Interdecadal changes in the storm track activity over the North Pacific and North Atlantic

Analysis of NCEP-NCAR I reanalysis data of 1948–2009 and ECMWF ERA-40 reanalysis data of 1958–2001 reveals several significant interdecadal changes in the storm track activity and mean flow-transient eddy interaction in the extratropics of Northern Hemisphere. First, the most remarkable transition in the North Pacific storm track (PST) and the North Atlantic storm track (AST) activities during the boreal cold season (from November to March) occurred around early-to-mid 1970s with the characteristics of global intensification that has been noticed in previous studies. Second, the PST activity in midwinter underwent decadal change from a weak regime in the early 1980s to a strong regime in the late 1980s. Third, during recent decade, the PST intensity has been enhanced in early spring whereas the AST intensity has been weakened in midwinter. Finally, interdecadal change has been also noted in the relationship between the PST and AST activities and between the storm track activity and climate indices. The variability of storm track activity is well correlated with the Pacific Decadal Oscillation and North Atlantic Oscillation prior to the early 1980s, but this relationship has disappeared afterward and a significant linkage between the PST and AST activity has also been decoupled. For a better understanding of the mid-1970s’ shift in storm track activity and mean flow-transient eddy interaction, further investigation is made by analyzing local barotropic and baroclinic energetics. The intensification of global storm track activity after the mid-1970s is mainly associated with the enhancement of mean meridional temperature gradient resulting in favorable condition for baroclinic eddy growth. Consistent with the change in storm track activity, the baroclinic energy conversion is significantly increased in the North Pacific and North Atlantic. The intensification of the PST and AST activity, in turn, helps to reinforce the changes in the middle-to-upper tropospheric circulation but acts to interfere with the changes in the low-tropospheric temperature field.     

北大西洋臭氧极小值和北太平洋极大值及其相互关系

利用1979～2002年TOMS卫星观测资料,采用臭氧总量纬向偏差和区域强迫的分析方法,研究北大西洋东北部大气臭氧低值与北太平洋西北部臭氧高值的季节变化过程和相互关系.研究表明,(1)北大西洋东北部存在一个大气臭氧极小值,年平均臭氧总量比纬向平均值低20 DU以上,冬季低50 DU以上; 北太平洋西北部存在一个大气臭氧极大值,年平均臭氧总量比纬向平均值高35 DU以上,冬季高70 DU以上.(2)上述两个地区大气臭氧的季节变化具有很强的区域特征,区域大气动力学输送和化学过程对上述两个地区大气臭氧季节变化的强迫分别为50.3%和42.6%.(3)上述两个地区大气臭氧纬向偏差的季节变化间存在很好的反相关,相关系数达到-0.98,说明其臭氧区域强迫之间存在良好的关系.     

Interannual variability of the surface heat budget over the northern North Atlantic and North Pacific Oceans

Summary The January anomaly time series for each term of the surface heat budget (solar and longwave radiation, sensible and latent heat fluxes) are calculated for Ocean Weather Stations (OWSs) in the North Pacific and North Atlantic Oceans. The data set used is the Comprehensive Ocean-Atmosphere Data Set (COADS). The dominant term is the latent heat flux. The results for OWS P in the northern North Pacific show that the interannual variability of the heat budget parameters is correlated with the synoptic variability of the Aleutian low. There is also an interdecadal signal present in the heat budget anomaly time series, with the sign of the anomaly persisting for about 8–10 years. In contrast, for OWS J in the northern North Atlantic, no correlation is found between the variability of the heat budget parameters and the corresponding synoptic variability of the Icelandic low. The station J air-sea heat fluxes also show a higher frequency variability, compared to those of station P. The results suggest the variability of the January air-sea heat exchange processes are fundamentally different over the two ocean basins.With 3 Figures     

Microwave measurements over the North Sea

We investigate the applicability of SLAR (Side-Looking Airborne Radar) to detect waves and other phenomena at sea, for future operational use. Especially, we investigate radar measurements of wave patterns, oil pollution, shipping traffic, and ice reconnaissance and relate these to sea-truth information. The SLAR program benefits from earlier clutter measurements at sea and in a wind-wave tank (carried out by the Physics Laboratory TNO and NIWARS), which have been further elaborated and extended. These are summarized. Results obtained since 1974 lead to the conclusion that the SLAR is applicable for the aforementioned purposes, albeit in a somewhat restricted way. The large resolution cell used, containing a vast number of independent samples, improves the dynamic resolution to about l dB and so turns the SLAR into a sensor eminently suited for the detection of very slight modulations of capillary waves. For the detection of shorter gravity waves, however, especially under severe wind conditions, a finer geometrical resolution might be needed. Results emphasize the need for further fundamental studies of sensor-object interaction.     

