On the force of vertical winds in the upper atmosphere: consequences for small biological particles

For many decades, vertical winds have been observed at high altitudes of the Earth’s atmosphere, in the mesosphere and thermosphere layers. These observations have been used with a simple one-dimensional model to make estimates of possible altitude climbs by biologically sized particles deeper into the thermosphere, in the rare occurrence where such a particle has been propelled to these altitudes. A particle transport mechanism is suggested from the literature on auroral arcs, indicating that an altitude of 120 km could be reached by a nanometre-sized particle, which is higher than the measured 77 km limit on the biosphere. Vertical wind observations in the upper mesophere and lower thermosphere are challenging to make and so we suggest that particles could reach altitudes greater than 120 km, depending on the magnitude of the vertical wind. Applications of the larger vertical winds in the upper atmosphere to astrobiology and climate science are explored.

Effects of Wind Disturbance on the Aerodynamic Performance of a Quadrotor MAV during Hovering

Wind disturbance could render thrust and power variation or even causing roll which is difficult to maintain a steady flight in gust especially when the horizontal or vertical wind is involved. In this paper, the horizontal wind and vertical wind are presented to study the influence of wind disturbance on aerodynamic characteristics of the quadrotor aircraft in hovering by experiments and numerical simulations. First, the simplified aerodynamic model with the wind disturbance was analyzed in detail. Also, the low-speed wind tunnel tests were performed to obtain the thrust and power variation of the quadrotor aircraft with rotor spacing ratio s = 1.1 -1.8 in both horizontal and vertical winds of 0-5 m/s with the rotational speed ranging from 1500 to 2300 rpm. Finally, the simulations are performed by utilizing the Computational Fluid Dynamics (CFD) software ANSYS to study the flow field distribution of quadrotor with the influence of the wind disturbance. The comparison between experimental results and simulation results shows that the quadrotor achieves better aerodynamic performance with larger thrust and smaller power consumption at rotor spacing ratio s = 1.8 . Additionally, the quadrotor can effectively resist the horizontal wind disturbance, which will bring larger power loading for the quadrotor, especially at 2.5 m/s. However, the vortices near blade-tip move upwards and deform with the influence of vertical wind, resulting in the reduction of thrust and aerodynamic performance of the quadrotor.

Observations of spectra of polar mesospheric summer echoes at 224 MHz using EISCAT radar during particle precipitation events – Some case studies from July 2019

<p>We present the initial results from investigation of polar mesospheric summer echoes (PMSE) spectra at 224 MHz observed by EISCAT VHF radar operated from Ramfjordmoen near Tromsø during July 2019. Since EISCAT UHF measurements were not available, we used the sudden enhancements in electron densities derived from the VHF observations above 90 km as indicators of particle precipitation. We note that the altitude extent of the PMSE increased along with an enhancement of the strength of the pre-existing PMSE. However, a closer examination reveals that the PMSE strengths vary significantly between different heights in the region of 80 to 90 km. Interestingly, the spectral widths show well separated regimes between the top and the bottom part of the PMSE layers following particle precipitation. In the altitudes where the maximum enhancement in PMSE backscatter occurred, there is no corresponding enhancement in the spectral widths. The frequency Doppler shifts showed alternating upward and downward motions without much difference before and after the particle precipitation. This indicates that the moderate levels of particle precipitation observed herein did not affect the vertical winds considerably. Further, after the particle precipitation subsided, the PMSE intensities continued to be stronger for a while.</p>

Atmospheric Rossiter–McLaughlin effect and transmission spectroscopy of WASP-121b with ESPRESSO

Context. Ultra-hot Jupiters are excellent laboratories for the study of exoplanetary atmospheres. WASP-121b is one of the most studied; many recent analyses of its atmosphere report interesting features at different wavelength ranges. Aims. In this paper we analyze one transit of WASP-121b acquired with the high-resolution spectrograph ESPRESSO at VLT in one-telescope mode, and one partial transit taken during the commissioning of the instrument in four-telescope mode. Methods. We take advantage of the very high S/N data and of the extreme stability of the spectrograph to investigate the anomalous in-transit radial velocity curve and study the transmission spectrum of the planet. We pay particular attention to the removal of instrumental effects, and stellar and telluric contamination. The transmission spectrum is investigated through single-line absorption and cross-correlation with theoretical model templates. Results. By analyzing the in-transit radial velocities we were able to infer the presence of the atmospheric Rossiter–McLaughlin effect. We measured the height of the planetary atmospheric layer that correlates with the stellar mask (mainly Fe) to be 1.052 ± 0.015 Rp and we also confirmed the blueshift of the planetary atmosphere. By examining the planetary absorption signal on the stellar cross-correlation functions we confirmed the presence of a temporal variation of its blueshift during transit, which could be investigated spectrum-by-spectrum thanks to the quality of our ESPRESSO data. We detected significant absorption in the transmission spectrum for Na, H, K, Li, Ca II, and Mg, and we certified their planetary nature by using the 2D tomographic technique. Particularly remarkable is the detection of Li, with a line contrast of ~0.2% detected at the 6σ level. With the cross-correlation technique we confirmed the presence of Fe I, Fe II, Cr I, and V I. Hα and Ca II are present up to very high altitudes in the atmosphere (~1.44 Rp and ~2 Rp, respectively), and also extend beyond the transit-equivalent Roche lobe radius of the planet. These layers of the atmosphere have a large line broadening that is not compatible with being caused by the tidally locked rotation of the planet alone, and could arise from vertical winds or high-altitude jets in the evaporating atmosphere.

