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31.
Yoo-Geun Ham Siegfried Schubert Yury Vikhliaev Max J. Suarez 《Climate Dynamics》2014,43(9-10):2415-2430
The seasonal forecast skill of the NASA Global Modeling and Assimilation Office atmosphere–ocean coupled global climate model (AOGCM) is evaluated based on an ensemble of 9-month lead forecasts for the period 1993 to 2010. The results from the current version (V2) of the AOGCM consisting of the GEOS-5 AGCM coupled to the MOM4 ocean model are compared with those from an earlier version (V1) in which the AGCM (the NSIPP model) was coupled to the Poseidon Ocean Model. It was found that the correlation skill of the Sea Surface Temperature (SST) forecasts is generally better in V2, especially over the sub-tropical and tropical central and eastern Pacific, Atlantic, and Indian Ocean. Furthermore, the improvement in skill in V2 mainly comes from better forecasts of the developing phase of ENSO from boreal spring to summer. The skill of ENSO forecasts initiated during the boreal winter season, however, shows no improvement in terms of correlation skill, and is in fact slightly worse in terms of root mean square error (RMSE). The degradation of skill is found to be due to an excessive ENSO amplitude. For V1, the ENSO amplitude is too strong in forecasts starting in boreal spring and summer, which causes large RMSE in the forecast. For V2, the ENSO amplitude is slightly stronger than that in observations and V1 for forecasts starting in boreal winter season. An analysis of the terms in the SST tendency equation, shows that this is mainly due to an excessive zonal advective feedback. In addition, V2 forecasts that are initiated during boreal winter season, exhibit a slower phase transition of El Nino, which is consistent with larger amplitude of ENSO after the ENSO peak season. It is found that this is due to weak discharge of equatorial Warm Water Volume (WWV). In both observations and V1, the discharge of equatorial WWV leads the equatorial geostrophic easterly current so as to damp the El Nino starting in January. This process is delayed by about 2 months in V2 due to the slower phase transition of the equatorial zonal current from westerly to easterly. 相似文献
32.
This study investigates the effects of air–sea interaction upon simulated tropical climatology, focusing on the boreal summer mean precipitation and the embedded intra-seasonal oscillation (ISO) signal. Both the daily coupling of ocean–atmosphere and the diurnal variation of sea surface temperature (SST) at every time step by accounting for the ocean mixed layer and surface-energy budget at the ocean surface are considered. The ocean–atmosphere coupled model component of the global/regional integrated model system has been utilized. Results from the coupled model show better precipitation climatology than those from the atmosphere-only model, through the inclusion of SST–cloudiness–precipitation feedback in the coupled system. Cooling the ocean surface in the coupled model is mainly responsible for the improved precipitation climatology, whereas neither the coupling itself nor the diurnal variation in the SST influences the simulated climatology. However, the inclusion of the diurnal cycle in the SST shows a distinct improvement of the simulated ISO signal, by either decreasing or increasing the magnitude of spectral powers, as compared to the simulation results that exclude the diurnal variation of the SST in coupled models. 相似文献
33.
Socioeconomic segregation in European capital cities. Increasing separation between poor and rich 总被引：1，自引：1，他引：0
Socioeconomic inequality is on the rise in major European cities, as are concerns over it, since it is seen as a threat to social cohesion and stability. Surprisingly, relatively little is known about the spatial dimensions of rising socioeconomic inequality. This paper builds on a study of socioeconomic segregation in 12 European cities: Amsterdam, Athens, Budapest, London, Madrid, Oslo, Prague, Riga, Stockholm, Tallinn, Vienna, and Vilnius. Data used derive from national censuses and registers for 2001 and 2011. The main conclusion is that socioeconomic segregation has increased. This paper develops a rigorous multifactor approach to understand segregation and links it to four underlying, partially overlapping, structural factors: social inequalities, globalization and economic restructuring, welfare regimes, and housing systems. Taking into account contextual factors resulted in a better understanding of actual segregation levels, while introducing time lags between structural factors and segregation outcomes will likely further improve the theoretical model. 相似文献
34.
