scholarly journals Northern Hemisphere summer temperature and specific humidity anomalies from two reanalyses

2013 ◽  
Vol 118 (15) ◽  
pp. 8297-8305 ◽  
Author(s):  
Emily C. Gill ◽  
Thomas N. Chase ◽  
Roger A. Pielke ◽  
Klaus Wolter
Keyword(s):  
Northern Hemisphere ◽  
Summer Temperature ◽  
Specific Humidity

scholarly journals The changing shape of Northern Hemisphere summer temperature distributions

2016 ◽  
Vol 121 (15) ◽  
pp. 8849-8868 ◽  
Author(s):  
Karen A. McKinnon ◽  
Andrew Rhines ◽  
Martin P. Tingley ◽  
Peter Huybers
Keyword(s):  
Northern Hemisphere ◽  
Summer Temperature ◽  
Temperature Distributions

scholarly journals Thermomechanical modelling of Northern Hemisphere ice sheets with a two-level mass-balance parameterization

1995 ◽  
Vol 21 ◽  
pp. 111-116 ◽  
Author(s):  
Philippe Huybrechts ◽  
Stephen T’ Siobbel
Keyword(s):  
Surface Temperature ◽  
Mass Balance ◽  
Northern Hemisphere ◽  
Three Dimensional ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Snow Accumulation ◽  
Summer Temperature ◽  
Balance Model ◽  
Geological Evidence

A three-dimensional time-dependent thermomechanical ice-sheet model was used together with a two-level (snow-accumulation/runoff) mass-balance model to investigate the Quaternary ice sheets of the Northern Hemisphere. The model freely generates the ice-sheet geometry in response to specified changes in surface temperature and mass balance, and includes bedrock adjustment, basal sliding and a full temperature calculation within the ice. The mass-balance parameterization makes a distinction between snowfall and melting. Yearly snowfall rates depend on the present precipitation distribution, and are varied proportionally to changes in surface temperature and the moisture content of the air. The ablation model is based on the positive-degree-day method, and distinguishes between ice and snow melting. This paper discusses steady-slate characteristics, conditions for growth and retreat, and response time-scales of ice sheets as a function of a prescribed lowering of summer temperature. Most notably, the modelled extents of the Eurasian ice sheet for a summer temperature lowering of 6–7 K and of the Laurentide ice sheet for a cooling of 9–10 K are in reasonable agreement with most reconstructions based on geological evidence, except for the presence of a large ice sheet stretching from Alaska across the Bering Strait to most of eastern Siberia. In addition, wet basal conditions turned out to be always confined to the margin, whereas central areas in these reconstructions remained always cold-based. This is of relevance for processes involving reduced basal traction.

Influence of volcanic eruptions on Northern Hemisphere summer temperature over the past 600 years

Nature ◽  
10.1038/30943 ◽  
1998 ◽  
Vol 393 (6684) ◽  
pp. 450-455 ◽  
Author(s):  
K. R. Briffa ◽  
P. D. Jones ◽  
F. H. Schweingruber ◽  
T. J. Osborn
Keyword(s):  
Northern Hemisphere ◽  
Volcanic Eruptions ◽  
Summer Temperature ◽  
The Past

scholarly journals Coherent Region-, Species-, and Frequency-Dependent Local Climate Signals in Northern Hemisphere Tree-Ring Widths*

2011 ◽  
Vol 24 (23) ◽  
pp. 5998-6012 ◽  
Author(s):  
Justin J. Wettstein ◽  
Jeremy S. Littell ◽  
John M. Wallace ◽  
Ze’ev Gedalof
Keyword(s):  
Time Series ◽  
Northern Hemisphere ◽  
Tree Ring ◽  
Ring Width ◽  
Frequency Component ◽  
Summer Temperature ◽  
Frequency Dependent ◽  
Local Climate ◽  
Temperature And Precipitation ◽  
Species Specific

