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61.
The second Madden–Julian Oscillation (MJO) event during the field campaign of the Dynamics of the MJO/Cooperative Indian Ocean Experiment on Intraseasonal Variability in the Year 2011 (DYNAMO/CINDY2011) exhibi ted an unusual double rainband structure. Using a wavenumber-frequency spectral filtering method, we unveil that this double rainband structure arises primarily from the Kelvin wave component. The zonal phase speed of the double rainbands is about 7.9 degree per day in the equatorial Indian Ocean, being in the range of convectively coupled Kelvin wave phase speeds. The convection and circulation anomalies associated with the Kelvin wave component are characterized by two anomalous convective cells, with low-level westerly (easterly) and high (low) pressure anomalies to the west (east) of the convective centers, and opposite wind and pressure anomalies in the upper troposphere. Such a zonal wind–pressure phase relationship is consistent with the equatorial free-wave dynamics. While the free-atmospheric circulation was dominated by the first baroclinic mode vertical structure, moisture and vertical motion in the boundary layer led the convection.The convection and circulation structures derived based on the conventional MJO filter show a different characteristic. For example, the phase speed is slower (about 5.9 degree per day), and there were no double convective branches. This suggests that MJO generally involves multi-scales and it is incomplete to extract its signals by using the conventional filtering technique. 相似文献
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This study investigates the impact of low-frequency (intraseasonal and interannual) steering flows on straight northward-moving (defined as a meridional displacement two times greater than the zonal displacement) typhoons over the western North Pacific using observational data. The year-to-year change in the northward-moving tracks is affected by the interannual change in the location and intensity of the subtropical high. A strengthened northward steering flow east of 120°E and a weakened easterly steering flow south of the subtropical high favor more frequent straight northward tracks. Examining each of the individual northward-moving typhoons shows that they interact with three types of intraseasonal (10–60-day) background flows during their northward journey. The first type is the monsoon gyre pattern, in which the northward-moving typhoon is embedded in a closed cyclonic monsoon gyre circulation. The second type is the wave train pattern, where a cyclonic (anticyclonic) vorticity circulation is located to the west (east) of the northward-moving typhoon center. The third type is the mid-latitude trough pattern, in which the northward-moving typhoon center is located in the maximum vorticity region of the trough. 相似文献
63.
The three-dimensional structure and evolution characteristics of tropical depression (TD) and mixed Rossby-gravity wave (MRG) type disturbances in the tropical western North Pacific during El Niño and La Niña summers are investigated based on observational and reanalysis data. A clear MRG-to-TD transition was observed during El Niño summers while such a transition is unclear during La Niña summers. The vertical structure of the TD-MRG waves appears equivalent barotropic during El Niño but becomes tilted eastward with height during La Niña. The diagnosis of barotropic energy conversion shows that both the rotational and divergent components of the background flow change associated with E1 Niño-Southern Oscillation (ENSO) are responsible for energy conversion from the mean flow to the TD-MRG perturbations. A further examination of the pure MRG mode shows that its intensity does not vary between El Niño and La Niña while its phase speed does. A faster (slower) westward propagation speed during La Niña (El Niña) is attributed to enhanced (reduced) mean easterlies in the western equatorial Pacific. The heating associated with the MRG wave appears more anti-symmetric during La Niña than during El Niño. In contrast to the MRG waves, the amplitude of the TD waves depends greatly on the ENSO phase. The enhanced (suppressed) TD disturbances during El Niño (La Niña) is attributed to greater (less) barotropic energy conversion associated with the background flow change. The vertical structure of the TD waves appears quasi-barotropic in the geopotential height field but baroclinic in the divergence field. 相似文献
64.
Thirty strong Madden-Julian Oscillation (MJO) events in boreal winter 1982-2001 are selected to investigate the triggering processes of MJO convection over the western equatorial Indian Ocean (IO). These MJO events are classified into three types, according to their dynamic and thermodynamic precursor signals in situ. In Type I, a remarkable increase in low-level moisture occurs, on average, 7 days prior to the convection initiation. This low-level moistening is mainly due to the advection of the background mean moisture by easterly wind anomalies over the equatorial IO. In Type II, lower-tropospheric ascending motion anomalies develop, on average, 4 days prior to the initiation. The cause of this ascending motion anomaly is attributed to the anomalous warm advection, set up by a suppressed MJO phase in the equatorial IO. In Type III, there are no clear dynamic and thermodynamic precursor signals in situ. The convection might be triggered by energy accumulation in the upper layer associated with Rossby wave activity fluxes originated from the midlatitudes. 相似文献
65.
