海南岛海风雷暴结构的数值模拟

本文利用高分辨率WRF模式对2012年7月20日发生在海南地区的一次海风雷暴过程进行模拟,探讨了海南岛复杂地形下海风雷暴的结构、发展演变过程及其触发机制.结果表明,海南岛北部向内陆传播的海风与南部受地形阻挡的海风相遇后会形成海风辐合带,辐合带能影响当地的散度和涡旋特征,为雷暴的发生发展提供有利的动力和热力学条件.海南岛受热带海洋的影响较大,当地的水汽条件和对流潜势长期保持着有利于对流发展的状态,自由对流高度始终处于较低的位置,一旦海风辐合带来的抬升运动克服对流抑制到达自由对流高度后,对流就能自主地发展起来,所以单纯的海风辐合也常常能触发当地的强雷暴.雷暴发生发展过程中对流参数存在明显的变化,其演变曲线的突变位置对雷暴的发生有一定的指示作用.海南岛的海风雷暴过程与当地的复杂地形密切相关,地形的动力阻挡作用影响着低层海风的辐合以及对流的发展.     

海陆风及沿海风速廓线在风电场风速预报中的应用

为了建立沿海风功率预报系统,本文探讨了中国沿海风电场风速预报问题,并利用数值模式RAMS对海陆风进行了模拟研究.发现海陆风发生时,海风和陆风阶段风速廓线存在较大差异,海风阶段风速的垂直切变明显小于陆风阶段.海陆风发生时,风速会呈现有规律的变化,即海风和陆风分别有两个时段：风速增加时段和风速减少时段.在为沿海风电场提供风速预报时,当模式预报到海陆风发生时,可以利用海陆风的这种特点,使用统计方法对预报出的风速进行有效的订正.并发现即使没有海陆风发生,当风向为海洋吹向陆地时,风速随高度的垂直切变同样小于陆地吹向海洋的时段.利用统计方法根据不同风向时风速廓线的特性,把数值模式计算高度上的预报结果,精确地插值到风机涡轮高度,会很大程度上减少风速预报的误差及风功率预报环节的误差.     

北京夏季晴天边界层特征及城市下垫面对海风影响的数值模拟

对耦合了Noah陆面模式和单层城市冠层模式的WRF(Weather Research and Forecasting)模式系统进行了改进和优化,通过对2010年8月6－7日北京地区晴天个例的模拟试验,检验了优化前后模式系统的模拟能力,分析研究了该个例中城市边界层的特征及日变化.另外,使用优化后的模拟系统通过两组敏感性试验研究了京津城市下垫面对海风的影响.结果表明,优化方案能够显著提高模式系统对该个例的模拟性能,模式系统基本能够模拟出北京夏季边界层的日变化特征,精确的地表使用类型分类等地理信息数据对提高模式预报的准确度有着至关重要的作用,京津城市对海风的发展和推进过程有明显影响,能够阻碍海风的推进、加强风场的水平辐合和垂直上升气流,北京城市下垫面还能在海风到达前增加其强度和推进速度,并在海风经过后延缓其消亡、增加其推进距离.     

辐射参数化对海南岛海风雷暴结构模拟的影响

本文利用高分辨率WRF模式探讨了两组短波、长波辐射参数化方案（Dudhia+RRTM、RRTMG+RRTMG）对海南岛一次海风雷暴模拟的影响及其可能的物理机制.结果表明,辐射参数化能影响大气的加热程度和近地面能量,决定海陆温差和气压差,改变海南岛的海风特征,最终影响海风雷暴的发生发展.Dudhia+RRTM方案模拟的短波、长波综合加热率、感热通量以及潜热通量都大于RRTMG+RRTMG方案,造成了前者模拟的近地面能量偏高,大气层结也表现得更加不稳定,进而使得该方案下的海陆温差和气压差相对较大,Dudhia+RRTM方案模拟的海风明显强于RRTMG+RRTMG方案,能提供更好的水汽输送和抬升条件,有利于海风雷暴的发生发展,因此其模拟的雷暴活动范围和对流中心强度都要大于RRTMG+RRTMG方案.

