NCEP Reanalysis Research Articles

The meso-<x content-type="symbol">β</x><sub><x content-type="symbol"> </x></sub>scale characteristics during the “0866” extremely heavy rainfall in South China by using SACDM

The research on heavy rainfall depended greatly on high-resolution data, which could be obtained by using the intensive observation, model simulation, radar detection, and satellite detection. However, it was difficult to discover the fine features of the heavy rainfall system because the limitation of the method of analyzing the big data mentioned above. Therefore, the paper aimed at introducing a new method (synthetical analysis and classifying diagnosis method, SACDM) for effectively analyzing various kinds of data. SACDM possessed a suit of scheme for the data processing and diagnosing. Firstly, the secondary processed data could be obtained by using various key techniques such as numerical simulation technology, numerical calculation technology, radar mosaic technology, and 3D wind field retrieval technology. Secondly, based on the idea of classifying diagnosis, different data were effectively used to analyze the corresponding features on heavy rainfall. Based on various high-resolution data including the intensive observation data from SCHeREX (South China Heavy Rainfall Experiment), the radar mosaic data, the radar retrieved data, the meso-scale model data, the satellite data, the convectional observation data, the automatic station data, and the NCEP (National Centers for Environmental Prediction) reanalysis data, the paper studied the fine features of the South China extremely heavy rainfall occurred at 5–7 June 2008 by using SACDM, and the following conclusions could be obtained. The unique coupling between the southerly upper level jet and low level jet (LLJ) was favorable for the South China rainfall event. An obvious low-latitude vortex was discovered. Different from most middle-high latitude vortexes, the vortex was greatly influenced by the southwesterly monsoon surges. Dynamical elements played more important roles than thermal elements during the formation period of vortex. During the mature period of vortex, thermal elements played more important roles than dynamical elements. Divergent wind produced positive kinetic energy crossing isobars, which was favorable of the vortex rainfall. The monsoon surges from the Bay of Bengal penetrated into a Key Zone (the southeast of vortex) and enhanced the southwesterly wind there. The monsoon surges also took advantageous physical quantities including water vapor, vorticity, divergence, and vertical velocity to the Key Zone. With the influence of favorable physical quantities, meso-scale convective system (MCS) frequently emerged at the southeast of vortex. MCS-E was the strongest convection in the heavy rainfall event. It possessed a southwest-northeast echo belt and a strong TBB (temperature of blackbody brightness) less than 200 K. A meso- β scale LLJ was also discovered to be parallel to MCS-E, and it indeed triggered and fed the linear convection according to high-resolution analysis. The accumulation and release of CAPE (convective available potential energy) was a key reason for the evolution of MCS-E. Active meso-γ scale convective cells prolonged the lifetime of MCS-E, and the convective cells directly produced the precipitation peaks in the rainfall center according to the 6-min rainfall and radar echo. As a result, all the aforementioned features were reduced to a suit of conceptual model to interpret the possible reasons of the heavy rainfall. SACDM could play an important role in studying the fine features of heavy rainfall according to this paper.

Stratospheric precursor of non-uniform variation in early spring surface temperature over Eurasia

The stratospheric influences on the non-uniform variation in early spring (March–April, MA) surface temperature over Eurasia is investigated based on the ERA-Interim, NCEP-1, and NCEP-2 reanalysis data for the period 1980–2016. A lead–lag correlation is found between preceding winter (December–February, DJF) stratospheric polar vortex displacements (SPVD) and the MA west–east seesaw pattern in surface temperature over Eurasia. Further analysis reveals that the East Asian jet stream may act as a bridge linking DJF SPVD and MA surface temperature over Eurasia. A positive change in SPVD is associated with a decelerated polar jet stream and an accelerated East Asian jet stream in the troposphere in DJF. The East Asian jet stream signal can persist into MA. As a result, anomalous southerly/northerly winds prevail over western/eastern Eurasia, accounting for the west–east surface temperature seesaw over Eurasia.

