Overlapping boundary layers in coastal oceans

Boundary layer turbulence in coastal regions differs from that in deep ocean because of bottom interactions. In this paper, we focus on the merging of surface and bottom boundary layers in a finite-depth coastal ocean by numerically solving the wave-averaged equations using a large eddy simulation method. The ocean fluid is driven by combined effects of wind stress, surface wave, and a steady current in the presence of stable vertical stratification. The resulting flow consists of two overlapping boundary layers, i.e. surface and bottom boundary layers, separated by an interior stratification. The overlapping boundary layers evolve through three phases, i.e. a rapid deepening, an oscillatory equilibrium and a prompt merger, separated by two transitions. Before the merger, internal waves are observed in the stratified layer, and they are excited mainly by Langmuir turbulence in the surface boundary layer. These waves induce a clear modulation on the bottom-generated turbulence, facilitating the interaction between the surface and bottom boundary layers. After the merger, the Langmuir circulations originally confined to the surface layer are found to grow in size and extend down to the sea bottom (even though the surface waves do not feel the bottom), reminiscent of the well-organized Langmuir supercells. These full-depth Langmuir circulations promote the vertical mixing and enhance the bottom shear, leading to a significant enhancement of turbulence levels in the vertical column.

An improved understanding of NOx emissions in South Asian megacities using TROPOMI NO2 retrievals

Identifying air pollutant emissions has played a key role in improving air quality and hence the health of billions of people around the world. This has been done using research from multiple directions, two of which are the development of emission inventories and mapping air pollution using satellite remote sensing. The TROPOspheric Monitoring Instrument (TROPOMI) has been providing high resolution vertical column densities of nitrogen dioxide since late October 2018. Using the flux divergence method and a Gaussian Mixture Model, we identify peak emission hotspots over 4 cities in South Asia: Dhaka, Kolkata, Delhi and Lahore. We analyze data from November 2018 to March 2021 and focus on the three dry seasons (November to March) for which retrievals are available. The retrievals are shown to have sufficient spatial resolution to identify individual point and area sources. We further analyze the length scale and eccentricities of the hotspots to better characterize the emission sources. The TROPOMI emission estimates are compared with the EDGAR global emission inventory and the REAS regional inventory. This reveals areas of agreement but also significant discrepancies that should enable improvements and refinements of the inventories in the future. For example, urban emissions are underestimated while power generation emissions are overestimated. Some areas of light manufacturing cause significant signatures in TROPOMI retrievals but are mostly missing from the inventories. The spatial resolution of the TROPOMI instrument is now sufficient to provide detailed feedback to developers of emission inventories as well as to inform policy decisions at the urban to regional scale.

Microbiomarkers of the local environment and interior of Neolithic and Eneolithic dwellings (settlements of Mergen 6 and 7)

The paper concerns the analysis of the local environment around the multi-layer settlements of Mergen 6 and 7 situated in the immediate vicinity of each other. The settlements existed successively (partly contempora-neously in the early and high Neolithic) in the forest-steppe belt of Western Siberia. Two methods were chosen to obtain the results: spore-and-pollen (palynological) and microbiomorphic analyses of the cultural layers of the settlements of Mergen 6 and Mergen 7. In the settlement of Mergen 6, the following samples were collected for the palynological and microbiomorphic investigation: a vertical column from the center of the ditch of the dwelling no.5; areal soil samples of the dwelling no.5 from underneath the pottery debris of the Neolithic and Eneolithic periods; areal samples from the bottom layer of the dwelling no.21. In the settlement of Mergen 7, two vertical core samples were selected for the pore-and-pollen analysis: in the ditch of the dwelling no.1; and in the inter-dwelling area. Samples from the hearthing of the dwellings and from the inter-dwelling space were collected for the microbiomorphic analysis. The obtained results show that both settlements existed during the forest-steppe conditions, although the original landscapes of the sites chosen by the people for building the settlements were different in the early and high Neolithic. It appears that during the early Neolithic, the settlement of Mergen 6 was associated with an open site with meadow-steppe vegetation; birch forests constituted a small part of the land-scape, whilst there were no pine forests in the close vicinity. During the middle Neolithic, people in the settlement of Mergen 7 preferred to settle in a birch wood, having cleared out a small area to build the dwelling. The results of the microbiomorphic analysis show that, despite the lack of pine forests nearby the settlements, people still used pine tim-ber in housebuilding, apparently, intentionally. The frequent occurrence of remains of the wood detritus at the level of the floor of the dwellings and under pottery supports the initial archaeological observations about timber decking inside the houses. However, pollen and phytolithic studies do not demonstrate a wide use of the wetland waterside vegetation in housebuilding, apparently, because the lake at the time was not overgrown on the banks by reed and cattail. There-fore, despite the close location of the two sites and their similar hunting-fishing specialization of the subsistences, their populations in different chronological periods preferred distinct local conditions.

