Downward longwave radiation in general circulation models: a case study at a semi‐arid continental site

The present case study evaluates the downward longwave radiation at the surface (DLR) in several high‐resolution (≈1°) general circulation models (GCMs) using surface observations from a semiarid continental site in New South Wales, Australia (Uardry, 34.39°S, 142.30°E). This site is located on a large grassland plain uniform in both its land use and landcover type, and is therefore particularly well suited for a comparison with GCM grid mean values. Monthly averages of newly constructed clear‐sky and all‐sky DLR climatologies and the resulting cloud‐radiative forcing are compared. It is shown that the GCMs exceed the observed DLR under cloud‐free conditions by 10–20 W m⁻² at this semiarid site on an annual basis, with a strong seasonal dependence. The calculated clear‐sky fluxes are overestimated during the warmer summer season, with large absolute values of DLR, while the biases are reduced in the colder and dryer winter season with smaller fluxes. This gives direct support for recent evidence that the DLR model biases depend systematically on the thermal and humidity structure of the cloudless atmosphere. Fluxes from strongly emitting atmospheres tend to be overestimated, but may be underestimated from atmospheres with smaller emission. This points to common problems inherent in the simulation of the emission from the cloudless atmosphere in current longwave radiation codes.
The comparisons of the all‐sky climatologies at Uardry show that the clear‐sky biases are partly masked in the models with an insufficient cloud‐radiative forcing, thereby counterbalancing the excessive DLR of the cloud‐free atmosphere. On the other hand, when the cloudradiative forcing is improved, the biases in the cloud‐free atmosphere become fully apparent in the all‐sky fluxes.     

The radiative and thermal effects of smoke aerosol over the region of Moscow during the summer fires of 2010

The shortwave radiative forcings of smoke aerosol in the cloudless atmosphere during the summer fires of 2010 in European Russia were quantitatively estimated for the land surface and the atmospheric upper boundary from measurement data obtained at the Zvenigorod Scientific Station of the Obukhov Institute of Atmospheric Physics (OIAP ZSS), Russian Academy of Sciences. Variations in the temperature of the surface air layer due to the smoke-induced attenuation of incoming solar radiation were estimated. The most intensive smoke generation in the atmosphere was observed on August 7–9, 2010, when the maximum aerosol optical thickness amounted to more than 4.0 at a wavelength of 550 nm. In this case, the albedo of single aerosol scattering amounted to ∼0.95–0.96 and the asymmetry factor amounted to ∼0.69–0.70. The maximum shortwave radiative forcing of aerosol amounted to about −360 W/m² for the land surface and almost −150 W/m² for the atmospheric upper boundary. During the period of intensive smoke generation, the cooling of the atmospheric surface layer over daylight hours (12 h) amounted, on average, to ∼6°C. The power character of the dependence of the shortwave radiative forcing of aerosol for the land surface on aerosol optical thickness up to its values exceeding 4.0, which was revealed earlier on the basis of data on aerosol optical thickness (up to 1.5) obtained at the OIAP ZSS during the summer forest and peatbog fires of 2002 in the region of Moscow, was supported.     

Radiative and Thermal Impacts of Smoke Aerosol Longwave Absorption during Fires in the Moscow Region in Summer 2010

The aerosol longwave radiative forcing of the atmosphere and heating rate of the near-surface aerosol layer are estimated for the extreme smoke conditions in the Moscow region in summer 2010. Thermal radiation fluxes in the atmosphere are determined using the integral transmission function and semiempirical aerosol model developed on the basis of standard aerosol models and measurements at the Zvenigorod Scientific Station, Obukhov Institute of Atmospheric Physics, Russian Academy of Sciences. The aerosol radiative forcing reached 33 W/m² at the lower atmospheric boundary and ranged between–1.0 and 1.0 W/m² at the upper atmospheric boundary. The heating rate of the 10-m atmospheric layer near surface was up to 0.2 K/h during the maximum smoke conditions on August 7–9. The sensitivity of the aerosol longwave radiative forcing to the changes in the aerosol absorption coefficient and aerosol optical thickness are estimated.     

