Persistence of Planetary Waves in the Lower Ionosphere     

Laštovička  Jan  Križan  Peter  Novotná  Dagmar 《Studia Geophysica et Geodaetica》2003,47(1):161-172

The transient planetary waves in the atmosphere and ionosphere seem to occur in the form of bursts of a couple of waves with limited persistence. To study persistence of planetary wave events in the lower ionosphere, data from two radio paths from Central Europe are used, Luxembourg – Panská Ves (f = 6.09 MHz, f _eq = 2.1-2.2 MHz) and Deutschlandfunk – Panská Ves (f = 1539 kHz, f _eq = 650-700 kHz). The absorption along the former radio paths is formed very predominantly at altitudes of about 90-100 km, whereas the latter absorption is formed mostly at altitudes of about 85-90 km. The persistence of planetary wave type oscillations is studied in three period bands centred at 5, 10 and 16 days. Waves with period T near 5 days reveal a typical persistence of wave events around 5 cycles. Waves with T = 10 days are less persistent with a typical persistence of 3-4 cycles. The typical persistence of waves T = 16 days is no more than 3 cycles. In terms of number of cycles, the persistence of oscillations evidently decreases with increasing period. On the other hand, in terms of number of days, the persistence seems rather to increase with increasing period.  相似文献   

夏季北半球500 hPa位势高度场持续性异常的地理分布及区域特征   总被引：10，自引：3，他引：10  

李金龙  纪立人 《大气科学》1994,18(2):163-172

本文利用２３年夏季3个月的５００ hPa位势高度场，对２０°Ｎ以北的热带以外地区的位势高度异常进行了分析，着重研究了持续时间超过天气尺度扰动时间（大约1周）的持续异常。结果表明:５００ hPa高度场上持续异常的产生?具有很大的地理依赖性，在以下几个地区最容易产生持续异常:（１）北太平洋中东部到阿拉斯加南部（ＮＥＰ）。（２）北大西洋东部到欧洲大陆西海?岸（ＥＡＴ）。（３）前苏联西北部的新地岛附近（ＷＮＳU）。（４）加拿大北部的哈得逊湾附近（ＮＣＡ）。（５）白令海峡以北的北冰洋地区（ＡＲＣ）。进一步对异常关键区统计分析得到:异常多发区特征显著地不同于异常少发区，正异常与负异常也有所差别。  相似文献   

Oil persistence on beaches in Prince William Sound - a review of SCAT surveys conducted from 1989 to 2002     

Taylor E  Reimer D 《Marine pollution bulletin》2008,56(3):458-474

In 2002, 13 years after the Exxon Valdez oil spill (EVOS), 39 selected sites in Prince William Sound (PWS) were re-surveyed following established shoreline cleanup assessment team (SCAT) field observation procedures to document surface and sub-surface oiling conditions in shoreline sediments and to compare results with those from previous Shoreline Cleanup Assessment Team (SCAT) surveys and other surveys in PWS. The selected sites are locations where EVOS oil persisted in 1992, at the time the Federal and State On-Scene Coordinators determined that the cleanup was complete and that further cleanup activities would provide no net environmental benefit. These sites had been included in a 2001 NOAA survey of shoreline oiling conditions and account for 88% of the sub-surface oil residues (SSO) oil documented by that study. The 2002 field survey found isolated occurrences of residual EVOS surface oil residues (SO) in the form of weathered asphalt pavement at 15 of the 39 sites. This residual SO typically consisted of asphalt in mixed sand/gravel substrate, located within a wave shadow effect created by boulders or bedrock in the upper intertidal to supratidal zone. Residual SO, expressed as a continuous oil cover, was less than 200 m(2) within the approximately 111,120 m(2) surveyed. A total of 1182 pits were dug at locations where SSO residues were present in 1992. Six of the 39 sites and 815 (68%) of the pits contained no residual SSO. Eighty-three percent of pits with SSO residues were found primarily in middle to upper intertidal locations. SSO residues commonly occurred in a discontinuous approximately 3 cm thick band 5-10 cm below the boulder/cobble or pebble/gravel veneer. The SO and SSO occurrences in the 2002 survey closely match the locations where they were found in 1992 and earlier surveys; however, in 2002 residual SSO patches are more discontinuous and thinner than they were in the earlier surveys. These sites are biased toward SSO persistence; those that have SSO residues represent less than 0.5% of the originally oiled shorelines in PWS. Despite evidence of continued oil weathering, both at the surface and in the sub-surface, it is clear that the natural cleaning processes at these particular locations are slow. The slow weathering rates are a consequence of the oil residue being incorporated in finer sediments (fine sand, silt, mix) and isolated from active weathering processes as boulders and outcrops, shallow bedrock asperities, or boulder-armoring create wave shadows and limit effective physical action on shorelines.  相似文献   