Formation and Maintenance of a Long-Lived Taiwan Rainband during 1–3 March 2003

Abstract Taiwan rainbands (TRs), defined here as convective lines, which form off the mountainous eastern coast of Taiwan under weakly synoptically forced weather conditions, are a well-known mesoscale phenomenon, but their formative processes remain the subject of debate. This study uses surface and radar observations within the coastal zone of eastern Taiwan and NCEP reanalysis data to document a long-lived TR with a lifetime of ~36 h during 1–3 March 2003 to advance the current general understanding of mechanisms responsible for the TR’s formation and maintenance. Detailed analyses indicate that the rainband was initiated by convergence that was produced as low-level environmental northeasterly/easterly onshore flow encountered topographically blocked northerlies that developed nearshore. The northerly blocked flow was observed to weaken and subsequently dissipate because of changing synoptic pressure patterns that caused prevailing southeasterlies/southerlies at low levels. However, colder nearshore air that resulted from the combined effects of orographic blocking, the evaporation of the TR’s precipitation, and radiative cooling over coastal land continued to persist and acted to provide a continuing source of lifting for the subsequent maintenance of moist convection. Temporal variations in the precipitation intensity of the studied TR were also shown to be consistent with the theoretical prediction of the interaction between the cold pool and ambient vertical shear. This study suggests that multiple precipitation mechanisms, which involve interactions of diurnally, topographically, and convectively generated circulations along the mountainous coast, may operate and contribute to the longevity of a TR event under suitable circumstances, such as the rapidly evolving synoptic flow observed in the present case.

Assessment of the quality of NCEP-2 and CFSR reanalysis daily temperature in China based on long-range correlation

The daily temperatures from observational data, NCEP-2 and CFSR reanalysis data all exhibit long-range correlation (LRC) characteristics, which provides a test bed for assessing the reliability of reanalysis data. In this study, the quality of the NCEP-2 and CFSR data in China are evaluated on the basis of the LRC characteristics of daily temperatures, including daily average temperature (DAT), daily maximum temperature (DMAT), daily minimum temperature (DMIT), and diurnal temperature range (DTR). Compared with the observations, the quality of NCEP-2 daily temperature is relatively good in central and eastern Northwest China, and most of central and eastern China, especially for NCEP-2 DMAT. However, the NCEP-2 reanalysis data as well as CFSR has a significant difference with the LRC of the observations in most of Sichuan, Qinghai-Tibet Plateau and some areas of southwestern Xinjiang at a significance level of Alpha = 0.05. In general, the LRC characteristics of NCEP-2 daily temperature perform better than that of CFSR data. As far as DAT is concerned, CFSR perform worse in central and eastern Northwest China, and better than NCEP-2 only in South China and eastern Jiangnan. The quality of the CFSR DMAT is worse than that of NCEP-2 in central and eastern Northwest China, western Inner Mongolia, and eastern China. The quality of NCEP-2 DMIT is better than CFSR in central and eastern Northwest China, most of Inner Mongolia, and is worse than it in most of South China and eastern Jiangnan. The reliability of the CFSR DTR is very low in most of China.

О низкочастотной изменчивости баланса осадки-испарение на границе океана и атмосферы в Атлантическом океане

Spatial distribution of climatic variables and linear trends of surface freshwater flux (precipitation minus evaporation) has been analyzed based on NCEP reanalysis monthly dataset for 1948-2012. Low- frequency surface freshwater flux variability’ (more than 10 and 30 years) has been estimated in the present study.

