scholarly journals Downwelling longwave flux over Summit, Greenland, 2010-2012: Analysis of surface-based observations and evaluation of ERA-Interim using wavelets

2014 ◽  
Vol 119 (21) ◽  
pp. 12,317-12,337 ◽  
Author(s):  
Christopher J. Cox ◽  
Von P. Walden ◽  
Gilbert P. Compo ◽  
Penny M. Rowe ◽  
Matthew D. Shupe ◽  
...  
Keyword(s):  
Longwave Flux

scholarly journals Ensemble daily simulations for elucidating cloud–aerosol interactions under a large spread of realistic environmental conditions

2020 ◽  
Vol 20 (11) ◽  
pp. 6291-6303
Author(s):  
Guy Dagan ◽  
Philip Stier
Keyword(s):  
Initial Conditions ◽  
Cloud Droplet ◽  
Large Data ◽  
Data Set ◽  
Cloud Properties ◽  
Large Spread ◽  
The Difference ◽  
Ice Content ◽  
Aerosol Effects ◽  
Longwave Flux

Abstract. Aerosol effects on cloud properties and the atmospheric energy and radiation budgets are studied through ensemble simulations over two month-long periods during the NARVAL campaigns (Next-generation Aircraft Remote-Sensing for Validation Studies, December 2013 and August 2016). For each day, two simulations are conducted with low and high cloud droplet number concentrations (CDNCs), representing low and high aerosol concentrations, respectively. This large data set, which is based on a large spread of co-varying realistic initial conditions, enables robust identification of the effect of CDNC changes on cloud properties. We show that increases in CDNC drive a reduction in the top-of-atmosphere (TOA) net shortwave flux (more reflection) and a decrease in the lower-tropospheric stability for all cases examined, while the TOA longwave flux and the liquid and ice water path changes are generally positive. However, changes in cloud fraction or precipitation, that could appear significant for a given day, are not as robustly affected, and, at least for the summer month, are not statistically distinguishable from zero. These results highlight the need for using a large sample of initial conditions for cloud–aerosol studies for identifying the significance of the response. In addition, we demonstrate the dependence of the aerosol effects on the season, as it is shown that the TOA net radiative effect is doubled during the winter month as compared to the summer month. By separating the simulations into different dominant cloud regimes, we show that the difference between the different months emerges due to the compensation of the longwave effect induced by an increase in ice content as compared to the shortwave effect of the liquid clouds. The CDNC effect on the longwave flux is stronger in the summer as the clouds are deeper and the atmosphere is more unstable.

scholarly journals Year-Round Observation of Longwave Radiative Flux Divergence in Greenland

2007 ◽  
Vol 46 (9) ◽  
pp. 1469-1479 ◽  
Author(s):  
S. W. Hoch ◽  
P. Calanca ◽  
R. Philipona ◽  
A. Ohmura
Keyword(s):  
Longwave Radiation ◽  
Radiative Flux ◽  
Radiative Cooling ◽  
Flux Divergence ◽  
Tower Structure ◽  
Order Of Magnitude ◽  
The Mean ◽  
Temperature Tendency ◽  
Radiation Measurements ◽  
Longwave Flux

Abstract Longwave radiative flux divergence within the lowest 50 m of the atmospheric boundary layer was observed during the Eidgenössische Technische Hochschule (ETH) Greenland Summit experiment. The dataset collected at 72°35′N, 38°30′W, 3203 m MSL is based on longwave radiation measurements at 2 and 48 m that are corrected for the influence of the supporting tower structure. The observations cover all seasons and reveal the magnitude of longwave radiative flux divergence and its incoming and outgoing component under stable and unstable conditions. Longwave radiative flux divergence during winter corresponds to a radiative cooling of −10 K day−1, but values of −30 K day−1 can persist for several days. During summer, the mean cooling effect of longwave radiative flux divergence is small (−2 K day−1) but exhibits a strong diurnal cycle. With values ranging from −35 K day−1 around midnight to 15 K day−1 at noon, the heating rate due to longwave radiative flux divergence is of the same order of magnitude as the observed temperature tendency. However, temperature tendency and longwave radiative flux divergence are out of phase, with temperature tendency leading the longwave radiative flux divergence by 3 h. The vertical variation of the outgoing longwave flux usually dominates the net longwave flux divergence, showing a strong divergence at nighttime and a strong convergence during the day. The divergence of the incoming longwave flux plays a secondary role, showing a slight counteracting effect. Fog is frequently observed during summer nights. Under such conditions, a divergence of both incoming and outgoing fluxes leads to the strongest radiative cooling rates that are observed. Considering all data, a correlation between longwave radiative flux divergence and the temperature difference across the 2–48-m layer is found.

On the consistency of CERES longwave flux and AIRS temperature and humidity profiles

2011 ◽  
Vol 116 (D17) ◽  
Author(s):  
Wenbo Sun ◽  
Bing Lin ◽  
Yongxiang Hu ◽  
Constantine Lukashin ◽  
Seiji Kato ◽  
...  
Keyword(s):  
Temperature And Humidity ◽  
Humidity Profiles ◽  
Longwave Flux

scholarly journals A new method to diagnose the contribution of anthropogenic activities to temperature: temperature tagging

2013 ◽  
Vol 6 (2) ◽  
pp. 417-427 ◽  
Author(s):  
V. Grewe
Keyword(s):  
Greenhouse Gases ◽  
Surface Temperature ◽  
Greenhouse Effect ◽  
Climate Model ◽  
Co2 Concentration ◽  
Base Case ◽  
Atmospheric Absorption ◽  
The Difference ◽  
The Impact ◽  
Longwave Flux

