highly correlated with fog occurrence. We applied the derived fog indices on climate model outputs and projected the fog trends and variability in the different future climate scenarios. The results from this study will be compared with those obtained from other methods and the implications will be discussed.</p>

scholarly journals The use of relaxation methods in the WRF model for the analysis of meteorological conditions in Ukraine over a long period

2020 ◽  
Vol 2 ◽  
pp. 30-42
Author(s):  
O.V. Khalchenkov ◽  
◽  
I.V. Kovalets ◽  
Keyword(s):  
Large Scale ◽  
Mesoscale Model ◽  
Soil Layer ◽  
Meteorological Conditions ◽  
Optimal Combination ◽  
Relaxation Methods ◽  
Advantages And Disadvantages ◽  
Long Period ◽  
Surface Measurements

The possibility of using grid and spectral relaxation methods and other options in the WRF mesoscale model for long-term continuous calculations has been investigated. Results of comparison of selected me-teorological parameters with surface measurements are presented. The basic recommendations for select-ing the optimal combination of long-term calculation parameters are given. The use of the selected param-eters allowed to obtain continuous meteorological fields over a long period (several months), which are well consistent with surface measurements, retain large scale synoptic structures and have a deviation from measurements commensurate with the results of short-term simulations over corresponding time peri-od. The selected optimal combination of parameters allowed us to perform continuous calculation for the period from January 1, 2019 to November 6, 2019 without accumulating errors. In a long-run calculation of meteorological conditions in Ukraine with spatial resolution 0.15 deg. for a temperature at a height of 2 meters was obtained a mean absolute error of MAE=2,05 ºC, a correlation coefficient of Corr=0,97, for a wind speed at a height of 10 meters of MAE=1.4 m/s, of Corr=0,75, and for a wind direction at a height of 10 meters of MAE=24,6 degrees, Corr=0,66. The influence of the parametrizations of the underlying sur-face and the active soil layer on the quality of calculation of meteorological fields is studied. Using the option to update the water surface temperature allowed to reduce the MAE for the temperature from 2,17 ºС to 2,05 ºС. Each of the investigated surface models showed its advantages and disadvantages. The pa-rameterizations RUC and NOAH LSM showed good agreement with the measurements for all studied pa-rameters and can be recommended for use in long-term continuous calculations. A long calculation made it possible to describe the process of accumulation and melting of snow correctly, and made it possible to reproduce the temperature of the upper soil layer correctly as well. The paper shows that the disadvantage of long- term calculations is the inability to determine the temperature of the lower layers of the soil cor-rectly.

scholarly journals Theoretical Understanding of the Linear Relationship between Convective Updrafts and Cloud-Base Height for Shallow Cumulus Clouds. Part I: Maritime Conditions

2019 ◽  
Vol 76 (8) ◽  
pp. 2539-2558 ◽  
Author(s):  
Youtong Zheng
Keyword(s):  
Cooling Rate ◽  
Large Scale ◽  
Buoyancy Flux ◽  
Cloud Base ◽  
Radiative Cooling ◽  
Cumulus Clouds ◽  
Shallow Cumulus ◽  
Surface Buoyancy ◽  
Cloud Base Height ◽  
Surface Buoyancy Flux

Abstract Zheng and Rosenfeld found linear relationships between the convective updrafts and cloud-base height zb using ground-based observations over both land and ocean. The empirical relationships allow for a novel satellite remote sensing technique of inferring the cloud-base updrafts and cloud condensation nuclei concentration, both of which are important for understanding aerosol–cloud–climate interactions but have been notoriously difficult to retrieve from space. In Part I of a two-part study, a theoretical framework is established for understanding this empirical relationship over the ocean. Part II deals with continental cumulus clouds. Using the bulk concept of mixed-layer (ML) model for shallow cumulus, I found that this relationship arises from the conservation law of energetics that requires the radiative flux divergence of an ML to balance surface buoyancy flux. Given a certain ML radiative cooling rate per unit mass Q, a deeper ML (higher zb) undergoes more radiative cooling and requires stronger surface buoyancy flux to balance it, leading to stronger updrafts. The rate with which the updrafts vary with zb is modulated by Q. The cooling rate Q manifests strong resilience to external large-scale forcing that spans a wide range of climatology, allowing the slope of the updrafts–zb relationship to remain nearly invariant. This causes the relationship to manifest linearity. The physical mechanism underlying the resilience of Q to large-scale forcing, such as free-tropospheric moisture and sea surface temperature, is investigated through the lens of the radiative transfer theory (two-stream Schwarzschild equations) and an ML model for shallow cumulus.

