冬季南海北部中尺度涡旋的数值研究

南海环流的一个主要特征是上层海洋环流具有多涡结构,海洋中尺度涡旋的演变(时间上的生消和空间上的迁移)是南海环流季节调整的可能方式。文中依据卫星遥感海面高度资料和实际海洋观测所揭示的南海北部存在中尺度涡旋体系的基本事实,采用一个改进了涡分辨(eddy-resolving)普林斯顿海洋模式(POM),对冬季处于强盛的东北季风强迫以及黑潮在巴士海峡入侵的共同作用下的南海北部环流的中尺度涡旋体系进行了数值研究,初步再现了冬季南海北部中尺度涡的生命史。计算结果表明,在实际的气候冬季风应力驱动下,具有的实际侧边界地形的南海北部呈现有强烈的中尺度涡旋。文中探讨了中尺度涡的垂直结构、温盐场的配置以及大尺度水平辐合辐散、海洋垂直运动与之相关的时空结构。由此可以得知,在冬季南海北部中尺度涡旋生命史的不同阶段,上述动力学因子的重要性是相对的。不同的敏感性试验表明,斜压调整是形成冬季南海中尺度涡旋体系的决定性因子;边界的入流和风应力驱动是影响中尺度涡旋运动的主要因素。     

多普勒雷达径向速度同化在淮河暴雨数值模拟中的应用

针对2007年7月淮河流域的一次强降雨过程,利用WRF中尺度数值模式及其三维变分同化系统(WRF-3DVAR),开展了多普勒雷达径向速度的三维变分同化对暴雨过程模拟效果的影响研究。结果表明:WRF-3DVAR能够有效地同化多普勒雷达径向速度资料,同化后使得模式初始场出现了一定的调整,包含更详尽的中尺度特征信息,进而显著改善模式对大暴雨过程前12h降水的模拟效果。在高分辨率中尺度数值模式中有效地利用多普勒天气雷达资料,能较好地提高中尺度降雨预报。     

不同辐射传输方案对中尺度降水影响的对比分析

在MM5非静力稳定中尺度气象模式中引进了建立在δ-4流近似和相关-k分布基础上的对云水、雨水、冰晶和霰的辐射特性进行详细描述的辐射传输方案。新建立的辐射传输方案和MM5中原有的辐射传输方案在华南暴雨中的模拟结果相互比较,并与天气实况的对比表明：辐射在中尺度暴雨中起着重要的作用;辐射传输方案对云辐射特性描述的准确程度对于地面降水影响是明显的;不同的辐射传输方案对地面降水的影响存在较大的差异,并且这些差异在白天比在夜间明显;辐射传输过程对地面降水影响的差异主要表现在降水中心上,而对降水的地理分布改变很小;相对而言,不同的辐射传输方案之间对短波描述的差异对地面降水的影响明显,而对长波描述差异的影响不大;新辐射传输方案能够在一定程度上改进MM5对中尺度降水的模拟能力。     

一次罕见冰雹天气的多普勒雷达回波分析

运用多普勒雷达的基本反射率(R)、风暴相对径向速度(SRM)、垂直积分液态含水量(VIL)等产品,分析了2004年6月20日华北南部罕见的冰雹大风天气过程。结果表明:这次冰雹大风天气过程主要是由超级单体回波中的中尺度气旋引起的;该过程持续时间比较长的原因是“指状”回波和超级单体回波的依次发生、发展。     

豫北一次区域性大暴雨的数值模拟分析

利用NECP 1°×1°6 h再分析资料和WRF中尺度数值模式对2006年7月2-3日豫北区域性大暴雨过程进行数值模拟,并用模拟结果对该过程作中尺度分析.结果表明:暴雨中尺度系统发展和维持期间,基本上是强涡度区对应强辐合区,使得垂直对流运动发生发展,为强降水发生和持续提供了动力条件;θse值大小和实况降水强弱演变对应关系很好,θse值越大,实况降水越强,反之,实况降水越弱;豫北地区出现强降水时,水汽通量中心位于豫南且分布在西南急流轴上,豫中南部始终维持一条明显的水汽输送带,水汽被源源不断地输送到豫北地区;豫北地区处于明显的水汽辐合区,强辐合区有一自西向东的移动过程,与实况强降水过程演变趋势一致;大暴雨区域上空从低层到对流层顶层垂直螺旋度均为正值,且强降水时段与螺旋度最强时段对应关系很好,降水峰值与正螺旋度中心出现时间吻合.     

