Atlantic watermass and circulation response to persistent freshwater forcing in two coupled general circulation models     

M. Harrison  A. Adcroft  R. Hallberg 《Climate Dynamics》2014,42(1-2):59-68

The sensitivity of the Atlantic circulation and watermasses to biases in the convergence of moisture into the basin is examined in this study using two different general circulation models. For a persistent positive moisture flux into the tropical Atlantic, the average salinity and temperature in the basin is reduced, mainly below mid-depths and in high latitudes. A transient reduction in the Atlantic overturning strength occurs in this case, with a recovery timescale of 1–2 centuries. In contrast, a similar amount of freshwater directed into the Subpolar North Atlantic results in a persistent reduction in overturning and an increase in basin heat and salt content. In the unperturbed pre-industrial simulations, the Atlantic is unambiguously warmer and saltier than historical observations below mid-depths and in the Nordic Seas. The models’ tropical freshwater flux sensitivities project strongly onto the spatial pattern of this bias, suggesting a common atmospheric deficiency. The integrated Atlantic plus Arctic surface freshwater flux in these models is between ?0.5 and ?0.6 Sv, compared with an observational estimate of ?0.28 Sv. Our results suggest that shortcomings in the models’ ability to reproduce realistic bulk watermass properties are due to an overestimation of the inter-basin moisture export from the tropical Atlantic.  相似文献   

Erratum to “The relationship between shrink–swell occurrence and climate in south-east England” [Proc. Geol. Assoc. 123 (2012) 556–575]     

A.M. Harrison  J.F.M. Plim  M. Harrison  L.D. Jones  M.G. Culshaw 《Proceedings of the Geologists' Association. Geologists' Association》2014

  相似文献   

Emission fluxes and atmospheric degradation of monoterpenes above a boreal forest: field measurements and modelling     

JÖRG SPANKE  ÜLLAR RANNIK  RENATE FORKEL  WALTER NIGGE  THORSTEN HOFFMANN 《Tellus. Series B, Chemical and physical meteorology》2001,53(4):406-422

  相似文献   

First Observations of Coronal Hole Structure and Evolution Using Soho-Cds     

J. E . Insley  V. Moore  R. A. Harrison 《Solar physics》1997,175(2):437-456

We report on initial observations of coronal holestructure and evolution by the Coronal Diagnostic Spectrometer (CDS) instrument on board the Solar and Heliospheric Observatory (SOHO). The data show that there is coronal activity on time scales of tens of minutes, manifested as brightenings at chromospheric network cell junctions in extreme ultraviolet (EUV) wavelengths. There are also significant differences in structure seen in different wavelengths in coronal holes. Finally, we show coronal hole EUV spectra and compare them to quiet-Sun spectra, also taken by CDS.  相似文献   

The geomorphology and sedimentology of the ‘Témpanos’ moraine at Laguna San Rafael,Chile     

Neil F. Glasser  Krister Jansson  Wishart A. Mitchell  Stephan Harrison 《第四纪科学杂志》2006,21(6):629-643

  相似文献   

On the detection of clouds     

A.W. Harrison  C.A. Coombes 《大气与海洋》2013,51(2):244-255

Abstract

Short‐ and long‐wave sky radiances measured with an all‐sky automatic recording radiometer are used to infer the sky cloud‐cover conditions at 10‐min intervals (night) and 20‐min intervals (day). During the day a simple net short‐wave detector provides supplementary data and can be employed as a clear‐sky indicator. This system of cloud detection is controlled by a PET microcomputer and provides a basis for the automatic computer programmed estimation of cloud cover.  相似文献   

Spatially resolved spectroscopy of the E+A galaxies in the z= 0.32 cluster AC 114   总被引：1，自引：0，他引：1  

Michael B. Pracy  Warrick J. Couch  Chris Blake  Kenji Bekki  Craig Harrison  Matthew Colless  Harald Kuntschner  Roberto de Propris 《Monthly notices of the Royal Astronomical Society》2005,359(4):1421-1432

