1.  学术系列报告：7.25-7.26 | | 报告人：Wen-Chau Lee
单位：Earth Observing Laboratory, National Center for Atmospheric Research
时间：7月25日（周一） 9:00-9:50
地点：教学行政楼1512/1514
题目：Chasing Tornadoes in VORTEX II (2009-2010)
摘要：
The largest coordinated tornado chasing experiment, VORTEX II, was conducted from April to June in 2009 and 2010. VORTEX II was a completely mobile experiment without a permanent home base. The entire team of 10 mobile Doppler radars, mesonet vehicles, mobile sounding, disdrometers, photogrammetry, and other in situ instruments was controlled by a mobile field control center. Wireless internet capability permitted the execution of this ambitious endeavor. There were over 100 scientists and 40 vehicles involved in VORTEX II.
VORTEX II was set out to answer the following scientific questions:
- How, when, and why do tornadoes form? Why some are violent and long lasting while others are weak and short lived?
- What is the structure of tornadoes? How strong are the winds near the ground? How exactly do they do damage?
- How can we learn to forecast tornadoes better?
This talk will give an overview and preliminary scientific findings in VORTEX II.
报告人：谢元富
单位：NOAA
时间：7月25日（周一） 10:00-10:50
地点：教学行政楼1512/1514
题目：全球高分辨预报模式的现状和未来发展方向
摘要：
​随着全球变暖，灾害性天气加强，发展高分辨率高精度的一体化的短期，中期和气候全球预报模式变得越来越重要了。各个国家除了大力发展观测系统（例如卫星遥感观测）以外，都投入了大量研发经费自己的全球模式，比如，欧洲中心，英国，美国，日本和韩国等， 以对应国家的经济发展和生活保障。未来高分辨高精度的全球预报模式着眼于3公里一下的非静力平衡的网格模式，目前朝这个方向发展的模式有，美国NOAA的FV3，NCAR的MPAS，日本的NICAM，英国工合模式等等。我们在这里介绍一下这些模式的发展状况，讨论新一代模式发展的未来。
报告人：Yuewei Liu
单位：Research Applications Laboratory, National Center for Atmospheric Research
时间：7月25日（周一） 11:00-11:50
地点：教学行政楼1512/1514
题目：WRF-VLES/LES and the Simulation of Summer Monsoon Convection Initiation at the U.S. Army White Sand Missile Range
摘要：
RTFDDA-VLES (real-time four-dimensional data assimilation and very large eddy simulation) model based on the National Center for Atmospheric Research (NCAR) WRF (Weather Research and Forecasting) Model is employed to study a summer monsoon convection case and a late spring severe wind case at the White Sands Missile Range (WSMR), New Mexico (NM). Both convection and high winds affect the missile test planning and execution at WSMR. Because the terrain is complex and the synoptic-scale forcing is relatively weak, so both cases are forced and modulated by the orography, especially by the surrounding San Andres Mountains and Sacramento Mountains. It is of great interest to study the capability of numerical weather prediction models for simulating such weather at high resolutions so that the fine scale terrain can be reasonably represented. WRF-based RTFDDA-VLES model is configured with five nested-grid domains at grid intervals of 8.1, 2.7, 0.9, 0.3, and 0.1 km, respectively. For these two cases, four dimensional (4D) data assimilation is activated on three coarse meshes. Preliminary modeling results show that smaller grid intervals increase the model’s ability of simulating fine-scale structure and intensity of moist convection and high wind. Spurious noise and phase shift of the simulated phenomena occurred on all domains. Sensitivity experiments reveal the impact of different sub-grid filters (diffusion schemes), terrain smoothing, and surface momentum fluxes and heat fluxes on the simulated convection.
报告人：Hao He
单位： Department of Atmospheric and Oceanic Science University of Maryland
时间：7月26日（周二） 9:00-9:50
地点：教学行政楼1512/1514
题目： Air Pollutant Concentrations and Trends over the Eastern U.S.: Impacts from regional and local emissions controls
摘要：
We examined long-term emissions and observations of air pollutants to characterize trends in air pollution over the Eastern U.S. From 1997 to 2012, regional control measures reduced NOx and SO2 emissions from power plants significantly, up to ~80% and~90%, respectively. The ground-level ozone shows a 0.6 ppbv/year decrease; aircraft measurements indicate that the daily net production of summertime tropospheric ozone decreased from ~20 ppbv/day in the late 1990s to ~7 ppbv/day in the early 2010s. Back trajectory cluster analysis demonstrates that emissions of air pollutants from upwind sources substantially influence the downwind ozone pollution. We also found at least 1/3 of the climate penalty factor (CPF) observed in the eastern U.S. can be attributed to the temperature dependence of NOx emissions.
