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News Article | May 2, 2017
Site: www.eurekalert.org

A new study by scientists from the Institute of Atmospheric Physics and Nanjing University of Information Science and Technology investigates the trends in the mean state and the day-to-day variability (DDV) of the surface weather conditions over northern and northeastern China (NNEC) using CN05.1 observational data. During 1961-2014, the surface temperature (wind speed) increased (decreased) over NNEC and the DDV of the surface temperatures and wind speeds decreased, indicating a trend towards a stable, warm and windless state of the surface weather conditions over NNEC. This finding implies a trend towards more persistent hot and windless episodes, which threaten human health and aggravate environmental problems. The trends were also examined in reanalysis data. Both the ERA-40 and NCEP data showed an increasing (decreasing) trend in the mean state of the surface temperatures (wind speeds). However, the reanalysis data only showed a consistent decreasing trend in the DDV of the surface weather conditions in spring. The underlying reason for the decreased DDV of the surface weather conditions was further analyzed, focusing on the spring season. "Essentially, the decreased DDV of the surface weather conditions can be attributed to a decrease in synoptic-scale wave activity, which is quantified using the 2-7-day bandpass filtered daily SLP [sea level pressure] in this study," explains Dr. SUN Bo, first author of the study. The authors found that the decreased synoptic-scale wave activity was caused by a decrease in the baroclinic instability. There was a contrasting change in the baroclinic instability over East Asia, showing a decreasing (increasing) trend north (south) of 40°N. This contrasting change in the baroclinic instability was primarily caused by a tropospheric cooling zone over East Asia at approximately 40°N, which led to a decreased (increased) meridional temperature gradient over the regions to the north (south) of 40°N.


(Institute of Atmospheric Physics, Chinese Academy of Sciences) A Chinese Program examined the impacts of astronomy and earth motion factors on climate change. Solar impacts on earth's climate are most sensitive in polar and tropical Pacific regions and the monsoon activity plays a crucial role in the propagation of solar signal between different latitudes.


Frequent occurrence of both anthropogenic pollution and natural dust in East Asian imposes great impact on regional air quality, human health and climate. Till now, their interaction and consequent effect on the dust morphology remain statistically unclear because even though traditional filter-based bulk sampling method can provide accurate chemical compounds, it cannot distinguish the mixing state of chemicals with dust particles. "Single-particles inspection using electro-microscopy can identify coated/contaminated dust particles," says Dr. PAN Xiaole from Institute of Atmospheric Physics, "but real-time measurement on the morphological variation of dust particles was difficult due to labor-intensively manual operations." In a recently published paper in Scientific Reports, PAN and his collaborators from China and Japan investigate polarization of oscillation direction of back-scattering signal of single dust particles online on the basis of a newly developed, bench-top optical particle counter. A real-time decrease in Asian dust depolarization was observed in North China for the first time. PAN reckons that it can only be caused by the decrease in the particle aspect ratio, which was reflected by the coating of an air pollutant, such as the deliquescent dust-nitrate Ca(NO3)2. "This phenomenon was obvious when the dust particles were stagnant in a polluted region with high relative humidity condition." Says PAN. The statistics highlight the significant importance of internally mixed "quasi-spherical" Asian dust particles, which were more hygroscopic and likely to act as cloud condensation nuclei (CCN). Because the NOx emission in East Asia has been rapidly increasing over the last decade, their findings imply that nitrate has become increasingly important on the morphological change of Asian dust and its subsequent spatial allocation. "Nitrate plays a leading role in regional climate change." PAN concludes. And he adds, "Many processes associated with the direct/indirect effects of dust-nitrate are still insufficiently understood, and this requires more attention from the public and poses another challenge for the observation and modeling communities." Their findings have been published and online in Scientific Reports.