scholarly journals Dry Tropical Nights and Wet Extreme Heat in Beijing: Atypical Configurations between High Temperature and Humidity

2014 ◽  
Vol 142 (5) ◽  
pp. 1792-1802 ◽  
Author(s):  
Ruidan Chen ◽  
Riyu Lu
Keyword(s):  
High Temperature ◽  
Solar Radiation ◽  
Large Scale ◽  
Longwave Radiation ◽  
Meteorological Conditions ◽  
Extreme Heat ◽  
Specific Humidity ◽  
Maximum Temperature ◽  
Dry Air ◽  
Radiation Cooling

Abstract Generally, tropical nights [TN; minimum temperature (Tmin) ≥25°C] occur under wet air conditions, while extreme heat [EH; maximum temperature (Tmax) ≥35°C] occurs under dry air conditions. This can be explained by higher humidity favoring TN through reducing longwave radiation cooling, and lower humidity favoring EH through enhancing solar radiation at the surface. The present study focuses on the atypical phenomena of dry TN (30% of all TN days) and wet EH (20% of all EH days) in Beijing during July and August, 1979–2008. It was found that meteorological conditions, including large-scale circulations and specific humidity, exhibit a resemblance between typical (wet TN and dry EH) and atypical (dry TN and wet EH) cases. That is, the meteorological anomalies for dry TN are similar to those for dry EH, and the anomalies for wet EH are similar to those for wet TN. For instance, descending anomalies, which lead to lower humidity and are thus associated with dry EH, appear for more than 70% of dry TN cases. In addition, the persistence of high temperature from day to night, and from night to day, also contribute significantly to dry TN and wet EH, respectively. About 50% of dry TN days and about 70% of wet EH days are preceded by EH and TN, respectively. It can be concluded from these results that both meteorological conditions and temperature persistence contribute greatly to dry TN and wet EH.

The deglaciation of Atlantic Canada as reconstructed from the postglacial relative sea-level record

1982 ◽  
Vol 19 (12) ◽  
pp. 2232-2246 ◽  
Author(s):  
Garry Quinlan ◽  
Christopher Beaumont
Keyword(s):  
Sea Level ◽  
Large Scale ◽  
Glacial Maximum ◽  
Atlantic Canada ◽  
Relative Sea Level ◽  
North Shore ◽  
The North ◽  
Exact Position ◽  
Late Wisconsinan ◽  
Ice Morphology

The post-Wisconsinan relative sea-level record from Atlantic Canada is used to reconstruct the morphology of late Wisconsinan age ice cover during its retreat from the Atlantic region. The proposed reconstruction has little or no grounded ice in the southern Gulf of St. Lawrence, an ice dome over the north shore of the St. Lawrence, and thin ice, often less than 1 km thick, over much of the rest of the area. A sensitivity analysis shows that the proposed reconstruction is not unique in its ability to account for the relative sea-level record but that the thickness of ice in any individual area of the reconstruction is unlikely to be in error by more than a factor of two. The exact position of the ice margin in some areas is not well constrained by the model; an example is in southeastern Newfoundland.The numerical model used to relate ice morphology to postglacial relative sea level assumes that the ice sheets are isostatically equilibrated at the glacial maximum and, therefore, that load changes associated with earlier ice-sheet growth may be ignored. This assumption is shown to be reasonable. The same rapid relaxation of the Earth that allows one to ignore the effects of glacial accumulation, however, prohibits one from recognizing the effects of large-scale ablation that may have occurred prior to the assumed glacial maximum. For this reason the proposed reconstruction may be representative of only a late stage in the ablation of much more extensive and thicker ice sheets.Surfaces of relative sea level are presented for Atlantic Canada at various times in the past. These surfaces coincide with observational data where such data exist and are felt to provide reasonable estimates of relative sea level at all other locations for at least the last 13 000 years.

scholarly journals PLAM – a meteorological pollution index for air quality and its applications in fog-haze forecasts in North China

2016 ◽  
Vol 16 (3) ◽  
pp. 1353-1364 ◽  
Author(s):  
Y. Q. Yang ◽  
J. Z. Wang ◽  
S. L. Gong ◽  
X. Y. Zhang ◽  
H. Wang ◽  
...  
Keyword(s):  
Air Quality ◽  
Large Scale ◽  
North China ◽  
Pollution Index ◽  
Meteorological Conditions ◽  
Bohai Bay ◽  
Emission Data ◽  
H Index ◽  
The North ◽  
Significance Levels

