A Parametric Radiative Forcing Model for Contrail Cirrus

AbstractA new parameterized analytical model is presented to compute the instantaneous radiative forcing (RF) at the top of the atmosphere (TOA) produced by an additional thin contrail cirrus layer (called “contrail” below). The model calculates the RF using as input the outgoing longwave radiation and reflected solar radiation values at TOA for a contrail-free atmosphere, so that the model is applicable for both cloud-free and cloudy ambient atmospheres. Additional input includes the contrail temperature, contrail optical depth (at 550 nm), effective particle radius, particle habit, solar zenith angle, and the optical depth of cirrus above the contrail layer. The model parameters (5 for longwave and 10 for shortwave) are determined from least squares fits to calculations from the “libRadtran” radiative transfer model over a wide range of atmospheric and surface conditions. The correlation coefficient between model and calculations is larger than 98%. The analytical model is compared with published results, including a 1-yr simulation of global RF, and is found to agree well with previous studies. The fast analytical model is part of a larger modeling system to simulate contrail life cycles (“CoCiP”) and can allow for the rapid simulation of contrail cirrus RF over a wide range of meteorological conditions and for a given size-dependent habit mixture. Ambient clouds are shown to have large local impact on the net RF of contrails. Net RF of contrails may both increase and decrease and even change sign in the presence of higher-level cirrus, depending on solar zenith angle.

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Using a Parameterization of a Radiative Transfer Model to Build High-Resolution Maps of Typical Clear-Sky UV Index in Catalonia, Spain

Journal of Applied Meteorology ◽

10.1175/jam2237.1 ◽

2005 ◽

Vol 44 (6) ◽

pp. 789-803 ◽

Cited By ~ 13

Author(s):

Jordi Badosa ◽

Josep-Abel González ◽

Josep Calbó ◽

Michiel van Weele ◽

Richard L. McKenzie

Keyword(s):

High Resolution ◽

Radiative Transfer ◽

Zenith Angle ◽

Solar Zenith Angle ◽

Absolute Error ◽

Single Scattering ◽

Radiative Transfer Model ◽

Transfer Model ◽

Uv Index ◽

Wide Range

Abstract To perform a climatic analysis of the annual UV index (UVI) variations in Catalonia, Spain (northeast of the Iberian Peninsula), a new simple parameterization scheme is presented based on a multilayer radiative transfer model. The parameterization performs fast UVI calculations for a wide range of cloudless and snow-free situations and can be applied anywhere. The following parameters are considered: solar zenith angle, total ozone column, altitude, aerosol optical depth, and single-scattering albedo. A sensitivity analysis is presented to justify this choice with special attention to aerosol information. Comparisons with the base model show good agreement, most of all for the most common cases, giving an absolute error within ±0.2 in the UVI for a wide range of cases considered. Two tests are done to show the performance of the parameterization against UVI measurements. One uses data from a high-quality spectroradiometer from Lauder, New Zealand [45.04°S, 169.684°E, 370 m above mean sea level (MSL)], where there is a low presence of aerosols. The other uses data from a Robertson–Berger-type meter from Girona, Spain (41.97°N, 2.82°E, 100 m MSL), where there is more aerosol load and where it has been possible to study the effect of aerosol information on the model versus measurement comparison. The parameterization is applied to a climatic analysis of the annual UVI variation in Catalonia, showing the contributions of solar zenith angle, ozone, and aerosols. High-resolution seasonal maps of typical UV index values in Catalonia are presented.

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Radiative forcing over the Arctic of aerosols from the August 2017 Canadian and Greenlandic wildfires

10.5194/egusphere-egu21-7405 ◽

2021 ◽

Author(s):

Filippo Calì Quaglia ◽

Daniela Meloni ◽

Alcide Giorgio di Sarra ◽

Tatiana Di Iorio ◽

Virginia Ciardini ◽

...