We present spatially resolved intermediate-resolution spectroscopy of a sample of 12 E+A galaxies in the   z = 0.32  rich galaxy cluster AC 114, obtained with the FLAMES multi-integral field unit system on the Very Large Telescope (VLT) of the European Southern Observatory. Previous integrated spectroscopy of all these galaxies by Couch & Sharples had shown them to have strong Balmer line absorption and an absence of [O  ii ]λ3727 emission – the defining characteristics of the 'E+A' spectral signature, indicative of an abrupt halt to a recent episode of quite vigorous star formation. We have used our spectral data to determine the radial variation in the strength of Hδ absorption in these galaxies and hence map out the distribution of this recently formed stellar population. Such information provides important clues as to what physical event might have been responsible for this quite dramatic change in star formation activity in the recent past of these galaxies. We find a diversity of behaviour amongst these galaxies in terms of the radial variation in Hδ absorption: four galaxies show little Hδ absorption across their entire extent; it would appear they were misidentified as E+A galaxies in the earlier integrated spectroscopic studies. The remainder show strong Hδ absorption, with a gradient that is either negative (Hδ equivalent width decreasing with radius), flat or positive . By comparison with numerical simulations we suggest that the first of these different types of radial behaviour provides evidence for a merger/interaction origin, whereas the latter two types of behaviour are more consistent with the truncation of star formation in normal disc galaxies with the Hδ gradient becoming increasingly positive with time after truncation. It would seem therefore that more than one physical mechanism is responsible for E+A formation in the same environment.  相似文献   

The timing and nature of recession of outlet glaciers of Hielo Patagónico Norte, Chile, from their Neoglacial IV (Little Ice Age) maximum positions   总被引：2，自引：1，他引：1  

Stephan Harrison  Vanessa Winchester  Neil Glasser 《Global and Planetary Change》2007,59(1-4):67

The dates of recession of eleven outlet glaciers of the Hielo Patagónico Norte (Northern Patagonian Icefield) from their recent maximum positions have been inferred from dendrochronology, lichenometry, radiocarbon dating and historical sources. We have refined the dating for part of the Little Ice Age period in this area placing a glacial advance to between AD 1650 and 1766 with the latter date favoured as conformable with historical records and an uncalibrated radiocarbon determination. Glacier recession from maximal positions began in the early 1860s–1870s. Recession was largely synchronous on the western and eastern sides of the Icefield. This synchronicity suggests that climate forcing over-rides second-order controls on glacier behaviour such as the nature of the terminal environment (e.g. calving/non-calving) or differences in glacier drainage basin area. We argue that this icefield-wide glacier recession represents a response to post-Little Ice Age warming, and provides further evidence for the global extent and near synchronous termination of the Little Ice Age.  相似文献   

The Earth's Distant Magnetic Field     

E. R. Harrison 《Geophysical Journal International》1962,6(4):479-492

  相似文献   

The climate of Europe 6000 years ago     

R. Cheddadi  G. Yu  J. Guiot  S. P. Harrison  I. Colin Prentice 《Climate Dynamics》1996,13(1):1-9

Palaeoclimates across Europe for 6000 y BP were estimated from pollen data using the modern pollen analogue technique constrained with lake-level data. The constraint consists of restricting the set of modern pollen samples considered as analogues of the fossil samples to those locations where the implied change in annual precipitation minus evapotranspiration (P–E) is consistent with the regional change in moisture balance as indicated by lakes. An artificial neural network was used for the spatial interpolation of lake-level changes to the pollen sites, and for mapping palaeoclimate anomalies. The climate variables reconstructed were mean temperature of the coldest month (T _c ), growing degree days above 5  °C (GDD), moisture availability expressed as the ratio of actual to equilibrium evapotranspiration (α), and P–E. The constraint improved the spatial coherency of the reconstructed palaeoclimate anomalies, especially for P–E. The reconstructions indicate clear spatial and seasonal patterns of Holocene climate change, which can provide a quantitative benchmark for the evaluation of palaeoclimate model simulations. Winter temperatures (T _c ) were 1–3 K greater than present in the far N and NE of Europe, but 2–4 K less than present in the Mediterranean region. Summer warmth (GDD) was greater than present in NW Europe (by 400–800 K day at the highest elevations) and in the Alps, but >400 K day less than present at lower elevations in S Europe. P–E was 50–250 mm less than present in NW Europe and the Alps, but α was 10–15% greater than present in S Europe and P–E was 50–200 mm greater than present in S and E Europe. Received: 3 January 1996 / Accepted: 15 July 1996  相似文献