Impacts of Indonesian Throughflow on seasonal circulation in the equatorial Indian Ocean

Impacts of the Indonesian Throughflow (ITF) on seasonal circulation in the equatorial eastern Indian Ocean are investigated using the ocean-only model LICOM by opening and closing ITF passages. LICOM had daily forcing from NCEP reanalysis data during 2000-2011. It can reproduce vertical profiles of mean density and buoyancy frequency of World Ocean Atlas 2013 data. The model also simulates well annual oscillation in the central Indian Ocean and semiannual oscillation in the eastern Indian Ocean of sea level anomalies (SLA) using satellite altimeter data, as well as the semiannual oscillation of surface zonal equatorial currents of Ocean Surface Current Analyses Real Time current data in the equatorial Indian Ocean. The wave decomposition method is used to analyze the propagation and reflection of equatorial long waves based on LICOM output. Wave analysis suggests that ITF blockage mainly influences waves generated from the Indian Ocean but not the Pacific Ocean, and eastern boundary reflections play an important role in semiannual oscillations of SLA and zonal current differences in the equatorial Indian Ocean associated with ITF. Reconstructed ITF-caused SLA using wave decomposition coefficient differences between closed and open ITF-passage experiments suggest both Kelvin and Rossby waves from the first baroclinic mode have comparable contributions to the semiannual oscillations of SLA difference. However, reconstructed ITF-caused surface zonal currents at the equator suggest that the first meridional-mode Rossby wave has much greater contribution than the first baroclinic mode Kelvin wave. Both reconstructed sea level and zonal currents demonstrate that the first baroclinic mode has a greater contribution than other baroclinic modes.

Moisture sources of extreme summer precipitation events in North Xinjiang and their relationship with atmospheric circulation

In this study, the daily observational precipitation data and NCEP reanalysis data during 1951–2014, Euler and Lagrangian method were used to investigate the moisture sources of summer extreme precipitation events in North Xinjiang. The results show that water vapor at low and upper levels of most summer heavy rain (more than 50 mm d−1 and less than 100 mm d−1) in North Xinjiang are mainly transported by westerly circulation from the North Atlantic Ocean and the Eurasian continent. However, rainstorms of more than 100 mm d−1, which are rarely observed, are dominated by vertically integrated moisture from the North Atlantic, Arctic Oceans, and the Eurasian continent, in addition to low-level moisture from the Indian Ocean. Among these sources, the anomalous low-level moisture from the Indian Ocean, which is closely associated with stronger meridional circulation, is considered to be more important with respect to rainstorms. On the days prior to rainstorm days, stronger meridional circulation leads to an anomalous pressure gradient force, which can transport low-level moisture from the Indian Ocean along the eastern periphery of the Tibetan Plateau to North Xinjiang. Furthermore, moisture from the North Atlantic, Arctic Oceans, the Eurasian continent, and the Indian Ocean converge together to influence rainstorm development in this region.

Simulation of extreme rainfall event of November 2009 over Jeddah, Saudi Arabia: the explicit role of topography and surface heating

In this paper, a nonhydrostatic Weather Research and Forecasting (WRF) model has been used to simulate the extreme precipitation event of 25 November 2009, over Jeddah, Saudi Arabia. The model is integrated in three nested (27, 9, and 3 km) domains with the initial and boundary forcing derived from the NCEP reanalysis datasets. As a control experiment, the model integrated for 48 h initiated at 0000 UTC on 24 November 2009. The simulated rainfall in the control experiment depicts in well agreement with Tropical Rainfall Measurement Mission rainfall estimates in terms of intensity as well as spatio-temporal distribution. Results indicate that a strong low-level (850 hPa) wind over Jeddah and surrounding regions enhanced the moisture and temperature gradient and created a conditionally unstable atmosphere that favored the development of the mesoscale system. The influences of topography and heat exchange process in the atmosphere were investigated on the development of extreme precipitation event; two sensitivity experiments are carried out: one without topography and another without exchange of surface heating to the atmosphere. The results depict that both surface heating and topography played crucial role in determining the spatial distribution and intensity of the extreme rainfall over Jeddah. The topography favored enhanced uplift motion that further strengthened the low-level jet and hence the rainfall over Jeddah and adjacent areas. On the other hand, the absence of surface heating considerably reduced the simulated rainfall by 30% as compared to the observations.