Keyword(s):

Radiative Transfer ◽

Radiative Forcing ◽

Solar Zenith Angle ◽

Surface Albedo ◽

High Arctic ◽

The Arctic ◽

Radiative Transfer Model ◽

Transfer Model ◽

Aerosol Layer ◽

Radiative Effect

Extended and intense wildfires occurred in Northern Canada and, unexpectedly, on the Greenlandic West coast during summer 2017. The thick smoke plume emitted into the atmosphere was transported to the high Arctic, producing one of the largest impacts ever observed in the region. Evidence of Canadian and Greenlandic wildfires was recorded at the Thule High Arctic Atmospheric Observatory (THAAO, 76.5&#176;N, 68.8&#176;W, www.thuleatmos-it.it) by a suite of instruments managed by ENEA, INGV, Univ. of Florence, and NCAR. Ground-based observations of the radiation budget have allowed quantification of the surface radiative forcing at THAAO.&#160;Excess biomass burning chemical tracers such as CO, HCN, H2CO, C2H6, and NH3 were&#160; measured in the air column above Thule starting from August 19 until August 23. The aerosol optical depth (AOD) reached a peak value of about 0.9 on August 21, while an enhancement of wildfire compounds was&#160; detected in PM10. The measured shortwave radiative forcing was -36.7 W/m2 at 78&#176; solar zenith angle (SZA) for AOD=0.626.MODTRAN6.0 radiative transfer model (Berk et al., 2014) was used to estimate the aerosol radiative effect and the heating rate profiles at 78&#176; SZA. Measured temperature profiles, integrated water vapour, surface albedo, spectral AOD and aerosol extinction profiles from CALIOP onboard CALIPSO were used as model input. The peak&#160; aerosol heating rate (+0.5 K/day) was&#160; reached within the aerosol layer between 8 and 12 km, while the maximum radiative effect (-45.4 W/m2) is found at 3 km, below the largest aerosol layer.The regional impact of the event that occurred on August 21 was investigated using a combination of atmospheric radiative transfer modelling with measurements of AOD and ground surface albedo from MODIS. The aerosol properties used in the radiative transfer model were constrained by in situ measurements from THAAO. Albedo data over the ocean have been obtained from Jin et al. (2004). Backward trajectories produced through HYSPLIT simulations (Stein et al., 2015) were also employed to trace biomass burning plumes.The radiative forcing efficiency (RFE) over land and ocean was derived, finding values spanning from -3 W/m2 to -132 W/m2, depending on surface albedo and solar zenith angle. The fire plume covered a vast portion of the Arctic, with large values of the daily shortwave RF (< -50 W/m2) lasting for a few days. This large amount of aerosol is expected to influence cloud properties in the Arctic, producing significant indirect radiative effects.

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Inter-Calibration of nine UV sensing instruments over Antarctica and Greenland since 1980: impact on global UV cloud albedo trends

10.5194/egusphere-egu2020-10856 ◽

2020 ◽

Author(s):

Clark Weaver ◽

Gordon Labow ◽

Dong Wu ◽

Pawan K. Bhartia ◽

David Haffner

Keyword(s):

Zenith Angle ◽

Forest Fires ◽

Solar Zenith Angle ◽

Radiative Transfer Model ◽

Transfer Model ◽

Cloud Albedo ◽

Enso Events ◽

Modeling Analysis ◽

Long Term Trend

A suite of NASA/NOAA UV (340nm) sensing satellite instruments, starting with Nimbus-7 SBUV in 1980, provides a global long-term record of cloud trends and cloud response from ENSO events. We present new method to inter-calibrate the radiances of all the SBUV instruments and the Suomi NPP OMPS mapper over both the East Antarctic Plateau and Greenland ice sheets during summer. First, the strong solar zenith angle dependence from the intensities are removed using an empirical approach rather than a radiative transfer model. Then small multiplicative adjustments are made to these solar zenith angle normalized intensities in order to minimize differences when two or more instruments temporally overlap. While the calibrated intensities show a negligible long-term trend over Antarctica, and a statistically insignificant UV albedo trend of -0.05 % per decade over the interior of Greenland, there are small episodic reductions in&#160;intensities which are often seen by multiple instruments. Three of these darkening events are explained by boreal forest fires using trajectory modeling analysis. Other events are caused by surface melting or volcanoes. We estimate a 2-sigma uncertainty&#160;of 0.35% for the calibrated radiances. Finally, we connect the estimated radiance uncertainties, derived from our calibration approach, to the tropical and midlatitude UV cloud albedo trends.

