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921.
922.
S. Yukimoto M. Endoh Y. Kitamura A. Kitoh T. Motoi A. Noda T. Tokioka 《Climate Dynamics》1996,12(10):667-683
Interannual and interdecadal variabilities in the Pacific are investigated with a coupled atmosphere-ocean GCM developed
at MRI, Japan. The model is run for 70 years with flux adjustments. The model shows interannual variability in the tropical
Pacific which has several typical characteristics shared with the observed ENSO. A basin-scale feature of the principal SST
variation for the ENSO time scale shows negative correlation in the central North Pacific with the tropical SST, similar to
that of the observed one. Associated variation of the model atmosphere indicates an intensification of the Aleutian Low and
a PNA-like teleconnection pattern as a response to the tropical warm SST anomaly. The ENSO time scale variability in the midlatitude
ocean consists of the westward propagation of the subsurface temperature signal and the temperature variation within the shallow
mixed layer forced by the anomalous atmospheric heat fluxes. For the interdecadal time scale, variation of the SST is simulated
realistically with a geographical pattern similar to that for the ENSO time scale, but it has a larger relative amplitude
in the northern Pacific. For the atmosphere, spatial structure of the variation in the interdecadal time scale is also similar
to that in the ENSO time scale, but has smaller amplitude in the northern Pacific. Long oceanic spin-up time (>∼10 y) in the
mid-high latitude, however, makes oceanic response in the interdecadal time scale larger than that in the ENSO time scale.
The lagged-regression analysis for the ocean temperature variation relative to the wind stress variation indicates that interdecadal
variation of the ocean subsurface at the mid-high latitudes is considered as enhanced ocean gyre spin-up process in response
to the atmospheric circulation change at the mid-high latitudes, remotely forced by the interdecadal variation of the tropical
SST.
Received: 6 November 1995 / Accepted: 19 April 1996 相似文献
923.
924.
Hossain Kaizar Yadav Sarita Quaik Shlrene Pant Gaurav Maruthi A. Y. Ismail Norli 《Theoretical and Applied Climatology》2017,129(3-4):1123-1132
Theoretical and Applied Climatology - The rise in the earth’s surface and water temperature is part of the effect of climatic change that has been observed for the last decade. The rates of... 相似文献
925.
The absorption properties of the water vapor continuum and a number of weak bands for H2O, O2, CO2, CO, N2O, CH4, and O3 in the solar spectrum are incorporated into the Fu-Liou radiation parameterization program by using the correlated k-distribution method (CKD) for the sorting of absorption lines. The overlap absorption of the H2O lines and the H2O continuum (2500-14500 cm-1) are treated by taking the two gases as a single-mixture gas in transmittance calculations. Furthermore, in order to optimize the computation efforts, CO2 and CH4 in the spectral region 2850-5250 cm-1 are taken as a new single-mixture gas as well. For overlap involving other absorption lines in the Fu-Liou spectral bands, the authors adopt the multiplication rule for transmittance computations under which the absorption spectra for two gases are assumed to be uncorrelated. Compared to the line-by-line (LBL) computation, it is shown that the errors in fluxes introduced by these two approaches within the context of the CKD method are small and less than 0.48% for the H2O line and continuum in the 2500-14500 cm-1 solar spectral region, -1% for H2O (line) H2O (continuum) CO2 CH4 in the spectral region 2850-5250 cm-1, and -1.5% for H2O (line) H2O (continuum) O2 in the 7700-14500 cm-1 spectral region. Analysis also demonstrates that the multiplication rule over a spectral interval as wide as 6800 cm-1 can produce acceptable errors with a maximum percentage value of about 2% in reference to the LBL calculation. Addition of the preceding gases increases the absorption of solar radiation under all sky conditions. For clear sky, the increase in instantaneous solar absorption is about 9%-13% (~12 W m~2) among which the H2O continuum produces the largest increase, while the contributions from O2 and CO2 rank second and third, respectively. In cloudy sky, the addition of absorption amounts to about 6-9 W m-2. The new, improved program with the incorporation of the preceding gases produces a smaller solar absorption in clouds due to the reduced solar flux reaching the cloud top. 相似文献
926.
Summary Idealized numerical simulations using the Weather and Research Forecast (WRF) model indicate that three flow regimes, based on the moist Froude number, can be identified for a conditionally unstable, rotational, horizontally homogeneous, uniformly stratified flow over an idealized, three-dimensional, mesoscale mountain stretched spanwise to the impinging flow: (I) a quasi-stationary upslope convective system and an upstream-propagating convective system, (II) a quasi-stationary upslope convective system, and (III) a stationary upslope convective system and a quasi-stationary downstream convective system. Several major differences from a similar type of flow with no rotation over a two-dimensional mountain range are found. One important finding is that relatively strong mean flow produces a quasi-stationary mesoscale convective system (MCS) and maximum rainfall on the windward slope (upslope rain), instead of on the mountain peak or over the lee side.We found that the Coriolis force helps produce heavy upslope rainfall by making transition from flow-around the eastern part of the upslope to flow-over the western part of the upslope (transits to a higher flow regime) by deflecting the incident southerly flow to become east–southeasterly barrier winds. We found that the addition of the western flank of the arc-shaped mountain helps slow down the barrier wind from east and causes the maximum rainfall to move east of the windward slope. A lower-Froude number flow tends to produce a rainfall maximum near the concave region.Several other important facts can also be found in this study. The ratio of the maximum grid scale rainfall to the sub-grid scale rainfall increases when the moist Froude number increases. When the CAPE decreases, it is found that the upstream moist flow tends to shift to a higher Froude-number regime. Therefore, the Froude number cannot solely be used to define a moist flow regime when different CAPEs are considered. In another word, other parameters, such as CAPE, might play an important role in determining moist flow regimes. 相似文献
927.