Salinity minimum in the North Pacific

Analyzed is the variability of seasonal salinity in the North Pacific. It is demonstrated that the formation and disappearance of salinity minimum in subsurface layers depends on the freshwater budget variability of different time scales. In general, the salinity minimum is a temporary phenomenon formed during the negative phase of freshwater budget, when the evaporation exceeds the precipitation. Seasonal variability of fresh water budget leads to the seasonal formation of salinity minimum on the boundary between the climatic zones. The existence of salinity minimum at intermediate depths in the tropics is caused by the negative phase of long-period variability of freshwater budget.     

Extreme waves in the North Atlantic

Analyzed are the reasons of extreme waves with the height of more than 14 m formed in the North Atlantic in 2002–2011 and the evolution of atmospheric processes causing the extreme waves. It is revealed that the extreme waves in the North Atlantic during that period were mainly (in 81% of cases) formed under the influence of “explosive” cyclones. The height of waves in these cyclones can reach 20 m and more.     

Storm cyclones in the North Atlantic

Considered are long-term features and characteristics of storm activity variability in the North Atlantic based on the method of automatic identification of cyclone centers using the data on sea level pressure as well as the estimates of the maximum speed of the surface wind in the area of cyclones. Integral regional parameters of the variability of storm cyclone frequency for the gradations of the surface wind speed are presented for some areas of the North Atlantic. Investigated is the interrelation between extremely deep and storm cyclones.     

Response of the North Atlantic subpolar gyre to persistent North Atlantic oscillation like forcing

The response of the North Atlantic subpolar gyre (SPG) to a persistent positive (or negative) phase of the North Atlantic oscillation (NAO) is investigated using an ocean general circulation model forced with idealized atmospheric reanalysis fields. The integrations are analyzed with reference to a base-line integration for which the model is forced with idealized fields representing a neutral state of the NAO. In the positive NAO case, the results suggest that the well-known cooling and strengthening of the SPG are, after about 10 years, replaced by a warming and subsequent weakening of the SPG. The latter changes are caused by the advection of warm water from the subtropical gyre (STG) region, driven by a spin-up of the Atlantic meridional overturning circulation (AMOC) and the effect of an anomalous wind stress curl in the northeastern North Atlantic, which counteracts the local buoyancy forcing of the SPG. In the negative NAO case, however, the SPG response does not involve a sign reversal, but rather shows a gradual weakening throughout the integration. The asymmetric SPG-response to the sign of persistent NAO-like forcing and the different time scales involved demonstrate strong non-linearity in the North Atlantic Ocean circulation response to atmospheric forcing. The latter finding indicates that analysis based on the arithmetic difference between the two NAO-states, e.g. NAO+ minus NAO?, may hide important aspects of the ocean response to atmospheric forcing.     

Surface fluxes of momentum and mechanical energy over the North Pacific and North Atlantic Oceans

Summary Using 6-hourly data from the National Centers for Environmental Prediction/National Center for Atmospheric Research reanalysis set (1958–1997) we have determined the winter and summer mean fluxes of momentum and mechanical energy into the Northern Hemisphere (NH) oceans. We have also diagnosed the contribution made to these by the mean wind speed and the covariances due to the temporal variability. In both seasons the greatest oceanic flux of momentum is found in the region to the south of Greenland and Iceland. The contributions to the total made by the transient term exhibited maxima in the north central Pacific and Atlantic and in winter, and accounts for about 15% of the mean stress in both extratropical ocean basins and both seasons. The rate at which mechanical energy is imparted to the ocean shows a similar spatial structure. The fluxes are typically three times larger in winter, and about one third of the input is associated with the transient part of the low level wind. The spatial and temporal structure of the part of fluxes contributed by the temporal variability shows a strong relationship with mean cyclone depth, a parameter known to represent an unbiased measure of cyclone activity. The fluxes exhibit significant positive winter trends (many of which are significant) over the extratropical Pacific and in the Atlantic north of about 40° N, and these have been found to result from reinforcing trends in the components associated with the mean wind speed and the temporally varying part. The changes are broadly in line with those in observed significant wave height over the northern oceans in recent decades, and are closely related to secular increases in the mean depth of cyclones. Positive trends in the number of extreme cyclones in key regions of the Pacific and Atlantic have been found. The trend is significant in the relevant part of the Pacific, but whether the increase in the Atlantic subregion should be regarded as above the noise is seen to depend on how such extremes are defined. We discuss how conclusions drawn in specific studies may depend critically on how cyclones and extreme events are characterized. Received November 2, 2001 Revised December 24, 2001     