Transience of channel head locations following disturbance          下载免费PDF全文

Ellen Wohl  Daniel N. Scott 《地球表面变化过程与地形》2017,42(7):1132-1139

We used annual re‐surveys of two populations of channel heads affected by a severe wildfire in 2012 to monitor changes in channel head location with time following disturbance. Relative to channel heads in surrounding unburned areas, the median contributing drainage area of burned channel heads decreased by two orders of magnitude immediately after the fire, but then returned to values comparable to unburned areas within four years. We distinguish three types of channel heads. Permanent channel heads, which constitute 4% of the total population, occur in well‐developed swales in association with stable features such as bedrock outcrops: these channel heads appear to have been unaffected by the fire. Persistent channel heads, which are 40% of the total population, also occur within hillslope concavities, but the exact location of the channel head moves upslope and downslope through time in response to varying inputs of water and sediment. Transient channel heads form on straight and convex slopes immediately following disturbance, but disappear as regrowth of ground cover limits overland flow and sediment movement. The majority of the position changes for persistent and transient channel heads occurred abruptly when viewed as annual time steps. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

一类具污染的捕食与被捕食者模型的研究     

刘宇红  刘志美 《广东海洋大学学报》2009,29(4):51-53

利用积分均值法,研究了一类具污染的捕食与被捕食者模型,得到了各种群平均持续生存与绝灭的阈值。  相似文献   

Short- and long-term patterns of sponge diversity on a rocky tropical coast: evidence of large-scale structuring factors   总被引：1，自引：0，他引：1  

Jose Luis Carballo  Cristina Vega  José Antonio Cruz-Barraza  Benjamin Yáñez  Héctor Nava  Enrique Ávila  & Miroslava Wilson 《Marine Ecology》2008,29(2):216-236

  相似文献   

测风塔风速的长程持续性特征研究     

李庆雷  陈丽凡  张志森  刘卫平 《气象科技》2023,51(2):262-268

基于中国陆上风能资源专业观测网提供的测风塔风速资料,本文利用去趋势波动分析(Detrended Fluctuation Analysis, DFA)方法,研究了103座测风塔在不同高度处观测的、不同分辨率的风速时间序列的长程持续性特征。结果表明：(1)同一测风塔观测的不同高度处的风速时间序列,存在一致的标度行为,与数据时间分辨率无关;(2)对于6 h平均风速序列而言,103座测风塔观测风速的DFA指数α数值范围基本在0.55～0.91之间,都表现出较强的长程持续性,区域特征不明显;(3)对于10 min平均风速序列,DFA标度指数曲线存在弯折,以24 h尺度为界,呈现出2个明显的独立标度区间：在较大的时间尺度上,标度指数α的数值大小为0.80,而在较小的时间尺度上,α的数值大小约为1.38。  相似文献   

Possible causes for the persistence barrier of SSTA in the South China Sea and the vicinity of Indonesia     

