•Mass transfer characteristics in and downstream of 90° elbow is studied.•Mass transfer characteristics is measured by plaster dissolution method.•Flow mechanism in elbow is studied by surface flow ...visualization.•Velocity field is measured by stereo PIV downstream of elbow.•Mechanism of mass transfer enhancement in elbow is examined.
Mass and momentum transfer characteristics in and downstream of a 90° elbow are studied experimentally with the aid of the plaster dissolution method, surface flow visualization in the elbow and the cross-sectional velocity field measurement by stereo particle image velocimetry (SPIV) downstream of the elbow. The experiments are carried out for the elbow with the radius to diameter ratio 1.5 at moderate Reynolds number Re=5×104. The mass transfer measurements in the elbow indicate that the major change of mass transfer coefficient is observed along the inner wall of the elbow, where low mass transfer coefficient is found in the first half of the inner wall and it increases abruptly in the second half of the elbow, which is followed by a gradual recovery of the mass transfer in the downstream, while the mass transfer on other wall does not change so much with that of the straight pipe. These features are mainly due to the flow acceleration in the first half of the inner wall and the following flow separation in the second half of the inner wall, where the high turbulent energy production is expected from the SPIV measurement downstream of elbow. These results indicate that the mass transfer coefficient in and downstream of the elbow is highly modified by the flow separation and secondary flow in the elbow, which may generate the high turbulent energy production in the second half of the inner wall in the elbow.
The monthly global and regional variability in Earth's radiation balance is examined using correlations and regressions between atmospheric temperatures and water vapor with top‐of‐atmosphere ...outgoing longwave (OLR), absorbed shortwave (ASR), and net radiation (RT = ASR − OLR). Anomalous global mean monthly variability in the net radiation is surprisingly large, often more than ±1 W m−2, and arises mainly from clouds and transient weather systems. Relationships are strongest and positive between OLR and temperatures, especially over land for tropospheric temperatures, except in the deep tropics where high sea surface temperatures are associated with deep convection, high cold cloud tops and thus less OLR but also less ASR. Tropospheric vertically averaged temperatures (surface = 150 hPa) are thus negatively correlated globally with net radiation (−0.57), implying 2.18 ± 0.10 W m−2 extra net radiation to space for 1°C increase in temperature. Water vapor is positively correlated with tropospheric temperatures and thus also negatively correlated with net radiation; however, when the temperature dependency of water vapor is statistically removed, a significant positive feedback between water vapor and net radiation is revealed globally with 0.87 W m−2 less OLR to space per millimeter of total column water vapor. The regression coefficient between global RT and tropospheric temperature becomes −2.98 W m−2 K−1 if water vapor effects are removed, slightly less than expected from blackbody radiation (−3.2 W m−2 K−1), suggesting a positive feedback from clouds and other processes. Robust regional structures provide additional physical insights. The observational record is too short, weather noise too great, and forcing too small to make reliable estimates of climate sensitivity.
Key Points
High-frequency fluctuations in Earth's top‐of‐atmosphere radiation are explored
Feedbacks of temperatures and water vapor on climate variability are documented
Extra radiation of 2.18 W m−2 goes to space for 1°C increase in temperature
Mass and momentum transfer characteristics in a 90° elbow with a radius to pipe diameter ratio of 1.5 are studied experimentally with the aid of the plaster dissolution method, planar velocity ...measurement by particle image velocimetry (PIV), and surface flow visualization in the Reynolds number (Re) range of 5×104 to 20×104. The experimental results indicate that the most significant change in mass transfer distribution occurs on the inner wall of the elbow. The mass transfer coefficient increases along the centerline of the first half of the elbow and decreases in the second half with increasing Reynolds number. The near-wall velocity measurements by PIV show that the flow accelerates on the first half of the inner wall and decelerates on the second half, which contributes to the growth of the turbulent intensities on the second half of the inner wall. The surface flow visualization indicates that the secondary flow is weak on the inner wall of the elbow with higher Reynolds number. These results show that the mass transfer characteristics change on the inner wall of the elbow with increase in the Reynolds number, even when it is larger than Re=5×104.