Biomass burning nitrogen dioxide emissions derived from space with TROPOMI: methodology and validation

Smoke from wildfires is a significant source of air pollution, which can adversely impact air quality and ecosystems downwind. With the recently increasing intensity and severity of wildfires, the threat to air quality is expected to increase. Satellite-derived biomass burning emissions can fill in gaps in the absence of aircraft or ground-based measurement campaigns and can help improve the online calculation of biomass burning emissions as well as the biomass burning emissions inventories that feed air quality models. This study focuses on satellite-derived NOx emissions using the high-spatial-resolution TROPOspheric Monitoring Instrument (TROPOMI) NO2 dataset. Advancements and improvements to the satellite-based determination of forest fire NOx emissions are discussed, including information on plume height and effects of aerosol scattering and absorption on the satellite-retrieved vertical column densities. Two common top-down emission estimation methods, (1) an exponentially modified Gaussian (EMG) and (2) a flux method, are applied to synthetic data to determine the accuracy and the sensitivity to different parameters, including wind fields, satellite sampling, noise, lifetime, and plume spread. These tests show that emissions can be accurately estimated from single TROPOMI overpasses. The effect of smoke aerosols on TROPOMI NO2 columns (via air mass factors, AMFs) is estimated, and these satellite columns and emission estimates are compared to aircraft observations from four different aircraft campaigns measuring biomass burning plumes in 2018 and 2019 in North America. Our results indicate that applying an explicit aerosol correction to the TROPOMI NO2 columns improves the agreement with the aircraft observations (by about 10 %–25 %). The aircraft- and satellite-derived emissions are in good agreement within the uncertainties. Both top-down emissions methods work well; however, the EMG method seems to output more consistent results and has better agreement with the aircraft-derived emissions. Assuming a Gaussian plume shape for various biomass burning plumes, we estimate an average NOx e-folding time of 2 ±1 h from TROPOMI observations. Based on chemistry transport model simulations and aircraft observations, the net emissions of NOx are 1.3 to 1.5 times greater than the satellite-derived NO2 emissions. A correction factor of 1.3 to 1.5 should thus be used to infer net NOx emissions from the satellite retrievals of NO2.

Compilation of ozonesonde observation over Schirmacher oasis east Antarctic from 1999-2007

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Calibration of water vapor Raman lidar measurements by use of radiosonde and microwave radiometer measurements

<p>Water vapor profiles with high vertical and temporal resolution were determined by use of the Raman lidar PollyXT within the MOSAiC campaign in the Arctic during the winter time 2019 – 2020. These measurements need a calibration. Usually, radiosonde data are utilized to calibrate the lidar data by the profile or the linear fit method, respectively. The radiosonde is drifting with the wind; thus, it is often measuring different atmospheric volumes compared to the lidar observations.</p> <p>The period 5-7 February 2020 is used to demonstrate the results. The correlation coefficient of the linear fit between the radiosonde and the lidar data varies with the different atmospheric conditions. The calibration results from the profile method coincide with those of the linear fit method, but the selection of the appropriate calibration setup is not straightforward. The varying correlation of the calibration results is attributed to the partly too low data-variability of the water vapor mixing ratio in the respective heights.  Moreover, the drift of the radiosondes with the wind and hence measurements of atmospheric volumes with lateral distances will have decreased the correlation between the lidar and the radiosonde measurements.</p> <p>During MOSAiC a microwave radiometer was collocated close to the lidar. This system was measuring the same atmospheric vertical column. Its product, the integrated water vapor, might be useful for the calibration of the lidar.</p> <p>Hence, the contribution will analyze the error of the lidar retrieved water vapor mixing ratio that includes the calibration with the radiosonde data and the microwave radiometer product.</p> <p> </p>

The Characterization of Haze and Dust Processes Using MAX-DOAS in Beijing, China

Haze and dust pollution have a significant impact on human production, life, and health. In order to understand the pollution process, the study of these two pollution characteristics is important. In this study, a one-year observation was carried out at the Beijing Southern Suburb Observatory using the MAX-DOAS instrument, and the pollution characteristics of the typical haze and dust events were analyzed. First, the distribution of aerosol extinction (AE) and H2O concentrations in the two typical pollution events were studied. The results showed that the correlation coefficient (r) between H2O and AE at different heights decreased during dust processes and the correlation slope (|k|) increased, whereas r increased and |k| decreased during haze periods. The correlation slope increased during the dust episode due to low moisture content and increased O4 absorption caused by abundant suspended dry crustal particles, but decreased during the haze episode due to a significant increase of H2O absorption. Secondly, the gas vertical column density (VCD) indicated that aerosol optical depth (AOD) increased during dust pollution events in the afternoon, while the H2O VCD decreased; in haze pollution processes, both H2O VCD and AOD increased. There were significant differences in meteorological conditions during haze (wind speed (WD) was <2 m/s, and relative humidity (RH) was >60%) and dust pollution (WD was >4 m/s, and RH was <60%). Next, the vertical distribution characteristics of gases during the pollution periods were studied. The AE profile showed that haze pollution lasted for a long time and changed slowly, whereas the opposite was true for dust pollution. The pollutants (aerosols, NO2, SO2, and HCHO) and H2O were concentrated below 1 km during both these typical pollution processes, and haze pollution was associated with a strong temperature inversion around 1.0 km. Lastly, the water vapor transport fluxes showed that the water vapor transport from the eastern air mass had an auxiliary effect on haze pollution at the observation location. Our results are of significance for exploring the pollution process of tropospheric trace gases and the transport of water vapor in Beijing, and provide a basis for satellite and model verification.