Circulation characteristics of persistent cold spells in central–eastern North America

The circulation patterns of persistent cold weather spells with durations longer than 10 days in central–eastern North America (United States and Canada; 32°–52°N, 95°–65°W) are investigated by using NCEP reanalysis data from 1948 to 2014. The criteria for the persistent cold spells are: (1) three-day averaged temperature anomalies for the regional average over the central–eastern United States and Canada must be below the 10th percentile, and (2) such extreme cold spells must last at least 10 days. The circulation patterns associated with these cold spells are examined to find the common signals of these events. The circulation anomaly patterns of these cold spells are categorized based on the El Nino–Southern Oscillation, Arctic Oscillation (AO), and other climate indices. The atmospheric circulation patterns that favor the cold spells are identified through composites of geopotential height maps for the cold spells. Negative AO phases favor persistent cold spells. Phases of sea surface temperature (SST) modes that are associated with warm SSTs in the eastern extratropical Pacific also favor persistent cold events in the study region. Stratospheric polar vortex breakdown alone is not a good predictor for the regional extreme cold spells in central–eastern North America. The meridional dispersions of quasi-stationary Rossby waves in the Pacific–North America sector in terms of cut-off zonal wavenumber modulated by background flow are analyzed to provide insight into the difference in evolution of the cold spells under different mean AO phases. The waveguide for AO > 1 is in a narrow latitudinal band centered on 40°N, whereas the waveguide for AO <–1 is in a broader latitudinal band from 40° to 65°N. The circulation patterns and lower boundary conditions favorable for persistent cold spells identified by this study can be a stepping-stone for improving winter subseasonal forecasting in North America.

Toward downscaling oceanic hydrodynamics – suitability of a high-resolution OGCM for describing regional ocean variability in the South China Sea

Summary We suggest to transfer the empirical downscaling methodology, which was developed mostly for atmospheric dynamics and impacts, to regional ocean problems. The major problem for doing so is the availability of decades-long and homogeneous and spatially detailed data sets. We have examined the performance of the STORM multidecadal simulation, which was run on a 0.1° grid and forced with 1950–2010 NCEP re-analyses, in the South China Sea and found the data suitable. For demonstration we build with this STORM-data downscaling model for the regional throughflow. The STORM data is compared with AVISO satellite observations and the ocean re-analysis dataset C-GLORS. We find the seasonal patterns and the inter-annual variability of sea surface height anomaly in both the C-GLORS data and the STORM simulation consistent with the AVISO-satellite data. Also the strong westward intensification and the seasonal patterns of South China Sea circulation steered by the monsoon have been presented well. As an important indicator of vertical movement, the sea surface temperature distribution maps are also very close, especially for the narrow upwelling region in summer. We conclude that the output of the STORM simulation is realistically capturing both the large-scale as well as the small-scale dynamical features in the South China Sea.

The uncertainties of residual diagnosis of atmospheric diabatic heating from ERA40 and NCEP reanalysis over Tibetan Plateau