Abstract Patterns of correlation between tree rings and local temperature or precipitation are investigated using 762 International Tree-Ring Data Bank standardized ring width site chronology time series, and a gridded dataset of temperature and precipitation. Coherent regional- and, in some cases, hemispheric-scale patterns of correlation are found in the extratropical Northern Hemisphere for both the summer prior to and the summer concurrent with ring width formation across different species and over large distances. Among those chronologies that are primarily linked to temperature, thicker ring widths are generally associated with anomalously cool prior summer temperature and anomalously warm concurrent summer temperature. Reconstructions of local summer temperature using prior, concurrent, and/or subsequent year ring widths as predictors demonstrate that useful climate–growth information generally exists in ring widths that are both concurrent with and subsequent to the summer temperature anomaly. Consistent prior summer temperature–ring width relationships have received relatively little previous attention. Among those chronologies that are primarily linked to precipitation, thicker ring widths are generally associated with high summer precipitation in both the year prior to and the year concurrent with ring formation. The magnitude and spatial consistency of temperature correlations are greater than those for precipitation, at least on the hemispheric scale. These results support and serve to generalize the conclusions of prior regionally restricted and/or species-specific studies relating ring width to energy and/or water limitations. Regional- and hemispheric-scale patterns of ring width–temperature or ring width–precipitation correlations show up more clearly in species-specific and frequency-dependent analyses. Different species respond differently to temperature and precipitation anomalies. Consistent with the hemispheric patterns described above, most standardized ring width time series more faithfully record the high frequency component of the temperature signal than the low frequency component. The potential for enhanced coherence in regionally restricted, species-specific, and frequency-dependent analyses is independently verified by examining the correlation between ring width time series over geographical distance. This broader characterization of relationships between tree-ring widths and local climate provides an objective basis for selecting tree ring or other similarly high-resolution proxy data for regional-, hemispheric-, or global-scale paleoclimate reconstructions.

scholarly journals Recent Changes in Surface Humidity: Development of the HadCRUH Dataset

2008 ◽  
Vol 21 (20) ◽  
pp. 5364-5383 ◽  
Author(s):  
Katharine M. Willett ◽  
Philip D. Jones ◽  
Nathan P. Gillett ◽  
Peter W. Thorne
Keyword(s):  
Relative Humidity ◽  
Northern Hemisphere ◽  
Research Unit ◽  
Specific Humidity ◽  
Climatic Research Unit ◽  
Global Trends ◽  
Dewpoint Temperature ◽  
Key Driver ◽  
Hadley Centre ◽  
The Tropics

Abstract Water vapor constitutes the most significant greenhouse gas, is a key driver of many atmospheric processes, and hence, is fundamental to understanding the climate system. It is a major factor in human “heat stress,” whereby increasing humidity reduces the ability to stay cool. Until now no truly global homogenized surface humidity dataset has existed with which to assess recent changes. The Met Office Hadley Centre and Climatic Research Unit Global Surface Humidity dataset (HadCRUH), described herein, provides a homogenized quality controlled near-global 5° by 5° gridded monthly mean anomaly dataset in surface specific and relative humidity from 1973 to 2003. It consists of land and marine data, and is geographically quasi-complete over the region 60°N–40°S. Between 1973 and 2003 surface specific humidity has increased significantly over the globe, tropics, and Northern Hemisphere. Global trends are 0.11 and 0.07 g kg−1 (10 yr)−1 for land and marine components, respectively. Trends are consistently larger in the tropics and in the Northern Hemisphere during summer, as expected: warmer regions exhibit larger increases in specific humidity for a given temperature change under conditions of constant relative humidity, based on the Clausius–Clapeyron equation. Relative humidity trends are not significant when averaged over the landmass of the globe, tropics, and Northern Hemisphere, although some seasonal changes are significant. A strong positive bias is apparent in marine humidity data prior to 1982, likely owing to a known change in reporting practice for dewpoint temperature at this time. Consequently, trends in both specific and relative humidity are likely underestimated over the oceans.

scholarly journals Thermomechanical modelling of Northern Hemisphere ice sheets with a two-level mass-balance parameterization

1995 ◽  
Vol 21 ◽  
pp. 111-116 ◽  
Author(s):  
Philippe Huybrechts ◽  
Stephen T’ Siobbel
Keyword(s):  
Surface Temperature ◽  
Mass Balance ◽  
Northern Hemisphere ◽  
Three Dimensional ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Snow Accumulation ◽  
Summer Temperature ◽  
Balance Model ◽  
Geological Evidence

A three-dimensional time-dependent thermomechanical ice-sheet model was used together with a two-level (snow-accumulation/runoff) mass-balance model to investigate the Quaternary ice sheets of the Northern Hemisphere. The model freely generates the ice-sheet geometry in response to specified changes in surface temperature and mass balance, and includes bedrock adjustment, basal sliding and a full temperature calculation within the ice. The mass-balance parameterization makes a distinction between snowfall and melting. Yearly snowfall rates depend on the present precipitation distribution, and are varied proportionally to changes in surface temperature and the moisture content of the air. The ablation model is based on the positive-degree-day method, and distinguishes between ice and snow melting. This paper discusses steady-slate characteristics, conditions for growth and retreat, and response time-scales of ice sheets as a function of a prescribed lowering of summer temperature. Most notably, the modelled extents of the Eurasian ice sheet for a summer temperature lowering of 6–7 K and of the Laurentide ice sheet for a cooling of 9–10 K are in reasonable agreement with most reconstructions based on geological evidence, except for the presence of a large ice sheet stretching from Alaska across the Bering Strait to most of eastern Siberia. In addition, wet basal conditions turned out to be always confined to the margin, whereas central areas in these reconstructions remained always cold-based. This is of relevance for processes involving reduced basal traction.