After the implementation of a local regulation on sulfur emissions, aircraft measurements indicated a ~40% decrease of tropospheric column SO2 and a ~20% decrease of AOD over Maryland, with similar trends observed from ground-level observations of SO2 and PM2.5 concentrations. OMI SO2 and MODIS AOD observations indicate decreasing trends in column SO2 (~60% decrease) and AOD (~20% decrease) over the eastern U.S. The decrease of upwind SO2 emissions also reduced aerosol loadings over the downwind Atlantic Ocean near the coast by ~20%, while indiscernible changes of SO2 column were observed.
The trends in air pollutants reveal the success of regulations implemented over the past decades and the importance of region-wide emission controls in the eastern United States. A step change of SO2 emissions in Maryland starting in 2009-2010 had an immediate and profound benefit in terms of local surface SO2 concentrations, but a modest impact on aerosol pollution, indicating that short-lived pollutants are effectively controlled locally while long-lived pollutants require regional measures.
报告人：Hanli Liu
单位: High Altitude Observatory, National Center for Atmospheric Research
时间：7月26日（周二） 10:00-10:50
地点：教学行政楼1512/1514
题目：Space environment variability and predictability pertaining to lower atmosphere forcing
摘要：
The Earth's thermosphere and ionosphere (TI) are characterized by perpetual variability as integral parts of the atmosphere system, with intermittent disturbances from solar and geomagnetic forcing. This talk examines how the TI variability is affected by processes originating from the lower atmosphere, and implications for quantifying and forecasting the TI. This aspect of the TI variability has been increasingly appreciated in recent years from both observational and numerical studies, especially during the last extended solar minimum. This talk focuses on the role of atmospheric waves, including tides, planetary waves, and gravity waves, which become increasingly significant as they propagate from their source region to the upper atmosphere. Recent studies have led to better understanding of how these waves directly or indirectly affect TI wind, temperature and compositional structures, the circulation pattern, neutral and ion species transport, and electric wind dynamo. The variability of these waves on daily to inter-annual scales has been found to significantly impact the TI variability. Several outstanding questions and challenges have been highlighted: (i) Large, seemingly stochastic, day-to-day variability of tides in the TI; (ii) Control of model error in the TI region by the lower atmosphere; (iii) The increasing importance of processes with shorter spatial and temporal scales at higher altitudes. Addressing these challenges requires model capabilities to assimilate observations of both lower and upper atmosphere, and higher model resolution to capture complex interactions among processes over a broad range of scales and altitude range.
报告人: Qian Wu
单位: High Altitude Observatory, National Center for Atmospheric Research
时间：7月26日（周二） 11:00-11:50
地点：教学行政楼1512/1514
题目： Thermospheric Wind Observations From High to Low Latitudes.
摘要：
Thermospheric wind is a key parameter for understanding the ionosphere from high to low latitudes. NCAR has a long history of performing thermospheric wind observations from high to mid latitudes. With support from the National Science Foundation and other funding agencies, NCAR is enhancing the observational capability in the polar regions and expanding into the equatorial region. The high latitude Fabry-Perot interferometers (FPI) at Resolute Canada (75N, 95W, MLAT 83) has been upgraded and augmented by another FPI at Eureka (80N, 86W, MLAT 88). In the mid latitudes, NCAR operates an FPI at Boulder (40N, 105W,MLAT 48) and at Palmer station Antarctica (64S, 64W, MLAT 54). Soon NCAR will have two FPIs deployed in Africa, Abuja (9.1N, 7.4E, MLAT 11) and Ivory Coast (9.4N, 5.6W, MLAT 13). These instruments will provide invaluable information for model development and space weather research related to the ionosphere. The high latitude observations help to validate a new ion convection model based on the SuperDARN observations for the NCAR TIEGCM. In the lower latitude, TIEGCM model simulation will be validated by new observations in Africa.
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