Reply on RC2

<strong class="journal-contentHeaderColor">Abstract.</strong> The mesoscale meteorology of lake breezes along Lake Michigan impacts local observations of high-ozone events. Previous manned aircraft and UAS observations have demonstrated non-uniform ozone concentrations within and above the marine layer over water and within shoreline environments. During the 2021 Wisconsin's Dynamic Influence of Shoreline Circulations on Ozone (WiscoDISCO-21) campaign, two UAS platforms, a fixed-wing (University of Colorado RAAVEN) and a multirotor (Purdue University DJI M210), were used simultaneously to capture lake breeze during forecasted high-ozone events at Chiwaukee Prairie State Natural Area in southeastern Wisconsin from 21–26 May 2021​​​​​​​. The RAAVEN platform (data DOI: <a href="https://doi.org/10.5281/zenodo.5142491">https://doi.org/10.5281/zenodo.5142491</a>, de Boer et al., 2021) measured temperature, humidity, and 3-D winds during 2 h flights following two separate flight patterns up to three times per day at altitudes reaching 500 m above ground level (a.g.l.). The M210 platform (data DOI: <a href="https://doi.org/10.5281/zenodo.5160346">https://doi.org/10.5281/zenodo.5160346</a>, Cleary et al., 2021a) measured vertical profiles of temperature, humidity, and ozone during 15 min flights up to six times per day at altitudes reaching 120 ma.g.l. near a Wisconsin DNR ground monitoring station (AIRS ID: 55-059-0019). This campaign was conducted in conjunction with the Enhanced Ozone Monitoring plan from the Wisconsin DNR that included Doppler lidar wind profiler observations at the site (data DOI: <a href="https://doi.org/10.5281/zenodo.5213039">https://doi.org/10.5281/zenodo.5213039</a>, Cleary et al., 2021b).

Existing information on the activity of bats in the aerosphere is restricted almost exclusively to altitudes that are within a few tens of meters above the ground. We report a total of 50.2 h of ultrasonic recordings made using radio microphonic bat detectors suspended from free-floating helium balloons and from kites. The data include a total of 22 353 echolocative calls from ground-level to 1118 m above ground level (AGL). These calls are attributed to Brazilian free-tailed bats based on acoustic features and the large numbers and high-altitude aerial dispersion of these bats over the local landscape. Bat activity varied significantly throughout the air column and was greatest at 400-500 m AGL and near ground level. Feeding buzzes, indicating feeding on aerial prey, were most abundant near ground level and at 400-500 m, and were detected to altitudes of ∼ 900 m AGL. The peak activity of bats at 400-500 m AGL is concordant with the altitude of the atmospheric boundary layer and the seasonal formation of the low-elevation southerly wind jet that has been identified as a major aeroecological corridor for the nocturnal dispersal of noctuid moths and other insects.

The finescale three-dimensional structure and evolution of the near-surface boundary layer of a tornado (TBL) is mapped for the first time. The multibeam Rapid-Scan Doppler on Wheels (RSDOW) collected data at several vertical levels, as low as 4, 6, 10, 12, 14, and 17 m above ground level (AGL), contemporaneously at 7-s intervals for several minutes in a tornado near Russell, Kansas, on 25 May 2012. Additionally, a mobile mesonet anemometer measured winds at 3.5 m AGL in the core flow region. The radar, anemometer, and ground-based velocity-track display (GBVTD) analyses reveal the peak wind intensity is very near the surface at ~5 m AGL, about 15% higher than at 10 m AGL and 25% higher than at ~40 m AGL. GBVTD analyses resolve a downdraft within the radius of maximum winds (RMW), which decreased in magnitude when varying estimates for debris centrifuging are included. Much of the inflow (from −1 to −7 m s−1) is at or below 10–14 m AGL, much shallower than reported previously. Surface outflow precedes tornado dissipation. Comparisons between large-eddy simulation (LES) predictions of the corner flow swirl ratio Sc and observed tornado intensity changes are consistent.

