Amplified water vapour feedback at high altitudes during winter

2012 ◽  
Vol 33 (4) ◽  
pp. 897-903 ◽  
Author(s):  
Imtiaz Rangwala
Keyword(s):  
Water Vapour ◽  
High Altitudes ◽  
Water Vapour Feedback

scholarly journals Technical Note: Calibration instrument for the krypton hygrometer KH20

2012 ◽  
Vol 5 (1) ◽  
pp. 1695-1715
Author(s):  
T. Foken ◽  
H. Falke
Keyword(s):  
Water Vapour ◽  
Low Temperatures ◽  
Path Length ◽  
Motor System ◽  
Humidity Sensor ◽  
Technical Note ◽  
Stepper Motor ◽  
High Altitudes ◽  
Over Time

Abstract. A calibration instrument for krypton hygrometers (KH20, Campbell Sci.) with variable path length is presented. This unit allows for in-situ calibrations of the krypton hygrometer, which is typically not very stable over time, during measuring campaigns. It was constructed mainly for application at high altitudes and low temperatures, where further improvements are needed to the IR-hygrometers which are normally used. The changing path length requires that a changing concentration of the absorber be simulated. Because oxygen absorbs more strongly than water vapour, the calibration is made against oxygen and transferred to water vapour. The design of the calibration instrument is made as one unit containing a stepper motor system, PC and humidity sensor. For the calibration, it is necessary to install the krypton hygrometer on this unit.

Gauging water-vapour feedback

Nature ◽  
1989 ◽  
Vol 342 (6251) ◽  
pp. 736-737 ◽  
Author(s):  
Robert D. Cess
Keyword(s):  
Water Vapour ◽  
Water Vapour Feedback

Water vapour, CO 2 and insolation over the last glacial-interglacial cycles

1993 ◽  
Vol 341 (1297) ◽  
pp. 253-261 ◽  
Keyword(s):  
Water Vapour ◽  
Northern Hemisphere ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Last Glacial ◽  
Ice Volume ◽  
Water Vapour Feedback ◽  
Astronomical Forcing ◽  
The Last Glacial Maximum ◽  
The Last Glacial

A two-dimensional model which links the atmosphere, the mixed layer of the ocean, the sea ice, the continents, the ice sheets and their underlying bedrock has been used to test the Milankovitch theory over the last two glacial-interglacial cycles. A series of sensitivity analyses have allowed us to understand better the internal mechanisms which drive the simulated climate system and in particular the feedbacks related to surface albedo and water vapour. It was found that orbital variations alone can induce, in such a system, feedbacks sufficient to generate the low frequency p art of the climatic variations over the last 122 ka. These simulated variations at the astronomical timescale are broadly in agreement with reconstructions of ice-sheet volume and of sea level independently obtained from geological data. Imperfections in the stimulated climate were the insufficient southward extent of the ice sheets and the too small hemispheric cooling at the last glacial maximum . These deficiencies were partly remedied in a further experiment by using the time-dependent atmospheric CO2 concentration given by the Vostok ice core in addition to the astronomical forcing. In this transient simulation, 70% of the Northern Hemisphere ice volume is related to the astronomical forcing and the related changes in the albedo, the rem aining 30% being due to the CO 2 changes. Analysis of the processes involved shows that variations of ablation are more important for the ice-sheet response than are variations of snow precipitation. A key mechanism in the deglaciation after the last glacial maxim um appears to be the ‘ageing’ of snow which significantly decreases its albedo. The other factors which play an important role are ice-sheet altitude, insolation, taiga cover, ice-albedo feedback, ice-sheet configuration (‘continentality’ and ‘desert’ effect), isostatic rebound, CO 2 changes and tem perature-water vapour feedback. Numerical experiments have also been carried out with a one-dimensional radiative-convective model in order to quantify the influence of the CO 2 changes and of the water vapour feedback on the climate evolution of the Northern Hemisphere over the last 122 ka. Results of these experiments indicate that 67% of the simulated cooling at the last glacial maximum can be attributed to the astronomical forcing and the subsequent surface albedo increase, the remaining 33% being associated with the reduced CO 2 concentration. Moreover, the water vapour feedback explains 40% of the simulated cooling in all the experiments done. The transient response of the clim ate system to both the astronomical and CO 2 forcing was also simulated by the LLN (Louvain-la-Neuve) 2.5-dimensional model over the two last glacial-interglacial cycles. It is particularly significant that spectral analysis of the simulated Northern Hemisphere global ice volume variations reproduces correctly the relative intensity of the peaks at the orbital frequencies. Except for variations with timescales shorter than 5 ka, the simulated long-term variations of total ice volume are comparable to that reconstructed from deep sea cores. For example, the model simulates glacial maxima of similar amplitudes at 134 ka BP and 15 ka BP, followed by abrupt deglaciations. The complete deglaciation of the three main Northern Hemisphere ice sheets, which is simulated around 122 ka BP, is in partial disagreement with reconstructions indicating that the Greenland ice sheet survived during the Eemian interglacial. The continental ice volume variations during the last 122 ka of the 200 ka simulation are, however, not significantly affected by this shortcoming.