This study examines the role of the marginal sea surface temperature (SST) on heat waves over Korea. It is found that sea surface warming in the south sea of Korea/Japan (122-138°E, 24- 33°N) causes heat waves after about a week. Due to the frictional force, the positive geopotential height anomalies associated with the south sea warming induce divergent flows over the boundary layer. This divergent flow induces the southerly in Korea, which leads to a positive temperature advection. On the other hand, over the freeatmosphere, the geostrophic wind around high-pressure anomalies flows in a westerly direction over Korea during the south sea warming, which is not effective in temperature advection. Therefore, the positive temperature advection in Korea due to the south sea warming decreases with height. This reduces the vertical potential temperature gradient, which indicates a negative potential vorticity (PV) tendency over Korea. Therefore, the high-pressure anomaly over the south sea of Korea is propagated northward, which results in heat waves due to more incoming solar radiation. 相似文献
35.
June-Yi Lee MinHo Kwon Kyung-Sook Yun Seung-Ki Min In-Hong Park Yoo-Geun Ham Emilia Kyung Jin Joo-Hong Kim Kyong-Hwan Seo WonMoo Kim So-Young Yim Jin-Ho Yoon 《Asia-Pacific Journal of Atmospheric Sciences》2017,53(2):257-272
Changma, which is a vital part of East Asian summer monsoon (EASM) system, plays a critical role in modulating water and energy cycles in Korea. Better understanding of its long-term variability and change is therefore a matter of scientific and societal importance. It has been indicated that characteristics of Changma have undergone significant interdecadal changes in association with the mid-1970s global-scale climate shift and the mid-1990s EASM shift. This paper reviews and revisits the characteristics on the long-term changes of Changma focusing on the underlying mechanisms for the changes. The four important features are manifested mainly during the last few decades: 1) mean and extreme rainfalls during Changma period from June to September have been increased with the amplification of diurnal cycle of rainfall, 2) the dry spell between the first and second rainy periods has become shorter, 3) the rainfall amount as well as the number of rainy days during August have significantly increased, probably due to the increase in typhoon landfalls, and 4) the relationship between the Changma rainfall and Western Pacific Subtropical High on interannual time scale has been enhanced. The typhoon contribution to the increase in heavy rainfall is attributable to enhanced interaction between typhoons and midlatitude baroclinic environment. It is noted that the change in the relationship between Changma and the tropical sea surface temperature (SST) over the Indian, Pacific, and Atlantic Oceans is a key factor in the long-term changes of Changma and EASM. Possible sources for the recent mid-1990s change include 1) the tropical dipole-like SST pattern between the central Pacific and Indo-Pacific region (the global warming hiatus pattern), 2) the recent intensification of tropical SST gradients among the Indian Ocean, the western Pacific, and the eastern Pacific, and 3) the tropical Atlantic SST warming. 相似文献
36.
The sensitivity of the precipitation responses to greenhouse warming can depend on the present-day climate. In this study, a robust linkage between the present-day precipitation climatology and precipitation change owing to global warming is examined in inter-model space. A model with drier climatology in the present-day simulation tends to simulate an increase in climatological precipitation owing to global warming. Moreover, the horizontal gradient of the present-day precipitation climatology plays an important role in determining the precipitation changes. On the basis of these robust relationships, future precipitation changes are calibrated by removing the impact of the present-day precipitation bias in the climate models. To validate this result, the perfect model approach is adapted, which treats a particular model’s precipitation change as an observed change. The results suggest that the precipitation change pattern can be generally improved by applying the present statistical approach. 相似文献
37.