Vertical profiles of O3, NO2 and PM in a major fine chemical industry park in the Yangtze River Delta of China detected by a sensor package on an unmanned aerial vehicle

The outcome of operations in a designated airspace is a function of the cooperation between flights in the airspace and the coordination of Air Traffic Control (ATC). A critical airspace is the approach airspace in which flights are sequenced and separated to minima to maximize utilization of the available runways. Airline procedures call for flights to meet “stable approach criteria” at 1000 ft. and 500 ft. above ground level (AGL). ATC procedures define the trajectories flown, including airspeed, to maximize throughput through the airspace and runways. The ability to achieve the stabilized approach criteria is therefore a function of the coordination of the flight crews and ATC. This paper describes a method for analysis of stabilized approaches using surveillance track data. Risk events and factors related to stabilized approach criteria are defined. A case study of 8,219 approaches is conducted at a runway of slot controlled airport with a dominant carrier. The results quantify the portion of the approaches which violate the stabilized approach criteria. Results show that 27.8% of the approaches exhibited more than 10 knots change in groundspeed after sequencing 1000 ft. AGL, 14.1% after sequencing 750 ft. AGL, and 4.4% after sequencing 500 ft. AGL. The flights with rate of descent in excess of 1000 feet per minute (fpm.) are also studied. The effects of factors such as the speed at Final Approach Fix (FAF) and the runway centerline/glidepath acquisition position are analyzed. Results show that a flight that acquires glidepath after FAF has a higher probability of having an excessive speed change from 1000 ft. AGL to the runway threshold. Aircraft weight classes are also studied. The results indicate a lower landing speed and higher deceleration rate for small aircraft. The implications of these results and the limitations of using surveillance track data for this purpose are discussed.

Airborne pollen concentrations vary depending on the location of the pollen trap with respect to the pollen sources. Two Hirst-type pollen traps were analyzed within the city of Munich (Germany): one trap was located 2 m above ground level (AGL) and the other one at rooftop (35 m AGL), 4.2 km apart. In general, 1.4 ± 0.5 times higher pollen amounts were measured by the trap located at ground level, but this effect was less than expected considering the height difference between the traps. Pollen from woody trees such as Alnus, Betula, Corylus, Fraxinus, Picea, Pinus and Quercus showed a good agreement between the traps in terms of timing and intensity. Similar amounts of pollen were recorded in the two traps when pollen sources were more abundant outside of the city. In contrast, pollen concentrations from Cupressaceae/Taxaceae, Carpinus and Tilia were influenced by nearby pollen sources. The representativeness of both traps for herbaceous pollen depended on the dispersal capacity of the pollen grains, and in the case of Poaceae pollen, nearby pollen sources may influence the pollen content in the air. The timing of the pollen season was similar for both sites; however, the season for some pollen types ended later at ground level probably due to resuspension processes that would favor recirculation of pollen closer to ground level. We believe measurements from the higher station provides a picture of background pollen levels representative of a large area, to which local sources add additional and more variable pollen amounts.

NCEP reanalysis data were analyzed in order to provide distribution of global wind resource and wind speed in the surface layer for the years 2000-2009. Wind speed at 10 m above ground level (AGL) was converted to wind speed at 80 m above the ground level using the power law. The global average 80 m wind speed shows a maximum value of at the storm track region. High wind speed over the land exists in Tibet, Mongolia, Central North America, South Africa, Australia, and Argentina. Wind speed over the ocean increased with a large value in the South China Sea, Southeast Asia, East Sea of the Korea. Sea surface wind in Western Europe and Scandinavia are suitable for wind farm with a value of . Areas with great potential for wind farm are also found in Eastern and Western coastal region of North America. Sea surface wind in Southern Hemisphere shows larger values in the high latitude of South America, South Africa and Australia. The distribution of low-resolution reanalysis data represents general potential areas for wind power and can be used to provide information for high-resolution wind resource mapping.

This paper presents the assessment of wind power, wind exponent, local air density and air turbulence intensity for an isolated site in Saudi Arabia. Overall average wind speeds of 4.7, 5.4 and 5.7 m/s were recorded at 20, 30 and 40 m above ground level (AGL), respectively. At 40 m AGL, the wind speed was found to be above 5.5 m/s for most of the time except between 2 a.m. and 8 a.m. The wind shear exponent obtained using the entire data set was 0.346 while it was 0.327 and 0.348 for the data sets of 2006 and 2007, respectively. The overall mean turbulence intensity values over the entire period of data collection were 0.173, 0.146 and 0.137 at 20, 30 and 40 m AGL, respectively. The monthly average minimum energy values of 698, 810 and 907 MWh were generated in November while maximum values of 978, 1081 and 1164 MWh were generated in June corresponding to hub heights of 60, 80 and 100 m, respectively.