Evaluation of the accuracy of downward radiative flux observations at the sea surface

Observations of downward radiative flux at the sea surface generally contain uncertainty due to limited numbers of observations and limitations of auxiliary equipment. The lack of shading from direct solar radiation and ventilation systems causes bias or random errors. To evaluate the error of radiation measurements at buoys, downward shortwave and longwave radiative fluxes are compared with International Satellite Cloud Climatology Project (ISCCP), Japanese 55-year Reanalysis (JRA55), and Moderate Resolution Imaging Spectroradiometer (MODIS) retrieved model calculations of 3-h and daytime averages. Cloud masking is evaluated by a combination of MTSAT-1R and in situ observations. Coincident observations from a land-surface station located near the buoy observatories are compared with satellite and reanalysis products. The bias at buoys, compared with retrievals, approximately over- and under-estimate for longwave and shortwave fluxes, respectively. The bias at buoys is larger and smaller than the land by 23–34 W m^?2 for longwave and 13–51 W m^?2 for shortwave radiation using 3-h averages under clear-sky conditions. The differences in bias decrease when using daytime averages for longwave, but the difference for shortwave increases with daytime averages. To evaluate the effect of environmental factors on buoy observations, we compared rainfall, wind speed, and solar zenith angle with the biases. We found that rainfall and wind speed affect buoy pyrgeometers such that they overestimate the longwave flux. The cosine of solar zenith angle does not cause overestimation for longwave flux, and the effect of dome heating is small. The strong wind causes underestimation of the shortwave radiative flux due to tilting. The effect of wind is reduced when daily averages are used.     

Influence of a high aerosol concentration on the thermal structure of the atmospheric boundary layer

The influence of increased concentrations of submicron aerosol produced by forest fires on thermal characteristics of the atmospheric boundary layer (ABL) in Moscow and its remote vicinity (the town of Zvenigorod) are analyzed on the basis of regular remote measurements of the ABL temperature profile with the use of MTP-5 profilers. In the air basin of a large city, additional aerosol and accompanying pollutants in early morning hours (at small heights of the Sun) most frequently did not cause substantial changes in the ABL thermal structure. In the locality remote from the megalopolis (Zvenigorod), the atmospheric pollution by aerosol led to noticeable changes in the ABL thermal characteristics. Especially strong changes were observed in the daytime, during the maximum supply of solar radiation. In morning hours, the heating rate of the lower 100-m layer of the polluted air exceeded the heating rate of a relatively pure air by more than one degree. In higher layers, the differences between the rates of temperature changes in a relatively clean atmosphere and in an atmosphere polluted by aerosol (in the suburb) were insignificant.     

北京市夏季低层大气NOx、O3垂直分布观测研究

根据 2 0 0 0年夏季在北京 32 5 m铁塔上的一次梯度观测实验 ,给出 8m,12 0 m和 2 80 m三层上的 NO、NO2 、O3 浓度的观测结果。对 NO,NO2 ,O3 小时平均浓度的日变化和垂直分布规律进行了分析 ,结果发现 :(1)各高度上的 NO,NO2 ,O3 浓度均有明显的日变化特征 ,阴雨天的日变化更加复杂 ;(2 ) O3 在晴朗白天有单、双及三峰型分布 ;(3)相对于 12 0 m和 2 80 m,近地面 8m处的 NO浓度最高 ,而 O3 浓度最低 ;(4) NO2 、O3 日平均浓度日变化振幅 12 0 m处最大 ;(5 )中午前后 NO,NO2 ,O3 浓度均在 12 0 m最高。     

