NOCTURNAL SURFACE INVERSIONS IN CENTRAL EASTERN INDIA

Monitoring of nocturnal su rface inversions in the vicinit y of Steel Authority of Ind ia lid. Steelplants at Bhila i. Bokaro. Durgapur and Rourk-cia in central eas tern Ind ia. for 40 niahu in January. February andMarch 1990. indi cated that surface inversions developed every night when weathe r conditions were favourable (clea rskies and light winds) , Th e ceiling heiaht of surface inversions eenerally increased as the niah t progressed. withrouahly two-th irds hiefler th an 100 m and a maximum record ed heigh t of 520 m. Th e maximum recorded surfaceinversio n strt"ngth (temperature difference between th e surface and the ceilingjwas 8.6C· at Dura:apur.1 .4C· at Bhilaiand aroun d 5-SC· at both Bokam and Rourkela. A reaso nable estimate of the .srrongest surface inversion would beJOC· to 12C· in the lOwnl 250 m of th e atmosphere.The proportion of surface invers ions greater than 4C· was 80%atDurgapur. .s5llb at 8hilal4.s% at Bokaro an d If.'" at Rourkela.These differences between loca tion!'wee- caused la l'iel yby varying weathe r conditions during the monit oring period.

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.

Quantifying energy balance regimes in the modern climate, their link to lapse rate regimes, and their response to warming

Energy balance and lapse rate regimes qualitatively characterize the low, mid, and high latitudes of Earth’s modern climate. Currently we do not have a complete quantitative understanding of the spatio-temporal structure of energy balance regimes (e.g., Radiative Convective Equilibrium, RCE, and Radiative Advective Equilibrium, RAE) and their connection to lapse rate regimes (moist adiabat and surface inversion). Here we use the vertically-integrated moist static energy budget to define a nondimensional number that quantifies where and when RCE and RAE are approximately satisfied in Earth’s modern climate. We find RCE exists yearround in the tropics and in theNorthern midlatitudes during summertime. RAE exists yearround over Antarctica and in the Arctic with the exception of early summer. We show lapse rates in RCE and RAE are consistent with moist adiabatic and surface inversion lapse rates, respectively. We use idealized models (energy balance and aquaplanet) to test the following hypotheses: 1) RCE occurs during midlatitude summer for land-like (small heat capacity) surface conditions and 2) sea ice is necessary for the existence of annual-mean RAE over a polar ocean, such as the Arctic. Consistent with 1), an aquaplanet configured with a shallow mixed layer transitions to RCE in the midlatitudes during summertime whereas it does not for a deep mixed layer. Furthermore, we confirm 2) using mechanism-denial aquaplanet experiments with and without thermodynamic sea ice. Finally, we show energy balance regimes of the modern climate provide a useful guide to the vertical structure of the warming response in the annual mean, and seasonally over the tropics and the Southern high latitudes.

Nocturnal Boundary Layer Evolution and Its Impacts on the Vertical Distributions of Pollutant Particulate Matter

To investigate the evolution of the nocturnal boundary layer (NBL) and its impacts on the vertical distributions of pollutant particulates, a combination of in situ observations from a large tethered balloon, remote sensing instruments (aerosol lidar and Doppler wind lidar) and an atmospheric environment-monitoring vehicle were utilized. The observation site was approximately 100 km southwest of Beijing, the capital of China. Results show that a considerable proportion of pollutant particulates were still suspended in the residual layer (RL) (e.g., the nitrate concentration reached 30 μg m−3) after sunset. The NBL height calculated by the aerosol lidar was closer to the top of the RL before midnight because of the pollutants stored aloft in the RL and the shallow surface inversion layer; after midnight, the NBL height was more consistent with the top of the surface inversion layer. As the convective mixing layer gradually became established after sunrise the following day, the pollutants stored in the nocturnal RL of the preceding night were entrained downward into the mixing layer. The early morning PM2.5 concentration near 700 m in the RL on 20 December decreased by 83% compared with the concentration at 13:34 on 20 December at the same height. The nitrate concentration also decreased significantly in the RL, and the mixing down of nitrate from the RL could contribute about 37% to the nitrate in the mixing layer. Turbulence activities still existed in the RL with the bulk Richardson number (Rb) below the threshold value. The corresponding increase in PM2.5 was likely to be correlated with the weak turbulence in the RL in the early morning.