     

Diurnal sea breeze effects on inner-shelf cross-shore exchange

Cross-shore exchange by strong (cross-shore wind stress, τ_sx>0.05 Pa) diurnal (7–25 h) sea breeze events are investigated using two years of continuous wind, wave, and ocean velocity profiles in 13 m water depth on the inner-shelf in Marina, Monterey bay, California. The diurnal surface wind stress, waves, and currents have spectral peaks at 1, 2, and 3 cpd and the diurnal variability represents about 50% of the total variability. During sea breeze relaxation (−0.05<τ_sx<0.05 Pa), a background wave-driven inner-shelf Eulerian undertow profile exists, which is equal and opposite to the Lagrangian Stokes drift profile, resulting in a net zero Lagrangian transport at depth. In the presence of a sea breeze (τ_sx>0.05 Pa), a uniform offshore profile develops that is different from the background undertow profile allowing cross-shore Lagrangian transport to develop, while including Lagrangian Stokes drift. The diurnal cross-shore current response is similar to subtidal (>25 h) cross-shore current response, as found by Fewings et al. (2008). The seasonality of waves and winds modify the diurnal sea breeze impact. It is suggested that material is not transported cross-shore except during sea breeze events owing to near zero transport during relaxation periods. During sea breeze events, cross-shore exchange of material appears to occur onshore near the surface and offshore near the sea bed. Since sea breeze events last for a few hours, the long-term cross-shore transport is incremental each day.     

近地层参数化对海南岛海风降水模拟的影响

利用WRF模式探讨了两种近地层参数化方案（MM5方案和Eta方案）对2013年5月31日海南岛一次海风降水过程模拟的影响.结果表明,改变近地层方案可对当地的海风环流及相应的降水特征产生明显影响,两个试验最重要的差别主要体现在模拟的海风及降水的强度差异上,与MM5试验相比,Eta试验的低层海风及辐合程度更强,相应的降水也更强,表现为岛屿总格点降水量、大于10 mm的降水区域、最大格点降水三个量化指标均比较大.通过分析两种方案在不同降水阶段的地表通量及近地层变量场,发现Eta试验模拟的降水前环境场更有利于对流的启动,随着午后热力湍流的不断增强,将MM5方案替换为Eta方案可使近地层感热通量、潜热通量分别增加约3.57%、5.65%,动量通量减小约10.79%,感热、潜热的增加使Eta试验中近地层大气的加热加湿作用更加明显,相应的低层大气不稳定度更高,再配合海风锋前较强的辐合上升运动,局地不稳定能量的释放变的更加容易,因此降水强度更大.

     

A first numerical simulation of the development and structure of the sea breeze on the Island of Mallorca

A numerical study of the development and structure of the sea breeze in Mallorca is presented using a meso- numerical model. The model includes a detailed representation of the soil and vegetation processes. The study covers a diurnal cycle. The results show that the model reproduces the main known features of the circulation and new ones appear, which seem to have an appreciable effect on the circulation during the decay of the sea breeze. The orography and soil dryness have been identified as the main factors determining the structure of the breeze. Three more experiments have been performed in order to isolate the effect of each factor.     

Observation of Sea Breeze Front and its Induced Convection over Chennai in Southern Peninsular India Using Doppler Weather Radar

Sea breeze, the onshore wind over a coastal belt during daytime, is a welcoming weather phenomenon as it modulates the weather condition by moderating the scorching temperature and acts as a favourable mechanism to trigger convection and induce precipitation over coastal and interior locations. Sea breeze aids dispersal of pollutants as well. Observational studies about its onset, depth of circulation and induced precipitation have been carried out in this paper for the period April to September, 2004–2005 using a S-band Doppler Weather Radar functioning at Cyclone Detection Radar Station, India Meteorological Department, Chennai, India. The onset of sea breeze has been observed to be between 0900 and 1000 UTC with the earliest onset at 0508 UTC and late onset at 1138 UTC. The frequency is greater during the southwest monsoon season, viz., June – September and the frequency of initial onset is greater in north Chennai. The modal length of sea breeze is between 20 and 50 km with extreme length as high as 100 km also having been observed. Though the inland penetration is on average 10 to 20 km, penetration reaching 100 km was also observed on a number of cases. The induced convection could be seen in the range 50–100 km in more than 53% of the cases. The mean depth of sea breeze circulation is 300–600 m but may go well beyond 1000 m on conducive atmospheric conditions.     

