Implications of sea surface temperature deviations in the prediction of wind and precipitable water over the Yellow Sea (original) (raw)
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Deep Sea Research Part II: Topical Studies in Oceanography, 2013
High-resolution reanalysis data of Sea Surface Temperature (SST) show pronounced seasonal variations in oceanic fronts in the coastal area of the Northern South China Sea (NSCS), which are accompanied by the seasonality of monsoons. The NSCS oceanic fronts cover a wider area of the coastal sea in winter than in summer as strong winter monsoons progress. Nonetheless, the average SST gradients of the frontal area in both seasons are comparable. The response of surface wind to SST perturbations attributed to oceanic fronts in the NSCS coastal area has also been investigated by the observation data of satellite borne scatterometers and the simulation data of the Weather Research and Forecasting (WRF) model. Both the satellite observations and the simulations of the WRF model show apparent positive linear SSTwind coupling for most months in 2008, indicating the local influence of coastal SST fronts on the sea surface wind in the NSCS. The SST-wind coupling coefficients in the NSCS coastal sea are larger than those observed at mid-latitude oceans but smaller than those observed near equatorial oceans. It is also found that the influence of topography on the sea surface wind could be more important than that of the SST front at the southern end of the Taiwan Strait in winter. The transition of the monsoon could also affect the SST-wind coupling in the NSCS.
Diurnal variations of precipitation over the South China Sea
Meteorology and Atmospheric Physics, 2010
In this study, the diurnal variations of precipitation and related mechanisms over the South China Sea (SCS) are studied using the TRMM and other auxiliary atmospheric data. We have found that: (1) the amplitude and peak time of the diurnal precipitation over SCS exhibit remarkable regional features and seasonal variations. Diurnal variations are robust all the year around over the southern SCS especially over the Kalimantan Island and its offshore area. Over the middle to northern SCS, however, diurnal variations are noticeable only in the summer and autumn; (2) over the northern SCS precipitation peaks in early morning, while over the southern SCS it has two diurnal peaks: one in the early morning and another in the late afternoon; (3) the diurnal variations of precipitation over the SCS are related to the activity of the SCS summer monsoon and the ENSO events. The late afternoon precipitation increases remarkably after the onset of the SCS summer monsoon over the northern SCS. The earlymorning rainfall peak is much more significant during La Nina years than during El Nino years; (4) the land-sea breeze is responsible for the diurnal cycle over the Kalimantan Island and its offshore area while the ''static radiation-convection'' mechanisms may result in the earlymorning rainfall peak over the SCS.
Journal of Geophysical Research: Atmospheres, 2016
A 34 year (1979-2012) high-resolution (7 km grid) atmospheric hindcast over the Bohai Sea and the Yellow Sea (BYS) has been performed using COSMO-CLM (CCLM) forced by ERA-Interim reanalysis data (ERA-I). The accuracy of CCLM in surface wind reproduction and the added value of dynamical downscaling to ERA-I have been investigated through comparisons with the QuikSCAT Level2B 12.5 km version 3 (L2B12v3) swath data and in situ observations. The results revealed that CCLM has a reliable ability to reproduce the regional wind characteristics over the BYS. Added value to ERA-I has been detected in the coastal areas with complex orography. CCLM wind quality had strong seasonal variability, with better performance in the summer relative to ERA-I, even in the offshore areas. CCLM was better able to represent light and moderate winds but had even more added value for strong winds relative to ERA-I. The spatial digital filter method was used to investigate the scale of the added value, and the results show that CCLM adds value to ERA-I mainly in medium scales of wind variability. Furthermore, wind climatology was investigated, and significant increasing trends in the south Yellow Sea especially in winter and spring were found for seasonal mean wind speeds. Satellite observations represent one alternative option for wind studies. With advanced satellite techniques, ocean surface wind studies are highly enhanced because spatial wind maps from satellites provide more LI ET AL.
Numerical Study of Circulation and Seasonal Variability in the Southwestern Yellow Sea
Journal of Marine Science and Engineering
A nested-grid ocean circulation modelling system (NGMS-swYS) is used for examining the impact of tides and winds on the three-dimensional (3D) circulation, hydrography and seasonal variability over the southwestern Yellow Sea (swYS). The modelling system is based on the Princeton Ocean Model (POM) and uses a nested-grid setup, with a fine-resolution (~2.7 km) inner model nested inside a coarse-resolution (~9.0 km) outer model. The domain of the outer model covers the China Seas and adjacent deep ocean waters. The domain of the fine-resolution inner model covers the swYS and adjacent waters. The NGMS-swYS is driven by a suite of external forcings, including the atmospheric forcing, tides, freshwater discharge and currents specified at the lateral open boundaries. A comparison of model results with observations and previous numerical studies demonstrates the satisfactory performance of the NGMS-swYS in simulating tides, seasonal mean circulation and distribution of temperature and sal...