scholarly journals Causal empirical estimates suggest COVID-19 transmission rates are highly seasonal

2020 ◽  
Author(s):  
Tamma Carleton ◽  
Kyle C. Meng
Keyword(s):  
Public Health ◽  
Southern Hemisphere ◽  
Northern Hemisphere ◽  
Global Scale ◽  
Specific Humidity ◽  
Local Temperature ◽  
Boreal Winter ◽  
Empirical Estimates ◽  
Novel Coronavirus ◽  
The Relationship

AbstractNearly every country is now combating the 2019 novel coronavirus (COVID-19). It has been hypothesized that if COVID-19 exhibits seasonality, changing temperatures in the coming months will shift transmission patterns around the world. Such projections, however, require an estimate of the relationship between COVID-19 and temperature at a global scale, and one that isolates the role of temperature from confounding factors, such as public health capacity. This paper provides the first plausibly causal estimates of the relationship between COVID-19 transmission and local temperature using a global sample comprising of 166,686 confirmed new COVID-19 cases from 134 countries from January 22, 2020 to March 15, 2020. We find robust statistical evidence that a 1°C increase in local temperature reduces transmission by 13% [−21%, −4%, 95%CI]. In contrast, we do not find that specific humidity or precipitation influence transmission. Our statistical approach separates effects of climate variation on COVID-19 transmission from other potentially correlated factors, such as differences in public health responses across countries and heterogeneous population densities. Using constructions of expected seasonal temperatures, we project that changing temperatures between March 2020 and July 2020 will cause COVID-19 transmission to fall by 43% on average for Northern Hemisphere countries and to rise by 71% on average for Southern Hemisphere countries. However, these patterns reverse as the boreal winter approaches, with seasonal temperatures in January 2021 increasing average COVID-19 transmission by 59% relative to March 2020 in northern countries and lowering transmission by 2% in southern countries. These findings suggest that Southern Hemisphere countries should expect greater transmission in the coming months. Moreover, Northern Hemisphere countries face a crucial window of opportunity: if contagion-containing policy interventions can dramatically reduce COVID-19 cases with the aid of the approaching warmer months, it may be possible to avoid a second wave of COVID-19 next winter.

Alpha-Effect, Current and Kinetic Helicities for Magnetically Driven Turbulence, and Solar Dynamo

2000 ◽  
Vol 179 ◽  
pp. 387-388
Author(s):  
Gaetano Belvedere ◽  
V. V. Pipin ◽  
G. Rüdiger
Keyword(s):  
Southern Hemisphere ◽  
Northern Hemisphere ◽  
Convection Zone ◽  
Solar Surface ◽  
Momentum Transport ◽  
Angular Momentum Transport ◽  
Magnetic Buoyancy ◽  
Alpha Effect ◽  
Current Helicity

Extended AbstractRecent numerical simulations lead to the result that turbulence is much more magnetically driven than believed. In particular the role ofmagnetic buoyancyappears quite important for the generation ofα-effect and angular momentum transport (Brandenburg & Schmitt 1998). We present results obtained for a turbulence field driven by a (given) Lorentz force in a non-stratified but rotating convection zone. The main result confirms the numerical findings of Brandenburg & Schmitt that in the northern hemisphere theα-effect and the kinetic helicityℋkin= 〈u′ · rotu′〉 are positive (and negative in the northern hemisphere), this being just opposite to what occurs for the current helicityℋcurr= 〈j′ ·B′〉, which is negative in the northern hemisphere (and positive in the southern hemisphere). There has been an increasing number of papers presenting observations of current helicity at the solar surface, all showing that it isnegativein the northern hemisphere and positive in the southern hemisphere (see Rüdigeret al. 2000, also for a review).

The Hemispheric Sign Rule of Current Helicity during the Rising Phase of Cycle 23

2000 ◽  
Vol 179 ◽  
pp. 303-306
Author(s):  
S. D. Bao ◽  
G. X. Ai ◽  
H. Q. Zhang
Keyword(s):  
Solar Cycle ◽  
Southern Hemisphere ◽  
Northern Hemisphere ◽  
Active Regions ◽  
Hemispheric Preference ◽  
Current Helicity

AbstractWe compute the signs of two different current helicity parameters (i.e., αbestandHc) for 87 active regions during the rise of cycle 23. The results indicate that 59% of the active regions in the northern hemisphere have negative αbestand 65% in the southern hemisphere have positive. This is consistent with that of the cycle 22. However, the helicity parameterHcshows a weaker opposite hemispheric preference in the new solar cycle. Possible reasons are discussed.

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