Diurnal-period,wind-forced ocean variability on the inner shelf off Concepción,Chile

We characterize the response of diurnal-period ocean current variability to the sea breeze using measurements of current velocity taken off the mouth of the Itata River and wind stress collected at Hualpen Point (central Chile) in spring of 2007 and summer of 2006 and 2008. During these three periods, the winds are predominately towards the northeast, following the coastal topography, with the highest variability found in the near-diurnal and synoptic frequency bands. The sea breeze amplitude is intermittent in time and is associated with synoptic-scale variability on the order of three to 15 days, so that the diurnal-period winds (and currents) are enhanced when the alongshore wind (i.e. upwelling-favorable) is strong. The water current variability in the near-diurnal band is significant, explaining up to 40% (spring 2007) of the total current variance in the first 15 m depth.     

Analysis of the influence of Taihu Lake and the urban heat islands on the local circulation in the Yangtze Delta

The influences of human activities on regional climate and weather are tremendous. The re-gional temperature and the distributing of wind field are influenced, whereas the precipitation in-tensity and the spatial and temporal distribution of the precipita…     

京津冀城市群地区夏季低层大气风速谱特征分析

利用京津冀城市群地区6个观测站风廓线雷达夏季一个月同步观测资料,对其进行了风功率谱和小波分析.越接近地面,测站之间风的周期变化特征差异越明显,离地面越远,差异不显著.各站大于1天周期的频谱特征差异小,而小于1天周期的频谱特征差异大.各站频谱在几百米高度有明显日变化.不同位置的测站其日变化周期信号随高度分布表现为不同程度的地形影响效应.部分测站1 km高度以下风功率谱在大于1天高频区近似满足-5/3幂分布规律.降水过程风频谱在低层普遍有小于1天的高频周期,这与降水过程高低空风速起伏和变化密切相关.各站平均风矢量日变化在5:00—6:00、20:00—21:00有明显风速变化和风向转换,1500 m以下风向变化差异显著,偏南风出现时间及影响高度与该地区的山谷风和海陆风相联系.各站之间风速相关系数随高度分布呈现出低层低、上层高的特点.最后还给出了风廓线雷达布网建议.     

Characteristics of local Winds at Athens,Greece

Summary The frequency of days having an uninterrupted sea breeze and of numbers of such consecutive days with sea breeze is given for all months and the year as a whole.—Some given characteristic elements, such as true azimuth, resultant run and velocity, and steadiness of the July sea breeze and uninterrupted Etesians were calculated with the aid ofLambert's formulas for 16 directions.     

Observations and Numerical Simulations of Urban Heat Island and Sea Breeze Circulations over New York City

Observations from two SOund Detection And Ranging (SODAR) units, a 10 m micrometeorological tower and five Automated Surface Observing Stations (ASOS) were examined during several synoptic scale flow regimes over New York City after the World Trade Center disaster on September 11, 2001. An ARPS model numerical simulation was conducted to explore the complex mesoscale boundary layer structure over New York City. The numerical investigation examined the urban heat island, urban roughness effect and sea breeze structure over the New York City region. Estimated roughness lengths varied from 0.7 m with flow from the water to 4 m with flow through Manhattan. A nighttime mixed layer was observed over lower Manhattan, indicating the existence of an urban heat island. The ARPS model simulated a sea-breeze front moving through lower Manhattan during the study period consistent with the observations from the SODARs and the 10-m tower observations. Wind simulations showed a slowing and cyclonic turning of the 10-m air flow as the air moved over New York City from the ocean. Vertical profiles of simulated TKE and wind speeds showed a maximum in TKE over lower Manhattan during nighttime conditions. It appears that this TKE maximum is directly related to the influences of the urban heat island.     