The TransCom 3 experiment was begun to explore the estimation of carbon sources and sinks via the inversion of simulated tracer transport. We build upon previous TransCom work by presenting the ...seasonal inverse results which provide estimates of carbon flux for 11 land and 11 ocean regions using 12 atmospheric transport models. The monthly fluxes represent the mean seasonal cycle for the 1992 to 1996 time period. The spread among the model results is larger than the average of their estimated flux uncertainty in the northern extratropics and vice versa in the tropical regions. In the northern land regions, the model spread is largest during the growing season. Compared to a seasonally balanced biosphere prior flux generated by the CASA model, we find significant changes to the carbon exchange in the European region with greater growing season net uptake which persists into the fall months. Both Boreal North America and Boreal Asia show lessened net uptake at the onset of the growing season with Boreal Asia also exhibiting greater peak growing season net uptake. Temperate Asia shows a dramatic springward shift in the peak timing of growing season net uptake relative to the neutral CASA flux while Temperate North America exhibits a broad flattening of the seasonal cycle. In most of the ocean regions, the inverse fluxes exhibit much greater seasonality than that implied by the ΔpCO2 derived fluxes though this may be due, in part, to misallocation of adjacent land flux. In the Southern Ocean, the austral spring and fall exhibits much less carbon uptake than implied by ΔpCO2 derived fluxes. Sensitivity testing indicates that the inverse estimates are not overly influenced by the prior flux choices. Considerable agreement exists between the model mean, annual mean results of this study and that of the previously published TransCom annual mean inversion. The differences that do exist are in poorly constrained regions and tend to exhibit compensatory fluxes in order to match the global mass constraint. The differences between the estimated fluxes and the prior model over the northern land regions could be due to the prior model respiration response to temperature. Significant phase differences, such as that in the Temperate Asia region, may be due to the limited observations for that region. Finally, differences in the boreal land regions between the prior model and the estimated fluxes may be a reflection of the timing of spring thaw and an imbalance in respiration versus photosynthesis.
Simultaneous observations of atmospheric potential oxygen (APO=O
2
+1.1×CO
2
) and air-sea O
2
flux, derived from dissolved oxygen in surface seawater, were carried out onboard the research vessel ...MIRAI in the northern North Pacific and the Arctic Ocean in the autumns of 2012-2014. A simulation of the APO was also carried out using a three-dimensional atmospheric transport model that incorporated a monthly air-sea O
2
flux climatology. By comparing the observed and simulated APO, as well as the observed and climatological air-sea O
2
fluxes, it was found that the large day-to-day variation in the observed APO can be attributed to the day-to-day variation in the local air-sea O
2
fluxes around the observation sites. It was also found that the average value of the observed air-sea O
2
fluxes was systematically higher than that of the climatological O
2
flux. This could explain the discrepancy between the observed and simulated seasonal APO cycles widely seen at various northern hemispheric observational sites in the fall season.
Simultaneous measurements of the atmospheric O
2
/N
2
ratio and CO
2
concentration were made at Ny-Ålesund, Svalbard, and Syowa, Antarctica for the period 2001-2009. Based on these measurements, the ...observed atmospheric potential oxygen (APO) values were calculated. The APO variations produced by changes in the oceanic heat content were estimated using an atmospheric transport model and heat-driven air-sea O
2
(N
2
) fluxes, and then subtracted from observed interannual variations of APO. The oceanic CO
2
uptake derived from the resulting 'corrected' secular trend of APO showed interannual variability of less than ±0.6 GtC yr
−1
, significantly smaller than that derived from the 'uncorrected' trend of APO (±0.9 GtC yr
−1
). The average CO
2
uptake during the period 2001-2009 was estimated to be 2.9±0.7 and 0.8±0.9 GtC yr
−1
for the ocean and terrestrial biosphere, respectively. By excluding the influence of El Niño around 2002-2003, the terrestrial biospheric CO
2
uptake for the period 2004-2009 increased to 1.5±0.9 GtC yr
−1
, while the oceanic uptake decreased slightly to 2.8±0.8 GtC yr
−1
.