基于探空数据的南海表面波导统计特征研究

Based on the global position system(GPS) radiosonde data near the sea surface, the surface duct characteristics over the South China Sea(SCS) were statistically analyzed. The annual surface duct occurrence over the SCS was about 64%. Of the observed surface ducts, duct heights mainly distributed between 18 and 42 m, with M slopes in the range of –0.3 to –0.2 M units/m. Those ducts accounted for about 80% of the ducting cases. For the total profiles, the duct occurrences in a day changed slowly and were more than 60% in all times. The surface ducts formed more easily in the daytime than in the nighttime and most of the duct height were at bellow about 32 m.Additionally, The seasonal variation of the SCS ducts appeared to be evident, except that the mean duct thickness was almost constant, about 33 m for all seasons. The highest occurrence was about 71% in the autumn, followed by in the summer, spring and winter. In spring, their top-height existed more often at a height of more than 48 m.Their mean duct strength became stronger trend from spring to winter, with the M-slope in the range between–0.26 and –0.18 M units/m. Those results agreed well with other studies, provided considering the data resolution.The statistical analysis was reliable and gave the duct estimation for the SCS. Such duct climatology not only has important implications for communication systems and the reliability of the radar observation, but also can provide useful information to improve the accuracy of the meteorological radar measurements.     

Simultaneous Ocean Wave Measurements by the Jason and Topex Satellites, with Buoy and Model Comparisons

The verification phase of the Jason-1 satellite altimeter mission presents a unique opportunity for comparing near-simultaneous, independent satellite measurements. Here we examine simultaneous significant wave height measurements by the Jason-1 and TOPEX/Poseidon altimeters. These data are also compared with in situ measurements from deep-ocean buoys and with predicted wave heights from the Wave Watch III operational model. The rms difference between Jason and TOPEX wave heights is 28 cm, and this can be lowered by half through improved outlier editing and filtering of high-frequency noise. Noise is slightly larger in the Jason dataset, exceeding TOPEX by about 7 cm rms at frequencies above 0.05 Hz, which is the frequency at which the coherence between TOPEX and Jason measurements drops to zero. Jason wave heights are more prone to outliers, especially during periods of moderate to high backscatter. Buoy comparisons confirm previous reports that TOPEX wave heights are roughly 5% smaller than buoy measurements for waves between 2 and 5 m; Jason heights in general are 3% smaller than TOPEX. Spurious dips in the TOPEX density function for 3- and 6-m waves, a problem that has existed since the beginning of the mission, can be solved by waveform retracking.     

Simultaneous Ocean Wave Measurements by the Jason and Topex Satellites,with Buoy and Model Comparisons Special Issue: Jason-1 Calibration/Validation

The verification phase of the Jason-1 satellite altimeter mission presents a unique opportunity for comparing near-simultaneous, independent satellite measurements. Here we examine simultaneous significant wave height measurements by the Jason-1 and TOPEX/Poseidon altimeters. These data are also compared with in situ measurements from deep-ocean buoys and with predicted wave heights from the Wave Watch III operational model. The rms difference between Jason and TOPEX wave heights is 28 cm, and this can be lowered by half through improved outlier editing and filtering of high-frequency noise. Noise is slightly larger in the Jason dataset, exceeding TOPEX by about 7 cm rms at frequencies above 0.05 Hz, which is the frequency at which the coherence between TOPEX and Jason measurements drops to zero. Jason wave heights are more prone to outliers, especially during periods of moderate to high backscatter. Buoy comparisons confirm previous reports that TOPEX wave heights are roughly 5% smaller than buoy measurements for waves between 2 and 5 m; Jason heights in general are 3% smaller than TOPEX. Spurious dips in the TOPEX density function for 3- and 6-m waves, a problem that has existed since the beginning of the mission, can be solved by waveform retracking.     