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Coupling sky images with three-dimensional radiative transfer models: a new method to estimate cloud optical depth

Atmospheric Measurement Techniques Discussions ◽

10.5194/amtd-8-11285-2015 ◽

2015 ◽

Vol 8 (10) ◽

pp. 11285-11321 ◽

Cited By ~ 1

Author(s):

F. A. Mejia ◽

B. Kurtz ◽

K. Murray ◽

L. M. Hinkelman ◽

M. Sengupta ◽

...

Keyword(s):

Radiative Transfer ◽

Optical Depth ◽

Zenith Angle ◽

Microwave Radiometer ◽

Three Dimensional ◽

Radiative Transfer Model ◽

Transfer Model ◽

Cloud Detection ◽

Cloud Optical Depth ◽

Direct Normal Irradiance

Abstract. A method for retrieving cloud optical depth (τc) using a ground-based sky imager (USI) is presented. The Radiance Red-Blue Ratio (RRBR) method is motivated from the analysis of simulated images of various τc produced by a 3-D Radiative Transfer Model (3DRTM). From these images the basic parameters affecting the radiance and RBR of a pixel are identified as the solar zenith angle (θ0), τc, solar pixel angle/scattering angle (&vartheta;s), and pixel zenith angle/view angle (&vartheta;z). The effects of these parameters are described and the functions for radiance, Iλ(τc, θ0, &vartheta;s, &vartheta;z) and the red-blue ratio, RBR(τc, θ0, &vartheta;s, &vartheta;z) are retrieved from the 3DRTM results. RBR, which is commonly used for cloud detection in sky images, provides non-unique solutions for τc, where RBR increases with τc up to about τc = 1 (depending on other parameters) and then decreases. Therefore, the RRBR algorithm uses the measured Iλmeas(&vartheta;s, &vartheta;z), in addition to RBRmeas(&vartheta;s, &vartheta;z) to obtain a unique solution for τc. The RRBR method is applied to images taken by a USI at the Oklahoma Atmospheric Radiation Measurement program (ARM) site over the course of 220 days and validated against measurements from a microwave radiometer (MWR); output from the Min method for overcast skies, and τc retrieved by Beer's law from direct normal irradiance (DNI) measurements. A τc RMSE of 5.6 between the Min method and the USI are observed. The MWR and USI have an RMSE of 2.3 which is well within the uncertainty of the MWR. An RMSE of 0.95 between the USI and DNI retrieved τc is observed. The procedure developed here provides a foundation to test and develop other cloud detection algorithms.

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A simple model for cloud radiative forcing

Atmospheric Chemistry and Physics ◽

10.5194/acp-9-5751-2009 ◽

2009 ◽

Vol 9 (15) ◽

pp. 5751-5758 ◽

Cited By ~ 37

Author(s):

T. Corti ◽

T. Peter

Keyword(s):

Energy Balance ◽

Simple Model ◽

Radiative Transfer ◽

Radiative Forcing ◽

Radiative Transfer Model ◽

Transfer Model ◽

Cloud Radiative Forcing ◽

Wide Range ◽

Model Equations ◽

Better Than

Abstract. We present a simple model for the longwave and shortwave cloud radiative forcing based on the evaluation of extensive radiative transfer calculations, covering a global range of conditions. The simplicity of the model equations fosters the understanding on how clouds affect the Earth's energy balance. In comparison with results from a comprehensive radiative transfer model, the accuracy of our parameterization is typically better than 20%. We demonstrate the usefulness of our model using the example of tropical cirrus clouds. We conclude that possible applications for the model include the convenient estimate of cloud radiative forcing for a wide range of conditions, the evaluation of the sensitivity to changes in environmental conditions, and as a tool in education. An online version of the model is available at http://www.iac.ethz.ch/url/crf.