The Calculation Method for Light Climate Parameters Based on Sun-Lighting Efficiency and the Comparative Analysis of Light Climate in Hanoi and Moscow

2019 ◽  
pp. 67-71
Author(s):  
Aleksei K. Solovyov ◽  
Thi Hanh Phuong Nguyen
Keyword(s):  
Comparative Analysis ◽  
Water Vapour ◽  
Calculation Method ◽  
Human Activities ◽  
The Sun ◽  
Light Climate ◽  
High Altitudes ◽  
Distribution Uniformity ◽  
High Level ◽  
Scattered Component

The main source of daylight is the Sun. The EarthТs atmosphere scatters its light due to the air, water vapour, ice particles (at high altitudes), dust, various gases, and other contaminants that appear in the air as a result of human activities. This forms a daylight diffuse (scattered) component, which is a data basis for calculation of daylight in buildings. This basis has its own features for a given region. This article shows a calculation of sun-lighting efficiency in Vietnam. We obtained a variation of horizontal daylight illuminance in Hanoi (21.03∞N). Comparing it with the variation of horizontal daylight illuminance in Moscow (55.70∞N), we can see a high level and a distribution uniformity of outdoor illuminance in Vietnam. The maximum levels of diffuse illuminance and total illuminance in Hanoi are 45.2 and 58.52 klx; the maximum levels of diffuse illuminance and total illuminance in Moscow are 28.3 and 53.1 klx. Besides, illuminance levels in winter months are much higher for Hanoi than for Moscow. This can be explained by different latitudes of these cities and by the Sun motion.

scholarly journals Radiative forcing and feedback by forests in warm climates – a sensitivity study

2015 ◽  
Vol 6 (2) ◽  
pp. 2577-2615
Author(s):  
U. Port ◽  
M. Claussen ◽  
V. Brovkin
Keyword(s):  
Water Vapour ◽  
High Latitude ◽  
Radiative Forcing ◽  
Sensitivity Study ◽  
Lapse Rate ◽  
Order Effects ◽  
Early Eocene ◽  
Max Planck ◽  
Water Vapour Feedback ◽  
Dark Soil

Abstract. The biogeophysical effect of forests in a climate with permanent high-latitude ice cover has already been investigated. We extend this analysis to warm, basically ice-free climates, and we choose the early Eocene, some 54 to 52 million years ago, as paradigm for such type of climate. We use the Max Planck Institute for Meteorology Earth System Model to evaluate the radiative forcing of forests and the feedbacks triggered by forests in early Eocene and pre-industrial climate, respectively. To isolate first-order effects, we compare idealised simulations in which all continents are covered either by dense forests or by deserts with either bright or dark soil. In comparison with desert continents covered by bright soil, forested continents warm the planet in the early Eocene climate and in the pre-industrial climate. The warming can be attributed to different feedback processes, though. The lapse-rate – water-vapour feedback is stronger in early Eocene climate than in pre-industrial climate, but strong and negative cloud-related feedbacks nearly outweigh the positive lapse-rate – water-vapour feedback in the early Eocene climate. Subsequently, global mean warming by forests is weaker in the early Eocene climate than in the pre-industrial climate. Sea-ice related feedbacks are weak in the almost ice-free climate of the early Eocene, thereby leading to a weaker high-latitude warming by forests than in the pre-industrial climate. When the land is covered with dark soils, forests cool the early Eocene climate stronger than the pre-industrial climate because the lapse-rate and water-vapour feedbacks are stronger in the early Eocene climate. Cloud-related feedbacks are equally strong in both climates. We conclude that radiative forcing by forests varies little with the climate state, while most subsequent feedbacks depend on the climate state.

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