Dry Air Layer Research Articles

Experimental studies on the operating characteristics of air-layer-integrated radiant cooling units

Radiant cooling is widely acknowledged as an energy-efficient approach to indoor thermal environment regulation. It offers an improved environment in terms of thermal comfort, compared to traditional air-cooling methods, but suffers from condensation risk and insufficient cooling power in hot and humid climates. To overcome these limitations, an Air-Layer-Integrated Radiant Cooling Unit (AIRCU) was developed, which seals a layer of dry air between an infrared transparent membrane and the radiant cooling surface. This innovative approach allows the use of lower radiant cooling temperatures to increase cooling power while concurrently maintaining the membrane at a higher temperature to minimize the risk of condensation. In our previous studies, the heat transfer model of AIRCUs was established, and the feasibility of the concept was verified. However, there is a lack of research on the operating characteristics of AIRCUs. In this paper, both experimental and numerical studies are conducted to investigate the operating characteristics of the AIRCUs under diverse cooling temperatures, chilled water flow rates, and cooling loads. Results indicated that the thermal environment created by the AIRCUs was uniform, and it can be characterized by uncooled surface temperature and radiant cooling surface temperature. Under different load conditions, the chilled water supply temperature was suggested as the control variable to adjust the thermal environment. To satisfy the thermal comfort, the operative temperature should be controlled within 23.6 °C ∼26.4°C. This study provides valuable guidance on operating variable settings and environmental control of the AIRCU and promotes its application.

Intensity Change of NORU (2017) During Binary Tropical Cyclones Interaction

In this study, the intensity change of tropical cyclone (TC) Noru (1705) is investigated by using numerical simulations. TC Noru experienced a weakening stage during the binary interaction with TC Kulap (1706). In the presence of Kulap, the model captures well the observed intensity change. On the contrary, once Kulap is removed, it fails to reproduce the weakening stage of Noru. Possible mechanisms are proposed as follows: During the mutual interaction, the competition of moisture supplies will lead to a dry air layer wrapped around Noru. Meanwhile, due to the circulation of nearby Kulap, the vertical shear is relatively larger in the adjacent of Noru. As proposed by previous studies, the negative impacts by dry air layer will be enhanced through two possible pathways. The first is that the dry air directly impacts the TC inner core convection under vertical wind shears. The second is through the downward entropy flux into boundary layer, by which reducing the boundary layer entropy and thus convection. Dynamically, along with the approach of Kulap, it will induce barotropic instability at the outer region, by which greatly enhances the inner-core asymmetry. The asymmetric component will grow at the expense of the mean flow, and thus TC intensity weakens.

Effects of Vertical Shears and Midlevel Dry Air on Tropical Cyclone Developments*

Abstract A set of idealized experiments using the Weather Research and Forecasting model (WRF) were designed to investigate the impacts of a midlevel dry air layer, vertical shear, and their combined effects on tropical cyclone (TC) development. Compared with previous studies that focused on the relative radial position of dry air with no mean flow, it is found that the combined effect of dry air and environmental vertical shear can greatly affect TC development. Moreover, this study indicates the importance of dry air and vertical shear orientations in determining the impact. The background vertical shear causes the tilting of an initially vertically aligned vortex. The shear forces a secondary circulation (FSC) with ascent (descent) in the downshear (upshear) flank. Hence, convection tends to be favored on the downshear side. The FSC reinforced by the convection may overcome the shear-induced drifting and “restore” the vertical alignment. When dry air is located in the downshear-right quadrant of the initial vortex, the dry advection by cyclonic circulation brings the dry air to the downshear side and suppresses moist convection therein. Such a process disrupts the “restoring” mechanism associated with the FSC and thus inhibits TC development. The sensitivity experiments show that, for a fixed dry air condition, a marked difference occurs in TC development between an easterly and a westerly shear background.

