Nocturnal Surface Inversion Research Articles

Impact of Seasonal Snow‐Cover Change on the Observed and Simulated State of the Atmospheric Boundary Layer in a High‐Altitude Mountain Valley

AbstractThe structure and evolution of the atmospheric boundary layer (ABL) under clear‐sky fair weather conditions over mountainous terrain is dominated by the diurnal cycle of the surface energy balance and thus strongly depends on surface snow cover. We use data from three passive ground‐based infrared spectrometers deployed in the East River Valley in Colorado's Rocky Mountains to investigate the response of the thermal ABL structure to changes in surface energy balance during the seasonal transition from low to high snow cover. Temperature profiles were retrieved from the infrared radiances using the optimal estimation physical retrieval Tropospheric Remotely Observed Profiling via Optimal Estimation. A nocturnal surface inversion formed in the valley during clear‐sky days, which was subsequently mixed out during daytime with the development of a convective boundary layer when snow cover was low. Over high snow cover, a very shallow convective boundary layer formed, above which the inversion persisted through the daytime hours. We compare these observations to NOAA's operational High‐Resolution‐Rapid‐Refresh model and find large warm biases on clear‐sky days resulting from the model's inability to form strong nocturnal inversions and to maintain the stable stratification in the valley during daytime when there was snow on the ground. We suggest several factors contributing to the large model errors. These are (a) the inability of the model to represent well‐developed thermally driven flows likely due to the too coarse horizontal grid spacing (3 km), (b) too much convective mixing during daytime, and (c) too strong vertical coupling between the valley atmosphere and the free troposphere.

Abrupt High PM Concentration in an Urban Calm Cavity Generated by Internal Gravity Waves and a Shallow Coastal Atmospheric Boundary Layer with the Influence of the Yellow Dust from China

Using GRIMM-1107 aerosol sampler, GOES-9 DCD satellite images, HYSPLIT model of backward trajectory and 3D-meteorological WRF-3.6 model, high particulate matter concentrations were investigated at Gangneung city in the Korean east coast which consists of Mt. Taeglyung in its west and the East Sea in its east on 00:00LST March 26~00:00 LST 4 April 2004. During a Yellow Dust period, the maximum PM10 (PM2.5 and PM1) concentration at the city was about 3.3 (1.1 and 1.01) times higher than one in the non-dust period. After the transported dust from the Gobi Desert and Nei-Mongo by strong northwesterly wind passed over Mt. Taegulyang and moved down toward the city. Then the dust was trapped inside a calm cavity generated by the confront of internal gravity waves (IGW) over the city and the eastward movement of the trapped dust is prohibited by the easterly onshore wind from the East Sea, and the trapped dust further combined with particulate and gaseous emitted from the road vehicles and heating boilers of the city at 09:00LST, March 30 (beginning time of office hours), causing high PM concentrations. On mid-day, as the combined dust due to daytime sufficient thermal convection rises up to the top of the thermal internal boundary layer (TIBL) of a 300 m depth from the coast to the top of the mountain, the ground-based PM concentrations in the city are much lower at 15:00LST due to the higher thickness of the TIBL than at 09:00LST. At night, particulates emitted from many road vehicles after the end of office hours and residential heating boilers could combine with both dust transported from the Nei-Mongo and falling dust uplifted from the ground surface of the city during the day, and they were trapped inside a calm cavity by the IGV under much shallower stable nocturnal surface inversion layer than the TIBL, causing more dust to be accumulated near the surface and showing the maximum PM concentrations at 20:00 LST.

