Combined Effects of Blocking and AO on a Prolonged Snowstorm in Jeju Island (original) (raw)
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Simulation of Snowstorm over the Yellow Sea Using a Mesoscale Coupled Model
This study aims to examine the favorable conditions for an ocean effect snowstorm across the Yellow Sea over the southwestern coast of Korea on 21 December 2005, using a coupled model with a Coupled Ocean/Atmosphere Mesoscale Prediction System as the atmospheric component and the Regional Ocean Modeling System as the oceanic component. Simulation of heavy snowfall event, which was 44.3 cm of snow accumulated in 24-hour, was performed to investigate the mesoscale structure, dynamics and development mechanisms in the snowstorm. As a result from 48-hour integration, the results of simulation showed that barotropic instability and turbulent heat fluxes played important roles in the formation of snowstorm. The enhanced surface diabatic heating was dominant in the latent heat flux, and eventually induced convective instability. An additional factor was the favorable condition of synoptic environment, accessing the cold air transport by the approach of the upper-level cold vortex over the warm ocean. Besides these factors, conditional symmetric instability (CSI) is a mechanism which can result in a heavy snowfall with sufficient moisture and upward vertical motion. A slantwise con-vection from the release of CSI could support a complex snowfall event with heavier than expected amounts. The result comparison between a coupled model and an uncoupled model supports that air-sea coupling has an impact of decreasing of about 10% in a snowfall amount on the snowstorm.
Characteristics of Heat Transfer over the Ice Covered Sea of Okhotsk during Cold-air Outbreaks
Journal of the Meteorological Society of Japan, 2003
Heat transfer coefficients, and relative importance of factors affecting surface turbulent heat flux in sea-ice covered ocean, were investigated using data obtained by rawinsonde observations over, and around, the southwestern region of the Sea of Okhotsk from Jan. to Feb. in 1998Feb. in , 1999Feb. in and 2000. The range of the fluxes estimated by an atmospheric heat budget analysis was large, associated with the ice concentration and synoptic situation. The turbulent heat fluxes from the open water surrounded by the sea ice are always positive (upward). However, the heat flux through sea-ice surface tends to be negative Corresponding author and Present affiliation:
‘Observations and Modelling of Cold-air Advection over Arctic Sea Ice’
Boundary-Layer Meteorology, 2005
Aircraft observations of the atmospheric boundary layer (ABL) over Arctic sea ice were made during non-stationary conditions of cold-air advection with a cloud edge retreating through the study region. The sea-ice concentration, roughness, and ABL stratification varied in space. In the ABL heat budget, 80% of the Eulerian change in time was explained by cold-air advection and 20% by diabatic heating. With the cloud cover and inflow potential temperature profile prescribed as a function of time, the air temperature and near-surface fluxes of heat and momentum were well simulated by the applied two-dimensional mesoscale model. Model sensitivity tests demonstrated that several factors can be active in generating unstable stratification in the ABL over the Arctic sea ice in March. In this case, the upward sensible heat flux resulted from the combined effect of clouds, leads, and cold-air advection. These three factors interacted non-linearly with each other. From the point of view of ABL temperatures, the lead effect was far less important than the cloud effect, which influenced the temperature profiles via cloud-top radiative cooling and radiative heating of the snow surface. The steady-state simulations demonstrated that under overcast skies the evolution towards a deep, well-mixed ABL may take place through the merging of two mixed layers: one related to mostly shear-driven surface mixing and the other to buoyancy-driven top-down mixing due to cloud-top radiative cooling.