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Inter-calibration of nine UV sensing instruments over Antarctica and Greenland since 1980

Atmospheric Measurement Techniques ◽

10.5194/amt-13-5715-2020 ◽

2020 ◽

Vol 13 (10) ◽

pp. 5715-5723

Author(s):

Clark J. Weaver ◽

Pawan K. Bhartia ◽

Dong L. Wu ◽

Gordon J. Labow ◽

David E. Haffner

Keyword(s):

Zenith Angle ◽

Solar Zenith Angle ◽

Radiative Transfer Model ◽

Transfer Model ◽

Term Trend ◽

Enso Events ◽

Angle Dependence ◽

Long Term Trend ◽

Cloud Response

Abstract. Nadir-viewed intensities (radiances) from nine UV sensing satellite instruments are calibrated over the East Antarctic Plateau and Greenland during summer. The calibrated radiances from these UV instruments ultimately will provide a global long-term record of cloud trends and cloud response from ENSO events since 1980. We first remove the strong solar zenith angle dependence from the intensities using an empirical approach rather than a radiative transfer model. Then small multiplicative adjustments are made to these solar zenith angle normalized intensities in order to minimize differences when two or more instruments temporally overlap. While the calibrated intensities show a negligible long-term trend over Antarctica and a statistically insignificant UV albedo trend of −0.05 % per decade over the interior of Greenland, there are small episodic reductions in intensities which are often seen by multiple instruments. Three of these darkening events are explained by boreal forest. Other events are caused by surface melting or volcanoes. We estimate a 2-sigma uncertainty of 0.35 % for the calibrated radiances.

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Inter-Calibration of nine UV sensing instruments over Antarctica and Greenland since 1980

10.5194/amt-2020-7 ◽

2020 ◽

Cited By ~ 1

Author(s):

Clark Weaver ◽

Pawan K. Bhartia ◽

Dong L. Wu ◽

Gordon Labow ◽

David Haffner

Keyword(s):

Zenith Angle ◽

Forest Fires ◽

Solar Zenith Angle ◽

Radiative Transfer Model ◽

Transfer Model ◽

Enso Events ◽

Angle Dependence ◽

Modeling Analysis ◽

Long Term Trend

Abstract. Nadir viewed intensities (radiances) from nine UV sensing satellite instruments are calibrated over the East Antarctic Plateau and Greenland during summer. The calibrated radiances from these UV instruments ultimately will provide a global long-term record of cloud trends and cloud response from ENSO events since 1980. We first remove the strong solar zenith angle dependence from the intensities using an empirical approach rather than a radiative transfer model. Then small multiplicative adjustments are made to these solar zenith angle normalized intensities in order to minimize differences when two or more instruments temporally overlap. While the calibrated intensities show negligible long-term trend over Antarctica, and a statistically insignificant UV albedo trend of −0.05 % per decade over the interior of Greenland, there are small episodic reductions in intensities which are often seen by multiple instruments. Three of these darkening events are explained by boreal forest fires using trajectory modeling analysis. Other events are caused by surface melting or volcanoes. We estimate a 2-sigma uncertainty of 0.35 % for the calibrated radiances.

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A new gas absorption optical depth parameterisation for RTTOV version 13

Geoscientific Model Development ◽

10.5194/gmd-14-2899-2021 ◽

2021 ◽

Vol 14 (5) ◽

pp. 2899-2915

Author(s):

James Hocking ◽

Jérôme Vidot ◽

Pascal Brunel ◽

Pascale Roquet ◽

Bruna Silveira ◽

...

Keyword(s):

Solar Radiation ◽

Radiative Transfer ◽

Optical Depth ◽

Weather Prediction ◽

Current Approach ◽

Gas Absorption ◽

Radiative Transfer Model ◽

Transfer Model ◽

Wide Range ◽

Microwave Radiances

Abstract. This paper describes a new gas optical depth parameterisation implemented in the most recent release, version 13, of the radiative transfer model RTTOV (Radiative Transfer for TOVS). RTTOV is a fast, one-dimensional radiative transfer model for simulating top-of-atmosphere visible, infrared, and microwave radiances observed by downward-viewing space-borne passive sensors. A key component of the model is the fast parameterisation of absorption by the various gases in the atmosphere. The existing parameterisation in RTTOV has been extended over many years to allow for additional variable gases in RTTOV simulations and to account for solar radiation and better support geostationary sensors by extending the validity to higher zenith angles. However, there are limitations inherent in the current approach which make it difficult to develop it further, for example by adding new variable gases. We describe a new parameterisation that can be applied across the whole spectrum, that allows for a wide range of zenith angles in support of solar radiation and geostationary sensors, and for which it will be easier to add new variable gases in support of user requirements. Comparisons against line-by-line radiative transfer simulations and against observations in the ECMWF operational system yield promising results, suggesting that the new parameterisation generally compares well with the old one in terms of accuracy. Further validation is planned, including testing in operational numerical weather prediction data assimilation systems.