A study of atmospheric electric field measurements at the CN Communications Tower in Toronto, Canada (height 553 m above ground level (AGL)) has been conducted during the period from 1978 to 1983. Of particular interest were the field conditions during the times when lightning struck the tower. Measurements were carried out using fixed radioactive probes and a movable Stanford‐University‐type field mill located at 366 m AGL. Results show that the electric field measurements at 366 m AGL are significantly influenced by their azimuthal location under cloudy conditions and that approximately 23% of the lightning strikes to the tower occur in the absence of a strong vertical electric field.

Dust transport pathways from The Great Basin

The experiments were conducted in a fully-productive olive orchard (cv. Frantoio) at the experimental farm of University of Pisa at Venturina (Italy) in 2015 to assess the ability of an unmanned aerial vehicle (UAV) equipped with RGB-NIR cameras to estimate leaf area index (LAI), tree height, canopy diameter and canopy volume of olive trees that were either irrigated or rainfed. Irrigated trees received water 4–5 days a week (1348 m3 ha-1), whereas the rainfed ones received a single irrigation of 19 m3 ha-1 to relieve the extreme stress. The flight altitude was 70 m above ground level (AGL), except for one flight (50 m AGL). The Normalized Difference Vegetation Index (NDVI) was calculated by means of the map algebra technique. Canopy volume, canopy height and diameter were obtained from the digital surface model (DSM) obtained through automatic aerial triangulation, bundle block adjustment and camera calibration methods. The NDVI estimated on the day of the year (DOY) 130 was linearly correlated with both LAI and leaf chlorophyll measured on the same date (R2 = 0.78 and 0.80, respectively). The correlation between the on ground measured canopy volumes and the ones by the UAV-RGB camera techniques yielded an R2 of 0.71–0.86. The monthly canopy volume increment estimated from UAV surveys between (DOY) 130 and 244 was highly correlated with the daily water stress integral of rainfed trees (R2 = 0.99). The effect of water stress on the seasonal pattern of canopy growth was detected by these techniques in correspondence of the maximum level of stress experienced by the rainfed trees. The highest level of accuracy (RMSE = 0.16 m) in canopy height estimation was obtained when the flight altitude was 50 m AGL, yielding an R2 value of 0.87 and an almost 1:1 ratio of measured versus estimated canopy height.

This paper introduces the X-band weather radar dual-polarization parameters of isolated convective cell precipitation and meso/microscale snowfall on Mount Everest and presents the first precipitation observations based on dual-polarization weather radar in this area. Compared with the Chengdu Plain, Mount Everest experienced convective precipitation on smaller horizontal and vertical scales with a narrower Zdr probability density spectrum (uniformly distributed around approximately 0). The Zh profile on Mount Everest displayed two peaks, unlike that over the plains, and the precipitation at the strong convective core was denser. Furthermore, during winter snowfall on the northern slope of Mount Everest, when the boundary layer exhibited sufficient water vapor and dynamic uplift, due to the low boundary layer temperature (&lt;0 °C), water vapor produced stratiform clouds in the middle and lower layers (approximately 1.5 km above ground level (AGL)). Water vapor condensation at 1.5–2.5 km AGL led to latent heat release, which increased the temperature of regional stratiform clouds with increasing height. Consequently, the temperature at the stratiform cloud top height (2.5 km AGL) unexpectedly exceeded 0 °C. Additionally, the −20 °C isotherm was at approximately 4 km AGL, indicating that the middle- and upper-layer atmospheric temperatures remained low. Therefore, thermal instability occurred between the stratiform cloud top height and the middle/upper atmosphere, forming convective motion. These findings confirm the occurrence of elevated winter snowfall convection above Mount Everest and may have certain reference value for retrieving raindrop size distributions, quantitatively estimating precipitation, and parameterizing cloud microphysical processes in numerical prediction models for the Qinghai-Tibetan Plateau.