《Marine Policy》2013
Croatia sits on the border of the European Union both politically and geographically. Political change towards a liberal democracy has taken time and many aspects of such a system, such as nature protection, have been slow in evolving. Marine conservation is not a priority in the country despite recognition that the islands, coast and adjacent marine area are of particular importance for foreign revenue. Tourism is the major driver of the local economy of these coastal regions and is heavily concentrated in the summer months of July and August. Coordinated management of natural coastal and marine resources with sustainable exploitation is urgently required in the tourism hotspots of the region. The Cres-Lošinj Special Marine Reserve (CLSMR) was designated in 2006 with the specific aim to conserve a local dolphin population and sustainably manage the use of the natural resources of the Cres-Lošinj archipelago. The archipelago is a nationally important region for tourism. Between July 2006 and July 2009 the CLSMR was the largest marine protected area (MPA) in the Adriatic Sea. The CLSMR represented Croatian commitments to many of the international environmental agreements signed by the government. However local development commitments made by the sitting political party was in direct conflict with the objectives of the MPA. As a result support for the concept was undermined and, coupled with State paralysis, the imbalance between local development and international commitments led to a proposed downgrading of the MPA and subsequent degazettement. 相似文献
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67.
Effect of vertical overturning circulation scale and moist static energy tendency on MJO phase speed 
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下载免费PDF全文 本文通过对1979-2019年ERA-I再分析资料进行诊断分析,研究了MJO垂直环流(VOC)纬向尺度和湿静力能(MSE)趋势纬向不对称性对MJO传播速度的综合影响.研究结果表明,MJO传播速度与VOC的纬向尺度和MSE趋势纬向梯度之间存在显著的正相关关系.基于上述两个参数,本文建立了线性回归模型,该模型可以较好的估计... 相似文献
68.
The distribution, biomass, and assemblages of vertically migrating micronekton/macrozooplankton were studied in relation to oceanographic conditions around Guam and the adjacent Northern Mariana Islands during Spring 2010, using 3-m2 Isaacs-Kidd Midwater Trawl (IKMT). The study area was located within the oligotrophic waters of the westward flowing North Equatorial Current (NEC). However, southern stations of the survey were situated close to the northern boundary of the more productive North Equatorial Countercurrent (NECC), where we observed the highest biomass, abundance, species richness, and diversity of pelagic organisms. Overall, we recorded 85 species from 20 families of mostly mesopelagic species in the area, with lanternfishes (Myctophidae—40 species) and dragonfishes (Stomiidae—18 species) being the most taxonomically diverse groups. Three genera of mesopelagic shrimps, Sergestes, Janicella and Sergia, dominated the decapod crustacean component of the micronekton community numerically and by biomass, while the contribution from cephalopods was relatively minor. Assemblages of major micronekton/macrozooplankton groups, based on biomass and abundance showed principal changes with latitude. However, the classification and ordination analysis, based on taxonomically resolved taxa (fishes and decapod shrimps), indicated additional zonal variation, with areas east and west of the island chain showing different community structure. The mean total micronekton biomass for the area near the productive boundary region between the NEC and NECC was 5.8 mg/m3, with a mean biomass of 1.2 mg/m3 obtained for stations in the oligotrophic NEC area. The corresponding biomass of mesopelagic fishes was 0.88 mg/m3 and 0.24 mg/m3 for these two areas, respectively. We reviewed and compared the available information on the quantitative distribution of midwater fish biomass in the western tropical Pacific and outlined major patterns of variation in the equatorial Pacific in general. 相似文献
69.
《Oceanologica Acta》2002,25(5):243-253
For most of history, the ocean has remained nearly opaque to study, and it has been difficult to understand where salmon or other marine animals go or how they use the ocean. This greatly limits the ability of oceanographers and fisheries biologists to improve the management of many marine resources. The technical and scientific basis now exists to track the ocean movements of individual marine fish for months or years at a time. In this article, we review how new technologies might be applied to salmon in particular. Our conclusion is that animals as small as juvenile Pacific salmon can be followed for months to years at sea, and thus over great distances. By identifying the migration pathways for individual salmon and specific populations of Pacific salmon, we can establish their ocean foraging grounds. We outline the approaches and initial results from the Census of Marine Life program pacific ocean salmon tracking (POST). The research program involves two distinct aspects: (1) the development of an acoustic array for tracking the movements of Pacific salmon during their shelf-resident phase of the life history and (2) the use of archival (data storage) tags to measure aspects of their local environment and to delineate their open ocean migration pathways off the shelf. We report on some of the preliminary findings from the first year of the field project using acoustic tags. 相似文献
70.
This paper documents a study to examine the sensitivity to cloud droplet effective radius and liquid water path and the alleviation the energy imbalance at the top of the atmosphere and at the surface in the latest version of the Grid-point Atmospheric Model of the State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics （LASG）, Institute of Atmospheric Physics （IAP） （GAMIL1.1.0）. Considerable negative biases in all flux components, and thus an energy imbalance, are found in GAMIL1.1.0. In order to alleviate the energy imbalance, two modifications, namely an increase in cloud droplet effective radius and a decrease in cloud liquid water path, have been made to the cloud properties used in GAMIL. With the increased cloud droplet effective radius, the single scattering albedo of clouds is reduced, and thus the reflection of solar radiation into space by clouds is reduced and the net solar radiation flux at the top of the atmosphere is increased. With the reduced cloud optical depth, the net surface shortwave radiation flux is increased, causing a net warming over the land surface. This results in an increase in both sensible and latent heat fluxes over the land regions, which is largely balanced by the increased terrestrial radiation fluxes. Consequently, the energy balance at the top of atmosphere and at the surface is achieved with energy flux components consistent with available satellite observations. 相似文献