A Modeling Study of an Atmospheric Bore Associated With a Nocturnal Convective System Over China

AbstractBores have been shown to play a role in the initiation and maintenance of mesoscale convective systems (MCSs), particularly during the night after the boundary layer stabilizes. To date, the generation, evolution, and structure of bores over China has received little attention. This study utilizes observations and simulations with the WRF‐ARW model to investigate the generation and evolution of an atmospheric bore observed over Yangtze‐Huai Plains of China. The bore was associated with a nocturnal MCS that first formed over elevated terrain. The bore was observed ahead of the MCS with a maximum lateral extension of ~100 km. The feature lasted for over 90 mins and propagated at a speed of ~13 m/s, slightly faster than the MCS. In the simulation, the bore evolved from the separating “head” of the convectively generated gravity current. The bore then continued to propagate ahead of the MCS, even after the dissipation of the feeder current, and took on the appearance of an undular bore. The bore lifted a layer of convectively unstable air above the nocturnal surface inversion, initiating new convection ahead of the MCS to help maintain the MCS. The Scorer parameter ahead of the bore revealed a low‐level wind profile with curvature of the vertical profile of horizontal wind, favoring the trapping of wave energy and the persistence of the bore. These results are generally consistent with the role of bores in the maintenance of nocturnal MCSs and emphasize the need for future studies into the relationship between bores and nocturnal MCSs over China.

Air temperature in the lower troposphere over moscow during heat wave in the summer of 2010

The dynamics of the air temperature in the lower 4-km layer have been studied during the heat wave in the summer of 2010 by the radio sounding data from Dolgoprudny and ground-based meteorological measurements at Moscow State University. The results have been compared with the aeroclimatic data for the previous 19 years. According to these data, the long-term average estimates of vertical thermal gradients and thickness and intensity of nocturnal surface inversions (200–300 m and 2.0°С, respectively) are presented for summer months in the Moscow region. A record high air temperature for the period from at least 1991 has been shown in the air layer up to 2 km above Moscow in the summer of 2010. Among others, the 30°С value has been detected for the first time in the air layer from 400 to 800 m. During the heat wave in 2010, as a result of clearly pronounced anticyclone conditions, the thickness and intensity of nocturnal surface inversions were higher than usual (up to 700 m and 12°С, respectively). The mean temperature profiles have been studied for different types of air masses. It is shown that the tropical air mass predominated over the Moscow region in the summer of 2010 during more than half of the period.

Atmospheric station Křešín u Pacova, Czech Republic – a Central European research infrastructure for studying greenhouse gases, aerosols and air quality

Abstract. Long-lasting research infrastructures covering the research areas of atmospheric chemistry, meteorology and climatology are of highest importance. The Atmospheric Station (AS) Křešín u Pacova, central Czech Republic, is focused on monitoring of the occurence and long-range transport of greenhouse gases, atmospheric aerosols, selected gaseous atmospheric pollutants and basic meteorological characteristics. The AS and its 250 m tall tower was built according to the recommendations of the Integrated Carbon Observation System (ICOS) and cooperates with numerous national and international projects and monitoring programmes. First measurements conducted at ground started in 2012, vertical profile measurements were added in 2013. A seasonal variability with slightly higher autumn and winter concentrations of elemental and organic carbon was revealed. The suitability of the doubly left-censored Weibull distribution for modelling and interpretation of elemental carbon concentrations, which are often lower than instrumental quantification limits, was verified. Initial data analysis also suggests that in summer, the tower top at 250 m is frequently above the nocturnal surface inversions, thus being decoupled from local influences.

Factors controlling pollutant plume length downwind of major roadways in nocturnal surface inversions

Abstract. A fitting method using a semi-empirical Gaussian dispersion model solution was successfully applied to obtain both dispersion coefficients and a particle number emission factor (PNEF) directly from ultrafine particle (UFP; particles smaller than <0.1 μm in diameter) concentration profiles observed downwind of major roadways in California's South Coast Air Basin (SoCAB). The effective Briggs' formulation for the vertical dispersion parameter σz was adopted in this study due to its better performance in describing the observed profiles compared to other formulations examined. The two dispersion coefficients in Briggs' formulation, α and β, ranged from 0.02 to 0.07 and from −0.5 × 10−3 to 2.8 × 10−3, respectively, for the four freeway transects studied and are significantly different for freeways passing over vs. under the street on which measurements of the freeway plume were made. These ranges are wider than literature values for α and β under stable conditions. The dispersion coefficients derived from observations showed strong correlations with both surface meteorology (wind speed/direction, temperature, and air stability) and differences in concentrations between the background and plume peak. The relationships were applied to predict freeway plume transport using a multivariate regression, and produced excellent agreement with observed UFP concentration profiles. The mean PNEF for a mixed vehicle fleet on the four freeways was estimated as 7.5 × 1013 particles km−1 vehicle−1, which is about 15% of the value estimated in 2001 for the I-405 freeway, implying significant reductions in UFP emissions over the past decade in the SoCAB.