Sea breezes drive currents on the inner continental shelf off southwest Western Australia

In southwest Western Australia, strong and persistent sea breezes are common between September and February. We hypothesized that on the inner continental shelf, in the absence of tidal forcing, the depth, magnitude, and lag times of the current speed and direction responses to sea breezes would vary though the water column as a function of the sea breeze intensity. To test this hypothesis, field data were used from four sites were that were in water depths of up to 13 m. Sites were located on the inner continental shelf and were on the open coast and in a semi-enclosed coastal embayment. The dominant spectral peak in currents at all sites indicated that the majority of the spectral energy contained in the currents was due to forcing by sea breezes. Currents were aligned with the local orientation of the shoreline. On a daily basis, the sea breezes resulted in increased current speeds and also changed the current directions through the water column. The correlation between wind–current speeds and directions with depth, and the lag time between the onset of the sea breeze and the response of currents, were dependent on the intensity of the sea breezes. A higher correlation between wind and current speeds occurred during strong sea breezes and was associated with shorter lag times for the response of the bottom currents. The lag times were validated with estimates of the vertical eddy viscosity. Solar heating caused the water column to stratify in summer and the sea breezes overcame this stratification. Sea breezes caused the mixed layer to deepen and the intensity of the stratification was correlated to the strength of the sea breezes. Weak sea breezes of <5 m s⁻¹ were associated with the strongest thermal stratification of the water column, up to 1°C between the surface and bottom layers (6 and 10 m below the surface). In comparison, strong sea breezes of >14 m s⁻¹ caused only slight thermal stratification up to 0.5°C. Apart from these effects on the vertical structure of water column, the sea breezes also influenced transport and mixing in the horizontal dimension. The sea breezes in southwest Western Australia rotated in an anticlockwise direction each day and this rotation was translated into the currents. This current rotation was more prominent in surface currents and in the coastal embayment compared to the open coast.     

Effects of onshore and offshore topography on sea breeze circulation: An observational study at eastern Attica,Greece

Field measurements of wind, air temperature and humidity were taken at the eastern part of the Attika district in June 1991, to examine the topographic influences exerted on the local sea breezes. These influences are due either to the elongated Evia island, faced by the northern half of Attica coastline some tens of kilometers offshore, or to the coast-parallel range of Hymettos mountain, rising steeply 12 km onshore. The instrumentation consisted mainly of three tethered meteorological balloons released at characteristic sires (i.e., the coast, a location between shoreline and mountain foot and the mountain top) and three autographic ground-based anemometers operating at selected locations. Data from the ground-based and upper air stations of the Hellenic National Meteorological Service, as well as the diurnal weather maps were also obtained and analyzed. Observations were made under different synoptic wind and the latter was found to determine remarkably the significance of the topographic effects. A preliminary two-dimensional numerical approach was also made concerning the sea breeze capability to reach the Hymettos mountain top in the case of a weak opposing geostrophic flow.     

Predictability of storm wave heights in the ice-free Beaufort Sea

A predictability study on wave forecast of the Arctic Ocean is necessary to help identify hazardous areas and ensure sustainable shipping along the trans-Arctic routes. To assist with validation of the Arctic Ocean wave model, two drifting wave buoys were deployed off Point Barrow, Alaska for two months in September 2016. Both buoys measured significant wave heights exceeding 4 m during two different storm events on 19 September and 22 October. The NOAA-WAVEWATCH III^? model with 16-km resolution was forced using wind and sea ice reanalysis data and obtained general agreement with the observation. The September storm was reproduced well; however, model accuracy deteriorated in October with a negative wave height bias of around 1 m during the October storm. Utilising reanalysis data, including the most up-to-date ERA5, this study investigated the cause: grid resolution, wind and ice forcing, and in situ sea level pressure observations assimilated for reanalysis. The analysis has found that there is a 20% reduction of in situ SLP observations in the area of interest, presumably due to fewer ships and deployment options during the sea ice advance period. The 63-member atmospheric ensemble reanalysis, ALERA2, has shown that this led to a larger ensemble spread in the October monthly mean wind field compared to September. Since atmospheric physics is complex during sea ice advance, it is speculated that the elevated uncertainty of synoptic-scale wind caused the negative wave model bias. This has implications for wave hindcasts and forecasts in the Arctic Ocean.     