The effects of anomalous atmospheres on the accuracy of infrared sea-surface temperature retrievals: Dry air layer intrusions over the tropical ocean

The effects of layers in the atmosphere with anomalously low moisture content on the accuracy of the sea-surface temperature (SST) derived from measurements of infrared radiometers on earth observation satellites are quantified using measurements taken from research cruises and numerical simulations. Radiosonde data from areas of the oceans that are seasonally affected by intrusions of dry air masses of continental origin were used with the Line-By-Line Radiative Transfer Model (LBLRTM) to simulate brightness temperatures measured in MODIS bands 31 and 32 (at wavelengths of ~11μm and ~12μm). The radiosonde datasets contained profiles with and without a dry layer, representing the baseline (no dry layer aloft) and the anomalous conditions (dry layer present). MODIS SST retrieval algorithm versions 5 and 6 were applied to the simulated brightness temperatures to obtain the SST and the retrieval errors were examined. Whereas the average errors for the baseline ‘no dry layer’ conditions range between 0.29 and 0.72K, in the case of very deep dry layers the errors can be >1K. Simulations were also performed for atmospheric profiles that were created from the measured profiles by ‘drying’ layers at various altitudes. It was found that the retrieval errors 1) depend on the amount of water vapor in the atmosphere, 2) change in a systematic way dependent on the presence and characteristics of a dry layer, 3) dry layers in the lower troposphere make the SST retrieval errors more positive, and dry layers in the upper troposphere tend to introduce SST retrieval errors that are more negative.

Vertical Change in Extinction and Atmospheric Particle Size in the Boundary Layers over Beijing: Balloon-borne Measurement

Aerosol size and number concentration were observed in the atmospheric boundary layer over Beijing (from near the ground to 1,200 m) on March 15 (a clear day) and 16 (a dusty day), 2005. The results were further compared with lidar measurements in order to understand the dependency of extinction on the particle size distribution and their vertical changes. The boundary layer atmosphere was composed of several sub-layers, and a dry air layer appeared between 400 and 1,000 m under the influence of dust event. In this dry air layer, the concentration of the fine-mode particles (diameter smaller than <TEX>$1.0\;{\mu}m$</TEX>) was slightly lower than the value on the clear day, while the concentration of coarse-mode particles (diameter larger than <TEX>$1.0\;{\mu}m$</TEX>) was remarkably higher than that on the clear day. This situation was attributed to the inflow of an air mass containing large amounts of Asian dust particles and a smaller amount of fine-mode particles. The results strongly suggest that the fine-mode particles affect light extinction even in the dusty atmosphere. However, quantitatively the relation between extinction and particle concentration is not satisfied under the dusty atmospheric conditions since laser beam attenuates in the atmosphere with high concentration of particles. Laser beam attenuation effect becomes larger in the relation between extinction and coarse particle content comparing the relation between extinction and fine particle content. To clarify this problem technically, future in situ measurements such as balloon-borne lidar are suggested. Here extinction was measured at 532 nm wavelength. Measurements of extinction at other wavelengths are desired in the future.

Five-Year Climatology of Midtroposphere Dry Air Layers in Warm Tropical Ocean Regions as Viewed by AIRS/Aqua

Abstract Many studies have commented on the presence of midtroposphere dry air layers in normally moist areas of the warm-pool region in the tropical western Pacific Ocean. In this study, 5 yr of relative humidity (RH) observations from the Atmospheric Infrared Sounder (AIRS) instrument aboard the Aqua satellite are analyzed to identify areas of anomalously dry air between 600 and 400 hPa over deep convective regions of the tropical oceans. A dry air layer is defined when midlevel RH is &amp;lt;20%, accounting for the lowest 10% of RH observations. Dry air layers appear to be more frequent over the Indian and Pacific Oceans than over the Atlantic Ocean. Large seasonal differences in the locations of dry air layers are apparent in each ocean basin. Large variations are also noted across the Pacific, suggesting limits on the applicability of case-study trends and observations of dry air layers to the Pacific as a whole. Back trajectories are then calculated for each observed parcel. The origin, or location of dehydration, is identified as the point along each trajectory at which the RH of the parcel is ≥100%. An analysis of the time between dehydration and dry air observation by AIRS suggests that dry air layers in June–August tend to last 1–2 days longer than those observed in other seasons. Although more dry air layers are observed to come from each hemisphere in its respective winter, most sources of dry air layers are subtropical and contribute anomalously dry air year-round. Other meteorological features are noted in the back trajectories, such as the eastward/westward wind transition from the subtropics to the tropics and the effects of the Indian monsoon on dry air distribution paths.