Shallow cumulus (SCu) clouds play an important role in the global redistribution of water and energy and in the transport of surface heat, moisture and momentum to the free troposphere. SCu clouds or fair-weather cumuli are characterized by their small size, relatively weak convection, and no precipitation, which is significantly different from cumulus congestus and deep convection clouds. SCu clusters can often be observed in summer over the Inner Mongolia Grassland (IMG), which is the largest grassland in China; and yet, despite this, few studies on SCu in this region have been conducted. Recently, a team led by Prof. Hongbin CHEN from the Institute of Atmospheric Physics, Chinese Academy of Sciences, provided an initial insight into the features of SCu over the IMG. An intensive radiosonde experiment was performed in the summer of 2014, and the findings published in Advances in Atmospheric Sciences (Shi et al., 2017) constitute the first report of SCu observations over this region. "We made some interesting discoveries regarding shallow cumulus over the IMG," explains Hongrong Shi, the first author of the paper. "The cloud base height of 3.4 km and cloud top height of 5 km over this region were far in excess of those over the sea, but were relatively close to those of the Southern Great Plains in the United States." Further analysis indicated that the formation and maintenance of SCu was in response to wind shear, subsidence, surface forcing and development of the boundary layer. CHEN, corresponding author, comments further that "...Although some interesting features associated with shallow cumulus have been revealed by the analysis of the intensive radiosonde measurements, we should keep it in mind that this is a preliminary study, since the results were mainly based on one case. Further studies of shallow cumulus in this specific key region are still required. A combination of radiosonde and satellite measurements, as well as model simulations, would shed new light on the formation and maintenance of these clouds".


The highest and largest plateau in the Northern Hemisphere, the Tibetan Plateau (TP), is in the subtropical region of Asia. The air quality above the TP is only 60% of the sea level. In addition, because the radiation over the plateau, especially in the boundary layer is significantly different from those in the low altitude region, the thermal process over the TP has obvious particularity. Through its special thermodynamic and dynamic effects, the TP and its adjacent Iran Plateau (IP) have significant impacts on the circulation and climate over the plateaus as well as the adjacent region and the globe. However, the interaction and feedback among the heat source of the TP and IP and circulation is not clear nowadays. Recent research papers have made new progress in this issue. Professors Wu Guoxiong and Liu Yimin and their students who come from the Institute of Atmospheric Physics, Chinese Academy of Sciences, conducted the study. With theoretical diagnostic analysis and simulations by regional model, the researchers have revealed the physical process of interaction and feedback between the two types of summertime heating, the surface sensible heating and condensation heating over TP and the surface sensible heating over Tibetan-Iranian Plateaus. They also discovered how this interaction influences the vertical thermodynamic structure near the tropopause over Asia and the atmospheric circulation in the globe. The maintenance of a steady state in the atmosphere is only possible by obtaining external energies, particularly through the transfer of surface sensible heating, evaporation-condensation heating. This study showed that the TP surface sensible heating can generate convective precipitation over the southern and eastern TP, whereas the precipitation over the TP can reduce the in situ surface sensible heating. This indicates the existence of a feedback or interaction process between the two types of diabatic heating over the TP. Furthermore they documented that the surface sensible heating over the two plateaus not only have mutual influences but also feedback to each other. The IP surface sensible heating can reduce the surface sensible heating and increase the condensation heating over the TP, whereas the TP surface sensible heating can increase IP sensible heating, thereby reaching quasi-equilibrium among the surface sensible heating and condensation heating over the TP, the IP surface sensible heating and the atmosphere vertical motion. Therefore, a so-called Tibetan-Iranian Plateau coupling system (TIPS) is constructed, which influences atmosphere circulation (Figure). "The interaction between surface sensible heating and latent heating over the TP plays a leading role in the TIPS" said Prof. Wu. The surface sensible heating of the IP and TP influences on other regions not only have superimposed effects but also mutually offset, the combined influence over TP and IP represents the major contribution to the convergence of water vapor transport in the Asian subtropical monsoon region. In addition, the heating of TIPS increases the upper tropospheric temperature maximum and lifts the tropopause, cooling the lower stratosphere. Combined with large-scale thermal forcing of the Eurasian continent, the TIPS produce a strong anticyclonic circulation and the South Asian High that warms the upper troposphere and cools the lower stratosphere, thereby affecting regional and global weather and climate. The results improved the understanding on the unique feature of the climate dynamics of the TP. It will also help the regional weather and climate prediction. The study was funded by the Key Program and integration Program of the Major Research Plan of the National Natural Science Foundation of China (No. 91437219 and .91637312) Liu Y M, Wang Z Q, Zhuo H F, Wu G X. 2017.Two types of summertime heating over Asian large-scale orography and excitation of potential-vorticity forcing II.Sensible heating over Tibetan-Iranian Plateau. Science China Earth Sciences, 60(4): 733-744 Wu G X, Zhuo H F, Wang Z Q, Liu Y M. 2016.Two types of summertime heating over the Asian large-scale orography and excitation of potential-vorticity forcing I. Over Tibetan Plateau. Science China Earth Sciences, 59 (10): 1996-2008


