影响春季热带太平洋地区海温变化的动力热力作用分析

厄尔尼诺—南方涛动（ENSO）春季预报障碍是ENSO预测的一个难点问题,弄清影响春季热带太平洋地区海表温度（SST）变化的动力和热力作用对于理解ENSO关键区SST的异常变化及ENSO春季预报障碍成因非常重要。本文利用BCC-CSM2-MR数值模式,模拟产生一套1986～2017年间相互协调的逐月海表风应力、感热、潜热、长波和短波净辐射能量、海洋流场等观测代用数据。利用这些数据对影响海温变化的动力和热力作用及其相对重要性进行了诊断分析,结果表明:（1）与其他季节相比,春季Ni?o3.4区海洋表层温度（后文中用T_S表示）呈现出独特的先增暖后趋冷的不对称季节性转换特征,这一变化主要是由于影响T_S的大气风应力、海流以及能量净通量在春季均表现出明显的季节性转换过程。进一步的分析表明,热力作用对局地海温的季节性变化影响最为重要,水平平流输送以反向作用为主,其中经向平流输送起到了反向作用,不利于该区域T_S的季节性转变,纬向平流输送仅在春季转为弱的正贡献,浅层垂直平流输送对春季T_S变化的影响很小。（2）动力热力作用与T_S异常的变化倾向相关关系也表明,春季Ni?o3.4区热力作用与T_S异常变化呈现显著的正相关,纬向海流异常的输送项也表现为正相关,而经向海流输送项展现出由负相关向正相关转化的特征。（3）对Ni?o3.4区T_S变化的方差贡献分析结果表明,春季热力作用对T_S的异常变化的贡献达50%以上,相关系数超0.7,其次是纬向、经向平流项贡献,各占10%～20%左右,但两者作用相反,其他项贡献较小。     

Inertial waves in the ‘gulf of St Lawrence: A study of geostrophic adjustment

Abstract

It is shown that inertial oscillations of significant magnitude can be generated by geostrophic adjustment in a shallow sea. Evidence of them in current‐meter data from the Gulf of St Lawrence is presented. The geostrophically unbalanced state required for the adjustment process is identified in the data by the occurrence of high accelerations of the currents. The difference between the inertial oscillations generated by different mechanisms, the intermittence and the frequency shift of the inertial waves are discussed.     

Cross‐shore variations of near‐surface wind velocity and atmospheric turbulence at the land‐sea boundary during CASP

Abstract

Airborne measurements of mean wind velocity and turbulence in the atmospheric boundary layer under wintertime conditions of cold offshore advection suggest that at a height of 50 m the mean wind speed increases with offshore distance by roughly 20% over a horizontal scale of order 10 km. Similarly, the vertical gust velocity and turbulent kinetic energy decay on scales of order 3.5 km by factors of 1.5 and 3.2, respectively. The scale of cross‐shore variations in the vertical fluxes of heat and downwind momentum is also 10 km, and the momentum flux is found to be roughly constant to 300 m, whereas the heat flux decreases with height. The stability parameter, z/L (where z = 50 m and L is the local Monin‐Obukhov length), is generally small over land but may reach order one over the warm ocean. The magnitude and horizontal length scales associated with the offshore variations in wind speed and turbulence are reasonably consistent with model results for a simple roughness change, but a more sophisticated model is required to interpret the combined effects of surface roughness and heat flux contrasts between land and sea.

Comparisons between aircraft and profile‐adjusted surface measurements of wind speed indicate that Doppler biases of 1–2 m s^?1 in the aircraft data caused by surface motions must be accounted for. In addition, the wind direction measurements of the Minimet anemometer buoy deployed in CASP are found to be in error by 25 ± 5°, possibly due to a misalignment of the anemometer vane. The vertical fluxes of heat and momentum show reasonably good agreement with surface estimates based on the Minimet data.     

