Cloud-resolving simulations of mercury scavenging and deposition in thunderstorms

Abstract. This study examines dynamical and microphysical features of convective clouds that affect mercury (Hg) wet scavenging and concentrations in rainfall. Using idealized numerical model simulations in the Regional Atmospheric Modeling System (RAMS), we diagnose vertical transport and scavenging of soluble Hg species – gaseous oxidized mercury (GOM) and particle-bound mercury (HgP), collectively Hg(II) – in thunderstorms under typical environmental conditions found in the Northeast and Southeast United States (US). Mercury scavenging efficiencies from various initial altitudes are diagnosed for a case study of a typical strong convective storm in the Southeast US. Assuming that soluble mercury concentrations are initially vertically uniform, the model results suggest that 60% of mercury deposited to the surface in rainwater originates from above the boundary layer (> 2 km). The free troposphere could supply a larger fraction of mercury wet deposition if GOM and HgP concentrations increase with altitude. We use radiosonde observations in the Northeast and Southeast to characterize three important environmental characteristics that influence thunderstorm morphology: convective available potential energy (CAPE), vertical shear (0–6 km) of horizontal wind (SHEAR) and precipitable water (PW). The Southeast US generally has lower SHEAR and higher CAPE and PW. We then use RAMS to test how PW and SHEAR impact mercury scavenging and deposition, while keeping the initial Hg(II) concentrations fixed in all experiments. We found that the mercury concentration in rainfall is sensitive to SHEAR with the nature of sensitivity differing depending upon the PW. Since CAPE and PW cannot be perturbed independently, we test their combined influence using an ensemble of thunderstorm simulations initialized with environmental conditions for the Northeast and Southeast US. These simulations, which begin with identical Hg(II) concentrations, predict higher mercury concentrations in rainfall from thunderstorms forming in the environmental conditions over the Southeast US compared to the Northeast US. A final simulation of a stratiform rain event produces lower mercury concentrations than in thunderstorms forming in environments typical of the Southeast US. The stratiform cloud scavenges mercury from the lowest ~ 4 km of the atmosphere, while thunderstorms scavenge up to ~ 10 km.

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Cloud-resolving simulations of mercury scavenging and deposition in thunderstorms

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-13-3575-2013 ◽

2013 ◽

Vol 13 (2) ◽

pp. 3575-3611

Author(s):

U. S. Nair ◽

Y. Wu ◽

C. D. Holmes ◽

A. Ter Schure ◽

G. Kallos ◽

...

Keyword(s):

United States ◽

Environmental Conditions ◽

Convective Available Potential Energy ◽

Atmospheric Modeling ◽

Vertical Shear ◽

Horizontal Wind ◽

Rain Event ◽

Free Troposphere ◽

Environmental Characteristics ◽

Southeast Us

Abstract. This study examines dynamical and microphysical features of convective clouds that affect mercury (Hg) wet scavenging and concentrations in rainfall. Using idealized numerical model simulations in the Regional Atmospheric Modeling System (RAMS), we diagnose vertical transport and scavenging of soluble Hg species in thunderstorms under typical environmental conditions found in the Northeast and Southeast United States (US). Three important environmental characteristics that impact thunderstorm morphology were studied: convective available potential energy (CAPE), vertical shear (0–6 km) of horizontal wind (SHEAR) and precipitable water (PW). We find that in a strong convective storm in the Southeast US that about 40% of mercury in the boundary layer (0–2 km) can be scavenged and deposited to the surface. Removal efficiencies are 35% or less in the free troposphere and decline with altitude. Nevertheless, if we assume that soluble Hg species are initially uniformly mixed vertically, then about 60% deposited mercury deposited by the thunderstorm originates in the free troposphere. For a given CAPE, storm morphology and Hg deposition respond to SHEAR and PW. Experiments show that the response of mercury concentration in rainfall to SHEAR depends on the amount of PW. For low PW, increasing SHEAR decreases mercury concentrations in high-rain amounts (>13 mm). However, at higher PW values, increasing SHEAR decreases mercury concentrations for all rainfall amounts. These experiments suggest that variations in environmental characteristics relevant to thunderstorm formation and evolution can also contribute to geographical difference in wet deposition of mercury. An ensemble of thunderstorm simulations was also conducted for different combinations of CAPE, SHEAR and PW values derived from radiosonde observations at five sites in the Northeast United States (US) and at three sites in the Southeast US. Using identical initial concentrations of gaseous oxidized mercury (GOM) and particle-bound mercury (HgP), from the GEOS-Chem model, the simulations predict higher mercury concentrations in rainfall from thunderstorms forming in the environmental conditions over the Southeast US compared to the Northeast US. Mercury concentrations in rainfall are also simulated for a typical stratiform rain event and found to be less than in thunderstorms forming in environments typical of the Southeast US. The stratiform cloud scavenges mercury from the lower ~4 km of the atmosphere, while thunderstorms scavenge up to ~10 km.