Concurrent increases of PM2.5 and Ozone observed in Seoul, May 2019

<p> In Seoul, PM<sub>2.5</sub> concentrations were frequently elevated with O<sub>3</sub> in May 2019. The most abundant constituent of PM<sub>2.5</sub> was nitrate, which was the best correlated with OC (organic carbon) as well as NH<sub>4</sub><sup>+</sup>. An intensive experiment was conducted in the eastern part of Seoul from March 29 to June 19, 2019. Measurement was made for PM<sub>2.5 </sub>and its chemical composition including NO<sub>3</sub><sup>-</sup>, SO<sub>4</sub><sup>2-</sup>, NH<sub>4</sub><sup>+ </sup>, OC, EC (elemental carbon), and reactive gases including O<sub>3</sub>, NO, NO<sub>2</sub>, CO, HONO, HNO<sub>3</sub>, NH<sub>3</sub>, and SO<sub>2</sub>, and meteorological variables including vertical winds and mixed layer height (MLH). The particle number concentration was measured using SMPS (Scanning Mobility Particle Sizer). All measurements were averaged for 1 hour according to the resolution of PM<sub>2.5</sub> chemical composition. For the entire experiment, the mean mass concentrations of PM<sub>2.5</sub>, NO<sub>3</sub><sup>-</sup>, SO<sub>4</sub><sup>2-</sup>, NH<sub>4</sub><sup>+</sup>, OC, and EC were 20.40 μg/m<sup>3</sup>, 4.07 μg/m<sup>3</sup>, 2.62 μg/m<sup>3</sup>, 2.01 μg/m<sup>3</sup>, 4.01 μg/m<sup>3</sup>, and 1.04 μg/m<sup>3</sup>, respectively. For reactive gases, the mean concentration was 1.03 ppbv for HONO, 0.70 ppbv for HNO<sub>3</sub>, 14.87 ppbv for NH<sub>3</sub>, 2.77 ppbv for SO<sub>2</sub>, and 48.79 ppbv for O<sub>3</sub>. </p><p> The maximum PM<sub>2.5</sub> concentration of 72.81 μg/m<sup>3 </sup>was observed under the influence of weak Asian dust event in the end of April. In May, there were three distinct episodes with highly enhanced PM<sub>2.5</sub>. In the early May, the maximum nitrate concentration (36.11 μg/m<sup>3</sup>) was observed with high HONO (2.41 ppbv) on 4 May. In the middle of May, PM<sub>2.5</sub> was raised with SO<sub>4</sub><sup>2-</sup> under stagnant condition. On 25 May, PM<sub>2.5</sub> was raised up to 92 μg/m<sup>3 </sup>with high nitrate concentration (18.56 μg/m<sup>3</sup>) , when O<sub>3</sub> reached 205 ppbv. In this episode, O<sub>3</sub> concentration remained around 90 ppbv at night and OC and EC were well correlated with highly enhanced K<sup>+</sup>. Thus, the concurrent enhancement of PM<sub>2.5</sub> and O<sub>3</sub> was likely due to the influence of aged biomass combustion plume laden air transported from southeast China. At the same time, HNO<sub>3</sub> and HONO concentration was highly elevated, indicating that heterogeneous reactions played a role.</p>

Characteristics and performance of vertical winds as observed by the radar wind profiler network of China

Vertical wind profiles are the foundation for numerical weather prediction systems research. Large-scale vertical wind data have been previously documented from network observations in several countries, but the nationwide vertical wind observations are poorly understood in China. In this study, the salient characteristics and performance of vertical winds as observed by the radar wind profiler network of China was investigated, which consists of more than 100 stations instrumented with 1290-MHz Doppler radar designed primarily for measuring vertical-resolved winds. This network has good spatial coverage, with denser sites in coastal areas. The vertical wind profiles observed by this network can provide the horizontal wind direction, horizontal wind speed, and vertical wind speed for every 120 m interval within the height of 0 to 3 km. The availability of the radar wind profiler network has been investigated in terms of effective detection height, data acquisition rate, data confidence, and data accuracy. Further comparison analysis with reanalysis data indicated that the observation data at 89 stations are recommended, and 17 stations are unrecommended. The vertical wind profiles can serve as important input dataset assimilated into numerical weather prediction system at both regional and global scales.

Evaluation of wake influence on high-resolution balloon-sonde measurements

Balloons are used for various in situ measurements in the atmosphere. On turbulence measurements from rising balloons there is a potential for misinterpreting wake-created fluctuations in the trail of the balloon for atmospheric turbulence. These wake effects have an influence on temperature and humidity measurements from radiosondes as well. The primary aim of this study is to assess the likelihood for wake encounter on the payload below a rising balloon. Therefore, we present a tool for calculating this probability based on radiosonde wind data. This includes a retrieval of vertical winds from the radiosonde and an uncertainty analysis of the wake assessment. Our wake evaluation tool may be used for any balloon–gondola distance and provides a significant refinement compared to existing assessments. We have analysed wake effects for various balloon–gondola distances applying atmospheric background conditions from a set of 30 radiosondes. For a standard radiosonde we find an average probability for wake encounter of 28 %, pointing out the importance of estimating wake effects on sounding balloons. Furthermore, we find that even millimetre-sized objects in the payload can have significant effects on high-resolution turbulence measurements, if they are located upstream of the turbulence sensor.