Intercomparison of GPS radiosonde soundings during the eastern tropical Indian Ocean experiment

Temperature and relative humidity profiles derived from two China-made global positioning system（GPS） radiosondes（GPS-TK and CF-06-A） during the east tropical Indian Ocean（ETIO） experiment were compared with Vaisala RS92-SGP to assess the performances of China-made radiosondes over the tropical ocean.The results show that there have relative large biases in temperature observations between the GPSTK and the RS92-SGP in the low troposphere,with a warm bias of greater than 2 K in the day and a cooling bias of 0.6 K at night.The temperature differences of the CF-06-A were small in the troposphere both in daytime and nighttime,and became large peak-to-peak fluctuations in the stratosphere.The intercomparison of the relative humidity showed that the CF-06-A had large random errors due to the limitation of sensors and the lack of correction scheme,and the GPS-TK had large systematic biases in the low troposphere which might be related to the temperature impact.GPS height measurements are clearly suitable for China-made radiosonde systems operation.At night,the CF-06-A and the GPS-TK could provide virtual potential temperature and atmospheric boundary layer height measurements of suitable quality for both weather and climate research.As a result of the intercomparison experiment,major errors in the Chinamade radiosonde systems were well indentified and subsequently rectified to ensure improving accuracy for historical and future radiosondes.     

Possibilities of X-band nautical radars for monitoring of wind waves near the coast

We present the results of development and testing of a coastal X-band radar system for monitoring wind waves and currents at the Black Sea (near Gelendzhik) created on the basis of nautical radars. Radar measurements of wave heights were validated by data from a wave buoy and a moored acoustic Doppler current profiler (ADCP). The conditions for successful radar measurements of waves in the coastal environment have been determined. It was shown that a radar with an aperture 1° could successfully measure wave heights at a distance of 1.2 km from the radar, when waves arrive at an angle of ±31° to the main sensing direction. In this case, for wave height measurements, the correlation coefficient between the radar and independent data is 0.82 and the standard deviation is 0.26 m.     

Technique and Results of Measurements of Turbulent Helicity in a Stratified Surface Layer

In August 2014, measurements of the turbulent velocity rotor, turbulent temperature gradient, turbulent helicity, and turbulent potential vortex were performed at the Obukhov Institute of Atmospheric Physics testing ground in Tsimlyansk under different stratification conditions. The measurements were carried out using the technique first used in the Tsimlyansk expedition in 2012 [1]. The measuring facility consisted of four three-component acoustic Gill Windmaster anemometers–thermometers placed at the vertices of a rectangular tetrahedron with a base scale of 0.7 m (in contrast to the experiment in 2012, when the base scale was 5 m). The measuring facility was placed on top of a mast with an adjustable height of 3.5, 5, 13.5, and 25 m and was equipped with a rotator. The temperature profile in the 10–600 m layer was continuously recorded by the Kadygrov microwave profiler [2]. The series of density of instantaneous helicity He = u_i'ω'_i = u₁'ω₁' + u₂'ω'₂ + u₃'ω'₃ and average values of the total and its summands were calculated for 12 daytime and 10 daytime 2-hour intervals. The helicity value averaged over 12 day realizations is about 0.2 m/s², and the average cosine is close to 0.08 ± 0.03. At night, the helicity is estimated as 0.07 ± 0.03 m/s², and the cosine is close to 0.025 ± 0.03. For the abovementioned 12 daytime and 10 daytime 2-hour intervals, the covariance and correlation matrices of temperature components, velocity rotor, velocity, and temperature gradient are calculated. The off-diagonal terms of the covariance matrix exceed by absolute values the diagonal terms several times. Similar characteristics of a potential vortex were estimated in the incompressibility approximation. The systematic error due to spatial averaging of the measured quantities is discussed.     

Additional radiative cooling of the upper mesosphere and lower thermosphere caused by tidal perturbations in temperature

The effect of tidal perturbations in temperature on the rate of cooling the upper mesosphere and lower thermosphere in the CO₂ 15-μm band is revised. It is shown that the effect of solar semidiurnal tide on radiative cooling can be neglected. However, the solar diurnal tide leads to a marked increase in the rate of radiative cooling (up to a relative increase by about 0.1 to 0.2) near the equator at altitudes below 100 km. It is possible that this additional cooling is responsible for the air descent observed in the near-equatorial thermosphere at altitudes above 105 km. Original Russian Text ? V.P. Ogibalov, A.I. Pogoreltsev, I.N. Fedulina, G.M. Shved, 2006, published in Izvestiya AN. Fizika Atmosfery i Okeana, 2006, Vol. 42, No. 1, pp. 92–101.     