鄱阳湖地区大气边界层特征的数值模拟

采用WRFV2.2中尺度数值模式对鄱阳湖地区200 km×200 km范围内,2009年11月5日00∶00至2009年11月6日12∶00不同高度的气象要素进行了数值模拟,得到了水平分辨率为1 km的鄱阳湖地区大气边界层风、温、湿度场和廓线分布的大气边界层物理特征.模拟结果发现:白天鄱阳湖面上空存在着冷岛效应并伴随湖风,而夜间湖面上空存在着热岛效应并伴随陆风,湖面与陆地之间最大温差可达6 ℃;同时地形以及下垫面类型对鄱阳湖区风场的分布具有很大影响,夜间存在一条东北西南走向的低空辐合带,白天逐渐消失;此外受风场和地形作用湖面上空的湿度分布也不均匀,白天湿度层厚度低而夜晚湿度层厚度高,湖中心右侧湿度值大于左侧湿度值.模拟结果能较好地反映鄱阳湖的大气边界层物理特征,有助于了解鄱阳湖地区区域气候的特点,以及由于地形、地理环境、地表特征所形成的不同高度上的风、温、湿的分布规律和大气边界层物理特征,为鄱阳湖地区局地天气预报、风能资源开发、环境保护等提供了科学依据.     

大气变率对北极地区近期海冰变化趋势影响数值模拟研究

为研究近期21年(1989—2009年)北极地区海冰变化原因,本文利用欧洲中期天气预报中心ERA-Interim数据集资料和美国麻省理工学院MITgcm全球海冰-海洋耦合模式开展了不同大气强迫条件下海冰变化的数值模拟研究.研究工作中共设计了6个数值试验,除1个试验全部采用1989—2009年每日4个时次的大气强迫场外,其余5个试验各有一种大气强迫(地表气温、地表大气比湿、向下短波辐射通量、向下长波辐射通量和地表风)采用1989年月平均结果.分析了各模拟试验结果中3月和9月北极地区海冰面积的年际变化特征及最小二乘拟合意义下的线性变化趋势,并以ERA-Interim结果为参照标准对各模拟试验结果进行了对比和检验,以说明不同大气强迫量变率对海冰变化的作用.结果表明:地表气温变率和向下长波辐射通量变率是造成海冰面积减少的主要原因;向下短波辐射通量变率对海冰面积变化影响几乎可以忽略;地表大气比湿变率对海冰面积线性变化趋势影响较小,但对海冰面积年际变化特征有调制作用;地表风变率对海冰季节变化、海冰面积线性变化趋势及年际变化特征均有明显影响,说明提高大气风应力精度是改善海冰数值模拟结果的重要手段.     

大气变率对北极地区近期海冰变化趋势影响数值模拟研究

为研究近期21年(1989—2009年)北极地区海冰变化原因,本文利用欧洲中期天气预报中心ERA-Interim数据集资料和美国麻省理工学院MITgcm全球海冰-海洋耦合模式开展了不同大气强迫条件下海冰变化的数值模拟研究.研究工作中共设计了6个数值试验,除1个试验全部采用1989—2009年每日4个时次的大气强迫场外,其余5个试验各有一种大气强迫(地表气温、地表大气比湿、向下短波辐射通量、向下长波辐射通量和地表风)采用1989年月平均结果.分析了各模拟试验结果中3月和9月北极地区海冰面积的年际变化特征及最小二乘拟合意义下的线性变化趋势,并以ERA-Interim结果为参照标准对各模拟试验结果进行了对比和检验,以说明不同大气强迫量变率对海冰变化的作用.结果表明:地表气温变率和向下长波辐射通量变率是造成海冰面积减少的主要原因;向下短波辐射通量变率对海冰面积变化影响几乎可以忽略;地表大气比湿变率对海冰面积线性变化趋势影响较小,但对海冰面积年际变化特征有调制作用;地表风变率对海冰季节变化、海冰面积线性变化趋势及年际变化特征均有明显影响,说明提高大气风应力精度是改善海冰数值模拟结果的重要手段.     

A Procedure for Calculating Extreme Characteristics of the Northern Caspian Sea Level

A procedure is proposed for calculating extreme characteristics of the level of a sea with allowance for positive and negative setups. Analysis is made of past storm events in the Northern Caspian Sea that have caused strong setups. Sixty-three storm weather patterns are chosen from a period of 45 years. Time ring synoptic maps are used to digitize the atmospheric pressure fields and calculate the field of its gradient and the wind near water surface. Based on these data, the sea level values and currents are calculated through two- and three-dimensional hydrodynamic models. A probabilistic model along with computer-aided data treatment procedures are used to calculate the fields of extreme characteristics of the sea level at the Lagan gage with the occurrence of once per N years at the average Caspian Sea level of 27 m below SL.