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A Statistical Analysis of Hail Events and Their Environmental Conditions in China during 2008–15

Journal of Applied Meteorology and Climatology ◽

10.1175/jamc-d-18-0109.1 ◽

2018 ◽

Vol 57 (12) ◽

pp. 2817-2833 ◽

Cited By ~ 5

Author(s):

Mingxin Li ◽

Da-Lin Zhang ◽

Jisong Sun ◽

Qinghong Zhang

Keyword(s):

South China ◽

Environmental Conditions ◽

North China ◽

Convective Available Potential Energy ◽

Vertical Wind Shear ◽

Precipitable Water ◽

Growth Zone ◽

The United States ◽

Reanalysis Data ◽

Low Level

AbstractAn 8-yr (i.e., 2008–15) climatology of the spatiotemporal characteristics of hail events in China and their associated environmental conditions are examined using hail observations, L-band rawinsondes, and global reanalysis data. A total of 1003 hail events with maximum hail diameter (MHD) of greater than 5 mm are selected and then sorted into three hail-size bins. Hail events with the largest MHD bin correspond to the median vertical wind shear in the lowest 6-km layer (SHR6) of 21.6 m s−1, precipitable water (PW) of 34.8 mm, and convective available potential energy (CAPE) of 2192 J kg−1. Hail with different MHD bins share similar freezing-level heights (FLHs) of about 4000 m. The thickness of the hail growth zone is thinner for hail events with the largest MHD bin. Hail events with different MHD bins display seasonal variations associated with the summer monsoon; that is, the hail season starts in South China in spring and then shifts to North China in summer. Larger hail is mainly observed during the spring in South China before monsoon onset in the presence of an upper-level jet and a low-level southwesterly flow accounting for large SHR6 and PW. In contrast, smaller-MHD hailstorms occur mainly during the summer in North China when surface heating is high and the low-level southerly flow shifts northward with pronounced baroclinicity providing large CAPE and PW, moderate SHR6, and low FLH. Environmental CAPE and SHR6 for large hailstones in China are comparable in magnitude to those in the United States but larger than those in some European countries.

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The Sensitivity of Simulated Storm Structure, Intensity, and Precipitation Efficiency to Environmental Temperature

Monthly Weather Review ◽

10.1175/mwr3015.1 ◽

2005 ◽

Vol 133 (10) ◽

pp. 3015-3037 ◽

Cited By ~ 31

Author(s):

Eugene W. McCaul ◽

Charles Cohen ◽

Cody Kirkpatrick

Keyword(s):