Monsoon convection in the Himalayan region as seen by the TRMM Precipitation Radar

AbstractThree‐dimensional structure of summer monsoon convection in the Himalayan region and its overall variability are examined by analyzing data from the Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar over the June–September seasons of 2002 and 2003. Statistics are compiled for both convective and stratiform components of the observed radar echoes.Deep intense convective echoes (40 dBZ echo reaching heights &gt; 10 km) occur primarily just upstream (south) of and over the lower elevations of the Himalayan barrier, especially in the northwestern concave indentation of the barrier. The deep intense convective echoes are vertically erect, consistent with the relatively weak environmental shear. They sometimes extend above 17 km, indicating that exceptionally strong updraughts loft graupel to high altitudes. Occasionally, scattered isolated deep intense convective echoes occur over the Tibetan Plateau.Wide intense convective echoes (40 dBZ echo &gt; 1000 km2 in horizontal dimension) also occur preferentially just upstream of and over the lower elevations of the Himalayas, most frequently in the northwestern indentation of the barrier. The wide intense echoes have an additional tendency to occur along the central portion of the Himalayas, and they seldom if ever occur over the Tibetan Plateau. The wide intense echoes exhibit three mesoscale structures: amorphous areas, lines parallel to the mountain barrier, and arc‐shaped squall lines perpendicular to and propagating parallel to the steep Himalayan barrier. The latter are rare, generally weaker than those seen in other parts of the world, and occur when a midlevel jet is aligned with the Himalayan escarpment.Deep and wide intense convective echoes over the northwestern subcontinent tend to occur where the low‐level moist layer of monsoon air from the Arabian Sea meets dry downslope flow, in a manner reminiscent of severe convection leeward of the Rocky Mountains in the central USA. As the low‐level layer of moist air from the sea moves over the hot arid northwestern subcontinent, it is capped by an elevated layer of dry air advected off the Afghan or Tibetan Plateau. The capped low‐level monsoonal airflow accumulates instability via surface heating until this instability is released by orographically induced lifting immediately adjacent to or directly over the foothills of the Himalayas.Broad (&gt;50 000 km2 in area) stratiform echoes occur in the eastern and central portions of the Himalayan region in connection with Bay of Bengal depressions. Their centroids are most frequent just upstream of the Himalayas, in the region of the concave indentation of the barrier at the eastern end of the range. The steep topography apparently enhances the formation and longevity of the broad stratiform echoes. Monsoonal depressions provide a moist maritime environment for the convection, evidently allowing mesoscale systems to develop larger stratiform echoes than in the western Himalayan region. Copyright © 2007 Royal Meteorological Society

Aerosol impact on the dynamics and microphysics of deep convective clouds

AbstractMechanisms through which atmospheric aerosols affect cloud microphysics, dynamics and precipitation are investigated using a spectral microphysics two‐dimensional cloud model. A significant effect of aerosols on cloud microphysics and dynamics has been found. Maritime aerosols lead to a rapid formation of raindrops that fall down through cloud updraughts increasing the loading in the lower part of a cloud. This is, supposedly, one of the reasons for comparatively low updraughts in maritime convective clouds. An increase in the concentration of small cloud condensation nuclei (CCN) leads to the formation of a large number of small droplets with a low collision rate, resulting in a time delay of raindrop formation. Such a delay prevents a decrease in the vertical velocity caused by the falling raindrops and thus increases the duration of the diffusion droplet growth stage, increasing latent heat release by condensation. The additional water that rises to the freezing level increases latent heat release by freezing. As a result, clouds developing in continental‐type aerosol tend to have larger vertical velocities and to attain higher levels.The results show that a decrease in precipitation efficiency of single cumulus clouds arising in micro‐physically continental air is attributable to a greater loss of the precipitating mass due to a greater sublimation of ice and evaporation of drops while they are falling from higher levels through a deep layer of dry air outside cloud updraughts. By affecting precipitation, atmospheric aerosols influence the net heating of the atmosphere. Simulations show that aerosols also change the vertical distribution of latent heat release, increasing the level of the heating peak.Clouds arising under continental aerosol conditions produce as a rule stronger downdraughts and stronger convergence in the boundary layer. Being triggered by larger dynamical forcing, secondary clouds arising in microphysically continental air are stronger and can, according to the results of simulations, form a squall line. The squall line formation was simulated both under maritime (GATE‐74) and continental (PRE‐STORM) thermodynamic conditions. In the maritime aerosol cases, clouds developing under similar thermodynamic conditions do not produce strong downdraughts and do not lead to squall line formation.Thus, the ‘aerosol effect’ on precipitation can be understood only in combination with the ‘dynamical effect’ of aerosols. Simulations allow us to suggest that aerosols, which decrease the precipitation efficiency of most single clouds, can contribute to the formation of very intensive convective clouds and thunderstorms (e.g. squall lines, etc.) accompanied by very high precipitation rates. Affecting precipitation, net atmospheric heating and its vertical distribution, as well as cloud depth and cloud coverage, atmospheric aerosols (including anthropogenic ones) influence atmospheric motions and radiation balance at different scales, from convective to, possibly, global ones. Copyright © 2005 Royal Meteorological Society.

