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| Hemispheric Energy Balance and Tropical Precipitation Shifts: The Impacts of Forcing Location | |
| 项目编号 | 1665247 |
| Dargan Frierson | |
| 项目主持机构 | University of Washington |
| 开始日期 | 2017-06-01 |
| 结束日期 | 05/31/2022 |
| 英文摘要 | Rainfall in the tropics can be highly variable, and much of the region's large population is vulnerable to water stress. Recent research has identified remote radiative heating and cooling, for example the cooling effect volcanic and anthropogenic aerosols, as a driver of north-south shifts in tropical precipitation associated with the intertropical convergence zones (ITCZs; narrow regions of high preciptation over the oceans near the equator). Such shifts are implicated in the prolonged drought in the Sahel region of North Africa during the latter half of the 20th century, and could be consequential for other regions as well. Research on the role of remote heating and cooling has also produced an explanation for why the Pacific and Atlantic ITCZs are typically north of the equator, and for the southward shift of the Atlantic ITCZ shown in proxy data from the last ice age, when much of the Northern Hemisphere was covered with highly reflective ice and snow. The relationship between ITCZ shifts and remote radiative forcing is explained in terms of inter-hemispheric heat transport: if one hemisphere is cooled relative to the other heat will be transported from the warmer hemisphere toward the colder hemisphere, and atmospheric energy transport across the equator will take place through the upper-tropospheric branch of the Hadley circulation. But the overturning motion of the Hadley cell requires that as energy is transported in one direction at upper levels moisture must be transported the other way near the surface. Thus moisture crosses the equator from the colder hemisphere to the warmer hemisphere, resulting in a shift of ITCZ precipitation toward the warmer hemisphere (in today's climate the Northern Hemisphere is colder on average than the Southern Hemisphere, thus the ITCZ is north of the equator). This project continues the PIs' exploration of the relationship between radiative forcing, inter-hemispheric heat transport, and north-south shifts of ITCZ precipitation. One key issue is that the theory assumes that cross-equatorial heat transport will occur in the atmosphere, and the theory was developed using atmospheric models coupled to "slab" ocean models which do not allow changes in ocean transport. Preliminary evidence suggests that the extent to which the transport occurs in the ocean rather than the atmosphere depends on where the radiative forcing occurs, for example heat transport in response to radiative forcing in the middle and high latitudes of the Southern Hemisphere appears to occur primarily in the ocean, while radiative forcing in the North Atlantic yields more transport in the atmosphere than in the ocean. The PIs perform experiments with the Community Earth System Model (CESM) to understand the dependence of the partitioning of heat transport between the atmosphere and ocean and to determine how this partitioning depends on the region in which the radiative forcing is applied. Other issues pursued here include differences in ITCZ response when the radiative forcing occurs over land rather than ocean surfaces, and differences in the response depending on the magnitude and sign (heating versus cooling) of the radiative forcing. Shifts in tropical precipitation are of great practical as well as scientific interest given the region's large population and vulnerability. Attempts to anticipate future changes in tropical precipitation rely on output from climate models, but such guidance is hampered by large differences in simulated precipitation change from one model to another. A theoretical framework for understanding precipitation change is thus highly desirable. Beyond the societal broader impacts of the research itself, the PIs perform a variety of outreach activities, including educational videos for grades K-12 and at local venues such as the Seattle Science Center. In addition, the project supports and mentors a graduate student and a postdoctoral research associate, thereby providing for the furture workforce in this research area. |
| 资助机构 | US-NSF |
| 项目经费 | $594,498.00 |
| 项目类型 | Continuing Grant |
| 国家 | US |
| 语种 | 英语 |
| 文献类型 | 项目 |
| 条目标识符 | http://gcip.llas.ac.cn/handle/2XKMVOVA/212986 |
| 推荐引用方式 GB/T 7714 | Dargan Frierson.Hemispheric Energy Balance and Tropical Precipitation Shifts: The Impacts of Forcing Location.2017. |
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