Abstract. This study presents a new methodology, called temperature tagging. It keeps track of the contributions of individual processes to temperature within a climate model simulation. As a first step and as a test bed, a simple box climate model is regarded. The model consists of an atmosphere, which absorbs and emits radiation, and of a surface, which reflects, absorbs and emits radiation. The tagging methodology is used to investigate the impact of the atmosphere on surface temperature. Four processes are investigated in more detail and their contribution to the surface temperature quantified: (i) shortwave influx and shortwave atmospheric absorption ("sw"), (ii) longwave atmospheric absorption due to non-CO2 greenhouse gases ("nC"), (iii) due to a base case CO2 concentration ("bC"), and (iv) due to an enhanced CO2 concentration ("eC"). The differential equation for the temperature in the box climate model is decomposed into four equations for the tagged temperatures. This method is applied to investigate the contribution of longwave absorption to the surface temperature (greenhouse effect), which is calculated to be 68 K. This estimate contrasts an alternative calculation of the greenhouse effect of slightly more than 30 K based on the difference of the surface temperature with and without an atmosphere. The difference of the two estimates is due to a shortwave cooling effect and a reduced contribution of the shortwave to the total downward flux: the shortwave absorption of the atmosphere results in a reduced net shortwave flux at the surface of 192 W m−2, leading to a cooling of the surface by 14 K. Introducing an atmosphere results in a downward longwave flux at the surface due to atmospheric absorption of 189 W m−2, which roughly equals the net shortwave flux of 192 W m−2. This longwave flux is a result of both the radiation due to atmospheric temperatures and its longwave absorption. Hence the longwave absorption roughly accounts for 91 W m−2 out of a total of 381 W m−2 (roughly 25%) and therefore accounts for a temperature change of 68 K. In a second experiment, the CO2 concentration is doubled, which leads to an increase in surface temperature of 1.2 K, resulting from a temperature increase due to CO2 of 1.9 K, due to non-CO2 greenhouse gases of 0.6 K and a cooling of 1.3 K due to a reduced importance of the solar heating for the surface and atmospheric temperatures. These two experiments show the feasibility of temperature tagging and its potential as a diagnostic for climate simulations.

scholarly journals On the Arctic Wintertime Climate in Global Climate Models

2011 ◽  
Vol 24 (22) ◽  
pp. 5757-5771 ◽  
Author(s):  
Gunilla Svensson ◽  
Johannes Karlsson
Keyword(s):  
Sea Ice ◽  
Arctic Region ◽  
Precipitable Water ◽  
Open Ocean ◽  
Global Climate Models ◽  
The Arctic ◽  
Turbulent Heat ◽  
Skin Temperatures ◽  
Longwave Flux ◽  
The Arctic Region

Abstract Energy fluxes important for determining the Arctic surface temperatures during winter in present-day simulations from the Coupled Model Intercomparison Project phase 3 (CMIP3) multimodel dataset are investigated. The model results are evaluated over different surfaces using satellite retrievals and ECMWF interim reanalysis (ERA-Interim). The wintertime turbulent heat fluxes vary substantially between models and different surfaces. The monthly median net turbulent heat flux (upward) is in the range 100–200 W m−2 and −15 to 15 W m−2 over open ocean and sea ice, respectively. The simulated net longwave radiative flux at the surface is biased high over both surfaces compared to observations but for different reasons. Over open ocean, most models overestimate the outgoing longwave flux while over sea ice it is rather the downwelling flux that is underestimated. Based on the downwelling longwave flux over sea ice, two categories of models are found. One group of models that shows reasonable downwelling longwave fluxes, compared with observations and ERA-Interim, is also associated with relatively high amounts of precipitable water as well as surface skin temperatures. This group also shows more uniform airmass properties over the Arctic region possibly as a result of more frequent events of warm-air intrusion from lower latitudes. The second group of models underestimates the downwelling longwave radiation and is associated with relatively low surface skin temperatures as well as low amounts of precipitable water. These models also exhibit a larger decrease in the moisture and temperature profiles northward in the Arctic region, which might be indicative of too stagnant conditions in these models.

scholarly journals Importance of longwave emissions from adjacent terrain on patterns of tropical glacier melt and recession

2017 ◽  
Vol 64 (243) ◽  
pp. 49-60 ◽  
Author(s):  
CAROLINE AUBRY-WAKE ◽  
DORIAN ZÉPHIR ◽  
MICHEL BARAER ◽  
JEFFREY M. McKENZIE ◽  
BRYAN G. MARK
Keyword(s):  
High Resolution ◽  
Radiation Budget ◽  
Net Radiation ◽  
Tropical Glaciers ◽  
Exposed Rock ◽  
Glacier Melt ◽  
Physically Based ◽  
Simulation Results ◽  
Thermal Infrared Imagery ◽  
Longwave Flux

ABSTRACTTropical glaciers constitute an important source of water for downstream populations. However, our understanding of glacial melt processes is still limited. One observed process that has not yet been quantified for tropical glaciers is the enhanced melt caused by the longwave emission transfer. Here, we use high-resolution surface temperatures obtained from the thermal infrared imagery of the Cuchillacocha Glacier, in the Cordillera Blanca, Peru in June 2014 to calculate a margin longwave flux. This longwave flux, reaching the glacier margin from the adjacent exposed rock, varies between 81 and 120 W m−2 daily. This flux is incorporated into a physically-based melt model to assess the net radiation budget at the modeled glacier margin. The simulation results show an increase in the energy available for melt by an average of 106 W m−2 during the day when compared with the simulation where the LWmargin flux is not accounted for. This value represents an increase in ablation of ~1.7 m at the glacier margin for the duration of the dry season. This study suggests that including the quantification of the glacier margin longwave flux in physically-based melt models results in an improved assessment of tropical glacier energy budget and meltwater generation.

Sign in / Sign up

Export Citation Format

Share Document