Journal of the Meteorological Society of Japan, 2009
During cold-air outbreaks in winter, a thick cloud band frequently appears over the northern Sea of Japan and produces localized heavy snowfall in the western coastal region of Hokkaido Island, northern part of Japan. The formation mechanism of this thick cloud band is investigated through a series of nonhydrostatic numerical simulations with a horizontal grid spacing of 5 km. The control simulation well reproduces the characteristics of an observed cloud band. The cloud band forms between relatively warm north-northwesterly winds on the northeast side and relatively cold northwesterly winds on the southwest side. Sensitivity experiments in which upstream topography is modified indicate that the formation and intensification of the cloud band depend on the following two e¤ects; one is the e¤ect of a specific mountain located near the coastline in the middle part of Russia's Sikhote-Alin mountain range (SAMR), and the other is the e¤ect of large-scale topography along the SAMR on synoptic-scale low-level cold northwesterlies. The specific mountain deflects the cold airflow and immediately a convergence zone forms downstream of the specific mountain, where the cloud band is initiated. On the northeastern side of this mountain, the Froude number is estimated to be about 0.4 from relatively high topography (@1.2 km), stable stratification (@0.02 s À1), and synoptic-scale wind speed of 10 m s À1. Thus, the relatively high topography strongly blocks a low-level cold air, whereas an upper air with high potential temperature flows downward over the sea. In contrast, on the southwestern side of the mountain, a low-level cold air can pass over the topography, because the Froude number is estimated to be about 1.6 from relatively low topography (@0.8 km) and weak stable stratification (@0.008 s À1). These two airs with di¤erent potential temperature create a mesoscale frontal zone over the sea, which causes the further development of the thick cloud band initiated by the coastal specific mountain in the SAMR.
Journal of Marine Science and Technology, 2012
The response of sea surface temperature (SST) before and after the passage of Typhoon-18 Songda in the vicinity of Chjeu Island in the southern sea of Korea was investigated using satellite-derived GOES-MCSST (SST), GOES infrared cloud image and a three dimensional WRF-3.0 model with FNL initial meteorological data on September 5 to 8, 2004. On September 4, before the typhoon passed by Cheju Island, the SST extending southwards and eastwards of the island was 27°C. However, after the typhoon passed by the island at 2100 LST, September 7, the SST decreased by 2°C to 25°C. Asymmetrical-cyclonic surface wind generated by the combination of the movement of the typhoon and the cyclonic winds of the typhoon itself, caused divergence of wind driven currents, which induced upwelling of deep sea colder water to the sea surface and outward spreading of cold waters near the island. This resulted in the decrease of SST and a negative maximum geopotential tendency of 500 hPa for 24 hours (∂Φ/∂t;...
The Arctic snow and air temperature budget over sea ice during winter
Journal of Geophysical Research, 1991
Arctic cooling through the fall-winter transition is calculated from a coupled atmosphere-sea ice thermal model and compared to temperature soundings and surface measurements made north of Svalbard during the Coordinated Eastern Arctic Experiment (CEAREX). A typical winter, clear-sky vertical temperature structure of the polar air mass is composed of a surface-based temperature inversion or an inversion above a very shallow (30-180 m) mechanically mixed boundary layer with temperatures-30 ø to-35øC, a broad temperature maximum layer of-20 ø to-25øC between 0.5 and 2 km, and a negative lapse rate aloft. Because the emissivity of the temperature maximum layer is less than that of the snow surface, radiative equilibrium maintains this low level temperature inversion structure. A 90-day simulation shows that heat flux through the ice is insufficient to maintain a local thermal equilibrium. Northward temperature advection by transient storms is required to balance outward longwave radiation to space. Leads and thin ice (<0.8 m) contribute 12% to the winter tropospheric heat balance in the central Arctic. CEAREX temperature soundings and longwave radiation data taken near 81øN show polar air mass characteristics by early November, but numerous storms interrupted this air mass during December. Snow temperature changes of 15øC occurred in response to changes in downward atmospheric longwave radiation of 90 W m-2 between cloud and clear sky. We propose that the strength of boundary layer stability, and thus the degree of air-ice momentum coupling, is driven by the magnitude of the radiation deficit (downward-outward longwave) at the surface and the potential temperature of the temperature maximum layer. This concept is of potential benefit in prescribing atmospheric forcing for sea ice models because a surface air temperature-snow temperature difference field is difficult to obtain and it may be possible to obtain a radiation deficit field via satellite sensors.
