Low visibility regime at aerodromes in European Russia

The characteristics are presented for the visibility regime at 42 aerodromes in European Russia calculated from the data of aerodrome observations reported in METAR telegrams with 30 minute (more rarely, 1 hour) time intervals. The occurrence frequency distributions of horizontal visibility ≤ 300 m and ≤ 800 m are calculated and analyzed over the period of 2001-2019. The tables are presented and discussed for the annual cycles of the occurrence frequency, as well as for its distributions under different weather phenomena. The occurrence frequency distributions depending on cloud base height, relative humidity, speed and direction of surface wind are presented. The results are also presented for the duration of low visibility episodes: it is demonstrated that such episodes are short, as a rule (for example, the visibility ≤ 300 m is continually observed for not more than 2 hours in 65-85 % of cases). The results of quantification of the correspondence between the occurrence or absence of low visibility and other weather characteristics observed at the same aerodromes demonstrate certain perspectives for developing (at least for several aerodromes) statistical methods to forecast this rather rare phenomenon basing on outputs of numerical atmosphere models. Keywords: visibility, aerodrome observations, annual cycle of low visibility, relative humidity, cloud base height, weather phenomena

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Perturbations in relative humidity in the boundary layer represent a possible mechanism for the formation of small convective clouds

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-13-28729-2013 ◽

2013 ◽

Vol 13 (11) ◽

pp. 28729-28749 ◽

Cited By ~ 1

Author(s):

E. Hirsch ◽

I. Koren ◽

O. Altaratz ◽

Z. Levin ◽

E. Agassi

Keyword(s):

Relative Humidity ◽

Inversion Layer ◽

Cloud Base ◽

Atmospheric Conditions ◽

Thermal Inversion ◽

Convective Clouds ◽

Air Pockets ◽

Lifting Condensation Level ◽

Shed Light ◽

Cloud Base Height

Abstract. An air parcel model was developed to study the formation of small convective clouds that appear under conditions of weak updraft and a strong thermal inversion layer above the clouds. Observations suggest that these clouds are characterized by a cloud base height far lower than the lifting condensation level. Considering such atmospheric conditions, the air parcel model shows that these clouds cannot be the result of classical thermals or plumes that are caused by perturbations in the temperature near the surface. We suggest that such clouds are the result of perturbations in the relative humidity of elevated air pockets. These results explain the existence of small clouds that standard methods fail to predict and shed light on processes related to the formation of convective clouds from the lowest end of the size distribution.

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Features of the Cloud Base Height and Determining the Threshold of Relative Humidity over Southeast China

Remote Sensing ◽

10.3390/rs11242900 ◽

2019 ◽

Vol 11 (24) ◽

pp. 2900 ◽

Cited By ~ 2

Author(s):

Yuzhi Liu ◽

Yuhan Tang ◽

Shan Hua ◽

Run Luo ◽

Qingzhe Zhu

Keyword(s):

Relative Humidity ◽

Hydrological Cycle ◽

Critical Role ◽

Global Radiation ◽

Radiation Budget ◽

Cloud Base ◽

Accurate Information ◽

Southeast China ◽

Environmental Relative Humidity ◽

Cloud Base Height

Clouds play a critical role in adjusting the global radiation budget and hydrological cycle; however, obtaining accurate information on the cloud base height (CBH) is still challenging. In this study, based on Lidar and aircraft soundings, we investigated the features of the CBH and determined the thresholds of the environmental relative humidity (RH) corresponding to the observed CBHs over Southeast China from October 2017 to September 2018. During the observational period, the CBHs detected by Lidar/aircraft were commonly higher in cold months and lower in warm months; in the latter, 75.91% of the CBHs were below 2000 m. Overall, the RHs at the cloud base were mainly distributed between 70 and 90% for the clouds lower than 1000 m, in which the most concentrated RH was approximately 80%. In addition, for the clouds with a cloud base higher than 1000 m, the RH thresholds decreased dramatically with increasing CBH, where the RH thresholds at cloud bases higher than 2000 m could be lower than 60%. On average, the RH thresholds for determining the CBHs were the highest (72.39%) and lowest (63.56%) in the summer and winter, respectively, over Southeast China. Therefore, to determine the CBH, a specific threshold of RH is needed. Although the time period covered by the collected CBH data from Lidar/aircraft is short, the above analyses can provide some verification and evidence for using the RH threshold to determine the CBH.

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Reducing misclassified precipitation phase in conceptual models using cloud base heights and relative humidity to adjust air temperature thresholds

Hydrology Research ◽

10.2166/nh.2021.072 ◽

2021 ◽

Author(s):

Lic James M. Feiccabrino

Keyword(s):