Lightning detection system in the North Caucasus

For the first time in Russia, the Vaisala LS 8000 lightning detector has been brought into operation which provides the acquisition, processing, and archiving of the lightning discharge data (coordinates, polarity, discharge type, currents, etc.) on the territory of the North Caucasus. For the purpose of operational hydrometeorological services, it is proposed to use the real-time combination of the synthesized chart of the echo of clouds and precipitation of the regional network of meteorological radars and the thunderstorm cells plotted from the lightning points (coordinates) using the cluster analysis. Presented is the analysis of the results of the registration of currents of surface discharges and of the time of their growth obtained during the period of operation since 2008.     

全新世北大西洋冷事件

对北大西洋冷事件的研究至今不过10a左右,这个问题之所以令人关注,主要是因为它一,能反映了北大西洋经向翻转环流（MOC）的强度变化。MOC足全球热盐环流（THC）的重要组成部分。发生冷事件时,北大西洋表层为融冰淡水所控制,这抑制了北大西洋深水（NADW）的形成,使得MOC减弱,向北输送的热量大为减少,给欧洲带来冷干气候。近年来对北大西洋冷事件有了比较详细的了解,得到了较为一致的年表。     

Sulfur dioxide in the North American Arctic

Determinations of atmospheric sulfur dioxide were made across the North American Aretic using gas chromatography with a detection limit of 25 parts per trillion by volume and a precision of 25% or better. The vertical distribution of sulfur dioxide in the Arctic atmosphere in April, 1986 was highly variable, with concentrations ranging from the detection limit to 15 parts-per-billion by volume (ppbv). While SO₂ exceeded 10 ppbv in an exceptional haze layer in the Alaskan Arctic, sulfur dioxide was sometimes in the 1 – 5 ppbv range when the haze was absent. This was particularly true for the Canadian Arctic in the vicinity of Alert. In the lower stratosphere over Ellesmere Island, sulfur dioxide was 0.85 ppbv.     

On the North Atlantic extreme cyclone activity

Compared are the parameters of the cyclone activity in some areas of the North Atlantic in the winter (from October to March) and summer (from April to September) seasons for the period from January 1, 1948 to March 31, 2010, as well as the activity for the cyclones with the moderate intensity with the pressure in the center from 1000 to 970 hPa and for extremely intense cyclones (970 hPa and lower). The characteristics of cyclone activity, the density and intensity of cyclones, are determined using a method of the automatic identification of cyclone centers from the data on the sea level pressure.     

Association between tropospheric temperature and tropical cyclone peak intensity over the North Pacific and North Atlantic

台风作为一种灾害性天气,其破坏性大小与自身强度有很大的关系.因此,本项研究利用NCEP-NCAR和MERRA再分析数据,考查了北大西洋,西北太平洋,东北太平洋台风强度峰值与对流层温度的关系.台风强度峰值与大气温度的相关系数,以及极大和极小台风强度峰值下大气温度的差值,共同显示:北大西洋台风强度峰值受到对流层顶低温和对流...     

