New Insights into the Reactivity of Detonation Nanodiamonds during the First Stages of Graphitization

The present study aims to compare the early stages of graphitization of the same DND source for two annealing atmospheres (primary vacuum, argon at atmospheric pressure) in an identical set-up. DND samples are finely characterized by a combination of complementary techniques (FTIR, Raman, XPS, HR-TEM) to highlight the induced modifications for temperature up to 1100 °C. The annealing atmosphere has a significant impact on the graphitization kinetics with a higher fraction of sp2-C formed under vacuum compared to argon for the same temperature. Whatever the annealing atmosphere, carbon hydrogen bonds are created at the DND surface during annealing according to FTIR. A “nano effect”, specific to the < 10 nm size of DND, exalts the extreme surface chemistry in XPS analysis. According to HR-TEM images, the graphitization is limited to the first outer shell even for DND annealed at 1100 °C under vacuum

The Okhotsk tropospheric cyclone and its role in the occurrence of extreme air temperature in January in 1950-2019

The field of Н500 geopotential height over the central part of the second natural synoptic region in January during 1950–2019 is analysed to determine regime characteristics of the Okhotsk tropospheric cyclone and its role in the formation of air temperature anomalies over the eastern coast of Asia. A mechanism of occurrence of extreme surface air temperatures using this technique is presented. Extremely low air temperature in the area of the minimum and related deep through are formed during the years when the Н500 minimum is localized over the Sea of Okhotsk. A methodology for constructing ellipses approximating the Н500 level lines in a small neighborhood of the Н500 minimum is developed, the ellipse characteristics are calculated, and their relation to the tropospheric cyclone evolution is analysed. The characteristics of the ellipses constructed in the neighborhood of the geopotential height minimum outside the Sea of Okhotsk significantly differ from those of the ellipses over the Sea of Okhotsk. A high compression of the ellipses towards the major axis is reported when the Far Eastern through intensity is reduced. In this case, an outflow of warm oceanic air masses to the Sea of Okhotsk is observed. The location of the Н500 minimum and the characteristics of the ellipses located within the center circle may be used to explain reasons for dramatic changes in air temperature in the study region. Keywords: Оkhotsk tropospheric cyclone, Н500 minima centers, extreme surface air temperature, ellipse characteristics

Extreme Surface Winds During Landfalling Atmospheric Rivers: The Modulating Role of Near-Surface Stability

Atmospheric rivers (ARs) are long and narrow regions of strong horizontal water vapor transport. Upon landfall, ARs are typically associated with heavy precipitation and strong surface winds. A quantitative understanding of the atmospheric conditions that favor extreme surface winds during ARs has implications for anticipating and managing various impacts associated with these potentially hazardous events. Here, a global AR database (1999–2014) with relevant information from MERRA-2 reanalysis, QuikSCAT and AIRS satellite observations are used to better understand and quantify the role of near-surface static stability in modulating surface winds during landfalling ARs. The temperature difference between the surface and 1 km MSL (ΔT; used here as a proxy for near-surface static stability), and integrated water vapor transport (IVT) are analyzed to quantify their relationships to surface winds using bivariate linear regression. In four regions where AR landfalls are common, the MERRA-2-based results indicate that IVT accounts for 22-38% of the variance in surface wind speed. Combining ΔT with IVT increases the explained variance to 36-52%. Substitution of QuikSCAT surface winds and AIRS ΔT in place of the MERRA-2 data largely preserves this relationship (e.g., 44% compared to 52% explained variance for USA West Coast). Use of an alternate static stability measure–the bulk Richardson number–yields a similar explained variance (47%). Lastly, AR cases within the top and bottom 25% of near-surface static stability indicate that extreme surface winds (gale or higher) are more likely to occur in unstable conditions (5.3%/14.7% during weak/strong IVT) than in stable conditions (0.58%/6.15%).

The Impact of Atmosphere–Ocean–Wave Coupling on the Near-Surface Wind Speed in Forecasts of Extratropical Cyclones

Accurate modelling of air–sea surface exchanges is crucial for reliable extreme surface wind-speed forecasts. While atmosphere-only weather forecast models represent ocean and wave effects through sea-state independent parametrizations, coupled multi-model systems capture sea-state dynamics by integrating feedbacks between the atmosphere, ocean and wave model components. Here, we investigate the sensitivity of extreme surface wind speeds to air–sea exchanges at the kilometre scale using coupled and uncoupled configurations of the Met Office’s UK Regional Coupled Environmental Prediction system. The case period includes the passage of extra-tropical cyclones Helen, Ali, and Bronagh, which brought maximum gusts of 36 m s$$^{-1}$$ - 1 over the UK. Compared with the atmosphere-only results, coupling to the ocean decreases the domain-average sea-surface temperature by up to 0.5 K. Inclusion of coupling to waves reduce the 98th percentile 10-m wind speed by up to 2 m s$$^{-1}$$ - 1 as young, growing wind waves reduce the wind speed by increasing the sea-surface aerodynamic roughness. Impacts on gusts are more modest, with local reductions of up to 1 m s$$^{-1}$$ - 1 , due to enhanced boundary-layer turbulence which partially offsets air–sea momentum transfer. Using a new drag parametrization based on the Coupled Ocean–Atmosphere Response Experiment 4.0 parametrization, with a cap on the neutral drag coefficient and reduction for wind speeds exceeding 27 m s$$^{-1}$$ - 1 , the atmosphere-only model achieves equivalent impacts on 10-m wind speeds and gusts as from coupling to waves. Overall, the new drag parametrization achieves the same 20% improvement in forecast 10-m wind-speed skill as coupling to waves, with the advantage of saving the computational cost of the ocean and wave models.