MM5和ETA相似理论近地层方案对农田下垫面通量模拟比较研究

近地层湍流通量计算对于中尺度数值模式有重要意义,湍流通量的参数化是当前大气边界层研究的重要课题之一.选择青藏高原东缘大理观象台边界层通量观测系统,离线测试了WRF区域模式中的两种常用的近地层参数化方案(MM5相似理论非迭代方案A和ETA相似理论迭代方案B),并将参数化方案计算结果与边界层铁塔涡动相关法的观测值进行对比分析.在大理观象台观测场不同植被随季节交替的状况下,根据边界层铁塔4层高度风速拟合,发现近地层空气动力学粗糙度随季节变化特征明显.将拟合的空气动力学粗糙度输入模式参数化方案进行通量计算.结果表明:稳定度是影响近地层参数化方案精度的重要因素,在不稳定条件下方案B低估了动量通量,方案A优于方案B,而在稳定条件下方案A低估了动量通量,方案B优于方案A,两种方案总体来看误差不大.对于大理边界层通量观测场农田植被交替的环境条件,不同季节下垫面植被类型的差异,以及植被的稀疏对近地层参数化方案湍流通量计算结果的精度有显着影响.方案B考虑了空气动力学粗糙度z₀和热量粗糙度z_0h的差异,不稳定条件下感热通量计算结果在裸土或稀少植被条件下明显优于方案A.针对方案B不稳定条件下感热通量计算结果在裸土下垫面仍出现高估的现象,使用了Zeng等1998年提出的用辐射地表温度订正裸土下垫面感热能量方法后,计算结果也有明显改善.     

Estimation of ground heat flux and its impact on the surface energy budget for a semi-arid grassland

Three approaches, i.e., the harmonic analysis (HA) technique, the thermal diffusion equation and correction (TDEC) method, and the calorimetric method used to estimate ground heat flux, are evaluated by using observations from the Semi-Arid Climate and Environment Observatory of Lanzhou University (SACOL) in July, 2008. The calorimetric method, which involves soil heat flux measurement with an HFP01SC self-calibrating heat flux plate buried at a depth of 5 cm and heat storage in the soil between the plate and the surface, is here called the ITHP approach. The results show good linear relationships between the soil heat fluxes measured with the HFP01SC heat flux plate and those calculated with the HA technique and the TDEC method, respectively, at a depth of 5 cm. The soil heat fluxes calculated with the latter two methods well follow the phase measured with the HFP01SC heat flux plate. The magnitudes of the soil heat flux calculated with the HA technique and the TDEC method are close to each other, and they are about 2 percent and 6 percent larger than the measured soil heat flux, respectively, which mainly occur during the nighttime. Moreover, the ground heat fluxes calculated with the TDEC method and the HA technique are highly correlated with each other (R² = 0.97), and their difference is only about 1 percent. The TDEC-calculated ground heat flux also has a good linear relationship with the ITHP-calculated ground heat flux (R² = 0.99), but their difference is larger (about 9 percent). Furthermore, compared to the HFP01SC direct measurements at a depth of 5 cm, the ground heat flux calculated with the HA technique, the TDEC method, and the ITHP approach can improve the surface energy budget closure by about 6 percent, 7 percent, and 6 percent at SACOL site, respectively. Therefore, the contribution of ground heat flux to the surface energy budget is very important for the semi-arid grassland over the Loess Plateau in China. Using turbulent heat fluxes with common corrections, soil heat storage between the surface and the heat flux plate can improve the surface energy budget closure by about 6 to 7 percent, resulting in a closure of 82 to 83 percent at the SACOL site.     

江西一次持续性梅雨锋暴雨过程水汽特征及源地

利用江西省气象观测站降水资料、NCEP/NCAR提供的FNL 再分析资料以及GDAS 资料,在分析2020年7月7—10日的梅雨锋连续区域大暴雨过程的环流形势和大尺度水汽特征基础上,引入NOAA开发的HYSPLIT模式,分析了此次连续暴雨过程的水汽源地。结果表明：1） 此次连续性暴雨过程是在梅雨锋暴雨天气形势下,东北冷涡引导冷空气南下与副高北侧暖湿气流在长江中下游交汇形成的;2） 暴雨过程中不同时段水汽通道不相同,前两日以西南方向和偏南方向的水汽输送为主,后两日则以西南方向的水汽通道为主,且水汽通量大值区与强降水有较好的对应;3） 后向轨迹模拟显示暴雨过程水汽轨迹有5条：大部分为1 500 m高度以上源自印度洋的水汽（77.6%),其次是1 500 m高度以下源自印尼群岛中部海域的水汽（13.2%）,其他三条路径总和不足10%。4） 垂直方向上,有多条水汽输送通道相互叠加后向暴雨区输送,导致江西上空产生强的水汽辐合。     