Parameter Space ◽

Environmental Temperature ◽

Deep Convection ◽

Convective Available Potential Energy ◽

Environmental Parameters ◽

Precipitable Water ◽

Vertical Shear ◽

Precipitation Efficiency ◽

The Impact ◽

Moist Layer

Abstract Prior parameter space studies of simulated deep convection are extended to embrace shifts in the environmental temperature. Within the context of the parameter space study design, shifts in this environmental temperature are roughly equivalent to changes in the ambient precipitable water (PW). Two series of simulations are conducted: one in a warm environmental regime that is associated with approximately 60 mm of precipitable water, and another with temperatures 8°C cooler, so that PW is reduced to roughly 30 mm. The sets of simulations include tests of the impact of changes in the buoyancy and shear profile shapes and of changes in mixed- and moist layer depths, all of which have been shown to be important in prior work. Simulations discussed here also feature values of surface-based pseudoadiabatic convective available potential energy (CAPE) of 800, 2000, or 3200 J kg−1, and a single semicircular hodograph having a radius of 12 m s−1, but with variable vertical shear. The simulations reveal a consistent trend toward stronger peak updraft speeds for the cooler temperature (reduced PW) cases, when the other environmental parameters are held constant. Roughly comparable increases in updraft speeds are noted for all combinations of mixed- and moist layer depths. These increases in updraft strength evidently result from both the reduction of condensate loading aloft and the lower altitudes at which the latent heat release by freezing and deposition commences in the cooler, low-PW environments. As expected, maximum storm precipitation rates tend to diminish as PW is decreased, but only slightly, and by amounts not proportionate to the decrease in PW. The low-PW cases thus actually feature larger environment-relative precipitation efficiency than do the high-PW cases. In addition, more hail reaches the surface in the low-PW cases because of reduced melting in the cooler environments. Although these experiments were designed to feature specified amounts of pseudoadiabatic CAPE, it appears that reversible CAPE provides a more accurate prediction of updraft strength, at least for the storms discussed here.

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Characteristics of Extratropical Cyclones That Cause Tornadoes in Italy: A Preliminary Study

Atmosphere ◽

10.3390/atmos12020180 ◽

2021 ◽

Vol 12 (2) ◽

pp. 180

Author(s):

Eigo Tochimoto ◽

Mario Marcello Miglietta ◽

Leonardo Bagaglini ◽

Roberto Ingrosso ◽

Hiroshi Niino

Keyword(s):

Environmental Conditions ◽

Convective Available Potential Energy ◽

Static Stability ◽

Extratropical Cyclones ◽

Cool Season ◽

Southeastern Us ◽

Different Seasons ◽

The Difference ◽

Upper Level ◽

Strong Evaporation

Characteristics of extratropical cyclones that cause tornadoes in Italy are investigated. Tornadoes between 2007 and 2016 are analyzed, and statistical analysis of the associated cyclone structures and environments is performed using the JRA-55 reanalysis. Tornadoes are distributed sporadically around the cyclone location within a window of 10° × 10°. The difference in the cyclone tracks partially explains the seasonal variability in the distribution of tornadoes. The highest number of tornadoes occur south of the cyclone centers, mainly in the warm sector, while a few are observed along the cold front. Composite mesoscale parameters are examined to identify the environmental conditions associated with tornadoes in different seasons. Potential instability is favorable to tornado development in autumn. The highest convective available potential energy (CAPE) in this season is associated with relatively high-temperature and humidity at low-levels, mainly due to the strong evaporation over the warm Mediterranean Sea. Upper-level potential vorticity (PV) anomalies and the associated cold air reduce the static stability above the cyclone center, mainly in spring and winter. On average, the values of CAPE are lower than for US tornadoes and comparable with those occurring in Japan, while storm relative helicity (SREH) is comparable with US tornadoes and higher than Japanese tornadoes, indicating that the environmental conditions for Italian tornadoes have peculiar characteristics. Overall, the conditions emerging in this study are close to the high-shear, low-CAPE environments typical of cool-season tornadoes in the Southeastern US.

