scholarly journals The impact of parameterising light penetration into snow on the photochemical production of NO<sub><i>x</i></sub> and OH radicals in snow

2015 ◽  
Vol 15 (14) ◽  
pp. 7913-7927 ◽  
Author(s):  
H. G. Chan ◽  
M. D. King ◽  
M. M. Frey
Keyword(s):  
Zenith Angle ◽  
Solar Zenith Angle ◽  
Rate Coefficient ◽  
Strong Dependence ◽  
Oh Radicals ◽  
Nitrate Anion ◽  
Actinic Flux ◽  
Photolysis Rate ◽  
Polar Snow ◽  
The Impact

Abstract. Snow photochemical processes drive production of chemical trace gases in snowpacks, including nitrogen oxides (NOx = NO + NO2) and hydrogen oxide radical (HOx = OH + HO2), which are then released to the lower atmosphere. Coupled atmosphere–snow modelling of theses processes on global scales requires simple parameterisations of actinic flux in snow to reduce computational cost. The disagreement between a physical radiative-transfer (RT) method and a parameterisation based upon the e-folding depth of actinic flux in snow is evaluated. In particular, the photolysis of the nitrate anion (NO3-), the nitrite anion (NO2-) and hydrogen peroxide (H2O2) in snow and nitrogen dioxide (NO2) in the snowpack interstitial air are considered. The emission flux from the snowpack is estimated as the product of the depth-integrated photolysis rate coefficient, v, and the concentration of photolysis precursors in the snow. The depth-integrated photolysis rate coefficient is calculated (a) explicitly with an RT model (TUV), vTUV, and (b) with a simple parameterisation based on e-folding depth, vze. The metric for the evaluation is based upon the deviation of the ratio of the depth-integrated photolysis rate coefficient determined by the two methods, vTUV/vze, from unity. The ratio depends primarily on the position of the peak in the photolysis action spectrum of chemical species, solar zenith angle and physical properties of the snowpack, i.e. strong dependence on the light-scattering cross section and the mass ratio of light-absorbing impurity (i.e. black carbon and HULIS) with a weak dependence on density. For the photolysis of NO2, the NO2- anion, the NO3- anion and H2O2 the ratio vTUV/vze varies within the range of 0.82–1.35, 0.88–1.28, 0.93–1.27 and 0.91–1.28 respectively. The e-folding depth parameterisation underestimates for small solar zenith angles and overestimates at solar zenith angles around 60° compared to the RT method. A simple algorithm has been developed to improve the parameterisation which reduces the ratio vTUV/vze to 0.97–1.02, 0.99–1.02, 0.99–1.03 and 0.98–1.06 for photolysis of NO2, the NO2- anion, the NO3- anion and H2O2 respectively. The e-folding depth parameterisation may give acceptable results for the photolysis of the NO3- anion and H2O2 in cold polar snow with large solar zenith angles, but it can be improved by a correction based on solar zenith angle and for cloudy skies.

scholarly journals The impact of parameterising light penetration into snow on the photochemical production of NO<sub>x</sub> and OH radicals in snow

2015 ◽  
Vol 15 (6) ◽  
pp. 8609-8646
Author(s):  
H. G. Chan ◽  
M. D. King ◽  
M. M. Frey
Keyword(s):  
Radiative Transfer ◽  
Zenith Angle ◽  
Solar Zenith Angle ◽  
Action Spectrum ◽  
Transfer Model ◽  
Oh Radicals ◽  
Nitrate Anion ◽  
Photolysis Rate ◽  
Polar Snow ◽  
The Impact

Abstract. Snow photochemical processes drive production of chemical trace gases, including nitrogen oxides (NO and NO2), and HOx radicals in snowpacks which are then released to the lower atmosphere. Coupled atmosphere–snow modelling on global scales requires simple parameterisations of actinic flux in snow to reduce computational cost. The disagreement between a physical radiative transfer method and a method based upon the e-folding depth of light-in snow is evaluated. In particular for the photolysis of the nitrate anion (NO3-), the nitrite anion (NO2-) and hydrogen peroxide (H2O2) within snow and photolysis of gas-phase nitrogen dioxide (NO2) within the snowpack interstitial air are considered. The emission flux from the snowpack is estimated as the depth-integrated photolysis rate, v, calculated (a) explicitly with a physical radiative transfer model (TUV), vTUV and (b) with a simple parameterisation based on e-folding depth, vze. The evaluation is based upon the deviation of the ratio of depth-integrated photolysis rate determined by the two methods,vTUV/vze, from unity. The disagreement in depth-integrated photolysis rate between the RT model and e-folding depth parameterisation depends primarily on the photolysis action spectrum of chemical species, solar zenith angle and optical properties of the snowpack, (scattering cross-section and a weak dependence on light absorbing impurity (black carbon) and density). For photolysis of NO2, the NO2- anion, the NO3- anion and H2O2 the ratio vTUV/vze varies within the range of 0.82–1.35, 0.88–1.28 and 0.92–1.27 respectively. The e-folding depth parameterisation underestimates for small solar zenith angles and overestimates at solar zenith angles around 60°. A simple algorithm has been developed to improve the parameterisation which reduced the ratio vTUV/vze to 0.97–1.02, 0.99–1.02 and 0.99–1.03 for photolysis of NO2, the NO2- anion, the NO3- anion and H2O2 respectively. The e-folding depth parameterisation may give acceptable results for the photolysis of the NO3- anion and H2O2 in cold polar snow with large solar zenith angles, but can be improved by a correction based on solar zenith angle.