Warm-Air Advection Over Melting Sea-Ice: A Lagrangian Case Study

Observations from the 2014 Arctic Clouds in Summer Experiment indicate that, in summer, warm-air advection over melting sea-ice results in a strong surface melting feedback forced by a very strong surface-based temperature inversion and fog formation exerting additional heat flux on the surface. Here, we analyze this case further using a combination of reanalysis dataset and satellite products in a Lagrangian framework, thereby extending the view spatially from the local icebreaker observations into a Langrangian perspective. The results confirm that warm-air advection induces a positive net surface-energy-budget anomaly, exerting positive longwave radiation and turbulent heat flux on the surface. Additionally, as warm and moist air penetrates farther into the Arctic, cloud-top cooling and surface mixing eventually erode the surface inversion downstream. The initial surface inversion splits into two elevated inversions while the air columns below the elevated inversions transform into well-mixed layers.

Voltage-induced ferromagnetism in a diamagnet

Increasingly impressive demonstrations of voltage-controlled magnetism have been achieved recently, highlighting potential for low-power data processing and storage. Magnetoionic approaches appear particularly promising, electrolytes and ionic conductors being capable of on/off control of ferromagnetism and tuning of magnetic anisotropy. A clear limitation, however, is that these devices either electrically tune a known ferromagnet or electrically induce ferromagnetism from another magnetic state, e.g., antiferromagnetic. Here, we demonstrate that ferromagnetism can be voltage-induced even from a diamagnetic (zero-spin) state suggesting that useful magnetic phases could be electrically induced in “nonmagnetic” materials. We use ionic liquid–gated diamagnetic FeS2 as a model system, showing that as little as 1 V induces a reversible insulator-metal transition by electrostatic surface inversion. Anomalous Hall measurements then reveal electrically tunable surface ferromagnetism at up to 25 K. Density functional theory–based modeling explains this in terms of Stoner ferromagnetism induced via filling of a narrow eg band.

The impacts of residual layer on the vertical distributions of pollutant particulate matter: combining large tethered balloon and remote sensing observations

<p>The combination of in situ observations from a large tethered balloon and remote sensing instruments (aerosol lidar and Doppler wind lidar) enabled the evolution of the residual layer (RL) to be observed during an intensive vertical detection experiment of the planetary boundary layer (PBL) conducted during December (Dec) 2018 in Wangdu County, China. This paper focused on the important role played by the RL in the variations of the vertical distributions of pollutant particulates. The results of the present analysis revealed the following. (1) A considerable proportion of pollutant particulates remained suspended in the RL (e.g., the nitrate concentration reached 30 µg m<sup>-3</sup>) in the nocturnal boundary layer (NBL). Multilayer pollutant structures appeared often, partly because of the existence of the RL. Because pollutants were still stored in the RL and the shallow surface inversion layer, the aerosol lidar-calculated PBL height was closer to the top of the RL before midnight in the NBL; after midnight, the PBL height was more consistent with the top of the surface inversion layer. (2) As the convective mixing layer gradually became established after sunrise the following day, the pollutants stored in the nocturnal RL of the preceding night were entrained downward into the mixing layer. The early morning PM<sub>2.5</sub> concentration near 700 m in the RL on Dec 20 decreased obviously compared with the concentration at 13:34 on Dec 20 at the same height (ranging from 30 µg m<sup>-3</sup> to 5 µg m<sup>-3</sup>). The nitrate concentration also decreased significantly in the RL, but its concentration increased to 12 µg m<sup>-3</sup> in the mixing layer. Near-surface PM<sub>2.5</sub> diffused upward more easily due to strong vertical mixing during the daytime, causing reductions in the surface concentration. The mixing layer heights in Wangdu County were estimated to be 600 m in the winter, and various emitted pollutant particulates eventually became well-mixed within the mixing layer. The daytime mixing layer heights were consistent with the PBL heights calculated by aerosol lidar representing the pollutant accumulation depth. (3) The RL was characterized by a Richardson number (Ri) below the threshold value of 0.25, revealing that turbulence still existed within the RL.</p>