Double Compressions of Atmospheric Depth by Geopotential Tendency, Vorticity, and Atmospheric Boundary Layer Affected Abrupt High Particulate Matter Concentrations at a Coastal City for a Yellow Dust Period in October

Using GRIMM-aerosol sampler, NOAA-HYSPLIT model, and 3D-WRF-3.3 model, the transportation of dusts from Gobi Desert toward Gangneung city, Korea was investigated from 09:00 LST October 27 to 04:00 LST October 28, 2003. Maximum PM10 (PM2.5, PM1) concentration was detected with 3.8 (3.4, 14.1) times higher magnitude than one in non-Yellow Dust period. The combination of dusts transported from the desert under westerly wind with particulate matters and gases from vehicles on the road of the city caused high PM concentrations near the ground surface at 09:00 LST and their maxima at 17:00 LST near sunset with further pollutants from heating boilers in the resident area. Positive geopotential tendency at the 500 hPa level of the city (∂Φ/∂t; m day−1) corresponding to negative vorticity of-4×10-5 sec−1(-2.5×10-5 sec−1) at 0900 LST (21:00 LST; at night) was +83 m day−1(+30 m day−1) and it caused atmospheric depth between 500 hPa level and the ground surface to be vertically expanded. However, its net reduction to −53 m/12 hrs until 21:00 LST indicated synoptic-scale atmospheric layer to be vertical shrunken, resulting in the increase of PM concentrations at 17:00 LST. Simultaneously, much shallower microscale stable nocturnal surface inversion layer (NSIL) than daytime thermal internal boundary layer induced particulate matters to be merged inside the NSIL, resulting in maximum PM concentrations at 17:00 LST.

Flow and turbulence in an industrial/suburban roughness canopy

A field study conducted to investigate the flow and turbulence structure of the urban boundary layer (UBL) over an industrial/suburban area is described. The emphasis was on morning and evening transition periods, but some measurements covered the entire diurnal cycle. The data analysis incorporated the dependence of wind direction on morphometric parameters of the urban canopy. The measurements of heat and momentum fluxes showed the possibility of a constant flux layer above the height $$z\approx 2{H}$$ , wherein the Monin-Obukhov Similarity Theory (MOST) is valid; here $$H$$ is the averaged building height. For the nocturnal boundary layer, the mean velocity and temperature profiles obeyed classical MOST scaling up to $$\sim 0.5\Lambda \left( {\sim 6{H}}\right) $$ , where $$\Lambda $$ is the Obukhov length scale, beyond which stronger stratification may disrupt the occurrence of constant fluxes. For unstable and neutral cases, MOST scaling described the mean data well up to the maximum measured height $$(\sim 6{H})$$ . Available MOST functions, however, could not describe the measured turbulence structure, indicating the influence of additional governing parameters. Alternative turbulence parameterizations were tested, and some were found to perform well. Calculation of integral length scales for convective and neutral cases allowed a phenomenological description of eddy characteristics within and above the urban canopy layer. The development of a significant nocturnal surface inversion occurred only on certain days, for which a criterion was proposed. The nocturnal UBL exhibited length scale relationships consistent with the evening collapse of the convective boundary layer and maintenance of buoyancy-affected turbulence overnight. The length and velocity scales so identified are useful in parameterizing turbulent dispersion coefficients in different diurnal phases of the UBL.

