Examination of the Mesoscale Features of the GALE Coastal Front of 24-25 January 1986

Zhang

et al. 2018

Aerosol Air Qual. Res.

A dense fog with the visibility less than 100 m over 6 hours occurred around the Hangzhou Bay off the coast of the western part of the East China Sea on 24-25 June 2013 during Meiyu period. This study focuses on the physical mechanism involved in the fog process by using in-situ observations and model. The analysis indicates that the land-sea thermal contrast played an essential role in the fog episode, while a weak low-pressure wedge associated with the Meiyu front and the diurnal variation in temperature provided background conditions. Induced by the strong land-sea thermal contrast, a secondary circulation formed in the lower levels of the atmospheric boundary layer (ABL) over the coast. The southeasterly wind and subsiding motion associated with the secondary circulation contributed to the moisture supply and the lowering of the boundary layer, favoring fog formation and maintenance. The fog maintained until the weakening of the temperature gradient between land and sea, when the downward flow was replaced by upward motion controlled by the approaching of a low-pressure center. These results are helpful for improving coastal fog forecast in Meiyu period and for our understanding of mechanisms involved in coastal fog processes.

Section: Effect Of Local Land-sea Thermal Contrastcontrasting

confidence: 64%

A Fog Event off the Coast of the Hangzhou Bay during Meiyu Period in June 2013

Zhang

et al. 2018

Aerosol Air Qual. Res.

Journal of the Meteorological Society of Japan

“…Mesoscale fronts, which form along the east coast of North America, especially in New England or the Carolinas, are widely known and called coastal fronts (Bosart 1975;Riordan 1990). Coastal fronts sometimes enhance precipitation or the formation of a mesoscale low.…”

Section: Introductionmentioning

confidence: 99%

Vertical Structure of Local Fronts Observed in Kanto, Japan

Seino¹,

Yoshikado

Kobayashi

et al. 2003

This paper focuses on two cases of a local front that formed ahead of a synoptic cold front under a southwesterly inflow in the Kanto region.Vertical sounding data provided by an observation network of the Tsukuba Area Precipitation Studies (TAPS) enabled a detailed investigation of the mesoscale structure in the vicinity of the local front from its formation through dissipation. Despite some differences in synoptic features, the local front exhibited essential similarities in vertical structure between the two cases, as well as in horizontal structure. The local front, with WSW-ENE orientation, was well defined even in the daytime. A stable layer with a thickness of about 400 m formed on the cold side of the developed local front. As in the upper layer of warm inflow, southwesterly winds prevailed in this stable layer, except for the lowest 50-200 m. The maintenance mechanism of the local front is discussed. The evolution of the local front largely depends on the development of the stable layer on its cold side. In both cases, frontal formation began in the nighttime. A nocturnal cooling on the land surface contributed to forming a cold air mass on the northern side of the local front. In addition, the southwesterly inflow caused warming just above the surface-based cooling layer, which intensified the stratification. Furthermore, the observed vertical structure suggests that the locally modified circulation affected the frontal evolution. Two orographic effects on the circulation, 1) intensification of the inflow over the eastern part, and 2) downslope wind over the western part, both related to the mountains in the west of the Kanto region are expected. Especially, the downslope wind can reasonably explain the daytime persistence of the local front through the enhancement of stratification by adiabatic warming, and resultant influences on the mass transport.

“…During the last two decades several observational, theoretical and numerical studies were carried out to understand the coastal fronts. Bosart (1984) studied the coastal fronts along the Gulf coast of Texas and the coastal fronts along the New England coast of US are investigated by Bosart et al [9]; Bosart [5]; Marks and Austin [24]; Ballentine [4]; Nielsen [25]; Nielsen and Neilley [26] and along the Carolina Coast By Carson [11]; Bosart [6]; Bosart and Lin [8]; Riordan et al [29]; Riordan [28]; Doyle and Warner [16]; and Holt and Raman [19]. Two unique processes that are frequently observed along the mid-Atlantic coastal region are due to the presence of the Appalachian mountains, which are located west of the coast, and the Gulf Stream.…”

Section: Discussionmentioning

confidence: 99%

“…Some of the highest wintertime energy transfers from the ocean to the atmosphere takes place (Raman and Riordan [27]; Wayland and Raman [32]; Grossman et al [18]) over the Gulf Stream region of Carolina coast. Sharp horizontal temperature gradients between the coast and the Gulf Stream play a significant role in the frontogenetic processes (Doyle and Warner [16]; Doyle and Warner [17]; Riordan [28]; Cione et al [14]). …”

Section: Discussionmentioning

confidence: 99%

Atmospheric Forecasting

Hyman¹,

Shi²,

Czarnaski³

et al. 2000

Numerical experiments were conducted to assess the impact of Omegadropwindsonde (ODW) data and Special Sensor Microwave/Imager (SSM/I) rain rates in the analysis and prediction of Hurricane Florence (1988). The ODW data were used to enhance the initial analysis that was based on the National Meteorological Center/Regional Analysis and Forecast System (NCEP/RAFS) 2.5° analysis at 0000 UTC 9 September 1988. The SSM/I rain rates at 0000 and 1200 UTC 9 September 1988 were assimilated into the Naval Research Laboratory's limited-area model during model integration.Four numerical simulations were performed to assess the impact of ODW data and SSM/I rain rates on numerical forecasts of Hurricane Florence (1988). A nested three-pass Barnes scheme objective analysis was used to enhance the NCEP/RAFS 2.5° analysis because of the relative high resolution of the ODW data near the center of Florence. The NCEP/RAFS 2.5° analysis and the ODW enhanced analysis were then used as the initial conditions for the numerical prediction experiments. We found that the forecast error of the intensity was reduced from 14 to 4 mb with the assimilation of the ODW data. It is also clear that the ODW data reduced the forecast error of the landfall time in the control experiment by 5 hours (down from 9 to 4 hours), and the landfall location error by 95% (down from 294 to 15 km). The impact of the ODW data was more pronounced in the first 24 hours of the integration and gradually decreased beyond 24 hours. This result is in agreement with Franklin and DeMaria (1992), in which a barotropic, nested, spectral hurricane track forecasting model was used to determine the impact of the ODW data. The advantage of using a three-dimensional primitive equation model with the inclusion of baroclinic and physical processes, as in this study, is that the model can simulate the hurricane structure in more detail (DeMaria et al., 1992).However, a major limitation of the ODW observations is that they do not provide information above 400 mb because of the altitude limitations of the NOAA WP-3D, while satellite-derived winds can provide some upper-level information . Detailed observations of the three-dimensional structure of the upper levels of tropical cyclones are extremely scarce. Dropsonde data collected from 200 mb to the surface by the recent TCM-90 experiment (Elsberry and Abbey, 1991) may be proven to be very useful in depicting the upper-level structure of tropical cyclones (Merrill and Velden, 1995).The rainfall rates retrieved from the SSM/I data at 0000 UTC and 1200 UTC 9September 1988 were assimilated into the NRL limited-area model initialized with the NCEP/RAFS 2.5° analysis (Exp. Control+SSMI) and the ODW enhanced analysis (Exp. ODW+SSMI). Results indicate that the assimilation of the SSM/I rain rates (Exp.Control+SSMI) reduced the 24-hour forecast errors in the landfall location in the control experiment by about 43% (down from 294 to 169 km), and the landfall time by 5 hours (down from 9 to 4 hours). At mean time, the 24-hour minimum SLP and ...