519 publications from this institution
No abstract is provided for this article.
No abstract is provided for this article.
This article briefly summarizes my views that have formed in recent years on communicating climate change in the light of first hand experiences in so-called “climategate”. latter term refers to the emails and personal information about individuals, including me, that were illegally taken from the University of East Anglia through a hacking incident. material published relates to the work of the globallyrespected Climatic Research Unit (CRU) and other scientists around the world. selective publication of some stolen emails taken out of context and distorted is mischievous and cannot be considered a genuine attempt to engage with the climate change issue in a responsible way. Instead there should be condemnation of the abuse, misuse and downright lies about the emails: that should be the real climategate! I was involved in just over 100 of the hacked email messages. In my case, one cherry-picked email quote went viral and at one point it was featured in over 110,000 items (in Google). Here is the quote: The fact is that we can't account for the lack of warming at the moment and it is a travesty that we can't. It is amazing to see this particular quote lambasted so often. It stems from a paper I published bemoaning our inability to effectively monitor the energy flows associated with short-term climate variability. It is quite clear from the paper that I was not questioning the link between anthropogenic greenhouse gas emissions and warming, or even suggesting that recent temperatures are unusual in the context of short-term natural variability. But that is the way a vast majority of the internet stories and blogs interpreted it.
On the basis of the current observational record of tropical cyclones and sea surface temperatures (SSTs) in the Atlantic, estimates are made of changes in surface sensible and latent heat fluxes and hurricane precipitation from 1970 to 2006. The best track data set of observed tropical cyclones is used to estimate the frequency that storms of a given strength occur after 1970. Empirical expressions for the surface fluxes and precipitation are based on simulations of hurricane Katrina in August 2005 with the advanced Weather and Research Forecasting (WRF) model at 4 km resolution without parameterized convection. The empirical relationships are computed for the surface fluxes and precipitation within 400 km of the eye of the storm for all categories of hurricanes based upon the maximum simulated wind and the observed sea surface temperature and saturation specific humidity. Strong trends are not linear but are better depicted as a step function increase from 1994 to 1995, and large variability reflects changes in SSTs and precipitable water, modulated by El Niño events. The environmental variables of SST and water vapor are nonetheless accompanied by clear changes in tropical cyclone activity using several metrics.
The mean and annual cycle of energy flowing into the climate system and its storage, release, and transport in the atmosphere, ocean, and land surface are estimated with recent observations. An emphasis is placed on establishing internally consistent quantitative estimates with discussion and assessment of uncertainty. At the top of the atmosphere (TOA), adjusted radiances from the Earth Radiation Budget Experiment (ERBE) and Clouds and the Earth’s Radiant Energy System (CERES) are used, while in the atmosphere the National Centers for Environmental Prediction–National Center for Atmospheric Research (NCEP–NCAR) reanalysis and 40-yr European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-40) estimates are used. The net upward surface flux (FS) over ocean is derived as the residual of the TOA and atmospheric energy budgets, and is compared with direct calculations of ocean heat content (OE) and its tendency (δOE/δt) from several ocean temperature datasets. Over land, FS from a stand-alone simulation of the Community Land Model forced by observed fields is used. A depiction of the full energy budget based on ERBE fluxes from 1985 to 1989 and CERES fluxes from 2000 to 2004 is constructed that matches estimates of the global, global ocean, and global land imbalances. In addition, the annual cycle of the energy budget during both periods is examined and compared with ocean heat content changes. The near balance between the net TOA radiation (RT) and FS over ocean and thus with OE, and between RT and atmospheric total energy divergence over land, are documented both in the mean and for the annual cycle. However, there is an annual mean transport of energy by the atmosphere from ocean to land regions of 2.2 ± 0.1 PW (1 PW = 1015 W) primarily in the northern winter when the transport exceeds 5 PW. The global albedo is dominated by a semiannual cycle over the oceans, but combines with the large annual cycle in solar insolation to produce a peak in absorbed solar and net radiation in February, somewhat after the perihelion, and with the net radiation 4.3 PW higher than the annual mean, as it is enhanced by the annual cycle of outgoing longwave radiation that is dominated by land regions. In situ estimates of the annual variation of OE are found to be unrealistically large. Challenges in diagnosing the interannual variability in the energy budget and its relationship to climate change are identified in the context of the episodic and inconsistent nature of the observations.
No abstract is provided for this article.
No abstract is provided for this article.
No abstract is provided for this article.
No abstract is provided for this article.
No abstract is provided for this article.