The Tibetan Plateau (TP), a giant elevated landscape, plays a key role in modulating the Asian summer monsoon via dynamic, thermodynamic, and mechanical lifting mechanisms. The spatial and temporal distribution of atmospheric diabatic heating (DH) is vitally important to understand the coupling of energy and moisture between the land surface and the atmosphere over TP. In this study, the residual diagnosis of DH from ERA40 and NCEP reanalysis, in combination with the precipitation and latent heating (LH) results from Tropical Rainfall Measuring Mission Precipitation Radar (TRMM PR) are investigated to reveal the uncertainties in DH over TP. Significant discrepancies of column integrated DH (CDH) between ERA40 and NCEP are found in the southern slope area of TP in summer. The CDH from ERA40 is much stronger than NCEP at high altitudes on the southern slope of TP. The area with strong ERA40 atmospheric heating extends from lower altitudes to higher altitudes exceeding 4000 m isohypse. However, in the heating diagnosis of NCEP, strong atmospheric heating is only located at altitudes lower than 4000 m isohypse. These differences are evident in DH at both the ground layer and 400–500 hPa layer, revealing a significant contribution from LH because sensible heating (SH) peaks at near-surface atmosphere and LH peaks at low to middle atmosphere. As an indicator of LH, the precipitation in southern TP estimated by ERA40 is strong (>10 mm/d) in the 25°–30°N area from April to October. The precipitation observations from TRMM PR and the diagnosis from NCEP diagnosis do not agree about this phenomenon. Instead, the precipitation detected by TRMM PR is mainly located in the area to the south of 25°N. The spatial pattern of overestimated precipitation by ERA40 mostly matches the DH overestimation. Based on the vertical cross-section of DH and the atmospheric circulation along 92.5°E, strong positive ERA40 DH (>4 K/d) over the high altitudes of southern TP (~25°–30°N) extends from surface to high troposphere (~300 hPa) vertically in summer. This fact indicates there is strong latent heating released from deep convective rains in those areas which makes a contribution to DH that is comparable with SH. The associated NCEP DH in the same area can reach only the low troposphere (~700 hPa) and the maximum heating generally is located in the near-surface atmosphere. This conclusion implies that in NCEP diagnosis, only shallow and weak rains can occur in this area and the surface SH dominates DH here. Even at the south edge of main body of TP (to north of 30°N), ERA40 DH in summer can be as high as 6–9 K/d and extend from the surface to ~350 hPa isobaric surface, while the associated NCEP DH is only less than 4 K/d. The diagnosis of vertical velocity and horizontal divergence at the 200 hPa layer from ERA40 is also stronger that from NCEP. The mean vertical profiles of ERA40 DH in summer show positive heating through the surface to 200 hPa and maximum value at 700 (500) hPa on the south (southwest) slope of TP. The shape agrees well with that of the TRMM LH profile, but the value of ERA40 DH is about 2–3 times that of TRMM LH. The NCEP DH profiles show a different shape with peaks at the near-surface layer indicating more contribution from surface SH than from LH, but its amplitude is relatively closer to TRMM LH. We hypothesize that the uncertainties of the vertical structure of precipitation and the associated LH in the southern slope area of TP are the main obstacles preventing us from understanding the real mechanisms of TP-atmosphere interaction.

Potential Value of Expert Elicitation for Determining Differential Credibility of Regional Climate Change Simulations: An Exercise with the NARCCAP co-PIs for the Southwest Monsoon Region of North America

Abstract In this brief article, we report the initial results of an expert elicitation with the co-PIs (regional climate modelers) of the North American Regional Climate Change Assessment Program regarding their evaluation of the relative quality of regional climate model simulations focusing on the subregion dominated by the North American monsoon (NAM). We assumed that an expert elicitation framework might reveal interesting beliefs and understanding that would be different from what would be obtained from calculating quantitative metrics associated with model quality. The simulations considered were of six regional climate models (RCMs) that used NCEP Reanalysis 2 as boundary conditions for the years 1980–2004. The domain covers most of North America and adjacent oceans. The seven participating regional modelers were asked to complete surveys on their background beliefs about model credibility and their judgments regarding the quality of the six models based on a series of plots of variables related to the NAM (e.g., temperature, winds, humidity, moisture flux, precipitation). The specific RCMs were not identified. We also compared the results of the expert elicitation with those obtained from using a series of metrics developed to evaluate a European collection of climate model simulations. The results proved to be quite different in the two cases. The results of this exercise proved very enlightening regarding regional modelers’ perceptions of model quality and their beliefs about how this information should or should not be used. Based on these pilot study results, we believe a more complete study is warranted.

