View-angle dependent AIRS cloud radiances: Implications for tropical anvil structures

Gong, Jie; Wu, Dong L.

doi:10.1029/2011gl047910

Cited by 5 publications

(19 citation statements)

References 23 publications

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“…For example, Gong andWu (2011, 2013) acknowledged the impact on AIRS cloudiness in the zonal direction, where they concluded that up to 50 % of AIRS view-angle asymmetry could be attributed to the systematic westward-tilted cloud structures in the UT. Aura Microwave Limb Sounder (MLS) day (night) forward-looking view is analogous to CloudSat northward (southward) looking view with a shallower viewing angle (∼ 86 • ).…”

Section: Formation Mechanism and Importance Of Systematic Ut Cloud Tiltmentioning

confidence: 99%

“…Systematic cloud tilt structures can have profound impacts on cloud remote sensing and radiation calculations. For example, they partially account for the anisotropy of the cloud radiative forcing (Fu et al, 2000;Gong and Wu, 2013) and modulate the hydrological cycle (Naud et al, 2010). Neglecting or misrepresenting the cloud tilt induces additional biases in satellite retrieval of cloud properties (e.g., Hong et al, 2005) and increases uncertainty of model CRE estimation (e.g., Li and Barker, 2002).…”

Section: Introductionmentioning

confidence: 99%

“…It is difficult for passive sensors because of their coarse vertical/horizontal resolutions and variable penetration depths, yielding ambiguous information about cloud internal structures. Nevertheless, Gong andWu (2011, 2013) were able to derive cloud tilt statistics of the upper troposphere cloud in the zonal direction using radiance data from NASA's Aqua Atmospheric Infrared Sounder (AIRS) and NOAA's Microwave Humidity Sounder (MHS). Groundbased radar observations, plotted in the time series domain, often show tilt structures, which are however contaminated by rainfall signals from time to time (Huang et al, 2012).…”

Section: Introductionmentioning

confidence: 99%

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Meridionally tilted ice cloud structures in the tropical upper troposphere as seen by CloudSat

Gong

Wu²,

Limpasuvan³

2015

Atmos. Chem. Phys.

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Abstract. It remains challenging to quantify global cloud properties and uncertainties associated with their impacts on climate change because of our poor understanding of cloud three-dimensional (3-D) structures from observations and unrealistic characterization of 3-D cloud effects in global climate models (GCMs). In this study we find cloud 3-D effects can cause significant error in cloud ice and radiation measurements if it is not taken into account appropriately.One of the cloud 3-D complexities, the slantwise tilt structure, has not received much attention in research and even less has been reported considering a global perspective. A novel approach is presented here to analyze the ice cloud water content (IWC) profiles retrieved from CloudSat and a joint radar-lidar product (DARDAR). By integrating IWC profiles along different tilt angles, we find that uppertroposphere (UT) ice cloud mass between 11 and 17 km is tilted poleward from active convection centers in the tropics [30 • S, 30 • N]. This systematic tilt in cloud mass structure is expected from the mass conservation principle of the Hadley circulation with the divergent flow of each individual convection/convective system from down below, and its existence is further confirmed from cloud-resolving-scale Weather Research and Forecasting (WRF) model simulations. Thus, additive effects of tilted cloud structures can introduce 5-20 % variability by its nature or produce errors to satellite cloud/hydrometeor ice retrievals if simply converting it from slant to nadir column. A surprising finding is the equatorward tilt in middle tropospheric (5-11 km) ice clouds, which is also evident in high-resolution model simulations but not in coarse-resolution simulations with cumulus parameterization. The observed cloud tilt structures are intrinsic properties of tropical clouds, producing synoptic distributions around the Intertropical Convergence Zone (ITCZ). These findings imply that current interpretations based on over-simplified cloud vertical structures could lead to considerable cloud measurement errors and have a subsequent impact on understanding cloud radiative, dynamical and hydrological properties.

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Section: Formation Mechanism and Importance Of Systematic Ut Cloud Tiltmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Meridionally tilted ice cloud structures in the tropical upper troposphere as seen by CloudSat

Gong

Wu²,

Limpasuvan³

2015

Atmos. Chem. Phys.

