Abstract

A large and intense West African squall line has been observed during the night of 27/28 May 1981 at Korhogo (in the north of Ivory Coast) during the COPT 81 experiment. The environmental conditions in which it occurred and its overall structure are slightly different from the previously analyzed COPT 81 cases on 22 and 23–24 June 1981. Unfortunately, in this situation, as only single-Doppler radar data available, it is not possible to obtain detailed information on the small scale structure of the leading convective region. Nevertheless talking advantage of the apparent stationarity of the mesoscale features, a new processing method (referred to as ABCD) has been developed for a combined processing of 12 successive conical scans, which allows deduction of three-dimensional wind and reflectivity fields in a domain of 260 × 60 × 15 km³, with resolutions of 20 km in the horizontal and 500 m in the vertical.

The deduced circulation displays classical characteristics of trailing straitform parts of mesoscale convective systems, with a mesoscale updraft above 4 km, a mesoscale downdraft below, and a relative rear-to-front flow of moderate intensity in the midlevels; all these features are slightly more intense than on 22 and 23–24 June 1981. One particularity here is that, because of the propagation of the squall line in a direction slightly different from that of the environmental winds, the velocity component parallel to the line is relatively important. Pressure and temperature fields retrieved from an improved analysis of the momentum equation and of the thermodynamic equation show a warming due to condensation in the mesoscale updraft, cooling due to evaporation below, hydrostatic low pressure in the midlevels and high pressure near the surface. The vertical component of vorticity is weak and correlated with the horizontal divergence, while there is an anticorrelation between the shearing deformation and the horizontal divergence. The cross-line component of vorticity is weak but not negligible, as compared with the along-line component. The baroclinic generation, due to the horizontal buoyancy gradient, is the dominant term in the budget of the along-line component of vorticity, however, the influence of the three-dimensional effects through the shearing-tilting term are ~ important in the leading part of the considered domain. The water budget, obtained through a microphysical mtdcvw in one vertical plane, provides values of the different components relatively similar to those obtained in previous studies, with, however, a ~r condensation rate due to the more important upward motions.

Abstract

Aerodynamic roughness length z _om is an important parameter for reliably simulating surface fluxes. It varies with wind speed, atmospheric stratification, terrain, and other factors. However, it is usually considered a constant. It is known that uncertainties in z _om result in latent heat flux (LE) simulation errors, since z _om links LE with aerodynamic resistance. The effects of z _om on sensible heat flux (SH) simulation are usually neglected because there is no direct link between the two. By comparing SH simulations with three types of z _om inputs, it is found that allowing z _om temporal variation in an SH simulation model significantly improves agreement between simulated and measured SH and also decreases the sensitivity of the SH model to the heat transfer coefficient C_t , which in turn determines the linkage between z _om and thermal roughness length z _oh.

Abstract

This study examines the relative importance of ice-phase microphysics and sedimentation velocity for hydrometeors in bulk microphysics schemes. The two bulk microphysics schemes having the same number of prognostic water substances, the Weather Research and Forecasting (WRF) Single-Moment 6-Class Microphysics Scheme (WSM6) and the Purdue–Lin scheme (PLIN), are evaluated for a 2D idealized storm case and for a 3D heavy rainfall event over Korea. The relative importance of microphysics and sedimentation velocity for ice particles is illuminated by the additional experiments that exchange the sedimentation velocity formula for graupel in the two schemes. In a 2D idealized storm simulation test bed, it is found that, relative to the PLIN scheme, the WSM6 scheme develops the storm late with weakened intensity because of a slower sedimentation velocity for graupel. Such a weakened intensity of precipitation also appears in a 3D model framework when the WSM6 scheme is used, in conjunction with the overall distribution of the precipitation band southward toward what was observed. The major reason is found to be the ice-phase microphysics of the WSM6 and related ice-cloud–radiation feedback, rather than the smaller terminal velocity for graupel in the WSM6 than in the PLIN scheme.

Abstract

This study investigated monthly and annual reference evapotranspiration changes over southwestern China (SWC) from 1960 to 2012, using the Food and Agriculture Organization of the United Nations’ report 56 (FAO-56) Penman–Monteith equation and routine meteorological observations at 269 weather sites. During 1960–2012, the monthly and annual decreased at most sites. Moreover, the SWC regional average trend in annual was significantly negative (p < 0.05); this trend was the same in most months. A new separation method using several numerical experiments was proposed to quantify each driving factor’s contribution to changes and exhibited higher accuracy based on several validation criteria, after which an attribution analysis was performed. Across SWC, the declining annual was mainly due to decreased net radiation (RN). Spatially, the annual changes at most sites in eastern SWC (excluding southeastern West Guangxi) were generally due to RN, whereas wind speed (WND) or vapor pressure deficit (VPD) was the determinant at other sites. Nevertheless, the determinants differed among 12 months. For the whole SWC, increased VPD in February and decreased WND in April, May, and October were the determinant of decreased ; however, decreased RN was the determinant in other months. Overall, the determinant of the monthly changes exhibited a complex spatial pattern. A complete analysis of changes and the related physical mechanisms in SWC is necessary to better understand hydroclimatological extremes (e.g., droughts) and to develop appropriate strategies to sustain regional development (e.g., water resources and agriculture). Importantly, this separation method provides new perspective for quantitative attribution analyses and thus may be implemented in various scientific fields (e.g., climatology and hydrology).

Abstract

The main purposes for establishing the Korea ocean research stations (KORS) are for advancing an overall understanding of atmospheric and oceanic phenomena in the Yellow and East China Seas; for providing core scientific data for the studies on global environmental change, typhoon dynamics, biogeochemical cycles, marine ecosystems and fisheries, atmospheric chemistry involving Asian dust and aerosols, air–sea interaction processes including sea fog, and regional oceanographic process studies; and for functioning as ground stations of ocean remote sensing. Here, ocean–atmosphere time series observations with data service and case studies of KORS applications that will facilitate collaboration among researchers in the international atmospheric and oceanographic communities are presented.

Abstract

Urbanization modifies atmospheric energy and moisture balances, forming distinct features [e.g., urban heat islands (UHIs) and enhanced or decreased precipitation]. These produce significant challenges to science and society, including rapid and intense flooding, heat waves strengthened by UHIs, and air pollutant haze. The Study of Urban Impacts on Rainfall and Fog/Haze (SURF) has brought together international expertise on observations and modeling, meteorology and atmospheric chemistry, and research and operational forecasting. The SURF overall science objective is a better understanding of urban, terrain, convection, and aerosol interactions for improved forecast accuracy. Specific objectives include a) promoting cooperative international research to improve understanding of urban summer convective precipitation and winter particulate episodes via extensive field studies, b) improving high-resolution urban weather and air quality forecast models, and c) enhancing urban weather forecasts for societal applications (e.g., health, energy, hydrologic, climate change, air quality, planning, and emergency response management). Preliminary SURF observational and modeling results are shown (i.e., turbulent PBL structure, bifurcating thunderstorms, haze events, urban canopy model development, and model forecast evaluation).