Evaluation of the air-sea bulk formula and sea-surface temperature variability from observations
Journal of Geophysical Research, 2006
1] Eddy-correlation fluxes are compared to air-sea fluxes predicted by a widely used bulk flux formulation without wave-state effects. Systematic discrepancies are found. For example, the model approximately equates the roughness lengths for heat and moisture; however, the observed roughness length for heat (z oh ) exceeds that for moisture (z oq ) by an order of magnitude or more, except in the strongest wind-speed conditions. This is apparently due to the dynamic nature of temperature, which dominates buoyancy generation of turbulence in these data sets. The observed correlation between temperature and vertical velocity fluctuations generally exceeds that for moisture. For 10-m wind speeds above a threshold value of 12 m s À1 , z oq exceeds z oh apparently owing to enhanced moisture flux associated with the onset of wave breaking coupled with advection of cold dry air from land. In near-collapsed turbulence, the observed momentum flux is smaller than predicted, and there is no clear indication of a smooth flow viscous regime. The scatter between observed and bulk fluxes generally decreases with averaging the observed fluxes over greater length scales even with variations in sea-surface temperature (SST). The reduction in random flux sampling errors more than compensates for capturing increased surface heterogeneity with increasing averaging scale. Since similarity theory does not apply to heterogeneous surfaces, the bulk model does break down in the extreme case where the averaging window includes a sharp SST front. The response of the flow to changes in SST is presented for different amplitudes of SST variability. The change in vertical structure and acceleration of the low-level wind over warm pools is discussed.
A study of low-frequency response of the atmosphere to the sea surface temperature variations
1991
Impact of the sea surface temperature anomalies (SST As) on atmospheric circulations are studied with emphasis on the winter climate in Japan with the use of an atmospheric general circulation model. The empirical orthogonal function analyses are performed for precipitation, geopotential height at 500 mb and surface air temperature. It is shown that leading eigenvectors of precipitation are zonally elongated in the tropics and that the distribution of positive and negative precipitation anomalies is dependent on the SST and precipitation field in the control run. Surface air temperature in East Asia is mostly governed by the temperature contrast between Japan-East China region and the Sea of Okhotsk. This is associated with high pressure anomalies in the North Pacific Ocean, which weakens the cold surge from Siberia. Thil circulation is found in the first eigenvector in the present experiment EI(Z500) and is dominant in the run which uses the composited January SSTA observed during warm winter in Japan. The simulated anomalies in mid-latitude circulation correspond well with the observations. An additional run with the SSTA over the equator east of the dateline gives the largest anticyclonic circulation response over the North Pacific Ocean and the warmest surface air temperature anomalies in East Asia. The pattern relevant to warm winter in Japan is not a simple atmospheric response to tropical heating. It is conceivable that inherently there is a dominant circulation mode like EI(Z500) and that this mode can be activated either by a direct and/or an indirect orographic effect or by anomalous heating induced by the SST A. This pattern can be understood as a response to subtropical mass source/sink distribution unaer the framework of a linear theory.
Intraseasonal variability in the summer South China Sea: Wind jet, cold filament, and recirculations
Journal of Geophysical Research, 2007
1] A recent study shows that the blockage of the southwest monsoon by the mountain range on the east coast of Indochina triggers a chain of ocean-atmospheric response, including a wind jet and cold filament in the South China Sea (SCS). We extend this climatological analysis by using higher temporal resolution (weekly) to study intraseasonal variability in summer. Our analysis shows that the development of the wind jet and cold filament is not a smooth seasonal process but consists of several intraseasonal events each year at about 45-day intervals. In a typical intraseasonal event, the wind jet intensifies to above 12 m/s, followed in a week by the development of a cold filament advected by an offshore jet east of South Vietnam on the boundary of a double gyre circulation in the ocean. The double gyre circulation itself also strengthens in response to the intraseasonal wind event via Rossby wave adjustment, reaching the maximum strength in 2 to 3 weeks. The intraseasonal cold filaments appear to influence the surface wind, reducing the local wind speed because of the increased static stability in the near-surface atmosphere. To first order, the above sequence of events may be viewed as the SCS response to atmospheric intraseasonal wind pulses, which are part of the planetary-scale boreal summer intraseasonal oscillation characterized by the northeastward propagation of atmospheric deep convection. The intraseasonal anomalies of sea surface temperature and precipitation are in phase over the SCS, suggesting an oceanic feedback onto the atmosphere. As wind variations are now being routinely monitored by satellite, the lags of 1-3 weeks in oceanic response offer useful predictability that may be exploited.
Boundary-Layer Meteorology, 2015
Wind fronts associated with cold-air outbreaks from the Chinese continent in the winter are often observed over the northern South China Sea and are well studied. However, wind fronts caused by another type of synoptic setting, the sudden increase or freshening of the northeast monsoon, which is caused by the merging of two anticyclonic regions over the Chinese continent, are also frequently encountered over the northern South China Sea. For the first time, such an event is investigated using multi-sensor satellite data, weather radar images, and a high-resolution atmospheric numerical model. It is shown that the wind front generated by the freshening of the northeast monsoon is quite similar to wind fronts generated by cold-air outbreaks. Furthermore, we investigate fine-scale features of the wind front that are visible on synthetic aperture radar (SAR) images through variations of the small-scale sea-surface roughness. The SAR image was acquired by the Advanced SAR of the European Envisat satellite over the South China Sea off the coast of Hong Kong and has a resolution of 150 m. It shows notches (dents) in the frontal line and also radar signatures of embedded rain cells. This (rare) SAR image, together with a quasi-simultaneously acquired weather radar image, provide excellent data with which to test the performance of the pre-operational version of the Atmospheric Integrated Rapid-cycle (AIR) forecast model system of the Hong Kong Observatory with respect to modelling rain cells at frontal boundaries. The calculations using a horizontal resolution with 3-km resolution show that the model reproduces quite well B Werner Alpers