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“…Complete details of the IASI/AIRS processing system can be found in the Algorithm Theoretical Basis Document (ATBD) available at http://www.star.nesdis.noaa.gov/smcd/spb/iosspdt/qadocs/IASI_Phase2/. Note that the NUCAPS system implemented at NESDIS/STAR is essentially the same processing system, but adapted to the JPSS CrIS/ATMS sensors currently being flown on Suomi NPP [Gambacorta et al, 2012].…”

Section: Ir Sounder Calc à Obs Analysesmentioning

confidence: 99%

“…The cloud-clearing methodologies for IASI and CrIMSS [e.g., the NOAA-Unique CrIS/ATMS Processing System, NUCAPS; Gambacorta et al, 2012], are essentially the same as that used for AIRS [Susskind et al, 2003], whereby a clear-column IR radiance spectrum is derived for a field-of-regard (FOR) consisting of a "golf-ball" of K = 2 Â 2 (for IASI), or K = 3 Â 3 (for CrIS/ATMS and AIRS), IR FOVs overlapping 1 microwave (MW) FOV, with a nadir spatial resolution of '50 km. The cloud-clearing method basically assumes that differences among the IR FOV are solely due to clouds, then proceeds to extrapolate a clear-column spectrum (the cloud-cleared radiance),R n , from a linear combination of collocated FOVs, that is [Susskind et al, 2003] …”

Section: Overview Of Ir Sounder Cloud-clearingmentioning

confidence: 99%

On the angular effect of residual clouds and aerosols in clear‐sky infrared window radiance observations 2. Satellite experimental analyses

et al. 2013

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[1] This paper continues an investigation into the zenith angular effect of cloud-contamination within "clear-sky" infrared (IR) radiance observations commonly used in the retrieval of environmental data records (EDRs), which include "cloud-cleared radiances" (as is typical from hyper/ultra spectral IR sounders), as well as "cloud-masked" data (as is typical from imagers). The simple probability of clear line of sight (PCLoS) models and sensitivity studies of Part 1 (Nalli et al., 2012a) are corroborated with experimental analyses of environmental satellite data products as functions of sensor zenith angle, including sounder cloud-cleared radiances (CCRs) and retrieved effective cloud fraction, as well as narrowband imager cloud masking. Analyses of hyperspectral microwindow calc À obs are performed using MetOp-A Infrared Atmospheric Sounding Interferometer (IASI) CCR observations matched to dedicated radiosonde observations (RAOBs) during intensive validation field campaigns. The IASI calc À obs are found to exhibit a systematic positive bias with a strong concave-up variation with satellite zenith angle (i.e., an increasing positive bias symmetric over the scanning range) on the order of 1-3 K in magnitude, a signal associated with both residual clouds and dust aerosols. This is corroborated by analysis of the IASI retrieved effective cloud fraction product compared to the expected angular variations predicted by the PCLoS models, which show that the observed concave-up calc À obs variation may be the result of contamination by mid-to-upper tropospheric clouds. Finally, a corollary global analysis of the MetOp-A Advanced Very High Resolution Radiometer (AVHRR) cloud-mask shows concave-up variation that may be underestimating the angular variation for global ensembles containing clouds with vertical development (i.e., aspect ratios >0.5). The results presented in this work thus support the sensitivity studies of Part 1, indicating that contamination by residual clouds and/or aerosols within clear-sky observations can have a measurable concave-up impact on the angular agreement of observations with calculations.

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View‐angle‐dependent AIRS cloudiness and radiance variance: Analysis and interpretation

Gong

2013

JGR Atmospheres

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[1] Upper tropospheric clouds play an important role in the global energy budget and hydrological cycle. Significant view-angle asymmetry has been observed in upper-level tropical clouds derived from 8 years of Atmospheric Infrared Sounder (AIRS) 15 mm radiances. Here we find that the asymmetry also exists in the extratropics. It is larger during day than that during night, more prominent near elevated terrain, and closely associated with deep convection and wind shear. The cloud radiance variance, a proxy for cloud inhomogeneity, has consistent characteristics of the asymmetry to those in the AIRS cloudiness. The leading causes of the view-dependent cloudiness asymmetry are the local time difference and small-scale organized cloud structures. The local time difference (1-1.5 h) of upper-level clouds between two AIRS outermost views can create parts of the observed asymmetry. On the other hand, small-scale tilted and banded structures of the upper-level clouds can induce about half of the observed view-angle-dependent differences in the AIRS cloud radiances and their variances. This estimate is inferred from analogous study using microwave humidity sounder radiances observed during the period of time when there were simultaneous measurements at two different view-angles from NOAA-18 and NOAA-19 satellites. The existence of tilted cloud structures and asymmetric 15 mm and 6.7 mm cloud radiances implies that cloud statistics would be view-angle-dependent, and should be taken into account in radiative transfer calculations, measurement uncertainty evaluations and cloud climatology investigations. In addition, the momentum forcing in the upper troposphere from tilted clouds is also likely asymmetric, which can affect atmospheric circulation anisotropically.

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View-angle dependent AIRS cloud radiances: Implications for tropical anvil structures

Cited by 5 publications

References 23 publications

Meridionally tilted ice cloud structures in the tropical upper troposphere as seen by CloudSat

Meridionally tilted ice cloud structures in the tropical upper troposphere as seen by CloudSat

On the angular effect of residual clouds and aerosols in clear‐sky infrared window radiance observations 2. Satellite experimental analyses

View‐angle‐dependent AIRS cloudiness and radiance variance: Analysis and interpretation

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