2012年9月2~3日浙中地区强对流过程分析

利用常规观测资料、NCEP实时再分析资料及多普勒雷达资料对2012年9月2~3日夜里浙中地区一次强对流天气过程进行诊断分析。结果表明：过程前期低层增温增湿有利于不稳定层结形成与不稳定能量积累，高空西北气流的引导作用下，冷空气和中低层切变线触发了这次强对流天气过程；对流区上空湿度层结结构的差异，导致本次强对流天气以短时强降水为主；高层存在下伸的θse呈漏斗状分布，在锋区上有较大的上升运动与比湿，有利于对流性天气产生；雷达回波图上以回波结构致密、低质心高效率的强降水回波为主；雷达反射率因子和径向速度特征变化揭示了强对流天气发展消散规律；金衢盆地地形对暴雨增幅以及强对流增强作用较明显。 The conventional observations, NCEP reanalysis grid data and Doppler Radar data, are used to diagnose and analyze a Strong Convection Event occurred in the central Zhejiang Province on 2nd to 3rd September 2012 .The results show that: The process early low-level warming humidification is conducive to the formation of unstable stratification and unstable energy accumulation; the guiding role of the high-altitude northwest flow of cold air and level wind shear line triggered the strong convection weather process; the differences of humidity stratification structure over the convection zone, resulting in the strong convective weather is given priority to with short-term heavy precipitation; the senior stretched out in the presence of θse, projecting funnel-shaped distribution, larger upward motion and specific humidity in the frontal zone, is advantageous to the convectional weather; the radar data showed the details of dense structure, high efficiency and low quality strong precipitation echo for the 2nd September event; the characteristics of radar reflectivity factor and radial velocity change reveals the law of development and dissipation occurred in the strong convection weather; the Jinqu basin topography played an important role in increasing the rainstorm and strengthen the strong convection.

Analysis of Meteorological Conditions for Fog and Haze in the Eastern and Central Regions of China during January, 2013

Based on the data of conventional meteorological observation, NCEP reanalysis data and atmospheric composition observation, a comprehensive analysis of the three kinds of persistent fog and haze in eastern China in January 2013 was carried out. The results show that the process of persistent fog and haze is in the background of static weather, and the zonal circulation in the middle and high latitudes is not conducive to the south of the cold air. In the eastern part of China, near-surface wind speed is low under the controlled of pressure field, which is conducive to the formation and maintenance of haze. The formation of inversion layer, the height of the mixed layer, the stratified structure of the upper dry layer, the ground wind speed and so on can represent the static stability of the atmosphere. In the actual forecast, fog and haze can be distinguished from the angle of relative humidity, PM2.5 concentration, diurnal variation characteristics, mixed layer height and energy structure, industrial structure and local and surrounding economic development level.

1330号台风“海燕”路径北翘的原因及其对华南的影响

利用常规气象观测资料、间隔为6小时的1˚ × 1˚NCEP再分析资料和卫星云图，对1330号“海燕”台风路径北翘东移的原因，以及其对华南地区所带来的强降水过程进行分析。结果表明：台风的路径和西太平洋副高的强度及位置演变密切相关，副高西伸加强时，台风位于副高南侧，受东风气流引导向西行，10日起，台风位于海南省南部，受冷空气影响，副高减弱东退，台风逐渐调整至副高西侧，10日20时，台风受南风气流引导而转向北行。台风登陆前，受台风倒槽影响，我国华南地区有充沛的水汽和强烈的上升运动，降水与850 hPa涡度场、散度场有较好的对应关系，强降水过程中有明显的水汽输送带和水汽辐合与动力条件相配合。台风登陆后，螺旋雨带降水逐渐减弱，广西东南部云系再生，从而产生又一波降水过程。 Based on the conventional meteorological observation data and the 1˚ × 1˚ NCEP reanalysis data and satellite cloud images with a time interval of 6 hours, the reason for the eastward migration of typhoon trail of “Haiyan” No. 1330 was analyzed. And the impact of typhoon in southern China which led to strong precipitation was also analyzed. The results show that the typhoon path is closely related to the intensity and position evolution of the western Pacific subtropical high. When the subtropical high is strengthened, the typhoon is located on the south side of the subtropical high, guided by the east wind flow westward. From 10 onwards, the typhoon is located in the south of Hainan Province, the typhoon is affected by cold air, subtropical high weakened eastward, and the typhoon gradually adjusts to the west side of the subtropical high. At 20 o’clock on the 10th, the typhoon was led by the south wind and turned northbound. Before typhoon landing, by the typhoon inverted trough, China’s southern region has abundant water vapor and a strong upward movement; precipitation and 850 hPa vorticity field, divergence field has a good correspondence. During the heavy rainfall, there is obvious water vapor conveyor belt, water vapor convergence and dynamic condition. When typhoon landed, the spiral rain gradually reduced and the southeastern Guangxi cloud regenerated, resulting in another wave of precipitation process.