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NAM Model Forecasts of Warm-Season Quasi-Stationary Frontal Environments in the Central United States

Weather and Forecasting ◽

10.1175/2010waf2222394.1 ◽

2010 ◽

Vol 25 (4) ◽

pp. 1281-1292 ◽

Cited By ~ 3

Author(s):

Shih-Yu Wang ◽

Adam J. Clark

Keyword(s):

United States ◽

Mesoscale Model ◽

Convective Available Potential Energy ◽

Warm Season ◽

Correlation Coefficients ◽

Precipitable Water ◽

Wind Fields ◽

Vapor Flux ◽

Convective Systems ◽

Central United States

Abstract Using a composite procedure, North American Mesoscale Model (NAM) forecast and observed environments associated with zonally oriented, quasi-stationary surface fronts for 64 cases during July–August 2006–08 were examined for a large region encompassing the central United States. NAM adequately simulated the general synoptic features associated with the frontal environments (e.g., patterns in the low-level wind fields) as well as the positions of the fronts. However, kinematic fields important to frontogenesis such as horizontal deformation and convergence were overpredicted. Surface-based convective available potential energy (CAPE) and precipitable water were also overpredicted, which was likely related to the overprediction of the kinematic fields through convergence of water vapor flux. In addition, a spurious coherence between forecast deformation and precipitation was found using spatial correlation coefficients. Composite precipitation forecasts featured a broad area of rainfall stretched parallel to the composite front, whereas the composite observed precipitation covered a smaller area and had a WNW–ESE orientation relative to the front, consistent with mesoscale convective systems (MCSs) propagating at a slight right angle relative to the thermal gradient. Thus, deficiencies in the NAM precipitation forecasts may at least partially result from the inability to depict MCSs properly. It was observed that errors in the precipitation forecasts appeared to lag those of the kinematic fields, and so it seems likely that deficiencies in the precipitation forecasts are related to the overprediction of the kinematic fields such as deformation. However, no attempts were made to establish whether the overpredicted kinematic fields actually contributed to the errors in the precipitation forecasts or whether the overpredicted kinematic fields were simply an artifact of the precipitation errors. Regardless of the relationship between such errors, recognition of typical warm-season environments associated with these errors should be useful to operational forecasters.

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On strongly nonlinear gravity waves in a vertically sheared atmosphere

Mathematics of Climate and Weather Forecasting ◽

10.1515/mcwf-2020-0103 ◽

2020 ◽

Vol 6 (1) ◽

pp. 63-74

Author(s):

Mark Schlutow ◽

Georg S. Voelker

Keyword(s):

Gravity Waves ◽

Lower Layer ◽

Vertical Shear ◽

Horizontal Wind ◽

Necessary Condition ◽

Mean Flow ◽

Individual Layer ◽

Strongly Nonlinear ◽

The Mean ◽

The Stability

Abstract We investigate strongly nonlinear stationary gravity waves which experience refraction due to a thin vertical shear layer of horizontal background wind. The velocity amplitude of the waves is of the same order of magnitude as the background flow and hence the self-induced mean flow alters the modulation properties to leading order. In this theoretical study, we show that the stability of such a refracted wave depends on the classical modulation stability criterion for each individual layer, above and below the shearing. Additionally, the stability is conditioned by novel instability criteria providing bounds on the mean-flow horizontal wind and the amplitude of the wave. A necessary condition for instability is that the mean-flow horizontal wind in the upper layer is stronger than the wind in the lower layer.

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A 7-Year Climatology of Warm-Sector Heavy Rainfall over South China during the Pre-Summer Months

Atmosphere ◽

10.3390/atmos12070914 ◽

2021 ◽

Vol 12 (7) ◽

pp. 914

Author(s):

Tao Chen ◽

Da-Lin Zhang

Keyword(s):