台风“灿鸿”影响下海浪的数值模拟研究

台风是影响中国黄东海的强天气现象,其引起的强风、巨浪和台风增水严重威胁着沿海地区人民的生命与财产安全。本文以海浪模式SWAN（Simulating Waves Nearshore）与区域海洋模式ROMS（Regional Ocean Modeling System）为基础,构建了中国黄东海海域在201509号台风“灿鸿”影响下的海浪-海洋耦合模式。通过浮标与Jason-2高度计有效波高数据验证了模式结果的准确性。进行了敏感性实验分析,对比耦合（ROMS+SWAN）与非耦合（SWAN）下以及使用不同地形数据（ETOPO1、ETOPO2、GEBCO）、不同物理参数化方案（风能输入、白冠耗散、底摩擦耗散）下的模拟结果差异。结果发现在射阳与前三岛浮标处,使用GEBCO地形数据（15弧秒间隔）下的模拟效果更好且稳定。在空间分布上,台风中心附近的浪流相互作用显著,在其前进方向右侧表现为耦合的有效波高值低于非耦合有效波高值,差值最高可达1米。选择不同风输入与耗散项方案时的模拟差异主要发生在最大波高处,选择不同的风能输入与白冠耗散项方案带来的差异接近0.4米,而底摩擦项方案选择不同带来的差异接近1米。因而在模拟实际的海况时,需要综合考虑这些因素带来的影响,才能达到SWAN海浪模型最好的海浪模拟效果。     

Upper ocean responses to category 5 typhoon Megi in the western north Pacific

Category 5 typhoon Megi was the most intense typhoon in 2010 of the world. It lingered in the South China Sea (SCS) for 5 d and caused a significant phytoplankton bloom detected by the satellite image. In this study, the authors investigated the ocean biological and physical responses to typhoon Megi by using chlorophylla (chla) concentration, sea surface temperature (SST), sea surface height anomaly (SSHA), sea surface wind measurements derived from different satellites and in situ data. The chla concentration (>3 mg/m³) increased thirty times in the SCS after the typhoon passage in comparison with the mean level of October averaged from 2002 to 2009. With the relationship of wind stress curl and upwelling, the authors found that the speed of upwelling was over ten times during typhoon than pretyphoon period. Moreover, the mixed layer deepened about 20 m. These reveal that the enhancement of chla concentration was triggered by strong vertical mixing and upwelling. Along the track of typhoon, the maximum sea surface cooling (6-8℃) took place in the SCS where the moving speed of typhoon was only 1.4-2.8 m/s and the mixed layer depth was about 20 m in pretyphoon period. However, the SST drop at the east of the Philippines is only 1-2℃ where the translation speed of typhoon was 5.5-6.9 m/s and the mixed layer depth was about 40 m in pretyphoon period. So the extent of the SST drop was probably due to the moving speed of typhoon and the depth of the mixed layer. In addition, the region with the largest decline of the sea surface height anomaly can indicate the location where the maximum cooling occurs.     

Using artificial neural networks in the temperature and humidity sounding of the atmosphere

The application of the radiative data inversion technique based on artificial neural networks (ANN) for the meteorological satellite sounding of the atmosphere is described. To increase the efficiency of solving inverse problems, the principal component method is used for the temperature and humidity profiles, as well as for IR radiation spectra, which allows the problem dimensionalities to be reduced substantially. Based on numerical experiments, errors of the temperature and humidity sounding are analyzed from the spectra of outgoing IR radiation (that were measured by the IKFS-2 instrument onboard the Meteor Russian satellite) using the iterative physical-mathematical (IPM) algorithm, multiple linear regression (MLR), and ANN-based methods. Appreciable advantages of the ANN-based method are revealed as compared to the MLR method. Therefore, in temperature sounding, the MLR method has a markedly large error at heights of 1–12 km (a difference of up to 1 K), while the IPM algorithm has almost the same error as the ANN method. The humidity determination error is about 10% when the ANN method is used at heights of 0–12 km. The IPM approach yields approximately the same error in the lower troposphere, but as the height increases the advantages of the ANN method grow.     