Prevalence of wide area impacts downwind of freeways under pre-sunrise stable atmospheric conditions

In urban areas, a large fraction of the population typically lives within 1.5–2 km of a freeway. In an earlier study, Hu et al. (2009) showed that in the pre-sunrise hours, with stable, nocturnal meteorological conditions, the vehicle-related pollution from a freeway in southern California extended more than 2 km downwind. This was in striking contrast to earlier studies in the U.S. and Australia showing that during the daytime pollutant concentrations extended no more than ∼300 m downwind of major roadways. The present study was designed to explore the variability of the large downwind pollutant impact zone observed by Hu et al. (2009) in the pre-sunrise hours on a wider geographic scale. An instrumented mobile platform was employed to measure vehicle-related pollutant concentrations on transects running upwind and downwind of four freeways in the coastal, central and eastern areas of the California South Coast Air Basin (SoCAB) during the pre-sunrise period (04:30–06:30). Extended freeway plumes were observed for ultrafine particles (UFP), nitric oxide and particle-bound polycyclic aromatic hydrocarbons (PAH) at all four sites during stable pre-sunrise periods. Plume lengths were measured to be ∼2 km or more with a dilution rate coefficient about a factor of ten lower than commonly observed for daytime. An average of 39 and 19% (±8–9%) of freeway plume peak concentrations of UFP remained 500 and 1500 m downwind, respectively, from the freeways for the four transects studied here. Because a large fraction of UFP and other vehicle related pollutants typically penetrate into indoor environments, and nocturnal surface inversions are widespread across the globe, our findings have significant implications for more extensive human exposures to vehicle-related pollutants than previously indicated based on daytime measurements of roadway plumes.

The relationships among the nocturnal surface inversion intensity, wind velocity and effective radiation observed at the suburbs of Kumagaya, Saitama, during December 2009 - May 2011

The relationships among the nocturnal surface inversion intensity, wind velocity and effective radiation observed at the suburbs of Kumagaya, Saitama, during December 2009 - May 2011

Nocturnal boundary layer characteristics and land breeze development in Houston, Texas during TexAQS II

The nocturnal boundary layer in Houston, Texas was studied using a high temporal and vertical resolution tethersonde system on four nights during the Texas Air Quality Study II (TexAQS II) in August and September 2006. The launch site was on the University of Houston campus located approximately 4 km from downtown Houston. Of particular interest was the evolution of the nocturnal surface inversion and the wind flows within the boundary layer. The land–sea breeze oscillation in Houston has important implications for air quality as the cycle can impact ozone concentrations through pollutant advection and recirculation. The results showed that a weakly stable surface inversion averaging in depth between 145 and 200 m AGL formed on each of the experiment nights, typically within 2–3 h after sunset. Tethersonde vertical winds were compared with two other Houston data sets (High Resolution Doppler Lidar and radar wind profiler) from locations near the coastline and good agreement was found, albeit with a temporal lag at the tethersonde site. This comparison revealed development of a land breeze on three nights which began near the coastline and propagated inland both horizontally and vertically with time. The vertical temperature structure was significantly modified on one night at the tethersonde site after the land breeze wind shift, exhibiting near-adiabatic profiles below 100 m AGL.

Sudden high concentration of TSP affected by atmospheric boundary layer in Seoul metropolitan area during duststorm period

Hourly concentrations of TSP, PM 10, PM 2.5 near the surface at Seoul city were examined from March 20 to March 25, 2001 (duststorm event) in order to investigate the effect of a duststorm generated in China on the local aerosol concentration in Korea, The ratios of fine to coarse particles such as TSP to PM 10, TSP to PM 2.5 and PM 10–PM 2.5 to PM 2.5 showed that a great amount of dust transported from the origin of the duststorm was remarkable with a maximum ratio of 9.77 between TSP and PM 2.5. Back trajectories every 6 h showed the movement of dust particles in the lower atmosphere near 500 m to 1500 m (atmospheric boundary layer), which implied transport from Baotou in inner Mongolia of northern China to the direction of Seoul city in Korea and then the back trajectories passed near the southern border of Mongolia and Baotou through Zengzhou in the midlevels (3000 m) and low levels (500 m) of China, finally reaching Seoul city. So, the TSP concentration at Seoul city was partially influenced by the duststorm, under the prevailing westerly wind and the transported aerosols could influence high concentrations of pollutants of TSP, PM 10 and PM 2.5 in Seoul. The sudden high concentrations of TSP and PM 10 were found for a few hours, especially at 1500 to 1800 LST, March 22. At 1200 LST, before the passage of a cold front through the Korean peninsula, the convective boundary layer (CBL) near Seoul was not shallow, but at 1500 LST, under the frontal passage, the CBL was remarkably thinner (less than 300 m), due to the compression of the boundary layer by the intrusion of cold air. This resulted in the increase of the TSP concentration, even though the mixed layer above maintained almost the same depth. At 1800 LST shortly after the frontal passage, that is, near sunset, the nocturnal cooling of the ground caused air parcels to cool, thereby enhancing the shallower nocturnal surface inversion layer and producing the maximum concentration of TSP of 1388 µg/m 3 near Seoul city.