South China ◽

Heavy Rainfall ◽

Large Scale ◽

Convective Available Potential Energy ◽

Potential Temperature ◽

Vertical Wind Shear ◽

Precipitable Water ◽

Atmospheric Parameter ◽

Low Level ◽

Warm Sector

In view of the limited predictability of heavy rainfall (HR) events and the limited understanding of the physical mechanisms governing the initiation and organization of the associated mesoscale convective systems (MCSs), a composite analysis of 58 HR events over the warm sector (i.e., far ahead of the surface cold front), referred to as WSHR events, over South China during the months of April to June 2008~2014 is performed in terms of precipitation, large-scale circulations, pre-storm environmental conditions, and MCS types. Results show that the large-scale circulations of the WSHR events can be categorized into pre-frontal, southwesterly warm and moist ascending airflow, and low-level vortex types, with higher frequency occurrences of the former two types. Their pre-storm environments are characterized by a deep moist layer with >50 mm column-integrated precipitable water, high convective available potential energy with the equivalent potential temperature of ≥340 K at 850 hPa, weak vertical wind shear below 400 hPa, and a low-level jet near 925 hPa with weak warm advection, based on atmospheric parameter composite. Three classes of the corresponding MCSs, exhibiting peak convective activity in the afternoon and the early morning hours, can be identified as linear-shaped, a leading convective line adjoined with trailing stratiform rainfall, and comma-shaped, respectively. It is found that many linear-shaped MCSs in coastal regions are triggered by local topography, enhanced by sea breezes, whereas the latter two classes of MCSs experience isentropic lifting in the southwesterly warm and moist flows. They all develop in large-scale environments with favorable quasi-geostrophic forcing, albeit weak. Conceptual models are finally developed to facilitate our understanding and prediction of the WSHR events over South China.

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Cloudburst events observed over Uttarakhand during monsoon season 2017 and their analysis

MAUSAM ◽

10.54302/mausam.v73i1.5084 ◽

2022 ◽

Vol 73 (1) ◽

pp. 91-104

Author(s):

BIKRAM SINGH ◽

ROHIT THAPLIYAL

Keyword(s):

Flash Flood ◽

Monsoon Season ◽

Convective Available Potential Energy ◽

Precipitable Water ◽

Interval Data ◽

Rain Gauge ◽

Thermodynamic Conditions ◽

North Pakistan ◽

June July ◽

Head Bay Of Bengal

Cloudburst is an extreme weather event characterised by the occurrence of a large amount of rainfall over a small area within a short span of time with a rainfall of 100 mm or more in one hour. It is responsible for flash flood, inundation of low lying areas and landslides in hills causing extensive damages to life and property. During monsoon season 2017 five number of cloudburst events are observed over Uttarakhand and analysed. Self Recording Rain Gauge (SRRG) and 15 minutes interval data from the newly installed General Packet Radio Service (GPRS) based Automatic Weather Station (AWS) are able to capture the cloudburst events over some areas in Uttarakhand. In this paper, an attempt has been made to find out the significant synoptic and thermodynamic conditions associated with the occurrence of the cloudburst events in Uttarakhand. These 5 cases of cloudburst events that are captured during the month of June, July and August 2017 in Uttarakhand are studied in detail. Synoptically, it is observed that the existence of trough at mean sea level from Punjab to head Bay of Bengal running close to Uttarakhand, the movement of Western Disturbance over north Pakistan and adjoining Jammu & Kashmir and existence of cyclonic circulation over north Rajasthan and neighbourhood are favourable conditions. Also, the presence of strong south-westerly wind flow from the Arabian Sea across West Rajasthan and Haryana on upper air charts are found during these events. Thermodynamically, the Convective Available Potential Energy (CAPE) is found to be high (more than 1100 J/Kg) during most of the cases and vertically integrated precipitable water content (PWC) is more than 55mm. The GPRS based AWS system can help in prediction of the cloud burst event over the specified location with a lead time upto half to one hour in association with radar products.

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Influence of Quasi-Periodic Oscillation of Atmospheric Variables on Radiation Fog over A Mountainous Region of Korea

Atmosphere ◽

10.3390/atmos11030230 ◽

2020 ◽

Vol 11 (3) ◽

pp. 230

Author(s):

Inyeob La ◽

Seong Soo Yum ◽

Ismail Gultepe ◽

Jae Min Yeom ◽

Jae In Song ◽

...