scholarly journals Generalizing Cloud Overlap Treatment to Include Solar Zenith Angle Effects on Cloud Geometry

2007 ◽  
Vol 64 (6) ◽  
pp. 2116-2125 ◽  
Author(s):  
Adrian M. Tompkins ◽  
Francesca Di Giuseppe
Keyword(s):  
Zenith Angle ◽  
Large Scale ◽  
Solar Zenith Angle ◽  
Forecast Model ◽  
Simple Extension ◽  
Scale Models ◽  
Field Geometry ◽  
The Mean ◽  
The Impact ◽  
First Time

Shortwave radiative transfer depends on the cloud field geometry as viewed from the direction of the sun. To date, the radiation schemes of large-scale models only consider a zenith view of the cloud field, and the apparent change in the cloud geometry with decreasing solar zenith angle is neglected. A simple extension to an existing cloud overlap scheme is suggested to account for this for the first time. It is based on the assumption that at low sun angles, the overlap between cloud elements is random for an unscattered photon. Using cloud scenes derived from radar retrievals at two European sites, it is shown that the increase of the apparent cloud cover with a descending sun is reproduced very well with the new scheme. Associated with this, there is a marked reduction in the mean radiative biases averaged across all solar zenith angles with respect to benchmark calculations. The scheme is implemented into the ECMWF global forecast model using imposed sea surface temperatures, and while the impact on the radiative statistics is significant, the feedback on the large-scale dynamics is minimal.

scholarly journals The impact of aerosol hygroscopic growth on the single-scattering albedo and its application on the NO<sub>2</sub> photolysis rate coefficient

2014 ◽  
Vol 14 (22) ◽  
pp. 12055-12067 ◽  
Author(s):  
J. C. Tao ◽  
C. S. Zhao ◽  
N. Ma ◽  
P. F. Liu
Keyword(s):  
Boundary Layer ◽  
Aerosol Particle ◽  
Rate Coefficient ◽  
Aerosol Particles ◽  
Single Scattering ◽  
Single Scattering Albedo ◽  
Hygroscopic Growth ◽  
Particle Population ◽  
Photolysis Rate ◽  
The Impact

Abstract. Hygroscopic growth of aerosol particles can significantly affect their single-scattering albedo (ω), and consequently alters the aerosol effect on tropospheric photochemistry. In this study, the impact of aerosol hygroscopic growth on ω and its application to the NO2 photolysis rate coefficient (JNO2) are investigated for a typical aerosol particle population in the North China Plain (NCP). The variations of aerosol optical properties with relative humidity (RH) are calculated using a Mie theory aerosol optical model, on the basis of field measurements of number–size distribution and hygroscopic growth factor (at RH values above 90%) from the 2009 HaChi (Haze in China) project. Results demonstrate that ambient ω has pronouncedly different diurnal patterns from ω measured at dry state, and is highly sensitive to the ambient RHs. Ambient ω in the NCP can be described by a dry state ω value of 0.863, increasing with the RH following a characteristic RH dependence curve. A Monte Carlo simulation shows that the uncertainty of ω from the propagation of uncertainties in the input parameters decreases from 0.03 (at dry state) to 0.015 (RHs > 90%). The impact of hygroscopic growth on ω is further applied in the calculation of the radiative transfer process. Hygroscopic growth of the studied aerosol particle population generally inhibits the photolysis of NO2 at the ground level, whereas accelerates it above the moist planetary boundary layer. Compared with dry state, the calculated JNO2 at RH of 98% at the height of 1 km increases by 30.4%, because of the enhancement of ultraviolet radiation by the humidified scattering-dominant aerosol particles. The increase of JNO2 due to the aerosol hygroscopic growth above the upper boundary layer may affect the tropospheric photochemical processes and this needs to be taken into account in the atmospheric chemical models.

scholarly journals Characterisation of <i>J</i>(O<sup>1</sup>D) at Cape Grim 2000–2005