赵霞  李建平 《大气科学进展》2009,26(6):1125-1136

The persistence barrier refers to the lag correlation of sea surface temperature anomalies (SSTA) showing a rapid and significant decline in a specific season, regardless of the starting month. This implies that there is a decrease in forecast skill for SSTA in this specific season. This paper investigates the possible causes for the persistence barrier of SSTA in the South China Sea (SCS) and its adjacent regions from the perspective of interannual-interdecadal time scales. The results show that the persistence barrier of SSTA exists not only in the SCS, but also in the vicinity of Indonesia south of the equator. The SCS barrier occurs around October--November, while the occurrence of the barrier in the Indonesia region is around November--December. For these two regions, the occurrence of the persistence barrier is closely associated with the interdecadal variability of SSTA, as well as the interannual variability. The persistence barriers in the SCS and the Indonesia region do not exist alone if the interdecadal variability is not considered, because SSTA have a short memory of less than 4 months, regardless of the starting month. Moreover, the influence of the interdecadal variability of SSTA on the persistence barrier of SSTA in the SCS and the Indonesia region may be associated with SSTA in the Indian Ocean and the western Pacific, but is not closely associated with the Pacific Decadal Oscillation. However, compared with the spring persistence barrier (SPB) of ENSO, the close relationship between the persistence barriers in the SCS and the Indonesia region and the interdecadal variability is unique, since the ENSO SPB is not significantly affected by such variability. In addition, although the persistence barriers in both the SCS and the Indonesia region are quite obvious in strong ENSO cases, the interdecadal variability of SSTA also plays a non-negligible role in this relationship.  相似文献   

Influence of the persistence of circulation patterns on warm and cold temperature anomalies in Europe: Analysis over the 20th century     

Jan Kyselý   《Global and Planetary Change》2008,62(1-2):147-163

Recent studies have pointed out that persistence of the atmospheric circulation over Europe, as measured by residence times of circulation types, has increased since the mid-1980s in all seasons and for most groups of the types. The greater persistence may affect surface climatic anomalies, particularly the frequency and severity of heat and cold waves associated with severe impacts on society and environment. In this paper, relationships between the persistence of circulation types over Europe and extreme surface air temperature anomalies are studied over the 20th century using the Hess–Brezowsky catalogue of large-scale circulation patterns and long-term temperature series at stations covering most of the European continent. Types significantly conducive to heat and cold waves are identified, and temperature anomalies are linked to their persistence. It is shown that more persistent circulation enhances the severity of temperature extremes over the whole area, which is slightly more important for warm than cold temperature anomalies. The changes in both frequencies and residence times of circulation patterns have been supporting sharply rising trends in warm temperature extremes observed over Europe in recent decades, and the circulation changes may also contributed to the fact that trends in cold temperature extremes have been less pronounced or absent in the same period. The findings also emphasize the need for taking into account the persistence of circulation types together with their frequencies when evaluating links between the atmospheric circulation and the surface climate. In global warming context, the effects of the future climate change on the occurrence and severity of temperature extremes may be exacerbated by a more persistent circulation related to a decreased cyclone activity over mid-latitudes and a northward shift of storm tracks.  相似文献   

辽宁省夏季降水的日变化特征   总被引：2，自引：0，他引：2  

杨森  周晓珊  高杰 《气象》2011,37(8):943-949

文章利用辽宁省25个气象观测站1961—2008年夏季6—8月的逐时降水自记资料,分析了辽宁省夏季降水日变化的基本特征。发现：降水日变化特征地域性较强,沿海站与内陆站存在差异。总体来说,沿海站降水量的最大值基本出现在午前04-08时,内陆站点则呈双峰值的形式,峰值分别出现在午前和午后,午后1 4—20时为降水量最大值出现的时间;降水频次的日变化特征和降水量基本相同;持续时间长的降水多在午前达到峰值,持续时间短的降水多在午后达到峰值;沿海站点午前的降水峰值区基本是由持续时间在6 h以上的长时间降水造成,内陆站点午后最大降水峰值则为持续时间6 h以内的短时降水,这与内陆下午对流能量强相适应。研究表明,降水日变化的存在能够影响到降水预报的评分。  相似文献