Keyword(s):

Periodic Oscillation ◽

Vertical Shear ◽

Horizontal Wind ◽

Simultaneous Increase ◽

Mountainous Region ◽

Helmholtz Instability ◽

Radiation Fog ◽

Quasi Periodic Oscillation ◽

Time Frequency ◽

Atmospheric Variables

To enhance our understanding of fog processes over complex terrain, various fog events that occurred during the International Collaborative Experiments for Pyeongchang 2018 Winter Olympics and Paralympics (ICE-POP) campaign were selected. Investigation of thermodynamic, dynamic, and microphysical conditions within fog layers affected by quasi-periodic oscillation of atmospheric variables was conducted using observations from a Fog Monitor-120 (FM-120) and other in-situ meteorological instruments. A total of nine radiation fog cases that occurred in the autumn and winter seasons during the campaign over the mountainous region of Pyeongchang, Korea were selected. The wavelet analysis was used to study quasi-period oscillations of dynamic, microphysical, and thermodynamic variables. By decomposing the time series into the time-frequency space, we can determine both dominant periods and how these dominant periods change in time. Quasi-period oscillations of liquid water content (LWC), pressure, temperature, and horizontal/vertical velocity, which have periods of 15–40 min, were observed during the fog formation stages. We hypothesize that these quasi-periodic oscillations were induced by Kelvin–Helmholtz instability. The results suggest that Kelvin–Helmholtz instability events near the surface can be explained by an increase in the vertical shear of horizontal wind and by a simultaneous increase in wind speed when fog forms. In the mature stages, fluctuations of the variables did not appear near the surface anymore.

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Mountain-Wave Turbulence Encounter of the Research Aircraft HALO above Iceland

Journal of Applied Meteorology and Climatology ◽

10.1175/jamc-d-19-0079.1 ◽

2020 ◽

Vol 59 (3) ◽

pp. 567-588 ◽

Cited By ~ 1

Author(s):

Martina Bramberger ◽

Andreas Dörnbrack ◽

Henrike Wilms ◽

Florian Ewald ◽

Robert Sharman

Keyword(s):

Polar Front ◽

Vertical Shear ◽

Horizontal Wind ◽

Mountain Wave ◽

Horizontal Wind Speed ◽

Wind Speeds ◽

Research Aircraft ◽

Strong Surface ◽

Flight Level ◽

Thrust Control

AbstractStrong turbulence was encountered by the German High-Altitude Long-Range Research Aircraft (HALO) at flight level 430 (13.8 km) on 13 October 2016 above Iceland. In this event the turbulence caused altitude changes of the research aircraft of about 50 m within a period of approximately 15 s. Additionally, the automatic thrust control of the HALO could not control the large gradients in the horizontal wind speed and, consequently, the pilot had to switch off this system. Simultaneously, the French Falcon of Service des Avions Français Instrumentés pour la Recherche en Environnement (SAFIRE), flying 2 km below HALO, also encountered turbulence at almost the same location. On that day, mountain-wave (MW) excitation and propagation was favored by the alignment of strong surface winds and the polar front jet. We use a combination of in situ observations, ECMWF and empirical turbulence forecasts, and high-resolution simulations to characterize the observed turbulent event. These show that a pronounced negative vertical shear of the horizontal wind favored overturning and breaking of MWs in the area of the encountered turbulence. The turbulent region was tilted upstream and extended over a distance of about 2 km in the vertical. The analyses suggest that HALO was flying through the center of a breaking MW field while the French Falcon encountered the lower edge of this region. Surprisingly, the pronounced gradients in the horizontal wind speeds leading to the deactivation of the automatic thrust control were located north of the breaking MW field. In this area, our analysis suggests the presence of gravity waves that could have generated the encountered modulation of the horizontal wind field.

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