Current changes of the lower troposphere temperature in the Moscow region

Modern climatic changes for 1991–2013 in the lower 4-km layer of the atmosphere in the Moscow region are discussed based on long-term measurements using radiosondes in Dolgoprudny near Moscow and sensors installed on a high mast in Obninsk and on a television tower in Ostankino in Moscow. It is shown that at the end of the 20th century and the beginning of the 21st century the mean-annual air temperature at all heights from 2 to 4000 m increased by an average of 0.1°C per year. In recent years, the warming has slowed. Over the last two decades, long-term changes were multidirectional, depending on the season: warming in May–December, cooling in January–February, and no statistically significant changes in March and April. The probable reason for the temperature decrease in the middle of the cold period is changes in the large-scale atmospheric circulation during recent years (the negative phase of the North Atlantic Oscillation in early 2010s). In recent years, the Moscow region climate continentality has increased because of warming in summer and cooling in winter, despite the secular decreasing trend, which was noted before. Mean daily and annual warming rates in Dolgoprudny were higher than in Obninsk. The probable reason is the northward construction expansion and the strengthening of the Moscow heat island. The highest annual temperature amplitude is recorded at heights of 200–300 m.     

基于SPOT6遥感影像的滩涂湿地入侵种互花米草植株高度的反演研究

本文以SPOT6 高空间分辨率遥感影像为数据源,通过植被覆盖度和地上生物量两个参数进行滩涂湿地入侵种互花米草植株高度的估算研究。结果表明,三沙湾滩涂湿地互花米草植株高度平均值为2.04 m,以1~2 m和2~3 m植株为主要分布高度,分布面积分别为6.83 km2和10.31 km2,占研究区互花米草总面积的33.83%和51.06%,小于1 m和大于3 m的互花米草仅占9.26%和5.84%。估算值与真实值之间的均方根误差为0.204,绝对误差为0.04~0.37 m。该方法是对高空间分辨率光学影像应用研究的重要尝试,其反演方法具有较好的可行性,可较为准确的获取滩涂湿地植株高度信息。     

Determining the accuracy of estimation of the two-dimensional stratospheric temperature field based on satellite measurements of limb radiation in the CO2 15-μm absorption band with high spectral resolution

The problem of reconstructing the temperature distribution along optical paths from satellite measurements of the Earth’s limb radiation in the CO₂ 15-μm absorption band with a high spectral resolution is formulated and analyzed on the basis of numerical experiments performed in accordance with the MIPAS experiment. It is shown that the two-dimensional temperature field can be obtained through the processing of radiation measurements on paths with different target heights provided that spectral channels with essentially different optical thicknesses are used. The error in the stratospheric temperature determination varies from 1.8 to 5.6 K and depends on the target height of the optical path and the distance from the target point. The best horizontal resolution is 73–100 km, and it is achieved for optical paths with a target height of about 18–20 km.     

Direct observation of radiative flux in the southern yellow sea

Direct measurements of four radiative components at air-sea boundary layer were conducted in the southern Yellow Sea during three cruises (seasons) in 2007. Simultaneous observations of meteorological (cloud cover, air temperature and humidity) and oceanographic (sea surface temperature) parameters were carried out. Observational results of radiative fluxes and meteorological and oceanographic parameters are presented. Mean diurnal cycles of four radiative components, net radiation, and sea surface albedo are calculated to achieve averages in different seasons. Net radiative fluxes in three seasons (winter, spring, autumn) are 8, 146, 60 W/m², respectively. Comparisons between the observed radiative fluxes and those estimated with formulas are taken.