AGS-PRF: The Diurnal Cycle, Cloud-Radiative Feedbacks, and Large-scale Tropical Dynamics

该奖项支持一个为期两年的博士后研究奖学金，其中PI将研究日周期对麦登-朱利安振荡（MJO）的影响。MJO是一大片对流和降雨区域，形成于印度洋上空，并缓慢向东传播至赤道太平洋中部。MJO影响着全球的天气和气候，影响着墨西哥湾飓风的形成、导致美国西海岸洪水和山体滑坡的大气河流、厄尔尼诺现象的发生以及其他影响。尽管它的重要性和几十年来的共同努力，MJO尚未得到充分的解释，天气和气候模式难以模拟和预测它。该奖项下的研究涉及日循环的两个方面，第一个方面是海表温度日循环对润湿上覆大气的影响。当MJO处于“抑制”阶段，即天气晴朗，没有有组织的对流和降雨时，海温具有相对明显的日循环。海温的日循环预计将导致更大的地表蒸发和整个低层大气中更强烈的水汽垂直混合，整体变湿有助于促进MJO“活跃”期的开始。一套计算机模拟被用来确定海温的日循环对于湿润大气和促进MJO的发生的重要性。进一步的研究考虑了在MJO的抑制和活跃阶段之间发生的云的日循环的变化。抑制相的小云和不发达云优先出现在下午，而活跃相的深层对流云在夜间最为突出。PI假设，最大云量时间的这种变化对太阳对大气的加热有影响，构成正反馈，在活动阶段增强对流，在抑制阶段抑制对流。将进行进一步的计算机模拟来验证这一假设。最后，PI将使用全球高分辨率非流体静力模型（ICON模型）对DYNAMO现场活动期间观测到的MJO事件进行模拟（见AGS-1022899）。模拟结果将用于进一步验证日循环对MJO的假设影响。如上所述，由于MJO对全球天气和气候的影响以及本研究改进MJO预报的潜力，这项工作具有更广泛的社会影响。此外，这项工作支持PI在其职业生涯的早期阶段，从而促进未来的劳动力在研究领域。此外，这项工作是在德国汉堡的马克斯普朗克气象研究所（MPI-M）进行的，由Cathy Hohenegger博士监督。主办机构是世界顶级气候模拟中心之一，美国PI和MPI-M科学家之间的科学合作有望对美国研究界有益。该奖项由国际科学与工程办公室以及气候与大规模动力学项目提供资金支持。

This award supports a 2-year Postdoctoral Research Fellowship in which the PI will study the influence of the diurnal cycle on the Madden-Julian Oscillation (MJO). The MJO is a large region of convection and rainfall that forms over the Indian Ocean and propagates slowly eastward into the central equatorial Pacific. The MJO influences weather and climate worldwide, affecting the formation of hurricanes in the Gulf of Mexico, atmospheric rivers that produce floods and landslides on the US west coast, and the onset of El Nino events, among other impacts. Despite its importance and concerted efforts over several decades, the MJO has not yet been adequately explained, and weather and climate models have difficulty simulating and predicting it.Research under this award addresses two aspects of the diurnal cycle, the first of which is the influence of the diurnal cycle of sea surface temperature (SST) in moistening the overlying atmosphere. When the MJO is in its "suppressed" phase, in which fair weather prevails in the absence of organized convection and rainfall, SST has a relatively pronounced diurnal cycle. The diurnal cycle of SST is expected to result in greater surface evaporation and more vigorous vertical mixing of moisture throughout the lower atmosphere, with the overall moistening serving to promote the onset of the "active" phase of the MJO. A suite of computer simulations is used to determine the importance of the diurnal cycle of SSTs for moistening the atmosphere and promoting MJO onset.Further research considers the change in the diurnal cycle of cloudiness that occurs between the suppressed and active phases of the MJO. The smaller and less developed clouds of the suppressed phase occur preferentially in the afternoon, while the deep convective clouds of the active phase are most prominent at night. The PI hypothesizes that this shift in the time of maximum cloudiness has implications for the solar heating of the atmosphere that constitute a positive feedback, enhancing convection during the active phase and inhibiting it in the suppressed phase. Further computer simulations will be performed to test this hypothesis.Finally, the PI will perform a simulation of an MJO event observed during the DYNAMO field campaign (see AGS-1022899) using a global high-resolution nonhydrostatic model (the ICON model). The results of the simulation will be used to further test the hypothesized effects of the diurnal cycle on the MJO. As noted above, the work has societal broader impacts due to the worldwide weather and climate impacts of the MJO and the potential of this research to improve MJO forecasts. In addition, the work supports the PI at an early stage of his career, thereby promoting the future workforce in the research area. Also, the work is conducted at the Max Planck Institute of Meteorology (MPI-M) in Hamburg, Germany, under the supervision of Dr. Cathy Hohenegger. The host institution is among the world's top climate modeling centers, and scientific collaboration between a US PI and MPI-M scientists is expected to be beneficial to the US research community.This award was supported with funding from the Office of International Science & Engineering as well as the Climate and Large-scale Dynamics Program.