The focus of this study is an intense heat episode that occurred on 9–13 July 2017 in Beijing, China, that resulted in severe impacts on natural and human variables, including record-setting daily electricity consumption levels. This event was observed and analyzed with a suite of local and mesoscale instruments, including a high-density automated weather station network, soil moisture sensors, and ground-based vertical instruments (e.g., a wind profiler, a ceilometer, and three radiometers) situated in and around the city, as well as electric power consumption data and analysis data from the U.S. National Centers for Environmental Prediction. The results show that the heat wave originated from dry adiabatic warming induced by the dynamic downslope and synoptic subsidence. The conditions were aggravated by the increased air humidity during subsequent days, which resulted in historically high records of the heat index (i.e., an index representing the apparent temperature that incorporates both air temperature and moisture). The increased thermal energy and decreased boundary layer height resulted in a highly energized urban boundary layer. The differences between urban and rural thermal conditions throughout almost the entire boundary layer were enhanced during the heat wave, and the canopy-layer urban heat island intensity (UHII) reached up to 8°C at a central urban station at 2300 local standard time 10 July. A double-peak pattern in the diurnal cycle of UHIIs occurred during the heat wave and differed from the single-peak pattern of the decadal average UHII cycles. Different spatial distributions of UHII values occurred during the day and night.
34Urbanization modifies atmospheric energy and moisture balances, forming distinct 35 features, e.g., urban heat islands (UHIs) and enhanced or decreased precipitation. 36These produce significant challenges to science and society, including rapid and incudes complex topography with mountains, plains, and coastal areas (Fig. 1a), and 261 seven of the 10 most polluted Chinese cities, with 40% of days during 2013 (mostly in 262 winter) having "very hazardous" air quality (CMEP 2014 adaptation, air quality, planning, and emergency-response management. 298The critical science needed to achieve these goals was identified as increased WUQ), and one rural (SDZ) tower (all PBL observational sites are shown in Fig. 1). 335Other operational PBL sensors ( conditions. Photos of a selection of these instruments and sites are shown in Fig. 2. flown over pre-approved flight paths (Fig. 1) at altitudes from 600 to 3 600 m (at 300 357 m intervals). The aircraft is equipped with atmospheric gas and aerosol instrumenta- Additional observation data (e.g., weather radar, aircraft, and lightning) will be added. BTH area centered on Beijing (a somewhat larger area than in Fig. 1a). 439Additional details on all of these steps are provided by Zhang et al. (2017a (Fig. 1) were used to show that the dominant linear relationship between * and also 494 exists over urban canopies. The strong wind shear from the rough urban surfaces produces 495 turbulence in near neutral urban stability conditions, shown by Bornstein 1968 to exist over 496 NYC, as stable boundary layers over urban canopies are thus hard to maintain. The role of 497 surface roughness on turbulent mixing is also reflected in the increasing slope (Fig. 4) Table 4a shows the average midday (1000-1400 LST) radiative and energy fluxes 515Although MIY has higher outgoing longwave radiation, the net all-wave radiations 516 are nearly equal. Significant differences existed, however, in the surface energy 517 partitions, as IAP has smaller turbulent sensible and latent heat fluxes, and thus a 518 larger (estimated) residual heat storage. Another contributing factor to urban heat 519 storage is its anthropogenic heat flux source (discussed below). 520Daily mean Bowen ratios (ratio of turbulent sensible to latent-heat flux; Table 4b Normalized relative backscatter (NRB) data from two MPL lidar (in a vertical to 545 zenith scan mode) were also used to concurrently estimate midday PBL heights on 11 546August 2015 from 1250-1402 LST, both alone a mobile route (Fig. 1b) and at a fixed 547 site (adjacent to the urban IAP tower). As MPL instruments cannot be absolutely Beijing and fluxes from the 140-m level of the IAP tower (Fig. 1b). The modeling 574 period was 4-11 July 2015, which included dry (6 th -11 th ) and wet (4 th -5 th ) days. 575Results show major improvement for daytime "total" sensible plus latent heat flux 576 values ( Fig. 7a and b), although the timing of its peak was about 2 h too late. The 577 increased latent heat flux during the EC simulation (ac...
Significant accelerated warming of the Sea Surface Temperature of 0.15 ∘ C per decade was recently detected, which motivated the research for the present consequences and future projections on the heat index and heat waves in the intra-Americas region. Present records every six hours are retrieved from NCEP reanalysis to calculate heat waves changes. Heat index intensification has been detected in the region since 1998 and driven by surface pressure changes, sinking air enhancement, and warm/weaker cold advection. This regional warmer atmosphere leads to heat waves intensification with changes in both frequency and maximum amplitude distribution. Future projections using a multimodel ensemble mean for five global circulation models were used to project heat waves in the future under two scenarios: RCP4.5 and RCP8.5. Massive heat waves events were projected at the end of the 21st century, particularly in the RCP8.5 scenario. Consequently, the regional climate change in the current time and in the future will require special attention to mitigate the more intense and frequent heat waves impacts on human health, countries' economies, and energy demands in the IAR.
We use various temperature profilers located in and around New York City to observe the structure and evolution of the thermal boundary layer. The primary focus is to highlight the spatial variability of potential-temperature profiles due to heterogeneous surface forcing in an urban environment during different flow conditions. Overall, the observations during the summer period reveal the presence of thermal internal boundary layers due to the interaction between the marine atmospheric boundary layer and the convective urban environment. The summer daytime potential-temperature profiles within the city indicate a superadiabatic layer is present near the surface beneath a mildly stable layer. Large spatial variability in the near-surface (0-300 m) potential temperature is detected, with the thermal profile in the lower atmosphere uniquely determined by the underlying surface forcing and the distance from the coast. The summer and winter average night-time potential-temperature profiles show that the atmosphere is still convective near the surface. The seasonal averages of mixing ratio show large variability in the vertical direction.Keywords Coastal boundary layer · Microwave radiometer · Moisture boundary layer · Thermal boundary layer · Urban boundary layer
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