Effect of upstream ponds on stream temperature 总被引：2，自引：0，他引：2
Many tributaries feeding streams are connected to ponds that heat up during summer months; however, the influence of these ponds on receiving stream temperature was not known. Stream temperature affects microfauna and fish habitats in aquatic ecosystems. Three tributaries with headwater ponds exposed to sunlight and one tributary unassociated with a large, upstream pond were selected for study within the Pennypack Creek watershed in the Philadelphia Metropolitan Area. Temperature loggers were installed in the pond (when applicable), associated tributary, and in the Pennypack Creek up and downstream of its confluence with the tributary. Although diurnal temperature fluctuations were apparent, the study showed no significant differences in temperature up and downstream of tributary discharge to Pennypack Creek. Pond water temperatures were up to 4°C warmer than the Pennypack Creek; however, temperatures downstream and upstream of the tributaries leading out of the ponds were within 1°C of each other. 相似文献
38.
This paper presents the numerical simulation of a creeping slope in Upper Austria, using a visco-hypoplastic material law
which describes the mechanical behavior of cohesive soils allowing for viscous effects, i.e. creep and relaxation. The method
consists of: (1) determination of the parameters of the material law, based on laboratory tests on soil samples taken from
the slope; (2) simulation of the laboratory tests with an element test program in which the used material law was implemented,
in order to test whether the model holds for the soils studied; and (3) simulation of slope movements at different sections
along the slope, assuming an infinite slope. The simulation results fit well with the field measurements. This demonstrates
that despite strongly simplified boundary conditions and limited availability of subsurface data (e.g. density) the visco-hypoplastic
law is a promising tool for predicting creep movements. 相似文献
39.
This study investigates the relation between channel changes, as mapped from aerial photography, and bed‐material transport along Chilliwack River, British Columbia. Detailed mapping of channel features was completed for five dates between 1952 and 1991 using an analytical stereoplotter. Data were transferred to a geographic information system (GIS) to analyse changes during four consecutive periods. Erosion and deposition volumes along channel reaches were estimated by multiplying measured areal changes by the bed‐material depth along each reach. Bed‐material transport rates are related to morphologic changes using a sediment budget approach. The highest rate of transport for the four study periods is estimated as 55 000 ± 10 000 m3 a−1 between 1983 and 1991. These rates are compared with estimates from short‐term (1–2 year) changes along the lower reach to investigate variations in sediment flux that may otherwise remain undetected. Significant morphologic change occurs roughly once every 5 years when flows are large enough to erode and entrain large volumes of bed material stored within the contemporary floodplain. In the absence of large floods, transport rates decline and vegetation begins to establish new floodplain. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
40.
The characteristics of the El-Nino Southern Oscillation (ENSO) simulated in free integrations using two versions of the Seoul National University (SNU) ocean–atmosphere coupled global climate model (CGCM) are examined. A revised version of the SNU CGCM is developed by incorporating a reduced air–sea coupling interval (from 1?day to 2?h), a parameterization for cumulus momentum transport, a minimum entrainment rate threshold for convective plumes, and a shortened auto-conversion time scale of cloud water to raindrops. With the revised physical processes, lower tropospheric zonal wind anomalies associated with the ENSO-related sea surface temperature anomalies (SSTA) are represented with more realism than those in the original version. From too weak, the standard deviation of SST over the eastern Pacific becomes too strong in the revised version due to the enhanced air–sea coupling strength and intraseasonal variability associated with ENSO. From the oceanic side, the stronger stratification and the shallower-than-observed thermocline over the eastern Pacific also contribute to the excessive ENSO. The impacts of the revised physical processes on the seasonal predictability are investigated in two sets of the hindcast experiment performed using the two versions of CGCMs. The prediction skill measured by anomaly correlation coefficients of monthly-mean SSTA shows that the new version has a higher skill over the tropical Pacific regions compared to the old version. The better atmospheric responses to the ENSO-related SSTA in the revised version lead to the basin-wide SSTA maintained and developed in a manner that is closer to observations. The symptom of an excessively strong ENSO of the new version in the free integration is not prominent in the hindcast experiment because the thermocline depth over the eastern Pacific is maintained as initialized over the arc of time of the hindcast (7?months). 相似文献