Abstract. Using surface meteorological observation and high-resolution emission data, this paper discusses the application of the PLAM/h index (Parameter Linking Air-quality to Meteorological conditions/haze) in the prediction of large-scale low visibility and fog-haze events. Based on the two-dimensional probability density function diagnosis model for emissions, the study extends the diagnosis and prediction of the meteorological pollution index PLAM to the regional visibility fog-haze intensity. The results show that combining the influence of regular meteorological conditions and emission factors together in the PLAM/h parameterization scheme is very effective in improving the diagnostic identification ability of the fog-haze weather in North China. The determination coefficients for four seasons (spring, summer, autumn, and winter) between PLAM/h and visibility observation are 0.76, 0.80, 0.96, and 0.86, respectively, and all of their significance levels exceed 0.001, showing the ability of PLAM/h to predict the seasonal changes and differences of fog-haze weather in the North China region. The high-value correlation zones are located in Jing-Jin-Ji (Beijing, Tianjin, Hebei), Bohai Bay rim, and southern Hebei–northern Henan, indicating that the PLAM/h index is related to the distribution of frequent heavy fog-haze weather in North China and the distribution of emission high-value zone. Through comparative analysis of the heavy fog-haze events and large-scale clear-weather processes in winter and summer, it is found that PLAM/h index 24 h forecast is highly correlated with the visibility observation. Therefore, the PLAM/h index has good capability in identification, analysis, and forecasting.

scholarly journals PLAM – a meteorological pollution index for air quality and its applications in fog-haze forecasts in north China

2015 ◽  
Vol 15 (6) ◽  
pp. 9077-9106 ◽  
Author(s):  
Y. Yang ◽  
J. Wang ◽  
S. Gong ◽  
X. Zhang ◽  
H. Wang ◽  
...  
Keyword(s):  
Air Quality ◽  
Large Scale ◽  
North China ◽  
Correlation Coefficients ◽  
Pollution Index ◽  
Meteorological Conditions ◽  
Bohai Bay ◽  
Emission Data ◽  
H Index ◽  
The North

Abstract. Using surface meteorological observation and high resolution emission data, this paper discusses the application of PLAM/h Index (Parameter Linking Air-quality to Meteorological conditions/haze) in the prediction of large-scale low visibility and fog-haze events. Based on the two-dimensional probability density function diagnosis model for emissions, the study extends the diagnosis and prediction of the meteorological pollution index PLAM to the regional visibility fog-haze intensity. The results show that combining the influence of regular meteorological conditions and emission factors together in the PLAM/h parameterization scheme is very effective in improving the diagnostic identification ability of the fog-haze weather in North China. The correlation coefficients for four seasons (spring, summer, autumn and winter) between PLAM/h and visibility observation are 0.76, 0.80, 0.96 and 0.86 respectively and all their significance levels exceed 0.001, showing the ability of PLAM/h to predict the seasonal changes and differences of fog-haze weather in the North China region. The high-value correlation zones are respectively located in Jing-Jin-Ji (Beijing, Tianjin, Hebei), Bohai Bay rim and the southern Hebei-northern Henan, indicating that the PLAM/h index has relations with the distribution of frequent heavy fog-haze weather in North China and the distribution of emission high-value zone. Comparatively analyzing the heavy fog-haze events and large-scale fine weather processes in winter and summer, it is found that PLAM/h index 24 h forecast is highly correlated to the visibility observation. Therefore, PLAM/h index has better capability of doing identification, analysis and forecasting.

Outgoing Long Wave Radiation Dipole of Tropical Cyclones

2020 ◽  
Author(s):  
Mohan Smith ◽  
Ralf Toumi
Keyword(s):  
Large Scale ◽  
Strong Association ◽  
Motion Vector ◽  
Longwave Radiation ◽  
Reanalysis Data ◽  
Wave Radiation ◽  
North West ◽  
The North ◽  
Dipole Pattern ◽  
Skill Improvement

<p>Remote (r ≤ 1800km) outgoing longwave radiation (OLR) fields are investigated in observations, the ECMWF ensemble forecast and reanalysis data. A large scale dipole pattern of low and high fluxes are found in both the observations and model. Low OLR regions are positioned within the cyclone circulation and high OLR regions are found 500-1500km to the north west of the TC. The position of the high OLR region rotates anticlockwise about the TC center as the TC motion vector rotates clockwise from westward to eastward. There is a strong association between the low level wind divergence fields and the high OLR remote region. We propose this remote high OLR region is of interest regarding TC track forecasts. Sub-ensembles selected upon the location of the remote high OLR region improved track forecasts improved by 15\% at 6hrs lead time. This technique out performs those sub-ensembles selected by the inner 750km TC OLR signal, however the best skill improvement in the study selects sub-ensembles by a 3600x3600km TC centered OLR field.</p>

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