Using the 40-yr European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-40) for 1958 to 2001, adjusted for bias over the southern oceans prior to 1979, an analysis is made of global patterns of monthly mean anomalies of atmospheric mass, which is approximately conserved globally. It differs from previous analyses of atmospheric circulation by effectively area weighting surface or sea level pressure that diminishes the role of high latitudes. To examine whether global patterns of behavior exist requires analysis of all seasons together (as opposite seasons occur in each hemisphere). Empirical orthogonal function (EOF) analysis, R-mode varimax-rotated EOF analysis, and cyclostationary EOF (CSEOF) analysis tools are used to explore patterns and variability on interannual and longer time scales. Clarification is given of varimax terminology and procedures that have been previously misinterpreted. The dominant global monthly variability overall is associated with the Southern Hemisphere annular mode (SAM), which is active in all months of the year. However, it is not very coherent from month to month and exhibits a great deal of natural unforced variability. The third most important pattern is the Northern Hemisphere annular mode (NAM) and associated North Atlantic Oscillation (NAO), which is the equivalent Northern Hemisphere expression. Neither of these is really a global mode, although they covary on long time scales in association with tropical or external forcing. For monthly data, the second mode is coherent with Niño-3.4 sea surface temperatures and thus corresponds to El Niño–Southern Oscillation (ENSO), which is truly global in extent. It exhibits more coherent evolution with time and projects strongest onto the interannual variability, where it stands out by far as the dominant mode in the CSEOF analysis. The CSEOF analysis extracts the patterns phase locked with annual cycle and reveals their evolution throughout the year. Standard EOF and varimax analyses are not able to evolve with time of year unless the analysis is stratified by season. Varimax analysis is able to extract the SAM, NAM, and ENSO modes very well, however.
We analyzed diurnal variations in precipitation, surface pressure, and atmospheric static energy over the United States from observations and NCAR regional climate model (RegCM) simulations. Consistent with previous studies, the mean (1963–1993) pattern of the diurnal cycle of summer U.S. precipitation is characterized by late afternoon maxima over the Southeast and the Rocky Mountains and midnight maxima over the region east of the Rockies and the adjacent plains. Diurnal variations of precipitation is weaker in other seasons, with early to late morning maxima over most of the United States in winter. The diurnal cycle in precipitation frequency accounts for most of the diurnal variations, while the diurnal variations in precipitation intensity are small. The broad pattern of the diurnal cycle of summer precipitation is fairly stable, but the interannual variability in the diurnal cycle of winter precipitation is large. The diurnal cycle of July connective available potential energy (CAPE) is dominated by a solar driven march of a high‐CAPE (2–4 kJ kg −1 ) tongue moving from the Southeast into the Northwest, with maximum values in the late afternoon to early evening over most of the United States. The solar driven diurnal and semidiurnal cycles of surface pressure result in significant large‐scale convergence over most of the western United States during the day and over the region east of the Rockies at night. The diurnal cycle of low‐level large‐scale convergence suppresses daytime convection and favors nighttime moist convection over the region east of the Rockies and the adjacent plains. The nocturnal maximum in the region east of the Rockies is also enhanced by the eastward propagation of late afternoon thunderstorms generated over the Rockies. Over the Southeast and the Rockies, both the static instability and the surface convergence favor afternoon moist convection in summer, resulting in very strong late afternoon maxima of precipitation over these regions. RegCM simulations of 1993 summer precipitation with three different cumulus convection schemes (Grell, Kuo, CCM3) all had deficiencies in capturing the broad pattern of the diurnal cycle of precipitation over the United States. The model also overestimated precipitation frequency and underestimated precipitation intensity. The simulated diurnal cycles of surface pressure and CAPE were weak compared to observations. All the schemes produced too much cloudiness over the Southeast for July 1993 which reduced surface solar radiation and thus daytime peak warming at the surface. The model's criteria for onset of moist convection appear to be too weak, so moist convection in the model starts too early and occurs too often with all the three schemes.
An evaluation is carried out of the moisture fields, the precipitation P and evaporation E, and the moisture transport and divergence in the atmosphere from the global atmospheric National Centers for Environmental Prediction (NCEP) reanalyses produced with four-dimensional-data assimilation. The moisture fields are summarized by the precipitable water which is compared with analyzed fields from NVAP based primarily on Special Sensor Microwave Imager (SSM/I) over the oceans and rawinsonde measurements over land, plus TIROS Operational Vertical Sounder (TOVS). The moisture budgets are evaluated through computation of the freshwater flux at the surface E - P using residual techniques from the divergence of the total moisture transport, and this is compared with the reanalysis E - P that is based upon a 6-hour integration of the assimilating model and thus depends on the model parameterizations. The P field is evaluated using Xie-Arkin Global Precipitation Climatology Project (GPCP) estimates. An atlas presents climatological means for the period 1979 1995 (17 years) and standard deviations for annual, seasonal and monthly values, and the differences between estimates.