An account of fog over Chennai

Climatologically (based on 1951-1980) the annual fog frequency of Chennai airport is 4.3 days. But, the operational aviation meteorological forecasters often experienced more number of foggy days during the past decade. Hence the fog frequency has been critically analysed based on current weather observations made by aerodrome meteorological office, Chennai during 1981-2002 (barring 1984 for which data is not readily available). It has been found that the annual frequency based on the present study has shot up to 21.5 days. The most favourable period for fog over Chennai airport has been identified as January followed by February and March. The formation of fog has been mostly observed during 0000-0200 UTC although in good number of cases it was during 2200-2400 UTC. The most common duration of fog is 60-120 minutes albeit duration as high as 540-570 minutes are also probable. The low level (surface) nocturnal inversion frequency has alarmingly increased during 1990s and the inversion is almost a day-to-day phenomenon during 2000s. Rapid urbanisation, vehicular traffic and industrial growth could be the cause for the increased atmospheric pollution which has increased the nocturnal stability conditions as well the fog frequency. Visibility as low as zero had been recorded on a number of cases and their causes have been analysed. Neutral or absolutely unstable stratification at 1200 UTC coupled with high relative humidity and high concentration of pollution cause the fog to form from 2200 UTC onwards and the nocturnal surface inversion / isotherm at 0000 UTC maintains the fog. Though the low level inversion maintains the fog once it is formed already, inversion alone is not a sufficient condition for the formation of fog.

An attempt at inferring the vertical gradient of potential temperature in the nocturnal surface inversion layer in terms of surface meteorological elements

An attempt at inferring the vertical gradient of potential temperature in the nocturnal surface inversion layer in terms of surface meteorological elements

Effects of atmospheric circulation and boundary layer structure on the dispersion of suspended particulates in the Seoul metropolitan area

A three-dimensional non-hydrostatic numerical model and lagrangian particle model (random walk model) were used to investigate the effects of the atmospheric circulation and boundary layer structure on the dispersion of suspended particulates in the Seoul metropolitan area. Initially, emitted particulate matter rises from the surface of the city towards the top of the convective boundary layer (CBL), owing to daytime thermal heating of the surface and the combined effect of an onshore wind with a westerly synoptic-scale wind. A reinforcing sea-valley breeze directed from the coast toward the city of Seoul, which is enclosed in a basin and bordered by mountains to its east, disperses the suspended particulate matter toward the eastern mountains. Total suspended particulate concentration (TSP) at ground level in the city is very low and relatively high in the mountains. Radiative cooling of the surface produces a shallow nocturnal surface inversion layer (NSIL) and the suspended particulate matter still present near the top of the CBL from the previous day, sinks to the surface. An easterly downslope mountain wind is directed into the metropolitan area, transporting particulate matter towards the city, thereby recycling the pollutants. The particulates descending from the top of the NSIL and mountains, combine with particulates emitted near the surface over the city at night, and under the shallow NSIL spread out, resulting in a maximum ground level concentration of TSP in the metropolitan area at 2300 LST. As those particles move toward the Yellow Sea through the topographically shaped outlet west of Seoul city under the influence of the easterly land breeze, the maximum TSP concentration occurs at the coastal site. During the following morning, onshore winds resulting from a combined synoptic-scale westerly wind and westerly sea breeze, force particulates dispersed the previous night to move over the adjacent sea and back over the inland metropolitan area. The recycled particulates combine with the particulates emitted from the surface in the central part of the metropolitan area, producing a high TSP and again rise towards the top of the CBL ready to repeat the cycle.