News Article | April 27, 2017
Site: www.eurekalert.org

Whether you prefer a cool summer night with a gentle breeze or a crystal clear and still winter day, the human perception of temperature, or thermal comfort, whilst largely dependent on the temperature itself, involves several other climate variables, such as humidity and wind speed. For example, during summer, high humidity can reduce the evaporation of sweat, needed for cooling, from the human body, consequently increasing levels of heat stress and making people feel uncomfortable or even sick. Meanwhile, a nice breeze around you removes heat by accelerating evaporation in hot conditions, leading to a cooling effect. In winter, the presence of a wind will remove heat through the process of convection, thereby further elevating the feeling of chilliness. In China, this is especially pronounced in the north of the country during periods when strong northerly winds blow cold air from Siberia. Meanwhile, owing to humid air conducting more heat, the wetter climate of southern China in winter typically leads to a perception of colder conditions for the human body. So how has thermal comfort changed in recent decades over China against the background of the global warming? To answer the question, scientists from the Institute of Atmospheric Physics of the Chinese Academy of Sciences, the National Climate Center of the China Meteorological Administration, and other institutes, carried out an investigation over the Chinese mainland using the index of effective temperature (ET), which combines the effects of temperature, humidity and wind speed. The human perception of temperature was classified on a scale based on the values of the ET index, ranging from very cold, cold, cool, comfortable, to warm, hot, and very hot. The study reveals an increase in ET in recent decades (1961-2014) over China, mostly due to the increase in temperature and decrease in wind speed. An average of 255 days of very cold and cold days per year was found, related to the fact that China is a country located in the mid and high latitudes, comprising several high-elevation areas (e.g., the vast Tibetan Plateau). However, a marked decline, at a rate of 3.5 days per decade was also found, indicating there were around 15 fewer cold days in the last decade compared to the 1960s. At the other end of the spectrum, warming led to an increase in the number of comfortable days (average of 27 per year) at a rate of 1.3 days per decade, i.e. an increase from 25 in the 1960s to 29 days in the last decade. However, the increase showed seasonal and geographical differences. For example, in summer, a significant decrease in the number of comfortable days dominated in eastern China, where there is a high population density. The number of hot and very hot days at the end of the study period amounted to only 11 per year; however, this figure had been increasing at a rate of 0.7 days per decade. In other words, 30% more hot and very hot days were observed in the last decade of the study period compared to the 1960s (12.5 vs. 9.5 days). The study's findings not only provide an interesting insight into the changes in thermal comfort that have already occurred, but also give us plenty to think about as the climate continues to change in the future. Indeed, GAO Xuejie, one of the study's authors from the Institute of Atmospheric Physics warns "We can expect further and possibly accelerating levels of change in the future under global warming and, as such, our group is currently working on high-resolution regional climate model simulations to build a clearer picture in this regard". The findings are published in the International Journal of Climatology.