Impact of the Barents Sea SST in Autumn on the Winter Climate in Northeast China

We studied effects of sea surface temperature anomaly (SSTA) in the Barents Sea in autumn on the atmospheric circulation in northeast China in winter, using the NCEP reanalysis data and sea surface temperature (SST) data of the Hadley Center. The results show that the ocean thermal conditions in the Barents Sea in autumn can be used as an important reference factor for predicting the cold air activity in China. When the sea surface temperature anomaly of the Barents Sea elevated in the autumn, the sea-level pressure anomaly elevated in eastern China on December, northeast China and southeastern Russia on January and February. In the years when the SSTA of the Barents Sea elevated in the autumn, the abnormal high-pressure ridge developed over Europe, and the geopotential height in western China appeared negative anomaly at 500 hPa. At 1000 hPa, the Mongolia high-pressure increased and the northerly airflow strengthened the cold high-latitude air broke out to the south, which was easy to affect northeast and north of China. In negative SSTA years, the high-pressure ridge was west to the north Atlantic, and the geopotential height in central and northern Siberia appeared negative anomaly at 500 hPa; the Mongolia high-pressure was weakened at 1000 hPa.

Impact of different cumulus convective parameterization schemes on the simulation of precipitation over China

The impact of two cumulus convective schemes on the simulation of the precipitation over China is investigated using the Weather Research and Forecasting (WRF) model. Simulations for the period of 1982–2004 are performed at a horizontal resolution of 30 km and forced by NCEP Reanalysis II data. Results show precipitation simulated with the WRF model is quite sensitive to the choice of Kain–Fritsch and Grell cumulus schemes. Both the schemes have distinct skills in predicting the seasonal mean pattern, annual cycle and interannual variation in precipitation. The results show that the Kain–Fritsch scheme tends to overestimate the magnitude of the summer and annual mean precipitation over the main rain-belts, while the Grell scheme tends to underestimate these effects, particularly the simulation of the summer extreme precipitation. However, the Kain–Fritsch scheme is more skilful in capturing the seasonal mean pattern and annual cycle with higher spatial correlations in the main rain-belts. The Grell scheme shows some advantages for northern China and the Tibetan Plateau, especially in representing the interannual variation. The optimal ensemble approach is used to determine the best combination of the two schemes, with the results giving a better overall performance than the individual schemes alone in predicting summer precipitation. The temporal correlation coefficient of precipitation for the ensemble is significantly higher, while the root mean square error of extreme precipitation is reduced compared with the Kain–Fritsch and Grell results. This shows that the ensemble approach based on the optimal ensemble weight combines the advantages of the two cumulus schemes efficiently.

Upper ocean response to typhoon Megi (2010)

In this paper, the response of the upper ocean to typhoon Megi is analyzed and studied by using the sea surface temperature (SST), 500hPa height field and wind field of NCEP reanalysis data and Argo buoy data. The results show that sea surface temperature (SST) will decrease significantly after typhoon, and on the right side of typhoon path cooling is more obvious than the left; the temperature changes dramatically on the right side of Megi path, and correspondingly the depth variation in mixed layer is also intense, and the distance between buoy and the center of the typhoon will al so affect the severity of the temperature variavtion, the salinity may increase or decrease after typhoon, it depends on the evaporation and precipitation or other relevant factors in this area.