2014 ◽  
Vol 14 (12) ◽  
pp. 18389-18419 ◽  
Author(s):  
S. R. Wilson
Keyword(s):  
Zenith Angle ◽  
Solar Zenith Angle ◽  
Wave Radiation ◽  
Total Column Ozone ◽  
Photolysis Rates ◽  
The Individual ◽  
The Impact ◽  
Ozone Column ◽  
Radiation Measurements ◽  
Cape Grim

Abstract. Estimates of the rate of production of excited oxygen atoms due to the photolysis of ozone J(O1D) have been derived from radiation measurements carried out at Cape Grim, Tasmania (40.6° S, 144.7° E). These estimates agree well with measurements made during SOAPEX-II and with model estimates of clear sky photolysis rates. Observations spanning 2000–2005 have been used to quantify the impact of season, cloud and ozone column amount. The annual cycle of J(O1D) has been investigated via monthly means. These means show an inter-annual variation (monthly standard deviation) of 9%, but in midsummer and midwinter this reduces to 3–4%. Factors dependent upon solar zenith angle and satellite derived total ozone column explain 87% of the observed signal variation of the individual measurements. The impact of total column ozone, expressed as a Radiation Amplification Factor (RAF), is found to be ~1.45, in agreement with model estimates. This ozone dependence explains 20% of the variation observed at medium solar zenith angles (30–50°). The impact of clouds results in a median reduction of 14% in J(O1D) for the same solar zenith angle range. At all solar zenith angles less than 50° approximately 10% of measurements show enhanced J(O1D) due to cloud scattering and this fraction climbs to 25% at higher solar angles. Including estimates of cloudiness derived from Long Wave Radiation measurements resulted in a statistically significant fit to observations but the quality of the fit did not increase significantly as measured by the reduced R2.

Surface and tethered-balloon observations of actinic flux: Effects of arctic stratus, surface albedo, and solar zenith angle

2001 ◽  
Vol 106 (D21) ◽  
pp. 27497-27507 ◽  
Author(s):  
Stephan R. de Roode ◽  
Peter G. Duynkerke ◽  
Wim Boot ◽  
Jeroen C. H. Van der Hage
Keyword(s):  
Zenith Angle ◽  
Solar Zenith Angle ◽  
Surface Albedo ◽  
Tethered Balloon ◽  
Actinic Flux

The impact of sea-glint upon limb radiance

2007 ◽  
Vol 85 (11) ◽  
pp. 1159-1176
Author(s):  
D A Degenstein ◽  
A E Bourassa ◽  
E J Llewellyn ◽  
N D Lloyd
Keyword(s):  
Radiative Transfer ◽  
Zenith Angle ◽  
Arabian Sea ◽  
Solar Zenith Angle ◽  
Imaging System ◽  
Radiative Transfer Model ◽  
Transfer Model ◽  
Test Case ◽  
Infra Red ◽  
The Impact

A simple radiative transfer model is developed to calculate the contribution of sea-glint to limb radiance. It is shown that the absolute sea-glint signal peaks between 70° and 80° solar zenith angle. Sea-glint can contribute 10–15% of the total limb radiance at wavelengths greater than 600 nm, which is several times brighter than an equivalent 5% reflecting Lambertian ocean surface. A test case was identified over the Arabian Sea in October 2002 and the model results compared to limb observations from the Optical Spectrograph and Infra-Red Imaging System (OSIRIS) on-board the Odin satellite. PACS Nos.: 94.10.Gb, 93.85.+q, 42.68.Ay, 42.68.Mj

scholarly journals Characterisation of <i>J</i>(O<sup>1</sup>D) at Cape Grim 2000–2005

2015 ◽  
Vol 15 (13) ◽  
pp. 7337-7349 ◽  
Author(s):  
S. R. Wilson
Keyword(s):  
Zenith Angle ◽  
Solar Zenith Angle ◽  
Wave Radiation ◽  
Total Column Ozone ◽  
Photolysis Rates ◽  
Column Ozone ◽  
The Impact ◽  
Radiation Measurements ◽  
Total Column ◽  
Cape Grim

Abstract. Estimates of the rate of production of excited oxygen atoms due to the photolysis of ozone (J(O1D)) have been derived from radiation measurements carried out at Cape Grim, Tasmania (40.6° S, 144.7° E). The individual measurements have a total uncertainty of 16 % (1σ). These estimates agree well with model estimates of clear-sky photolysis rates. Observations spanning 2000–2005 have been used to quantify the impact of season, clouds and ozone column amount. The annual cycle of J(O1D) has been investigated via monthly means. These means show an interannual variation (monthly standard deviation) of 9 %, but in midsummer and midwinter this reduces to 3–5 %. Variations in solar zenith angle and total column ozone explain 86 % of the observed variability in the measured photolysis rates. The impact of total column ozone, expressed as a radiation amplification factor (RAF), is found to be ~ 1.53, in agreement with model estimates. This ozone dependence explains 20 % of the variation observed at medium solar zenith angles (30–50°). The impact of clouds results in a median reduction of 30 % in J(O1D) for the same solar zenith angle range. Including estimates of cloudiness derived from long-wave radiation measurements resulted in a statistically significant fit to observations, but the quality of the fit did not increase significantly as measured by the adjusted R2.

