Cyclone tracks from AMPS NWP system for 2001-2007 using the University of Melbourne tracking scheme

Small (< 1000 km across) cyclones over the Southern Ocean represent an important element in the global circulations of heat and moisture and hence the maintenance of Southern Hemisphere climate. The primary objectives of this project are to advance the understanding of atmospheric processes responsible for the development and decay of small Southern Ocean cyclones and to explore the interactions between these cyclones and the underlying surface conditions, including sea ice extent, thickness, concentration, motion, and temperature. To attain these objectives we use satellite imagery and datasets, archived output and new experiments from a numerical weather prediction model, and many pre-existing in-situ observations.The primary objectives of the research are to:* advance the understanding of atmospheric processes responsible for the development, intensification, and decay of mesoscale cyclones over the Southern Ocean and;* explore the interactions and feedbacks between mesoscale cyclones and surface conditions including ice extent, thickness, concentration and motion, and sea surface temperature.Low pressure system statistics derived from the Antarctic Mesoscale Prediction System (AMPS) and NCEP, NCEP2 and JRA25 re-analysis products are compared by using an automatic cyclone tracking scheme. Since AMPS model spatial and temporal resolutions are much higher than the ones of the re-analyses, this study provides a valuable insight of the ability of numerical models to simulate low pressure systems with an increasing resolution. Results based on AMPS data agree relatively well with re-analyses based results when looking at the seasonal variability and spatial patterns of low pressure system properties over large scales. Results differ systematically close to the Antarctic ice sheet, where the horizontal resolution is important in resolving the continental topography. This appears as lower AMPS system densities and smaller system sizes close to the Antarctic coast. Results differ most during winter when the correct parametrization of surface energy balance is crucial over the sea-ice covered ocean. AMPS data show more systems at around and south of 60◦S in the Antarctic Circumpolar Trough, where re-analyses display systems of larger size. Earlier studies of cyclonic systems over the Southern Ocean show that there is a spectrum of atmospheric systems, where small synoptic systems merge into meso-scale lows. Accordingly a high resolution model setup with appropriate physics parametrization, like AMPS, is required to generate small systems. This study highlights that when new data become available it is important to update low pressure system statistics to gain a better understanding of high latitude processes over intermediate scales.Contributor: Monash University. Faculty of Arts. School of Geography and Environmental Science; University of Melbourne.Related publication: Uotila, P.; Pezza, A. B.; Cassano, J. J.; Keay, K.; Lynch, A. H. (2009), A comparison of low pressure system statistics derived from a high-resolution NWP output and three reanalysis products over the Southern Ocean, Journal of Geophysical Research, Volume 114, Issue D17, CiteID D17105 DOI: 10.1029/2008JD011583Copyright 2008. P. Uotila; A. B. Pezza; J. J. Cassano; K. Keay; A. H. Lynch

南大洋上直径小于1000公里的小型气旋，是全球热量与水汽循环的重要组成部分，对南半球气候的稳定维持具有关键作用。
本项目的核心目标在于深化对南大洋小型气旋生成与消亡相关大气过程的认知，并探究此类气旋与下垫面条件（包括海冰范围、厚度、密集度、运动状态及海表温度）之间的相互作用。为达成上述目标，本研究采用卫星影像与数据集、数值天气预报模式的存档输出与新试验数据，以及大量已有的原位观测资料。
本研究的核心目标具体包括：
* 深化对南大洋中尺度气旋生成、增强及消亡相关大气过程的认知；
* 探究中尺度气旋与下垫面条件（包括海冰范围、厚度、密集度、运动状态及海表温度）之间的相互作用与反馈机制。
本研究采用自动气旋追踪方案，对源自南极中尺度预报系统（Antarctic Mesoscale Prediction System, AMPS）以及NCEP、NCEP2、JRA25再分析产品的低压系统统计特征进行对比分析。
由于AMPS模式的时空分辨率远高于再分析资料，本研究可为探究数值模式在提升分辨率后模拟低压系统的能力提供宝贵视角。在大尺度范围内分析低压系统特征的季节变化与空间分布时，基于AMPS数据的结果与再分析结果吻合度较高。但在南极冰盖附近区域，两类结果存在系统性差异——该区域的水平分辨率对准确模拟大陆地形至关重要，具体表现为南极海岸附近的AMPS模拟气旋密度更低、系统尺度更小。冬季时两类结果的差异最为显著，此时海冰覆盖海域的地表能量平衡参数化方案准确性至关重要。在南极绕极槽区域的60°S附近及以南海域，AMPS数据模拟出的气旋数量更多，而再分析资料显示该区域的气旋尺度更大。
此前针对南大洋气旋系统的研究表明，大气系统存在连续谱系，小型天气尺度系统会合并为中尺度低压系统。因此，要模拟小型气旋系统，需要采用具备合适物理参数化方案的高分辨率模式，如AMPS。本研究强调，当获取新的观测数据时，及时更新低压系统统计特征有助于更深入地理解中尺度高纬度区域的大气过程。
贡献单位：莫纳什大学文学院地理与环境科学学院；墨尔本大学
相关发表文献：Uotila, P.; Pezza, A. B.; Cassano, J. J.; Keay, K.; Lynch, A. H.（2009），《南大洋区域高分辨率数值天气预报输出与三种再分析产品的低压系统统计特征对比》，《地球物理研究杂志》，第114卷，D17期，文献编号D17105，DOI: 10.1029/2008JD011583
版权所有©2008 P. Uotila、A. B. Pezza、J. J. Cassano、K. Keay、A. H. Lynch