Monitoring of Arctic surface sudden warming events in late December 2015 with satellite remote sensing data

The explosively sudden warming of synoptic scale at the Arctic surface is often caused by meridional transport of lower latitude warm air or the ocean warm currents into the Arctic. The explosively sudden warming event that the Arctic surface temperature reached above 0°C on 29th December 2015 caused global concern. In the present paper, a variety of remote sensing data obtained by the AIRS (Atmospheric Infrared Sounder) flying on board NASA’s Aqua satellite were applied to monitor the abrupt changes in the atmospheric temperature, water vapor and ozone over the Flam Strait. AIRS measurements showed that the water vapor and temperature increased significantly beginning on December 27th, reached a peak on the 29th, then began to fall and oscillate, remaining above the December average value until January 2nd. At the same time, the atmospheric ozone showed the opposite change, having significantly reduced beginning on the 27th, and reached the minimum value on the 29th, after which it began to rebound and oscillate, then returned to near the December average value until January 2nd. The water vapor mainly changed from the surface to the 100 hPa height. On December 29th, the maximum increase of water vapor reached six times that of the December average at the 400 hPa height, the temperature changes mainly occurring from the surface to the 250 hPa height. The surface temperature reached to above 0°C on the 29th. The total amount of ozone changes became faster and greater. Compared to December 26th, the total amount of ozone reduced by 102 DU, thus reaching more than 1/3 of the December average. The ozone vertical profile mainly changed at the 400–5 hPa height. Compared to the 27th, the reduction of the ozone vertical profile accounted for 80%–90% of the total amount at this height on December 29th. Using NCEP reanalysis data, further combined with HYSPLIT air mass backward trajectory tracking, the analysis showed that the functionary mechanism which caused the surface explosively sudden warming was that the North Atlantic low-pressure storms rapidly transported large amounts of warm and moist air at low latitudes to the Arctic, which led to a dramatic increase in the low layer temperature and water vapor content. Additionally, the atmosphere was transported from low latitudes to higher latitudes, thereby harmonizing with the vertical motion of the atmosphere from the low level to the upper level. This led to the dramatic changes in ozone distribution from the upper troposphere to the stratosphere, in turn resulting in dramatic changes in the total ozone and vertical profiles. A typical example of satellite remote sensing monitoring showed that it was the power transmission of the synoptic scale which caused the rapid and dramatic changes of heat, water vapor and ozone in the Arctic.

Validation of INSAT-3D sounder data with in situ measurements and other similar satellite observations over India

Abstract. To date, several satellites measurements are available which can provide profiles of temperature and water vapour with reasonable accuracies. However, the temporal resolution has remained poor, particularly over the tropics, as most of them are polar orbiting. At this juncture, the launch of INSAT-3D (Indian National Satellite System) by the Indian Space Research Organization (ISRO) on 26 July 2013 carrying a multi-spectral imager covering visible to long-wave infrared made it possible to obtain profiles of temperature and water vapour over India with higher temporal and vertical resolutions and altitude coverage, besides other parameters. The initial validation of INSAT-3D data is made with the high temporal (3 h) resolution radiosonde observations launched over Gadanki (13.5° N, 79.2° E) during a special campaign and routine evening soundings obtained at 12:00 UTC (17:30 LT). We also compared INSAT-3D data with the radiosonde observations obtained from 34 India Meteorological Department stations. Comparisons were also made over India with data from other satellites like AIRS, MLS and SAPHIR and from ERA-Interim and NCEP reanalysis data sets. INSAT-3D is able to show better coverage over India with high spatial and temporal resolutions as expected. Good correlation in temperature between INSAT-3D and in situ measurements is noticed except in the upper tropospheric and lower stratospheric regions (positive bias of 2–3 K). There is a mean dry bias of 20–30 % in the water vapour mixing ratio. Similar biases are noticed when compared to other satellites and reanalysis data sets. INSAT-3D shows a large positive bias in temperature above 25° N in the lower troposphere. Thus, caution is advised when using these data for tropospheric studies. Finally it is concluded that temperature data from INSAT-3D are of high quality and can be directly assimilated for better forecasts over India.