A central monitoring computer was installed on each ranch. The computers were connected by communication cables to 50 turbines on the Souza Ranch and 150 turbines on the Jess Ranch. Anemometers were installed on every other turbine on 12-foot booms at 35 feet above ground level (AGL). Spacing between anemometers was approximately 200 feet in the crosswind direction by 500 feet in the parallel direction. A total of 23 turbines on the Souza Ranch was instrumented in this fashion, as well as two multi-level meteorological towers. On the Jess Ranch, 77 turbines were instrumented; about half at 35 feet AGL and half at 50 feet AGL, plus four additional towers. Wind data were collected for approximately a 100 hour period on each ranch. All turbines were shut down during these periods so that no turbine wakes would be present. The data periods were selected by the meteorologist to insure that they occurred during typical spring-summer flow regimes. The terrain features upwind of the site appear to play as significant a role in the flow variability as terrain features within the site.

Ozone concentrations have been measured in the northern Congo, near Impfondo (1°37 N, 18°04 E) during the DECAFE experiment in February 1988. This period corresponds to the dry season in the northern part of the equatorial region. The measurements were carried out simultaneously (1) at ground level in a large clearing, (2) inside the forest between 0 and 30 m, and (3) above the forest with a captive balloon flying up to 400 m. The results presented here are compared with the data obtained in the Mayombe forest in the southern part of Congo, near Dimonika in June 1988, during the dry season. For both northern and southern forested areas the ozone concentrations measured at ground level in a large clearing exhibit daily variations with maxima in the afternoon range between 10 and 30 parts per billion by volume (ppbv) and minima at the end of the night between 4 and 15 ppbv. The characterics of each surface ozone cycle are analyzed. Inside the forest, ozone concentrations are found very low near the ground and rarely exceed 15 ppbv above the canopy. At night the ozone concentrations are always close to zero at any level from the ground to the top of the canopy. Ozone removal processes are mainly located in the canopy. The ozone concentration above the forest is seen to increase in the early morning. Likely, this ozone production has a photochemical origin, the precursors coming from soils and biomass burning. The relationships among the vertical profiles of ozone, temperature, and water vapor are discussed.

Abstract. Trends in the composition of the lower atmosphere (0–1500 m altitude) and surface air quality over the Baltimore/Washington area and surrounding states were investigated for the period from 1997 to 2011. We examined emissions of ozone precursors from monitors and inventories as well as ambient ground-level and aircraft measurements to characterize trends in air pollution. The US EPA Continuous Emissions Monitoring System (CEMS) program reported substantial decreases in emission of summertime nitrogen oxides (NOx) from power plants, up to ∼80% in the mid-Atlantic States. These large reductions in emission of NOx are reflected in a sharp decrease of ground-level concentrations of NOx starting around 2003. The decreasing trend of tropospheric column CO observed by aircraft is ∼0.8 Dobson unit (DU) per year, corresponding to ∼35 ppbv yr−1 in the lower troposphere (the surface to 1500 m above ground level). Satellite observations of long-term, near-surface CO show a ∼40% decrease over western Maryland between 2000 and 2011; the same magnitude is indicated by aircraft measurements above these regions upwind of the Baltimore/Washington airshed. With decreasing emissions of ozone precursors, the ground-level ozone in the Baltimore/Washington area shows a 0.6 ppbv yr−1 decrease in the past 15 yr. Since photochemical production of ozone is substantially influenced by ambient temperature, we introduce the climate penalty factor (CPF) into the trend analysis of long-term aircraft measurements. After compensating for inter-annual variations in temperature, historical aircraft measurements indicate that the daily net production of tropospheric ozone over the Baltimore/Washington area decreased from ∼20 ppbv day−1 in the late 1990s to ∼7 ppbv day−1 in the early 2010s during ozone season. A decrease in the long-term column ozone is observed as ∼0.2 DU yr−1 in the lowest 1500 m, corresponding to an improvement of ∼1.3 ppbv yr−1. Our aircraft measurements were conducted on days when severe ozone pollution was forecasted, and these results represent the decreasing trend in high ozone events over the past 15 yr. Back trajectory cluster analysis demonstrates that emissions of air pollutants from Ohio and Pennsylvania through Maryland influence the column abundances of downwind ozone in the lower atmosphere. The trends in air pollutants reveal the success of regulations implemented over the past decades and the importance of region-wide emission controls in the eastern United States.