Summary Analysis of ozonesonde data shows that in the lower troposphere above Hong Kong, there is a relative maximum with respect to height in all seasons except winter. In the upper troposphere, there is with respect to height a relative minimum in the seasonally averaged ozone mixing ratio in winter. Ozone mixing ratios in the upper troposphere in winter and spring can be significantly enhanced by stratospheric intrusions associated with the passage of cold fronts and upper cut-off lows.For Hong Kong, the seasonally averaged total ozone has the highest value in spring, and the lowest in winter. The seasonally averaged total tropospheric ozone also has the highest value in spring, but the lowest in summer. In a relative sense, total tropospheric ozone contributes most to the total ozone in spring and the least in summer.The phase of the total ozone anomaly above Hong Kong is influenced by the Quasi-Biennial Oscillation (QBO), with the positive anomaly associated with the easterly phase of QBO, and the negative anomaly the westerly phase. 相似文献
928.
Bistability of the thermohaline circulation identified through comprehensive 2-parameter sweeps of an efficient climate model 总被引:2,自引:0,他引:2
R. Marsh A. Yool T. M. Lenton M. Y. Gulamali N. R. Edwards J. G. Shepherd M. Krznaric S. Newhouse S. J. Cox 《Climate Dynamics》2004,23(7-8):761-777
The effect of changes in zonal and meridional atmospheric moisture transports on Atlantic overturning is investigated. Zonal transports are considered in terms of net moisture export from the Atlantic sector. Meridional transports are related to the vigour of the global hydrological cycle. The equilibrium thermohaline circulation (THC) simulated with an efficient climate model is strongly dependent on two key parameters that control these transports: an anomaly in the specified Atlantic–Pacific moisture flux (Fa) and atmospheric moisture diffusivity (Kq). In a large ensemble of spinup experiments, the values of Fa and Kq are varied by small increments across wide ranges, to identify sharp transitions of equilibrium THC strength in a 2-parameter space (between Conveyor On and Off states). Final states from this ensemble of simulations are then used as the initial states for further such ensembles. Large differences in THC strength between ensembles, for identical combinations of Fa and Kq, reveal the co-existence of two stable THC states (Conveyor On and Off)—i.e. a bistable regime. In further sensitivity experiments, the model is forced with small, temporary freshwater perturbations to the mid-latitude North Atlantic, to establish the minimum perturbation necessary for irreversible THC collapse in this bistable regime. A threshold is identified in terms of the forcing duration required. The model THC, in a Conveyor On state, irreversibly collapses to a Conveyor Off state under additional freshwater forcing of just 0.1 Sv applied for around 100 years. The irreversible collapse is primarily due to a positive feedback associated with suppressed convection and reduced surface heat loss in the sinking region. Increased atmosphere-to-ocean freshwater flux, under a collapsed Conveyor, plays a secondary role. 相似文献
929.
Nicolas Fauchereau B. Pohl C. J. C. Reason M. Rouault Y. Richard 《Climate Dynamics》2009,32(4):575-591
A cluster analysis of daily outgoing longwave radiation (OLR) anomalies from 1979 to 2002 over the Southern Africa/Southwest
Indian Ocean (SWIO) region for the November to February season reveals seven robust and statistically well separated recurrent
patterns of large-scale organized convection. Among them are three regimes indicative of well defined tropical–temperate interactions
linking the hinterland parts of Southern Africa to the mid-latitudes of the SWIO. Preferred transitions show a tendency for
an eastward propagation of these systems. Analysis of daily rainfall records for South Africa shows that six of the OLR regimes
are associated with spatially coherent and significant patterns of enhanced or reduced daily rainfall over the country. Atmospheric
anomalies from the NCEP/DOE II reanalysis dataset show that the OLR regimes are associated with either regional or near-global
adjustments of the atmospheric circulation, the three regimes representative of tropical–temperate interactions being in particular
related to a well-defined wave structure encompassing the subtropical and temperate latitudes, featuring strong vertical anomalies
and strong poleward export of momentum in the lee of the location of the cloud-band. The time-series of OLR regimes seasonal
frequency are correlated to distinctive anomaly patterns in the global sea-surface-temperature field, among which are shown
to be those corresponding to El Nino and La Nina conditions. The spatial signature of El Nino Southern Oscillation’s (ENSO)
influence is related to the combination of an increased/decreased frequency of these regimes. It is shown in particular that
the well-known “dipole” in convection anomalies contrasting Southern Africa and the SWIO during ENSO events arises as an effect
of seasonal averaging and is therefore not valid at the synoptic scale. This study also provides a framework to better understand
the observed non-linearities between ENSO and the seasonal convection and rainfall anomalies over the region. 相似文献
930.
To begin exploring the underlying mechanisms that couple vegetation to cloud formation processes, we derive the lifting condensation
level (LCL) to estimate cumulus cloud base height. Using a fully coupled land–ocean–atmosphere general circulation model (HadCM3LC),
we investigate Amazonian forest feedbacks on cloud formation over three geological periods; modern-day (a.d. 1970–1990), the last glacial maximum (LGM; 21 kya), and under a future climate scenario (IS92a; a.d. 2070–2090). Results indicate that for both past and future climate scenarios, LCL is higher relative to modern-day. Statistical
analyses indicate that the 800 m increase in LCL during the LGM is related primarily to the drier atmosphere promoted by lower
tropical sea surface temperatures. In contrast, the predicted 1,000 m increase in LCL in the future scenario is the result
of a large increase in surface temperature and reduced vegetation cover. 相似文献