伊犁一次区域性暴雨分析

利用伊宁新一代天气雷达资料,结合高空和地面观测资料,分析了2010年7月19日伊犁地区一次局地暴雨天气过程。结果表明：此次强对流天气过程的主要影响系统为500 hPa中亚低槽、200hpa高空急流、低层风速辐合和地面雷暴高压。较强的层结不稳定和低层垂直风切变有利于对流的产生;云图和雷达资料分析表明,此次局地暴雨是由中尺度强对流云团产生,具有典型的对流单体形成、发展成回波短带合并形成带状回波,该带状回波最后演变成一个尺度较大的弓形回波。     

Primary production and implications for metabolic balance in Hawaiian lee eddies

Recent discrepancies between geochemical and biological approaches for determining whether ocean ecosystems are net heterotrophic or net autotrophic have led to uncertainty in the net metabolic state of open ocean ecosystems. Geochemical approaches indicate that the oceans are net positive autotrophic, but direct observations based on short-term incubation techniques suggest that the ocean is in a state of net heterotrophy. One hypothesis for the apparent discrepancy is that net autotrophic production occurs in aperiodic “bursts,” which are superimposed on a more constant background state of net heterotrophy. Mixing events, which introduce new nutrients to the surface ocean, provide one mechanism for fueling such aperiodic bursts of net production. In conjunction with the Eddy Flux (E-Flux) program in the lee of the Hawaiian Islands during winter 2004–2005, we examined the relationship between photosynthesis and irradiance (P vs. E) in surface waters inside and outside of two cold-core, cyclonic eddies, and conducted five incubation experiments to examine the metabolic response of mixed-layer plankton communities to nutrient-rich deep-sea water additions. Our results showed that in the mixed layer, maximum rates of light-saturated photosynthesis, derived from photosynthesis–irradiance experiments were not significantly different inside vs. outside the eddies (p=0.35 and 0.44 for E-Flux I and E-Flux III, respectively). Addition of nutrients to mixed-layer water showed that (1) gross primary production (GPP) became decoupled from a more constant rate of respiration and (2) net system metabolism shifted from approximate balance, or slight net heterotrophy, to a demonstrably net autotrophic system. From these results, we determined that the threshold GPP for net autotrophic production for the mixed layer of the study region was 1.65 mmol O₂ m⁻³ d⁻¹, which is consistent with previous estimates for the oligotrophic open ocean.     

Eddies and Tropical Instability Waves in the eastern tropical Pacific: A review

Mesoscale eddies and tropical instability waves in the eastern tropical Pacific, first revealed by satellite infrared imagery, play an important role in the dynamics and biology of the region, and in the transfer of mass, energy, heat, and biological constituents from the shelf to the deep ocean and across the equatorial currents.From boreal late autumn to early spring, four to 18 cyclonic or anticyclonic eddies are formed off the coastal region between southern Mexico and Panama. The anticyclonic gyres, which tend to be larger and last longer than the cyclonic ones, are the best studied: they typically are 180–500 km in diameter, depress the pycnocline from 60 to 145 m at the eddy center, have swirl speeds in excess of 1 m s⁻¹, migrate west at velocities ranging from 11 to 19 cm s⁻¹ (with a slight southward component), and maintain a height signature of up to 30 cm. The primary generating agents for these eddies are the strong, intermittent wind jets that blow across the isthmus of Tehuantepec in Mexico, the lake district in Nicaragua and Costa Rica, and the Panama canal. Other proposed eddy-generating mechanisms are the conservation of vorticity as the North Equatorial Counter Current (NECC) turns north on reaching America, and the instability of coastally trapped waves/currents.Tropical Instability Waves (TIWs) are perturbations in the SST fronts on either side of the equatorial cold tongue. They produce SST variations on the order of 1–2 °C, have periods of 20–40 days, wavelengths of 1000–2000 km, phase speeds of around 0.5 m s⁻¹ and propagate westward both north and south of the Equator. The Tropical Instability Vortices (TIVs) are a train of westward-propagating anticyclonic eddies associated with the TIWs. They exhibit eddy currents exceeding 1.3 m s⁻¹, a westward phase propagation speed between 30 and 40 km d⁻¹, a signature above the pycnocline, and eastward energy propagation. Like the TIWs, they result from the latitudinal barotropically unstable shear between the South Equatorial Current (SEC) and the NECC with a potential secondary source of energy from baroclinic instability of the vertical shear with the Equatorial Undercurrent (EUC).This review of mesoscale processes is part of a comprehensive review of the oceanography of the eastern tropical Pacific Ocean.     

冬季黑潮海温场对台湾地区流场及降水影响的数值模拟

本文用ＰＳＵ／ＮＣＡＲ中尺度模式ＭＭ４对冬季黑潮暖流海温场对台湾地区流场和降水的影响进行了数值模拟分析。结果表明：冬季黑潮暖流海温场明显改变台湾地区的局地流场特征;台湾岛上的降水分布特征取决于台湾岛的地形特征,而黑潮暖流海温场的分布对台湾岛上降水量的大小有着决定性的影响。     

平流计算方案对一次江淮梅雨暴雨模拟的影响

为对比MM5模式中原中央差平流方案和新型半拉格朗日插值计算方案CIP的模拟差别,针对2006年7月5~6日的江淮流域梅雨暴雨过程进行了模拟,证实了CIP方案对这次暴雨过程具有较好的模拟效果,它更加真实地再现了梅雨锋降水的中尺度结构,改进了模式的模拟结果,特别是对梅雨锋内对流运动结构的模拟,显示了CIP对刻画大梯度分布和强对流运动计算的良好性能。平流的高精度计算对提高这类系统的模拟精度非常重要。