Relative Humidity ◽

Air Temperature ◽

Conceptual Models ◽

Phase Changes ◽

Cloud Base ◽

Temperature Threshold ◽

Air Temperatures ◽

Low Cloud ◽

Precipitation Phase ◽

Cloud Base Height

Abstract In cold region, conceptual models assigned precipitation phase, liquid (rain) or solid (snow), cause vastly different atmospheric, hydrological, and ecological responses, along with significant differences in evaporation, runoff, and infiltration fates for measured precipitation mass. A set air temperature threshold (ATT) applied to the over 30% annual precipitation events occurring with surface air temperatures between −3 and 5 °C resulted in 11.0 and 9.8% misclassified precipitation in Norway and Sweden, respectively. Surface air temperatures do not account for atmospheric properties causing precipitation phase changes as snow falls toward the ground. However, cloud base height and relative humidity (RH) measured from the surface can adjust ATT for expected hydrometeor-atmosphere interactions. Applying calibrated cloud base height ATTs or a linear RH function for Norway (Sweden) reduced to 4.3% (2.8%) and 14.6% (8.9%) misclassified precipitation, respectively. Cloud base height ATTs had lower miss-rates with low cloud bases, 100 m in Norway and 300 m in Sweden. Combining the RH method with cloud base ATT in low cloud conditions resulted in 16.1 and 10.8% reduction in misclassified precipitation in Norway and Sweden, respectively. Therefore, the conceptual model output should improve through the addition of available surface data without coupling to an atmospheric model.

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A 42 year inference of cloud base height trends in the Luquillo Mountains of northeastern Puerto Rico

Climate Research ◽

10.3354/cr01529 ◽

2018 ◽

Vol 76 (1) ◽

pp. 87-94 ◽

Cited By ~ 5

Author(s):

PW Miller ◽

TL Mote ◽

CA Ramseyer ◽

AE Van Beusekom ◽

M Scholl ◽

...

Keyword(s):

Puerto Rico ◽

Cloud Base ◽

Luquillo Mountains ◽

Cloud Base Height

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Cloud Base Height and Effective Cloud Emissivity Retrieval with Ground-Based Infrared Interferometer

Atmospheric and Oceanic Science Letters ◽

10.1080/16742834.2012.11447021 ◽

2012 ◽

Vol 5 (5) ◽

pp. 439-444

Author(s):

Pan Lin-Jun ◽

Lu Da-Ren

Keyword(s):

Cloud Base ◽

Cloud Base Height

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Cloud base height determination in rain, snow, and fog with a low-cost eye-safe lidar

10.1117/12.221057 ◽

1995 ◽

Cited By ~ 1

Author(s):

Christoph Muenkel

Keyword(s):

Low Cost ◽

Cloud Base ◽

Height Determination ◽

Cloud Base Height

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Why sometimes its simply sunny (in the trades)

10.5194/egusphere-egu21-15408 ◽

2021 ◽

Author(s):

Bjorn Stevens ◽

Ilya Serikov ◽

Anna Lea Albright ◽

Sandrine Bony ◽

Geet George ◽

...

Keyword(s):

Boundary Layer ◽

Water Vapor ◽

Marine Boundary Layer ◽

Cloud Base ◽

Lidar Signal ◽

Cloud Base Height

<p>Cloud free skies are rare in the trades. &#160;We analyze conditions in which cloud-free conditions prevail. &#160;For this purpose Raman water vapor measurements from the Barbados Cloud Observatory, complemented by ship-based measurements during EUREC4A are used to explore water vapor variability in the marine boundary layer. &#160; We explore the consistency of the inferred cloud base height with estimates of temperature and water vapor from the lidar signal, and examine the co-variability of these quantities. &#160;After having established the properties of these measurements, we seek to use them as well as others, to explain in what ways periods of cloud-free conditions are maintained, investigating the hypothesis that only when the wind stills is it simply sunny.</p>

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Intensification of Tilted Tropical Cyclones Over Relatively Cool and Warm Oceans in Idealized Numerical Simulations

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-21-0051.1 ◽

2021 ◽

Author(s):

David A. Schecter

Keyword(s):

Relative Humidity ◽

Tropical Cyclones ◽

Inner Core ◽

Structural Parameters ◽

Deep Convection ◽

Surface Wind ◽

Vertical Wind Shear ◽

Surface Wind Speed ◽

Cloud Resolving Model ◽

Complete Alignment

Abstract A cloud resolving model is used to examine the intensification of tilted tropical cyclones from depression to hurricane strength over relatively cool and warm oceans under idealized conditions where environmental vertical wind shear has become minimal. Variation of the SST does not substantially change the time-averaged relationship between tilt and the radial length scale of the inner core, or between tilt and the azimuthal distribution of precipitation during the hurricane formation period (HFP). By contrast, for systems having similar structural parameters, the HFP lengthens superlinearly in association with a decline of the precipitation rate as the SST decreases from 30 to 26 °C. In many simulations, hurricane formation progresses from a phase of slow or neutral intensification to fast spinup. The transition to fast spinup occurs after the magnitudes of tilt and convective asymmetry drop below certain SST-dependent levels following an alignment process explained in an earlier paper. For reasons examined herein, the alignment coincides with enhancements of lower–middle tropospheric relative humidity and lower tropospheric CAPE inward of the radius of maximum surface wind speed rm. Such moist-thermodynamic modifications appear to facilitate initiation of the faster mode of intensification, which involves contraction of rm and the characteristic radius of deep convection. The mean transitional values of the tilt magnitude and lower–middle tropospheric relative humidity for SSTs of 28-30 °C are respectively higher and lower than their counterparts at 26 °C. Greater magnitudes of the surface enthalpy flux and core deep-layer CAPE found at the higher SSTs plausibly compensate for less complete alignment and core humidification at the transition time.

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