Deriving CO2 emissions of localized sources from OCO-3 XCO2 and TROPOMI NO2 satellite data

&lt;p&gt;Carbon dioxide (CO&lt;sub&gt;2&lt;/sub&gt;) is the most important anthropogenic greenhouse gas and the main driver of global warming. Its atmospheric concentrations have risen more than 40% since pre-industrial times. Almost 90% of this increase results from fossil fuel combustion, emitting CO&lt;sub&gt;2&lt;/sub&gt; predominantly from localized sources. In order to track the reduction efforts to comply with the objectives of the Paris Agreement, emissions need to be monitored. For this purpose, bottom-up emission estimates are regularly reported in the national greenhouse gas inventories. Top-down observation-based estimates can complement and verify these inventories. Satellite observations have an important role in this context, since they can provide global information.&lt;/p&gt; &lt;p&gt;Due to CO&lt;sub&gt;2&lt;/sub&gt;'s long lifetime and large fluxes of natural origin, the column-average concentrations resulting from anthropogenic emissions from individual source points are usually small compared to the background concentration, and these enhancements are often barely larger than the satellite's instrument noise. This makes the detection of CO&lt;sub&gt;2&lt;/sub&gt; emission plumes and the quantification of anthropogenic fluxes challenging.&lt;/p&gt; &lt;p&gt;NO&lt;sub&gt;2&lt;/sub&gt; is co-emitted with CO&lt;sub&gt;2&lt;/sub&gt; in the combustion of fossil fuels. It has a much shorter lifetime, and as a result, its vertical column densities can exceed background values and sensor noise by orders of magnitude in emission plumes. This makes it a suitable tracer for recently emitted CO&lt;sub&gt;2&lt;/sub&gt;.&lt;/p&gt; &lt;p&gt;The objective of this study is to quantify the CO&lt;sub&gt;2&lt;/sub&gt; emissions from localized sources such as power plants by using XCO&lt;sub&gt;2&lt;/sub&gt; (the column-averaged dry air mole fraction of CO&lt;sub&gt;2&lt;/sub&gt;) retrievals from the Orbiting Carbon Observatory 3 (OCO-3) in its snapshot area mode. Our presentation describes a plume detection method using NO&lt;sub&gt;2&lt;/sub&gt; as a tracer for recently emitted CO&lt;sub&gt;2&lt;/sub&gt; and an inversion technique to quantify CO&lt;sub&gt;2&lt;/sub&gt; emissions from detected CO&lt;sub&gt;2&lt;/sub&gt; plumes.&lt;/p&gt;

Study of SO2 and NO2 behaviour during the ozone-hole event at Antarctica by Brewer Spectrophotometer

Vertical column density of sulphur dioxide has been measured at Maitri (70.7°S, 11.7°E), the Indian station in the Antarctica from September, 1999 to December, 2006 by a Brewer Spectrophotometer. Simultaneously, nitrogen dioxide, ozone and the maximum value of UV-B have also been measured, we found an increase in SO2 during spring. An increase in NO2 column was also found during this period but not identical with that of SO2. These variations in SO2 and NO2 are not in phase with the increase in UV-B flux at the ground due to the decrease of ozone column in the stratosphere. The variation of SO2 column is explained by the downward shift of penetration depth of UV-B radiation during the ozone-hole event.

Inter-Comparison of Two Regional Climate Models (RegCM and WRF) in Downscaling CFSv2 For the Seasonal Prediction of Indian Summer Monsoon

The efficacy of two latest versions of regional climate models (RegCM and WRF) for simulating the Indian summer monsoon (JJAS) is tested in this study. The CFSv2 hindcast outputs are downscaled over the Indian monsoon domain for 11 contrasting monsoon seasons using the regional models. The April start ensembles of the CFSv2 are averaged to generate the initial and lateral boundary conditions for driving the WRF and RegCM. The regional models perform better in simulating the Indian summer monsoon features better than the parent CFSv2 model. The rainfall pattern as well as the intensities are improved with the dynamical downscaling and the errors in the rainfall are minimized over the GCM hindcast. On comparing the two regional models, the RegCM overestimates the rainfall during the excess and normal monsoon seasons. The RCMs improve the skill of rainfall prediction as compared to the GCM and WRF shows better skill in particular. One peculiar finding of this study is that the daily rainfall biases averaged over all the years of simulation shows that the two RCMs show similar biases with RegCM showing stronger biases occasionally. It may be implied that the errors from GCM in the form of the ICBC might be influencing the simulation in the RCMs. The upper air and surface parameters analysis shows that the WRF performs better in representing the semi-permanent features of the Indian summer monsoon which may be helping in improving the rainfall over the RegCM. The wind pattern as well as the relative humidity along the vertical column of the atmosphere are captured better in the WRF model. Diagnostics of CAPE & vertically integrated moisture transport supports the finding of the rainfall being simulated better in the WRF model.