Spatial and temporal variations of atmospheric CO2 concentrations contain information about surface sources and sinks, which can be quantitatively interpreted through tracer transport inversion. ...Previous CO2 inversion calculations obtained differing results due to different data, methods and transport models used. To isolate the sources of uncertainty, we have conducted a set of annual mean inversion experiments in which 17 different transport models or model variants were used to calculate regional carbon sources and sinks from the same data with a standardized method. Simulated transport is a significant source of uncertainty in these calculations, particularly in the response to prescribed “background” fluxes due to fossil fuel combustion, a balanced terrestrial biosphere, and air–sea gas exchange. Individual model‐estimated fluxes are often a direct reflection of their response to these background fluxes. Models that generate strong surface maxima near background exchange locations tend to require larger uptake near those locations. Models with weak surface maxima tend to have less uptake in those same regions but may infer small sources downwind. In some cases, individual model flux estimates cannot be analyzed through simple relationships to background flux responses but are likely due to local transport differences or particular responses at individual CO2 observing locations. The response to the background biosphere exchange generates the greatest variation in the estimated fluxes, particularly over land in the Northern Hemisphere. More observational data in the tropical regions may help in both lowering the uncertain tropical land flux uncertainties and constraining the northern land estimates because of compensation between these two broad regions in the inversion. More optimistically, examination of the model‐mean retrieved fluxes indicates a general insensitivity to the prior fluxes and the prior flux uncertainties. Less uptake in the Southern Ocean than implied by oceanographic observations, and an evenly distributed northern land sink, remain in spite of changes in this aspect of the inversion setup.
Since 1993, atmospheric carbon dioxide (CO2) has been continuously observed by the Japan Meteorological Agency at Minamitorishima station (24°18′N, 153°58′E), located about 2000 km off the Asian ...continent in the western North Pacific. The long‐term record shows high‐frequency measurements with interesting episodic events with extremely low CO2 mixing ratios 5–10 ppm below the background seasonal cycle. These extremely low CO2 (ELC) events occur several times each year, primarily in July, August, and September, although the number of events varies from year to year. The origins of air masses associated with the ELC events were defined by backward trajectory analyses as well as chemical characterizations using simultaneous observations of other trace gases (CO, CH4, and O3). The results indicate that the air masses with extremely low CO2 were influenced by active biospheric uptake in summer over different continental sink regions in Siberia, northern Asia, and Southeast Asia due to rapid long‐range transport driven by strong northerly or southerly winds. The spatial scale of the widespread low‐CO2 distribution for the ELC events in 2001 was captured by a simulation experiment using a three‐dimensional chemical transport model. It clearly revealed that the Intertropical Convergence Zone around 20°N in the western North Pacific during summer blocked further southward intrusion of ELC events through the lower troposphere.
Temporal variations of carbon monoxide (CO) were observed simultaneously at seven surface stations located in east Asia/western North Pacific from 24°N to 43°N during the East Asian Regional ...Experiment (EAREX) 2005 campaign in March 2005. Three major pollution events with enhanced CO levels were recorded around the same time at four stations over the East China Sea and at two northern stations of Japan. These pollution events were also observed 3–4 d later at Minamitorishima, located far from the Asian continent. A synoptic weather analysis showed that all of the major CO enhancements were brought about by the passages of cold fronts associated with the eastward migrating cyclonic development. The CO distribution simulated by a three‐dimensional transport model showed that the polluted air masses exported from the continent were trapped behind the cold fronts and then merged into elongated belts of enriched CO before spreading over the western North Pacific. Transport of regionally tagged CO tracer simulated by the model indicated that the Chinese and Korean emissions were the major contributors to the pollution over the East China Sea, while the Japanese emissions had impacts at relatively higher latitude regions during the campaign. The simulation results also showed that the CO enhancements detected at Minamitorishima were caused by a long‐range transport of pollution emissions from various regions in east Asia. The CO‐enriched plumes from Southeast Asia and south Asia emissions were found above the boundary layer in the frontal zone but not at the surface.
Systematic measurements of the atmospheric O
2
/N
2
ratio have been made using aircraft and ground-based stations in Japan since 1999. The observed seasonal cycles of the O
2
/N
2
ratio and ...atmospheric potential oxygen (APO) vary almost in opposite phase to that of the CO
2
concentration at all altitudes, and their amplitudes and phases are generally reduced and delayed, respectively, with increasing altitude. Simulations of APO using two atmospheric transport models reproduce general features of the observed seasonal cycle, but both models fail to reproduce the phase at an altitude ranging from 8 km to the tropopause. By analysing the observed secular trends of APO and CO
2
concentration, and assuming a global net oceanic O
2
outgassing of 0.2±0.5 GtC yr
−1
, we estimate global average terrestrial biospheric and oceanic CO
2
uptake for the period 2000-2010 to be 1.0±0.8 and 2.5±0.7 GtC yr
−1
, respectively.
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