News Article | February 15, 2017
Site: www.eurekalert.org

Global warming increases the water holding capacity of the atmosphere and thus precipitation characteristics are expected to change. Changing precipitation characteristics directly affect society through their impacts on drought and floods, hydro-dams and urban drainage systems. An understanding of the changes in precipitation characteristics is not only important for climate research but also of great significant merit in the management of water resources and agricultural activities. "To address climate change, detection and attribution studies of precipitation are essential. Nonetheless, the detection of regional precipitation change has been a challenge, especially at regional scale. Whether anthropogenic climate change is manifested through a detectable effect on East Asian precipitation remains unknown." Said the first author Dr. Shuangmei Ma of a recent study published in Journal of Climate. Ma currently works at Chinese Academy of Meteorological Sciences. Supervised by her Ph.D advisor, Prof. Tianjun Zhou from the Institute of Atmospheric Physics/Chinese Academy of Sciences, her Ph. D research focused on detection and attribution of anthropogenic precipitation change over China. Their recently published work was the first attempt to investigate the changes in the distribution of the daily precipitation amount over China during the last five decades using observation data sets. They and their American and European collaborators applied the optimal fingerprinting detection and attribution method to assess the anthropogenic contribution to precipitation changes, based on the outputs of the CMIP5 models. "The results show that anthropogenic forcing has had a detectable and attributable in?uence on the distribution of daily precipitation amounts over eastern China (EC) during the second half of the twentieth century." Prof. Tianjun Zhou, who is the corresponding author of the paper, summarized their findings. "We have also found evidences suggesting that the observed shift from weak precipitation to intense precipitation is primarily due to the contribution of greenhouse gas (GHG) forcing, with anthropogenic aerosol (AA) forcing offsetting some of the effects of the GHG forcing." Under GHG-induced warming, increased atmospheric precipitable water and enhanced land-sea thermal contrast cause the water vapor transport to EC from the adjacent oceans via southerly and midlatitude westerly winds to strengthen, thereby favoring heavier precipitation over EC. However, the countering effects of surface cooling induced by anthropogenic aerosols meant that some of this enhanced transport is cancelled out by AA forcing. "We should also note that while the GHG forcing to the observed precipitation change is attributable and detectable, the signal of AA forcing is not as robust as GHG due to the limitations of aerosol schemes used in the current state of the art models." Zhou is hopeful that "the new models used in the Global Monsoons Modeling Inter-comparison Project (GMMIP) for the 6th Coupled Model Inter-comparison Project (CMIP6) would have improvement in this regard".


News Article | February 15, 2017
Site: www.eurekalert.org

Beijing MST (Mesosphere-Stratosphere-Troposphere) Radar is one of the largest facilities within the Chinese Meridian Project (a chain of diverse ground-based remote sensing facilities for monitoring and forecasting the space environment), and is one of only two domestic MST radars. It was built by the Institute of Atmospheric Physics (IAP), Chinese Academy of Sciences (CAS), and is located at the IAP's Xianghe field observatory in Hebei province (39°45'14.40"N, 116°59'24.00"E). Since July 2011, the Beijing MST radar has been in continuous operation observing the vertical distribution of winds and turbulence in the troposphere-lower stratosphere and mesosphere-lower thermosphere regions. As one of two MST radars within mainland China, it has produced long-term quality controlled data for understanding various significant processes and their interaction within and among layers. Using these long-term observational data, Prof. Daren Lü and postdoctoral researcher Yufang TIAN from IAP, CAS, investigated the detection capability and data reliability of Beijing MST Radar. "To our delight, the horizontal winds derived by Beijing MST Radar and those measured by operational radiosondes in the height range of 3-25 km were highly consistent." According to Lü and TIAN, the relatively larger differences at certain heights and in certain seasons "were mainly due to the synoptic characteristics of the horizontal wind field itself and the temporal and spatial scales of the weather systems in which the two instruments were simultaneously detecting." They also said that "compared with similar studies conducted elsewhere in the world, the present work covered the largest height range, used the most comparison profiles and data pairs, and covered a more complete range of horizontal wind elements, including speed, direction, and the meridional and zonal components of wind." Exciting results have been achieved with Beijing MST Radar's detection of the mesosphere-lower thermosphere. Lü and TIAN explain that "within the range of 60-80 km, the MST radar can obtain data during daytime, and with a maximum data acquisition rate of 80% within the range of 70-80 km. Meanwhile, within the range of 80-100 km, data were available both day and night. In June and July during daytime, Beijing MST Radar can detect at heights up to 120 km. Their analysis also revealed that "horizontal winds within 80-100 km measured by Beijing MST Radar and the nearby Langfang Meteor Radar showed good agreement and were also consistent with HWM07 model results". Overall, these results, published in Advances in Atmospheric Sciences, show that Beijing MST Radar operates at an internationally advanced level in terms of its detecting capability and data quality, and will continue to play a significant role in studies of lower-, middle- and upper-atmosphere dynamics.