20世纪90年代以后华北初春低温增强和北大西洋海温关系

本文利用ECMWF再分析资料及Hadley中心提供的海温数据分析了20世纪90年代以后华北地区初春低温增强的原因,并通过数值模拟结果予以验证。结果表明,北大西洋“马蹄型”海温模态与影响我国华北地区的欧亚波列存在显著的相关关系。同时该海温模态与1997年以后北大西洋关键区垂直波作用通量有着较密切的相关关系,1997年以后北大西洋地区的500 hPa环流模态,整体呈现出东移南撤的趋势。1997年以后格陵兰岛东侧表面温度受异常热力强迫导致正值区增多,同时此处西风急流加大,有利于Rossby波向下游传播,导致其下游欧洲大陆地区形成暖脊。通过局地多尺度能量涡度分析法（Localized Multiscale Energy and Vorticity Analysis,简称MS-EVA）证明格陵兰岛东侧关键区表面温度的异常热力强迫作用与气压梯度力在对流层整层做正功,导致高层动能的增加并向外辐散,使得脊加强向北伸展。通过欧亚波列致使下游华北地区上空气旋式异常加强,促使亚洲极涡加强和稳定维持,华北地区温度下降剧烈,极端低温事件增多。最后通过CAM5.1模式模拟研究了北大西洋“马蹄型”海温模态对大气环流异常及华北地区极端低温的影响。模拟结果很好地验证了观测结果,进一步表明该海温模态可以通过激发出欧亚波列,影响欧亚大陆大气环流异常,进而导致我国华北地区气旋性加强和经向环流加大,极端低温事件增多。     

1—3月北极涛动对北半球热带太平洋和大西洋对流活动的可能影响

利用1979—2008年日分辨率的向外长波辐射资料以及NCEP再分析资料,去除ENSO影响后,分析了1—3月北极涛动对热带太平洋和热带大西洋对流活动及降水的可能影响。结果表明北极涛动偏强(弱)时,热带太平洋和大西洋对流活动显著偏强(弱)。北半球热带大洋冬季平均向外长波辐射与北极涛动指数的相关系数存在两个显著负相关区:一个位于中太平洋区,大致包括13°—20°N、160°E—170°W;另外一个位于热带大西洋,显著区覆盖的范围大体包括5°—20°N、15°—70°W。这些区域的降水量也表现出显著的正相关。向外长波辐射、强对流面积指数、强对流强度指数、平均降水量等指标与北极涛动指数的相关均以冬季同期最高,随时间滞后相关迅速减弱。与此对应的对流层低层大气环流也有显著变化,850hPa风场的变化表现为热带太平洋有异常的气旋性环流,气旋中心区与显著强对流和降水异常区一致。而热带大西洋有显著的经向环流辐合和风切变,与异常对流和降水区吻合。海洋模式的模拟结果表明,与北极涛动有关联的海温分布,很大程度上与大气强迫有关,说明热带1—3月降水和对流活动与海温的关联较弱。北极涛动与热带太平洋、大西洋对流和降水活动之间主要是通过大气环流的变动产生联系的。     

加强新时期气象部门财务管理与监督的思考

利用连续气流纵向热梯度云凝结核仪对华北地区空中云凝结核（CCN）进行观测研究.2009年飞机观测结果表明,同一块云内CCN数浓度变化范围和平均数浓度随高度增加逐渐减小,云的低层CCN数浓度变化趋势与云滴变化呈负相关,中高空CCN数浓度的水平分布规律与CN并不完全相关;比较三类不同天气条件下不同高度层的CCN谱分布特征发现,阴天和晴天谱型变化较小且较雨天的谱宽,雨天谱分布不连续.     

Numerical simulation of the North American monsoon system

Summary ¶This paper deals with the systematic evolution of the North American monsoon system by analyzing the evolution of tropospheric circulation, precipitation, moisture fluxes and the adjoining sea surface temperatures from observations and the Florida State University Nested Regional Spectral Model embedded within a coupled atmosphere–ocean coupled model. The atmospheric part is a global spectral model with triangular truncation T63 and a nested regional spectral model. The global atmospheric model is coupled with the Hamburgs Global Ocean Model. This model was integrated for six-months with 50km resolution in the North American monsoon domain. The NCEP/NCAR reanalysis were used as the observed state for comparison. The analyzed model results shows that the above model has the capability of capturing some of the features of the North American monsoon system. Besides the evolution of the monsoon system, the out-of-phase relationship between the Mexican monsoon with south-central United States precipitation and the largest moisture supply from the Gulf of Mexico are the principal findings of this study. It is also noted that during the mature phase of the monsoon, the Gulf of California and the Pacific Ocean dominates the Gulf of Mexico in order of moisture supply but immediately after the mature phase, the Gulf of Mexico dominates.Received January 18, 2002; accepted July 7, 2002 Published online: June 12, 2003