Top-of-atmosphere albedo bias from neglecting three-dimensional cloud radiative effects

2021 ◽  
Author(s):  
Clare E. Singer ◽  
Ignacio Lopez-Gomez ◽  
Xiyue Zhang ◽  
Tapio Schneider
Keyword(s):  
Radiative Transfer ◽  
Zenith Angle ◽  
Solar Zenith Angle ◽  
3D Structure ◽  
Three Dimensional ◽  
Radiative Flux ◽  
Monte Carlo Code ◽  
Radiative Effects ◽  
Cloud Radiative Effects ◽  
The Impact

AbstractClouds cover on average nearly 70% of Earth’s surface and regulate the global albedo. The magnitude of the shortwave reflection by clouds depends on their location, optical properties, and three-dimensional (3D) structure. Due to computational limitations, Earth system models are unable to perform 3D radiative transfer calculations. Instead they make assumptions, including the independent column approximation (ICA), that neglect effects of 3D cloud morphology on albedo. We show how the resulting radiative flux bias (ICA-3D) depends on cloud morphology and solar zenith angle. We use high-resolution (20–100 m horizontal resolution) large-eddy simulations to produce realistic 3D cloud fields covering three dominant regimes of low-latitude clouds: shallow cumulus, marine stratocumulus, and deep convective cumulonimbus. A Monte Carlo code is used to run 3D and ICA broadband radiative transfer calculations; we calculate the top-of-atmosphere (TOA) reflected flux and surface irradiance biases as functions of solar zenith angle for these three cloud regimes. Finally, we use satellite observations of cloud water path (CWP) climatology, and the robust correlation between CWP and TOA flux bias in our LES sample, to roughly estimate the impact of neglecting 3D cloud radiative effects on a global scale. We find that the flux bias is largest at small zenith angles and for deeper clouds, while the albedo bias is most prominent for large zenith angles. In the tropics, the annual-mean shortwave radiative flux bias is estimated to be 3.1±1.6 W m−2, reaching as much as 6.5 W m−2 locally.

scholarly journals Improved model for correcting the ionospheric impact on bending angle in radio occultation measurements

2017 ◽  
Author(s):  
Matthew J. Angling ◽  
Sean Elvidge ◽  
Sean B. Healy
Keyword(s):  
Zenith Angle ◽  
Solar Zenith Angle ◽  
Radio Occultation ◽  
Neutral Atmosphere ◽  
Night Time ◽  
Bending Angle ◽  
Height Range ◽  
Improved Model ◽  
The Impact ◽  
Bending Angles

Abstract. The standard approach to remove the effects of the ionosphere from neutral atmosphere GPS radio occultation measurements is to estimate a corrected bending angle from a combination of the L1 and L2 bending angles. This approach is known to result in systematic errors and an extension has been proposed to the standard ionospheric correction that is dependent on the squared L1/L2 bending angle difference and a scaling term (κ). The variation of κ with height, time, season, location and solar activity (i.e. the f10.7 flux) has been investigated by applying a 1D bending angle operator to electron density profiles provided by a monthly median ionospheric climatology model. As expected, the residual bending angle is well correlated (negatively) with the vertical TEC. However, κ is more strongly dependent on the solar zenith angle. Furthermore, over the height range of interest (40–80 km) κ is approximately linear with height. A simple κ model has also been developed. It is independent of ionospheric measurements, but incorporates geophysical dependencies (i.e. solar zenith angle, solar flux, altitude). The global mean error (i.e. bias) and the standard deviation of the residual errors are reduced to −2.2 × 10−10 rad and 2.0 × 10−9 rad respectively. Although a fixed scalar κ also reduces bias for the global average the selected value of κ (14 rad−1) is only appropriate for a small band of locations around the solar terminator. In the day time, the scalar κ is consistently too high and this results in an over correction of the bending angles and a positive bending angle bias. Similarly, in the night time, the scalar κ is too low. However, in this case, the bending angles are already small and the impact of the choice of κ is less pronounced.

Effect of solar zenith angle on satellite cloud retrievals based on O2–O2 absorption band

2021 ◽  
Vol 42 (11) ◽  
pp. 4224-4240
Author(s):  
Gyuyeon Kim ◽  
Yong-Sang Choi ◽  
Sang Seo Park ◽  
Jhoon Kim
Keyword(s):  
Absorption Band ◽  
Zenith Angle ◽  
Solar Zenith Angle
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