A detailed analysis of hourly precipitation from 60°N to 60°S for the covariability is performed at 0.25° resolution using the new CMORPH dataset. For all points, correlations are computed with surrounding points both concurrently and for various leads and lags up to a day. Results are more coherent over the oceans than land; the contours of constant correlation tend to be elliptical, oriented northeast–southwest in the northern extratropics and southeast–northwest in the southern extratropics. An ellipse is fitted to the correlation pattern, and major and minor axis vectors and eccentricity are mapped. Based upon both the isotropic correlations and ellipse, points are allocated to one of 20 clusters, and 16 are documented. Over the main extratropical ocean storm tracks, correlations exceed 0.8 for points 50 km distant and fall to about 0.3 at about 5° radius. In the tropics values drop to 0.65 within 50 km and 0.2 at 5° radius. Over land, values are lower in summer and drop to 0.1 at 5° radius. Decorrelation e-folding distances range from less than 50 km over land to 200 km over extratropical ocean storm tracks. The movement of precipitation is compared with mean atmospheric winds. The lead–lag relationships indicate movement of systems but reveal the relatively short lifetimes of precipitation, of less than 12 h, even taking movement into account. The orientation of the ellipse reflects the structures of rain phenomena (fronts, etc.) rather than movement. These statistics demonstrate that daily averages fail to capture the essential character of precipitation.
The increased concentration of greenhouse gases in the atmosphere from human activities traps heat within the climate system and increases ocean heat content (OHC). Here, we provide the first analysis of recent OHC changes through 2021 from two international groups. The world ocean, in 2021, was the hottest ever recorded by humans, and the 2021 annual OHC value is even higher than last year's record value by 14 ± 11 ZJ (1 zetta J = 1021 J) using the IAP/CAS dataset and by 16 ± 10 ZJ using NCEI/NOAA dataset. The long-term ocean warming is larger in the Atlantic and Southern Oceans than in other regions and is mainly attributed, via climate model simulations, to an increase in anthropogenic greenhouse gas concentrations. The year-to-year variation of OHC is primarily tied to the El Niño-Southern Oscillation (ENSO). In the seven maritime domains of the Indian, Tropical Atlantic, North Atlantic, Northwest Pacific, North Pacific, Southern oceans, and the Mediterranean Sea, robust warming is observed but with distinct inter-annual to decadal variability. Four out of seven domains showed record-high heat content in 2021. The anomalous global and regional ocean warming established in this study should be incorporated into climate risk assessments, adaptation, and mitigation.人类活动导致大气中温室气体的浓度上升,造成了地球系统的净热量吸收和海洋热含量增加。本文发布了两个国际机构的2021年海洋热含量数据,数据表明:2021年海洋升温持续——成为有现代海洋观测记录以来海洋最暖的一年。相对于2020年,2021年全球海洋上层2000米热含量上升了14 ± 11 ZJ (1 zetta J = 1021 J)(IAP/CAS数据)、以及16 ± 10 ZJ(NOAA/NCEI数据)。海洋长期变暖趋势在南大洋、中低纬度大西洋区域更强,地球系统模式的单个因子强迫实验证明,温室气体增加是主要的驱动因子;而年际尺度的海洋热含量变化主要受到厄尔尼诺-南方涛动模态调控。此外,本文给出了全球7个主要海域的海洋变暖测算,发现地中海、北大西洋、南大洋、北太平洋海区温度均创历史新高。最后,本文提出需要充分将全球和区域海洋变暖的影响纳入气候风险评估、气候变化影响和应对当中。.
No abstract is provided for this article.
The hydrological cycle is described. Because the climate is changing from human activities, and there is a direct effect on the hydrological cycle, water resources will also change. The effects of climate change on precipitation, evaporation, and extremes of floods...
A comprehensive comparison is made among four sea surface temperature (SST) datasets: the optimum interpolation (OI) and the empirical orthogonal function reconstructed SST analyses from the National Centers for Environmental Prediction (NCEP), the Global Sea-Ice and SST dataset (GISST, version 2.3b) from the United Kingdom Meteorological Office, and the optimal smoothing SST analysis from the Lamont-Doherty Earth Observatory (LDEO). Significant differences exist between the GISST and NCEP 1961–90 SST climatologies, especially in the marginal sea-ice zones and in regions of important small-scale features, such as the Gulf Stream, which are better resolved by the NCEP product. Significant differences also exist in the SST anomalies that relate strongly to the number of in situ observations available. In recent years, correlations between monthly anomalies are less than 0.75 south of about 10°N and are lower still over the southern oceans and parts of the tropical Pacific where root-mean-square differences exceed 0.6°C. While adequate for many purposes, the SST datasets all contain problems of one sort or another. Noise is evident in the GISST data and realistic temporal persistence of SST anomalies after 1981 is lacking. Trends in recent years are quite different between the GISST and NCEP analyses, and this can be partially traced to differences in the processing of in situ data and an increasing cold bias in the NCEP 01 data arising from incompletely corrected satellite data. Significant discrepancies also exist in centennial trends from the LDEO and GISST datasets, and these likely reflect the separate treatment of the very low frequency signal in the GISST analysis and questionable assumptions about the stationarity of statistics in the LDEO method. Ensembles of integrations with an atmospheric general circulation model (AGCM) are used with three of the SST datasets as lower boundary conditions to show that the differences among them imply physically important differences in the atmospheric circulation. Over the Tropics, where masking by internal atmospheric variability is small, SST differences affect moist convection and systematically produce strong responses in the local divergent circulation. A case study shows that analyzed SST differences in the tropical Pacific can be as large as for a moderate El Niño. Such large discrepancies induce local rainfall anomalies up to 8 mm day−1 and, in addition to the tropical circulation anomalies, are associated with global teleconnections that influence temperatures and precipitation around the world. Results also show the limitations to using AGCMs when forced by specified SSTs. The likely sources of the problems evident in the different SST products are identified and discussed. Several of the problems are being addressed by current efforts to reprocess the SST data, which is strongly recommended, but remaining problems demand further attention and attempts to resolve them should continue. The choice among SST analyses used for AGCM simulations, for the atmospheric reanalysis projects, for identifying climate signals, and for monitoring climate is important, as known flaws in the global analyses can compromise the results.