Suppression of deep convection over the tropical North Atlantic by the Saharan Air Layer

The effects of the dust‐laden Saharan Air Layer (SAL) on the occurrence of deep convection over the eastern and central tropical North Atlantic Ocean off‐shore of the African continent during August–September 2002 are investigated. We show that the SAL is associated with suppressed convection in this region. To determine the possible cause of the suppressed convection, the thermodynamic structure and dust content of the SAL are investigated. We find that the SAL is associated with warmer and dryer air below 700 hPa with the largest temperature anomalies located around 850 hPa. This warm and dry air layer raises the lifting condensation level and level of free convection, and increases the energetic barrier to convection that leads to reduced occurrence of deep convection.

Plume patterns in radiative–convective flows

We study the dynamics of a simplified model of atmospheric convection. The modelrepresents a layer of dry air kept in statistically stationary radiative–convectiveequilibrium. We discuss the behaviour and the spatial organization of the pattern ofconvective plumes that emerge in the system, and analyse the intermittency properties ofthe heat flux field.

Role of Gravity Waves in Triggering Deep Convection during TOGA COARE

The role of gravity waves in the initiation of convection over oceanic regions during the Tropical Ocean Global Atmosphere Coupled Ocean‐Atmosphere Response Experiment (TOGA COARE) experiment is investigated. First, an autocorrelation method is applied to infrared temperature observations of convective events from satellite images. It reveals that new deep convective cells often occur a few hours after a previous intense event at a typical distance of a few hundred kilometers. Such fast moving modes (faster than 15 m s 21) are interpreted as the trace of gravity waves excited by previous convection and contributing to trigger further convection. Second, the specific case of 11‐12 December 1992, during which an active squall line is generated after the collapse of a previous mesoscale convective system (MCS) nearby, is analyzed with a nonhydrostatic model. The triggering of the second MCS is well reproduced explicitly, owing to the use of the two-way interactive grid nesting. The convective source appears to emit pulses of gravity waves on a wide range of small scales. On the contrary, the troposphere response to the convective source exhibits a spectral simplicity. A slowly evolving mode, characterized by an ascent in the PBL and a compensating subsidence in the free troposphere, favors shallow convection and inhibits deep convection, respectively. Traveling modes propagating away from the convective source are characterized by a fast mode (;50 m s21) and a slower mode (; 25 ms 21) associated with the convective and stratiform development of the source, respectively, in agreement with previous studies. A budget analysis reveals the different factors leading to the deep convection triggering. First, an active PBL characterized by strong surface fluxes and mean ascent, initiates shallow convection, lasting about 2 h, inhibited above by the subsiding motions maintaining a dry layer. Second, horizontal advection of moist and cooler air at midlevels, and detrainment from cumuli, contribute to destroy the dry air layer capping the shallow convective layer. Finally, vertical advection induced by the gravity waves passage modulates the vapor and temperature evolution. Ascending phases favor moistening and cooling, whereas subsiding phases stop these effects, delaying the deep convection onset. The triggering occurs after a strong subsidence, when the ascent phases of deep and shallow modes are combined.