Monthly Weather Review, 2009
In January 2008, central and southern China experienced persistent low temperatures, freezing rain, and snow. The large-scale conditions associated with the occurrence and development of these snowstorms are examined in order to identify the key synoptic controls leading to this event. Three main factors are identified: 1) the persistent blocking high over Siberia, which remained quasi-stationary around 658E for 3 weeks, led to advection of dry and cold Siberian air down to central and southern China; 2) a strong persistent southwesterly flow associated with the western Pacific subtropical high led to enhanced moisture advection from the Bay of Bengal into central and southern China; and 3) the deep inversion layer in the lower troposphere associated with the extended snow cover over most of central and southern China. The combination of these three factors is likely responsible for the unusual severity of the event, and hence a long return period.
Terrestrial, Atmospheric and Oceanic Sciences, 2014
We examined the sensitivity of simulated snowfall to prescribed sea surface temperature (SST) data using the Weather Research and Forecasting (WRF) model and the Operational Sea Surface Temperature and Sea Ice Analysis (OSTIA) SST dataset for the Korean Peninsula. The OSTIA data were initially compared with in situ buoy measurements from three coastal sites in the Yellow Sea and was shown to be in good agreement with the in situ data with root mean square errors of 0.14-0.17 K for the daily mean values. Next, we conducted several WRF simulations, including a baseline simulation with the OSTIA data and sensitivity simulations with a temporally and spatially varying SST. The simulations were run for the Yellow Sea during December 2012 when a severe snowfall occurred in Korea. The baseline model generally captured the observed spatial and temporal variations of snowfall, surface air temperature and surface pressure in Korea. The sensitivity simulations with an increased and decreased SST resulted in a variation of +0.8/-0.7 K for the surface air temperature, ±0.6 hPa for the surface pressure, and ±0.3 m s-1 for the surface wind speed, in relation to the baseline simulation. The SST deviation affected the precipitation variability with changes of ±9% for snowfall and ±18% for rainfall, indicating considerable model sensitivity to SST perturbations. The change in the meteorological variables of the upper layer induced by the SST perturbations showed a symmetrical structure with respect to warmer and colder SST. Nevertheless, ice represented a nonlinear combination of the results at the low and mid-levels.
Origin and predictability of the extreme negative NAO winter of 2009/10
1] The winter of 2009/2010 was one of the most negative winters of the North Atlantic Oscillation (NAO) during the last 150 years. While most operational extended-range forecasting systems had difficulties in predicting the onset of the negative NAO phase, once established, extended-range forecasts were relatively skilful in predicting its persistence. Here, the origin and predictability of the unusual winter of 2009/10 are explored through numerical experimentation with the ECMWF Monthly forecasting system. More specifically, the role of anomalies in sea surface temperature (SST) and sea ice, the tropical atmospheric circulation, the stratospheric polar vortex, solar insolation and near surface temperature (proxy for snow cover) are examined. None of these anomalies is capable of producing the observed NAO anomaly, especially in terms of its magnitude. The results of this study support the hypothesis that internal atmospheric dynamical processes were responsible for the onset and persistence of the negative NAO phase during the 2009/10 winter.
The influence of spatial surface temperature changes over the Arctic Ocean on the 2-m air temperature variability is estimated using backward trajectories based on ERA-Interim and the JRA25 wind fields. They are initiated at Alert, Barrow and at the Tara drifting station. Three different methods are used. The first one compares mean ice sur-5 face temperatures along the trajectories to the observed 2-m air temperatures at the stations. The second one correlates the observed temperatures to air temperatures obtained using a simple Lagrangian box model which only includes the effect of sen-sible heat fluxes. For the third method, mean sensible heat fluxes from the model are correlated with the difference of the air temperatures at the model starting point and the 10 observed temperatures at the stations. The calculations are based on MODIS ice sur-face temperatures and four different sets of ice concentration derived from SSM/I and AMSR-E data. Under nearly cloud free conditions, up t...