Clear air echoes from the atmospheric boundary layer over Chennai – A study using S-band Doppler Weather Radar

During December 2002 – early April 2003, between 2345 and 0215 UTC and between 1230 and 1400 UTC covering the twilight period, radar reflectivities as high as 28-38 dBZ were measured in the atmospheric boundary layer by the Doppler Weather Radar (DWR) installed at Cyclone Detection Radar station, Chennai regularly. On analysis, it was found that these radar returns were not from precipitating clouds but from some other invisible source(s). The contributory mechanisms for this high order of reflectivity have been analysed from meteorological and non-meteorological angles. Thermodynamical parameters and potential radio refractive index have been computed and analysed. The refractive index structure constant (Cn2) has been computed from the 0000 and 1200 UTC RS/RW data as well as from the radar reflectivity data. The prevalence of convectively unstable atmosphere in the first layer adjacent to the surface (upto 350 m a.g.l) at 1200 UTC and nocturnal surface inversion at 0000 UTC contribute to the enhanced Cn2 in the range of 3.58 ´ 10-12 to 10-15 m-2/3 in the layers upto 900 m a.g.l. This sort of Bragg scattering with high Cn2 could have contributed to radar reflectivity factor as high as +0.8 dBZ only. During the last three decades, there is an alarming increase in nocturnal surface inversion frequencies over Chennai presumably due to high concentration of suspended particulate matters and respirable dust particles. The contribution by these pollutants to the radar reflectivity factor is restricted to a maximum of about – 0.9 dBZ only. Migratory birds of about eight to twelve thousand in number with 10 – 50 cm2 radar cross section and possibly innumerable insects appear as sources of the enhanced reflectivity.

Seasonal variation of the temperature inversions over Athens, Greece

This study examines the frequency of appearance and the characteristics of temperature inversions over Athens, up to the pressure level of 500 hPa, for the time period 1974–2001 on a seasonal basis. The analysis is carried out separately for daytime and nocturnal inversions. Moreover, the study includes a brief reference to the synoptic conditions that favour the formation of inversions for each season. The results of the analysis show that nocturnal surface inversions appear with great frequency during all seasons and that the majority of the rest of the inversions appear in winter, in the region between the 800 and 900 hPa pressure levels. Copyright © 2005 Royal Meteorological Society

대기경계층과 연안순환에 의한 부유입자의 재순환

The dispersion of suspended particulates in the coastal complex terrain of mountain-inland basin (city)-sea, considering their recycling was investigated using three-dimensional non-hydrostatic numerical model and lagrangian particle model (or random walk model). Convective boundary layer under synoptic scale westerly wind is developed with a thickness of about I km over the ground in the west of the mountain, while a thickness of thermal internal boundary layer (TIBL) is only confined to less than 200m along the eastern slope of the mountain, below an easterly sea breeze circulation. At the mid of the eastern slop of the mountain, westerly wind confronts easterly sea breeze, which goes to the height of 1700 m above sea level and is finally eastward return flow toward the sea. At this time, particulates floated from the ground surface of the city to the top of TIBL go along the eastern slope of the mountain in the passage of sea breeze, being away the TIBL and reach near the top of the mountain. Then those particulates disperse eastward below the height of sea-breeze circulation and widely spread out over the coastal sea. Total suspended particulate concentration near the ground surface of the city is very low. On the other hand, nighttime radiative cooling produces a shallow nocturnal surface inversion layer (NSIL) of 200 m thickness over the inland surface, but relatively thin thickness less than 100m is found near the mountain surface. As synoptic scale westerly wind should be intensified under the association of mountain wind along the eastern slope of mountain to inland plain and further combine with land-breeze from inland plain toward sea, resulting in strong wind as internal gravity waves with a hydraulic jump motion bounding up to about 1km upper level in the atmosphere in the west of the city and becoming a eastward return flow. Simultaneously, wind near the eastern coastal side of the city was moderate. Since the downward strong wind penetrated into the city, the particulate matters floated near the top of the mountain in the day also moved down along the eastern slope of the mountain, reaching the. downtown and merging in the ground surface inside the NSIL with a maximum ground level concentration of total suspended particulates (TSP) at 0300 LST. Some of them were bounded up from the ground surface to the 1km upper level and the others were forward to the coastal sea surface, showing their dispersions from the coastal NSIL toward the propagation area of internal gravity waves. On the next day at 0600 LST and 0900 LST, the dispersed particulates into the coastal sea could return to the coastal inland area under the influence of sea breeze and the recycled particulates combine with emitted ones from the ground surface, resulting in relatively high TSP concentration. Later, they float again up to the thermal internal boundary layer, following sea breeze circulation.