A method for aerosol profiling in the lower troposphere with coupled scatter and meteorological rawindsondes and first data from the tropical Atlantic off Sahara

We developed a simple prototype balloonborne aerosol scattering profiler by coupling a small nephelometer with a meteorological sonde and we performed one sounding over Sal Island, Cape Verde, in February 1996 during a turbid episode of dust transport with an aerosol optical thickness (AOT) larger than 0.6 at 870 nm . We also monitored space and time variations in AOT with both Meteosat and a Sun photometer. This allows us to document for the first time the vertical distribution of aerosols during the typical winter situation of low-altitude transport of African dust in the trade winds of the tropical North Atlantic. We derive the vertical profile of aerosol extinction from side-scattering nephelometer measurements by applying corrections for aerosol optical properties. We find that most of the aerosol extinction occurs between about 600 and 1400 m in altitude in a layer of dry air above the atmospheric marine boundary layer (MBL). Our results suggest that about 90% of the dust is transported above the MBL. They confirm previous findings of well-structured African dust layers observed at north mid-latitudes with lidar systems.

Modelling of stratospheric intrusions within a mid‐latitude synoptic‐scale disturbance

AbstractThe results of a run of the UK Universities' Global Atmospheric Modelling Programme (UGAMP) General Circulation Model (GCM) is presented, initialized with European Centre for Medium‐Range Weather Forecasts data for 6 October 1990. the dates correspond with observations of a trough made during a Transport of Ozone and Stratosphere/Troposphere Exchange campaign. This anticyclonic wrapping system is compared with a cyclonic wrapping system studied in a previous paper. the fate of stratospheric air is followed using potential vorticity (PV) and specific humidity. the run gives good agreement with radiosonde data for the development of the trough, which involves a tropopause fold and a ‘streamer’, both with regard to the position and evolution of a layer of dry air. Analysis of the height of the tropopause shows that PV values (in PV units) in the range 1‐5 agree well with the thermal tropopause outside the trough, but in order to capture the layer of dry air seen in the radiosonde data, a value of PV of order 1 is required within the trough. Use of PV values in the range 3‐4 may therefore not follow the evolution of dry stratospheric air entering the troposphere, even though such values may on average follow the thermal tropopause. Most of the dry region is visible as a dark band in the Meteosat data, although the lowest levels of dry air (at approx. 800 mb) are too low to be seen by the satellite. Thus Meteosat observations may not capture all processes involved in stratosphere‐troposphere exchange, and the images must be interpreted with caution when using them to follow the movement of dry stratospheric air.

TOGA-COARE集中観測期間中の混合層の構造と海面フラックスの評価

The surface and aerological observations made by the Japanese research vessel Hakuho-maru on 11-27 November, 1992 at 0°, 156°E during TOGA-COARE IOP period were used to analyze the evolution and structure of mixed layer over the ocean, and to estimate surface fluxes by using bulk schemes. The Part I of this study is devoted to the problem of the mixed layer. The main finding is that the regional wind field can greatly modify the structure of the mixed layer. For the east trade régime, the mixed layer had a relatively great depth, mostly reaching 800-900m. Above this level was a dry layer without any significant inversion. For the west wind régime created by four westerly wind bursts, the height of the mixed layer was considerably depressed, or even disappeared. A deep saturation layer was often observed.Two events of the intrusion of the extremely dry air layer greatly enhanced and elevated the mixed layer, up to about 1.5km. The reason for these events was discussed.

Microclimatic Investigation of Waste Heap

The author investigated the microclimate on the waste heap from the forest point of view. That is, the slopes were favourable to the sliding down of cold air and the rising of warm air, on the slopes, the layer of air near the ground had the peculiar meteorological properties.Like a skin of air it clothes and determined the climatic habitate of the plants growing thereon. There were 10 observation points located on the slopes of different direction and high degree.The sketch map (Fig. 1) shows by the configuration of the contours how regular the cone is on all sides, and it lies at an average inclination of 30°. All the points of maximum and minimum temperature readings were taken at a height of 30cm in winter, and vertical distribution of temperature and humidity readings were taken at o-150cm height in spring & summer. Fig. 6-9.Fig. 1-Fig. 4 show the distribution of maximum and minimum temperature on the waste heap on average for winter days.It was to be found that the lowest temperature and maximum temperature range would be found on the south slope, and results of humidity measurement on the south slope, had dry air layer, so the plants did not easy grow there.