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On the Choice of Average Solar Zenith Angle

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-13-0392.1 ◽

2014 ◽

Vol 71 (8) ◽

pp. 2994-3003 ◽

Cited By ~ 38

Author(s):

Timothy W. Cronin

Keyword(s):

Solar Radiation ◽

Energy Budget ◽

Zenith Angle ◽

Radiative Forcing ◽

General Circulation ◽

Solar Zenith Angle ◽

Transfer Model ◽

Global Energy ◽

Global Energy Budget ◽

Planetary Albedo

Abstract Idealized climate modeling studies often choose to neglect spatiotemporal variations in solar radiation, but doing so comes with an important decision about how to average solar radiation in space and time. Since both clear-sky and cloud albedo are increasing functions of the solar zenith angle, one can choose an absorption-weighted zenith angle that reproduces the spatial- or time-mean absorbed solar radiation. Calculations are performed for a pure scattering atmosphere and with a more detailed radiative transfer model and show that the absorption-weighted zenith angle is usually between the daytime-weighted and insolation-weighted zenith angles but much closer to the insolation-weighted zenith angle in most cases, especially if clouds are responsible for much of the shortwave reflection. Use of daytime-average zenith angle may lead to a high bias in planetary albedo of approximately 3%, equivalent to a deficit in shortwave absorption of approximately 10 W m−2 in the global energy budget (comparable to the radiative forcing of a roughly sixfold change in CO2 concentration). Other studies that have used general circulation models with spatially constant insolation have underestimated the global-mean zenith angle, with a consequent low bias in planetary albedo of approximately 2%–6% or a surplus in shortwave absorption of approximately 7–20 W m−2 in the global energy budget.

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Radiative Forcing by Light-Absorbing Particles in Snow in Northeastern China Retrieved from Satellite Observations

10.5194/acp-2018-1306 ◽

2019 ◽

Author(s):

Wei Pu ◽

Jiecan Cui ◽

Tenglong Shi ◽

Xuelei Zhang ◽

Cenlin He ◽

...

Keyword(s):

Wet Deposition ◽

Radiative Forcing ◽

Solar Zenith Angle ◽

Atmospheric Correction ◽

Northeastern China ◽

Radiative Transfer Model ◽

Transfer Model ◽

Spatial Variance ◽

Snow Albedo

Abstract. Light-absorbing particles (LAPs) deposited on snow can decrease snow albedo and affect climate through the snow-albedo radiative forcing. In this study, we use MODIS observations combined with a snow albedo model (SNICAR) and a radiative transfer model (SBDART) to retrieve the radiative forcing by LAPs in snow (RFLapsMODIS) across Northeastern China (NEC) in January–February from 2003 to 2017. RFLapsMODIS presents distinct spatial variability, with the minimum (22.3 W m−2) in western NEC and the maximum (64.6 W m−2) near industrial areas in central NEC. The regional mean RFLapsMODIS is ~ 45.1 ± 6.8 W m−2 in NEC. The positive (negative) uncertainties of retrieved RFLapsMODIS due to atmospheric correction range from 14 % to 57 % (−14 % to −47 %) and the uncertainty value basically decreased with the increased RFLapsMODIS. We attribute the variations of radiative forcing based on remote sensing and find that the spatial variance of RFLapsMODIS in NEC is 74.6 % due to LAPs, while 21.2 % and 4.2 % due to snow grain size, and solar zenith angle. Furthermore, based on multiple linear regression, the BC dry and wet deposition and snowfall could totally explain 81 % of the spatial variance of LAP contents, which confirms the reasonability of the spatial patterns of retrieved RFLapsMODIS in NEC. We validate RFLapsMODIS using in situ radiative forcing estimates. We find that the biases in RFLapsMODIS are negatively correlated with LAP concentrations and range from ~ 5 % to ~ 350 % in NEC.

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