An analysis has been made of the spatial and frequency dependence of transient eddy statistics in the Southern Hemisphere at 500 mb. This study emphasizes summer versus winter differences in order to complement previous results of Trenberth (1981), which are shown to nearly correspond to the mean of the summer plus winter statistics. Variance fields of geopotential height, the north–south and east–west geostrophic velocity components, the transient kinetic energy and the poleward transient eddy momentum flux have been analyzed for nine winter and eight summer 128-day seasons from 1972–80. The fields are examined in the frequency domain using Lorenz' (1979) “poor man's spectral analysis” technique. The total fields and the contributions from two broad frequency bands covering periods of 2–8 and 8–64 days are geographically mapped and their zonal means are presented. The spatial distribution of the eddy statistics is quite similar in summer and winter, although the variances in winter are larger and of broader latitudinal extent, thereby indicating a more vigorous circulation overall than in summer. The seasonal changes in eddy statistics closely follow corresponding changes in the mean westerly wind field and are very small over the Indian Ocean, while the largest changes occur in the Pacific Ocean region. A storm track, as indicated by the high frequency fluctuations, exists in the Indian Ocean along 50°S in both summer and winter. The main low frequency variations including blocking-type phenomena occur south of New Zealand and southeast of South America in both seasons, but with small changes in location. Storms in the Pacific Ocean region have a somewhat longer time scale than over the Indian Ocean. A comparison has been made with results from previous studies and, in particular, with statistics based upon station data analyzed at GFDL. The GFDL analyses produce relatively weaker wind speeds over the data sparse oceans. The variance fields are comparable in magnitude but differ in detail, and the GFDL analyses fail to capture the characteristic patterns in the storm track and blocking regions of the hemisphere.
The atmospheric and ocean environment has changed from human activities in ways that affect storms and extreme climate events. The main way climate change is perceived is through changes in extremes because those are outside the bounds of previous weather. The average anthropogenic climate change effect is not negligible, but nor is it large, although a small shift in the mean can lead to very large percentage changes in extremes. Anthropogenic global warming inherently has decadal time scales and can be readily masked by natural variability on short time scales. To the extent that interactions are linear, even places that feature below normal temperatures are still warmer than they otherwise would be. It is when natural variability and climate change develop in the same direction that records get broken. For instance, the rapid transition from El Niño prior to May 2010 to La Niña by July 2010 along with global warming contributed to the record high sea surface temperatures in the tropical Indian and Atlantic Oceans and in close proximity to places where record flooding subsequently occurred. A commentary is provided on recent climate extremes. The answer to the oft-asked question of whether an event is caused by climate change is that it is the wrong question. All weather events are affected by climate change because the environment in which they occur is warmer and moister than it used to be.
The state of knowledge and outstanding challenges and opportunities in global water cycle observations, research and modeling are briefly reviewed to set the stage for the reasons behind the new thrusts promoted by the World Climate Research Programme (WCRP) as Grand...
A new method of estimating the decay time, mean period and forcing statistics of El Niño-Southern Oscillation (ENSO) has been found. It uses a two-dim
The oceans cover about 71% of the Earth’s surface and contain 97% of the Earth’s water (see Trenberth 2001). Through their fluid motions, their high heat capacity, and their ecosystems, the oceans play a central role in shaping the Earth’s climate and its variability. Changes in sea level have major impacts on coastal regions and storm surges. Accordingly, it is vital to monitor and understand changes in the oceans and their effects on weather and climate, and improve the verisimilitude of model ocean simulations. In this introduction, we outline these aspects and provide a justification for the ocean variables that should be observed and the networks and methods whereby this is achieved.