News Article | March 3, 2017
Site: www.gizmag.com

Simply altering our flight routes could reduce the airline industry's impact on climate change by up to 10 percent An international research team has published a study claiming that airlines could significantly reduce their impact on the climate through implementing minor changes to some flight routes. Although the proposed changes would only increase airline operating costs by around 1 percent, their impact on the climate could be reduced by up to 10 percent. Since high-altitude airliners release emissions near or in the stratosphere, researchers have long concluded that their effects on anthropogenic climate change are more significant than if the same emissions were released on the ground. Generally, emissions weighting factors calculate that aviation CO emissions are around twice as damaging as equivalent land-based emissions. In addition to CO emissions, the aviation industry emits several other greenhouse gases that result in higher climate impacts due to their high-altitude releases. A new study, conducted by a team with members from the University of Reading's Meteorology Department, the DLR Institute of Atmospheric Physics in Germany, Eurocontrol in Brussels, and the Center for International Climate and Environmental Research (CICERO) in Oslo, shows that by dynamically examining flight routes and identifying where emissions are having the greatest effect, the overall impact of aviation on climate change could be reduced by up to 10 percent. "Aviation is different from many other sectors, since its climate impact is largely caused by non-CO2 effects, such as contrails and ozone formation," lead author in the study, Volker Grewe explains. "These non-CO2 effects vary regionally, and, by taking advantage of that, a reduction of aviation's climate impact is feasible. Our study looked at how feasible such a routing strategy is. We took into account a representative set of weather situations for winter and summer, as well as safety issues, and optimized all trans-Atlantic air traffic on those days." The team used emission calculations and air traffic simulations spanning 400 flights across 85 routes over the North Atlantic to show that across all-weather conditions, flight paths could be optimized to result in reduced impact of emissions, while altered flight paths would only result in additional operating costs of 1 percent to the airlines. There are undeniably several uncertainties that would need to be overcome before any pragmatic implementation of climate-optimal routing could be enacted. The research team, fully aware of the hurdles admitted, "The concept of climate-optimal routing is not mature enough to be directly implemented in the real world." They noted issues surrounding air traffic management, costs for airlines, and the need for greater scientific certainty in their estimations, as major hurdles to overcome in the coming years. Professor Grewe explained that before any movement towards realistically implementing these ideas, "the calculation of the climate-change functions must be robust, and fast enough to become operational, and we must have high confidence in the forecast weather conditions." If these issues can be resolved, the research points to a relatively simple and low-cost way to reduce the climate impact of an industry that is only getting bigger from year to year.


News Article | March 3, 2017
Site: www.eurekalert.org

The increasing rate of the global mean surface temperature was reduced from 1998 to 2013, known as the global warming hiatus or pause. Great efforts have been devoted to the understanding of the cause. The proposed mechanisms include the internal variability of the coupled ocean-atmosphere system, the ocean heat uptake and redistribution, among many others. However, the atmospheric footprint of the recent warming hiatus has been less concerned. Both the dynamical and physical processes remain unclear. In a recent paper published in Scientific Report, LIU Bo and ZHOU Tianjun from the Institute of Atmospheric Physics, Chinese Academy of Sciences have investigated the atmospheric anomalous features during the global warming hiatus period (1998-2013). They show evidences that the global mean tropospheric temperature also experienced a hiatus or pause. To understand the physical processes that dominate the warming hiatus, they decomposed the total temperature trends into components due to processes related to surface albedo, water vapor, cloud, surface turbulent fluxes and atmospheric dynamics. The results demonstrated that the hiatus of near surface temperature warming trend is dominated by the decreasing surface latent heat flux compared with the preceding warming period, while the hiatus of upper tropospheric temperature is dominated by the cloud-related processes. Further analysis indicated that atmospheric dynamics are coupled with surface turbulent heat fluxes over lower troposphere and coupled with cloud processes over upper troposphere. As to why the surface latent heat flux, atmospheric dynamics and cloud-related processes showed such large differences between 1983-1998 and 1998-2013, LIU, first author of the paper, explained, "They are dominated by the Hadley Circulation and Walker Circulation changes associated with the phase transition of Interdecadal Pacific Oscillation (IPO)." According to LIU, the IPO is a robust, recurring pattern of sea surface temperature anomalies at decadal time scale. During a positive phase of IPO, the west Pacific and the mid-latitude North Pacific becomes cooler and the tropical eastern ocean warms, while during a negative phase, the opposite pattern occurs. The IPO has shifted from the positive phase to negative phase since 1998/1999, and this transition has led to the weakening of both Hadley Circulation and Walker Circulation, which served as a hub linking the three processes mentioned above. "Though the heat capacity of the atmosphere is nearly negligible compared with the ocean", said ZHOU, corresponding author of the paper, "understanding the atmospheric footprint is essential to gain a full picture of how internal climate variability such as IPO affects the global climate from the surface to the troposphere. The new findings also provide useful observational metrics for gauging climate model experiments that are designed to understand the mechanism of global warming hiatus".

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