CO2 concentration and flux near ground in marsh of the Sanjiang plain of Northeast China

There is limited information available on CO₂ concentration and flux over marsh. The objective of this work was to characterize CO₂ concentration and flux within and above marsh plant (Carex lasiocarpa Ehrh. and C. pseudocuraica F. Schm) canopy at heights 0.5, 1.0 and 1.5 m. CO₂ concentration was measured sequentially every 3 hours by using an infrared gas analyzer. Soil and air temperature, wind speed, net radiation and soil heat flux were also measured simultaneously. Extremely daily minimum and maximum CO₂ concentration ranged from 250 to 754 μmd/mol for the 4-year work. The typical minimum and maximum values ranged from 314 to 464 μmol/mol at the height of marsh plant (about 0.5 m) during the fruiting period and mature date. The seasonal changes in CO₂ concentration show that the minimum CO₂ concentration occurred in the fruiting period and mature date, and both of their minimum values were 314 μmol/mol. This illustrates that CO₂ consumed by photosynthesis was stable during the period. The flux of CO₂ can be thought as a turbulent diffusion phenomenon. By micrometeorological methods, the diurnal CO₂ fluxes were measured in the flowering period, fruiting period, early mature date, late mature date and yellow-ripe stage. Their values were −0.18, 38.15,24.13,10.9 and 4.91 μmol/mol respectively.     

Far infrared emission from three new planetary nebulae

As dust emission in the far infrared (FIR) is a characteristic property of planetary nebulae we searched the Infrared Astronomical Satellite (IRAS) point-source catalogue for confirmatory evidence on the two new possible planetary nebulae S 68 and 248 - 5 identified by Fesen, Gull & Heckathorn (1983) and the high-excitation planetary nebula 76 + 36 detected by Sanduleak (1983). We identify the nebulae 248 - 5 and 76 + 36 with IRAS sources 07404 - 3240 and 17125 + 4919, respectively and have determined their dust temperature, total FIR emission and optical depth. We also set a lower limit ranging in value from 1.2 × 10^-6 to 3.7 × 10^-5 forM _dust /M _bd of the nebula 248 - 5 depending on whether its grain material is silicate or graphite. S 68 could not be identified with an IRAS source.     

CO_2 CONCENTRATION AND FLUX NEAR GROUND IN MARSH OF THE SANJIANG PLAIN OF NORTHEAST CHINA

I.INTRODUCTIONIntherecentyears,theresearchershavepaidattentiontotheproblemsofcarbonbalanceandcarboncycleintheearthecosystem,withtheincreaseofCQZamountintheearthatmosphere.Mireisoneoftheecotypesinwhichcarbonaccumulationrateisthefastest,anditisthestrongestsinkforac(Branirgd,1980).Butthereislicitedinformationavailableaboutopconcentrationovermire.SomemeasurementsaboutthetemPOralandspatialgradientofopconcentrationhavebeenmadewithinoraboveasugarbeetcanopy(Brown,1970),corncanopy(Alien,1971;R…     

STUDY ON FLUXES OF MOMENTUM AND SENSIBLE HEAT,THE DRAG COEFFICIENT C_D AND ROUGHNESS Z_O

In this paper,fluxes of momentum and sensible heat are discussed with the data callected by tetheredballoon sounding system over the Philippine Sea during the cruise of the R/V SCIENCE 1 from Septem-ber through October in 1987.These fluxes were calculated using the semiempirical flux-profile relationshipsof Monin-Obkhov similarity theory with observed data.The friction velocity U.was determined by theobserved data's least-square fit with the similarity formulae under stable,neutral and unstable conditions.The roughness Z_0 was determined by Z_0=a_1(U./g),then substituted into the similarity formulae to com-pute U.again.The final values of U.and Z_0 could be determined through this iteration.The fluxtemperature θ.was calculated from the temperature profile with Z_0 determined above.Finally the fluxes'of momentum and sensible heat,and the drag coefficient C_D were obtained by computation with U.,θ.and the wind speed(U_(10))at 10 meters above the sea surface.