The impact of atmosphere-ocean-wave coupling on extreme surface wind forecasts

&lt;p&gt;Accurate modelling of air-sea surface exchanges is crucial for reliable extreme surface wind forecasts.&amp;#160; While atmosphere-only weather forecast models represent ocean and wave effects through sea-state independent parametrizations, coupled multi-model systems capture sea-state dynamics by integrating feedbacks between atmosphere, ocean and wave model components.&lt;/p&gt;&lt;p&gt;Here, we present the results of studying the sensitivity of extreme surface wind speeds to air-sea exchanges at kilometre scale using coupled and uncoupled configurations of the Met Office's UK Regional Coupled Environmental Prediction (UKC4) system. The case period includes the passage of extra-tropical cyclones Helen, Ali, and Bronagh, which brought maximum gusts of 36 ms&lt;sup&gt;-1&lt;/sup&gt; over the UK.&lt;/p&gt;&lt;p&gt;Compared to the atmosphere-only results, coupling to ocean decreases the domain-average sea surface temperature by up to 0.5 K. Inclusion of coupling to waves decreases the 98th percentile 10-m wind speed by up to 2 ms&lt;sup&gt;-1&lt;/sup&gt; as young, growing wind waves decrease wind speed by increasing the sea aerodynamic roughness. Impacts on gusts are more modest, with local reductions of up to 1ms &lt;sup&gt;-1,&lt;/sup&gt; due to enhanced boundary-layer turbulence which partially offsets air-sea momentum transfer.&lt;/p&gt;&lt;p&gt;Using a new drag parametrization based on the COARE~4.0 scheme, with a cap on the neutral drag coefficient and decrease for wind speeds exceeding 27 ms&lt;sup&gt;-1 &lt;/sup&gt;, the atmosphere-only model achieves equivalent impacts on 10-m wind speeds and gusts as from coupling to waves. Overall, the new drag parametrization achieves the same 20% improvement in forecast 10-m wind skill as coupling to waves, with&amp;#160; the&amp;#160; advantage&amp;#160; of saving the computational cost of the ocean and wave models.&amp;#160;&lt;/p&gt;

Conformal subgroup extreme surface

Conformal subgroup extreme surface

Extreme surface comlex and suface integral

Extreme surface comlex and suface integral

Spatiotemporal dynamics of land development intensity and summertime extreme surface urban heat island effect in Greater Shanghai (1990-2017)

&lt;p&gt;Greater Shanghai, one of China&amp;#8217;s top megacities, is susceptible to extreme heat events during the summer. This study investigated the spatiotemporal dynamics of land development intensity and its influence on summertime extreme surface urban heat island (SUHI) effect in Greater Shanghai, during 1990 and 2017. Driven by the robust economic development and population growth, the formation of Greater Shanghai has dramatically changed from a traditionally compact city to an explosively urbanizing region in 1990&amp;#8211;2017. The results revealed an overall increase in regional LDI of Greater Shanghai in the loss of cropland and water bodies. Simultaneously, the intensified SUHI effect was measured by the increasing relative SUHI intensity (from 1.81&amp;#8451; in 1990 to 3.16&amp;#8451; in 2017) and magnitude (from 306.80 km&lt;sup&gt;2&lt;/sup&gt; in 1990 to 1570.56 km&lt;sup&gt;2&lt;/sup&gt; in 2017). The urban-rural gradient analysis based on centric buffers and the representative transects further revealed the spatiotemporal heterogeneity of LDI and its linkage with the evolutionary pattern of the SUHI effect. As indicated, the areal extent of downtown Shanghai within the 0&amp;#8211;15 km buffer increased by 201.70 km&lt;sup&gt;2&lt;/sup&gt; in 1990&amp;#8211;2017. However, its stably decreasing trends in LDI and associated SUHI effect were observed across the study period. In contrast, the urban periphery and exurban area, which attracted huge investment to develop the infrastructure required for population resettlement and the industrial restructure, experienced a dramatic increase in 1660.57km&lt;sup&gt;2&lt;/sup&gt; of newly developed land. Concurrently, the remarkably increases in LDI and associated SUHI effect the urban periphery and exurban area were notable. Finally, focusing on the overall alarming situation of the summertime SUHI effect in Greater Shanghai, policy implications, and practical suggestions towards sustainable land development and UHI mitigation were discussed.&amp;#160; &amp;#160;&lt;/p&gt;