The perception about whether a place is a nice place to live often depends on how often it rains (or snows). The frequency relates to how dreary the weather appears, and it is the duration much more than the amount that clouds perceptions. Yet, information about the frequency of rainfall, or precipitation in general, is spotty at best. Here, we analyze a new near-global (60°N–60°S) dataset at hourly time scales and 0.25° resolution. The dataset, the newly calibrated Climate Prediction Center morphing technique (CMORPH), enables comparison of results with 3-hourly and daily data, which is what has previously been available, and seasonal aspects are also examined. The results are quite sensitive to both the spatial scales of the data and their temporal resolutions, and it is important to get down to hourly values to gain a proper appreciation of the true frequency. At 1° resolution, values are 35% higher than for 0.25°. At 3-hourly resolution, they are about 25% higher than hourly, and at daily resolution, they are about 150% higher than hourly on average. Overall, near-global (60°N–60°S) precipitation occurs 11.0% ± 1.1% (1 sigma) of the time or, alternatively, 89.0% of the time it is not precipitating. But outside of the intertropical and South Pacific convergence zones, where values exceed 30%, and the arid and desert regions, where values are below 4%, the rates are more like 10% or so, and over land where most people live, values are closer to about 8%.
No abstract is provided for this article.
A comprehensive description is given of the global monsoon as seen through the large-scale overturning in the atmosphere that changes with the seasons, and it provides a basis for delimiting the monsoon regions of the world. The analysis focuses on the mean annual cycle of the divergent winds and associated vertical motions, as given by the monthly mean fields for 1979–93 reanalyses from the National Centers for Environmental Prediction–National Center for Atmospheric Research (NCEP–NCAR) and European Centre for Medium-Range Weather Forecasts (ECMWF), which are able to reproduce the dominant modes. A complex empirical orthogonal function analysis of the divergent circulation brings out two dominant modes with essentially the same vertical structures in all months of the year. The first mode, which depicts the global monsoon, has a simple vertical structure with a maximum in vertical motion at about 400 mb, divergence in the upper troposphere that is strongest at 150 mb and decays to zero amplitude above 70 mb, and convergence in the lower troposphere with a maximum at 925 mb (ECMWF) or 850 mb (NCEP). However, this mode has a rich three-dimensional spatial structure that evolves with the seasons. It accounts for 60% of the annual cycle variance of the divergent mass circulation and dominates the Hadley circulation as well as three overturning transverse cells. These include the Pacific Walker circulation; an Americas–Atlantic Walker circulation, both of which comprise rising motion in the west and sinking in the east; and a transverse cell over Asia, the Middle East, North Africa, and the Indian Ocean that has rising motion in the east and sinking toward the west. These exist year-round but migrate and evolve considerably with the seasons and have about a third to half of the mass flux of the peak Hadley cell. The annual cycle of the two Hadley cells reveals peak strength in early February and early August in both reanalyses. A second monsoon mode, which accounts for 20% of the variance, features relatively shallow but vigorous overturning with the maximum vertical velocities near 800 mb, outflow from 750 to 350 mb, and inflow peaking at 925 mb. It is especially strong over Africa where the shallow, mostly meridional overturning migrates back and forth across the equator with the seasons. It influences the Middle East, has a signature over Australia, and is also an important component of the overturning in the tropical eastern Pacific and Atlantic, and thus of the convergence zones in these regions. The relationship of the global monsoon to the regional monsoons is described over six zonal sectors: Africa, Australia–Asia, North America, South America, and the Pacific and Atlantic Oceans. Only the two ocean areas do not undergo a seasonal reversal required for monsoons, although they have direct overturning cells and they nevertheless participate in the global monsoon through the changes in large-scale overturning. The regional meridional cross sections highlight the importance of the shallow overturning cell in lower-troposphere monsoon activity. The steadiness of the overturning circulation is determined by comparing the signal of the seasonal mean vertical motions at 500 mb with the standard deviation of the transient daily variations. Locations where this signal exceeds 60% of the daily noise correspond closely with the regional centers of the monsoon.
In order to help establish a global climate record data sets of global analyses from the U.S. National Meteorological Center (NMC) and the European Centre for Medium Range Weather Forecasts (ECMWF) have been comprehensively evaluated. A detailed chronology of the changes in the analysis-forecast system at NMC and ECMWF has been compiled and the main impacts on the analyses have been identified. Discontinuities have been found in certain characteristics of the analyses when major changes occur. The main quantities so affected are the divergent wind component and associated vertical motion fields, and the moisture fields. A detailed intercomparison of the two data sets and statistical results show fairly widespread agreement between the analyses from the two centers over the Northern Hemisphere extratropics. In general, the quality of the analyses is much lower in the tropics and Southern Hemisphere. This is reflected in much greater differences in wind fields south of 20°N, with root-mean-square differences in the north-south and east-west components often exceeding 5ms−1 above ~500 mb throughout most of this region. Much greater differences in geopotential height south of ~30°S exist. Major problems at NMC prior to May 1986 occur south of ~50°S. ECMWF has also experienced difficulties over and around Antarctica, especially prior to 1982. In the tropics, there are major disagreements between the analyses of the divergent wind field and associated vertical motions which have become more intense and more realistic with time, but still appear to be poorly known. The relative humidity field is the poorest known and has undergone major changes with time at both centers. Possible reasons for these results are discussed and some implications and recommendations are given.