Recycling of suspended particulates by the interaction of sea-land breeze circulation and complex coastal terrain

The dispersion of recycled particulates in the complex coastal terrain surrounding Kangnung city, Korea was investigated using a three-dimensional non-hydrostatic numerical model and lagrangian particle model (or random walk model). The results show that particulates at the surface of the city that float to the top of thermal internal boundary layer (TIBL) are then transported along the eastern slope of the mountains with the sea breeze passage and nearly reach the top of the mountains. Those particulates then disperse eastward at this upper level over the coastal sea and finally spread out over the open sea. Total suspended particulate (TSP) concentration near the surface of Kangnung city is very low. At night, synoptic scale westerly winds intensify due to the combined effect of the synoptic scale wind and land breeze descending the eastern slope of the mountains toward the coast and further seaward. This increase in speed causes development of internal gravity waves and a hydraulic jump up to a height of about 1 km above the surface over the city. Particulate matter near the top of the mountains also descends the eastern slope of the mountains during the day, reaching the central city area and merges near the surface inside the nocturnal surface inversion layer (NSIL) with a maximum ground level concentration of TSP occurring at 0300 LST. Some particulates are dispersed following the propagation area of internal gravity waves and others in the NSIL are transported eastward to the coastal sea surface, aided by the land breeze. The following morning, particulates dispersed over the coastal sea from the previous night, tend to return to the coastal city of Kangnung with the sea breeze, developing a recycling process and combine with emitted surface particulates during the morning. These processes result in much higher TSP concentration. In the late morning, those particulates float to the top of the TIBL by the intrusion of the sea breeze and the ground level TSP concentration in the city subsequently decreases.

Persistent high concentration of ozone during windstorm conditions in southern Korea

Prior to and following the development of a windstorm in the mountainous coastal area of southern Korea, ground level ozone (O3)-concentrations near Kangnung city, on the lee side of the mountains, show a maximum value at approximately 1300 LST, owing to a photolytic cycle of NO2–NO–O3 during the day and a minimum in concentrations at night as a result of the reverse cycle. During the development period of the windstorm, ozone concentrations are generally high all day, and slightly higher during the night. This distribution pattern of ozone is very different from the typical distribution of ozone in the absence of windstorms. High daytime concentrations of ozone during the windstorm are due to both the increase in the amount of ozone from photochemical reactions involving NOx and the increase in O3-concentration due to a decrease in the convective boundary layer thickness under the influence of downslope windstorm conditions on the lee-side of the mountains. At night, the windstorm increases in intensity as the westerly winds combine with a katabatic wind blowing downslope toward the surface at the coast. This causes momentum transport of air parcels in the upper levels toward the surface at the coast and the development of internal gravity waves, which generate a hydraulic jump directed upward over the coast and the East sea, thereby reducing to very thin the thickness of the nocturnal surface inversion layer (NSIL). The higher O3-concentration at night depends mainly upon the shallow NSIL and on some O3 being transported by the momentum transfer from the upper troposphere toward the ground in windstorm conditions.