scholarly journals Climatological Diurnal Cycles in Clear-Sky Brightness Temperatures from the High-Resolution Infrared Radiation Sounder (HIRS)

2011 ◽  
Vol 28 (10) ◽  
pp. 1199-1205 ◽  
Author(s):  
Anders V. Lindfors ◽  
Ian A. Mackenzie ◽  
Simon F. B. Tett ◽  
Lei Shi
Keyword(s):  
Monte Carlo ◽  
Fourier Series ◽  
High Resolution ◽  
Infrared Radiation ◽  
Lower Troposphere ◽  
Sampling Bias ◽  
Diurnal Cycles ◽  
Clear Sky ◽  
Brightness Temperatures ◽  
Sky Brightness

Abstract A climatology of the diurnal cycles of HIRS clear-sky brightness temperatures was developed based on measurements over the period 2002–07. This was done by fitting a Fourier series to monthly gridded brightness temperatures of HIRS channels 1–12. The results show a strong land–sea contrast with stronger diurnal cycles over land, and extending from the surface up to HIRS channel 6 or 5, with regional maxima over the subtropics. Over seas, the diurnal cycles are generally small and therefore challenging to detect. A Monte Carlo uncertainty analysis showed that more robust results are reached by aggregating the data zonally before applying the fit. The zonal fits indicate that small diurnal cycles do exist over sea. The results imply that for a long-lived satellite such as NOAA-14, drift in the overpass time can cause a diurnal sampling bias of more than 5 K for channel 8 (surface and lower troposphere).

Monitoring of VIIRS ocean clear-sky brightness temperatures against CRTM simulation in ICVS for TEB/M bands

2017 ◽  
Author(s):  
Ninghai Sun ◽  
Quanhua Liu ◽  
Wenhui Wang ◽  
Bin Zhang ◽  
Fuzhong Weng ◽  
...  
Keyword(s):  
Clear Sky ◽  
Brightness Temperatures ◽  
Sky Brightness

scholarly journals Clear-Sky Mask for the Advanced Clear-Sky Processor for Oceans

2010 ◽  
Vol 27 (10) ◽  
pp. 1609-1623 ◽  
Author(s):  
B. Petrenko ◽  
A. Ignatov ◽  
Y. Kihai ◽  
A. Heidinger
Keyword(s):  
High Resolution ◽  
Radiative Transfer ◽  
Weather Prediction ◽  
Radiative Transfer Model ◽  
Transfer Model ◽  
Clear Sky ◽  
Brightness Temperatures ◽  
Spatial Uniformity ◽  
Uniformity Test ◽  
Cross Platform

Abstract The Advanced Clear Sky Processor for Oceans (ACSPO) generates clear-sky products, such as SST, clear-sky radiances, and aerosol, from Advanced Very High Resolution Radiometer (AVHRR)-like measurements. The ACSPO clear-sky mask (ACSM) identifies clear-sky pixels within the ACSPO products. This paper describes the ACSM structure and compares the performances of ACSM and its predecessor, Clouds from AVHRR Extended Algorithm (CLAVRx). ACSM essentially employs online clear-sky radiative transfer simulations enabled within ACSPO with the Community Radiative Transfer Model (CRTM) in conjunction with numerical weather prediction atmospheric [Global Forecast System (GFS)] and SST [Reynolds daily high-resolution blended SST (DSST)] fields. The baseline ACSM tests verify the accuracy of fitting observed brightness temperatures with CRTM, check retrieved SST for consistency with Reynolds SST, and identify ambient cloudiness at the boundaries of cloudy systems. Residual cloud effects are screened out with several tests, adopted from CLAVRx, and with the SST spatial uniformity test designed to minimize misclassification of sharp SST gradients as clouds. Cross-platform and temporal consistencies of retrieved SSTs are maintained by accounting for SST and brightness temperature biases, estimated within ACSPO online and independently from ACSM. The performance of ACSM is characterized in terms of statistics of deviations of retrieved SST from the DSST. ACSM increases the amount of “clear” pixels by 30% to 40% and improves statistics of retrieved SST compared with CLAVRx. ACSM is also shown to be capable of producing satisfactory statistics of SST anomalies if the reference SST field for the exact date of observations is unavailable at the time of processing.

scholarly journals Climate Model–Simulated Diurnal Cycles in HIRS Clear-Sky Brightness Temperatures

2012 ◽  
Vol 25 (17) ◽  
pp. 5845-5863 ◽  
Author(s):  
Ian A. MacKenzie ◽  
Simon F. B. Tett ◽  
Anders V. Lindfors
Keyword(s):  
Water Vapor ◽  
Brightness Temperature ◽  
Climate Models ◽  
Tropospheric Temperature ◽  
Diurnal Variability ◽  
Diurnal Cycles ◽  
Clear Sky ◽  
Recent Climate ◽  
Diurnal Behavior ◽  
Sky Brightness

Abstract Clear-sky brightness temperature measurements from the High-Resolution Infrared Radiation Sounder (HIRS) are simulated with two climate models via a radiative transfer code. The models are sampled along the HIRS orbit paths to derive diurnal climatologies of simulated brightness temperature analogous to an existing climatology based on HIRS observations. Simulated and observed climatologies are compared to assess model performance and the robustness of the observed climatology. Over land, there is good agreement between simulations and observations, with particularly high consistency for the tropospheric temperature channels. Diurnal cycles in the middle- and upper-tropospheric water vapor channels are weak in both simulations and observations, but the simulated diurnal brightness temperature ranges are smaller than are observed with different phase and there are also intermodel differences. Over sea, the absence of diurnal variability in the models’ sea surface temperatures causes an underestimate of the small diurnal cycles measured in the troposphere. The simulated and observed climatologies imply similar diurnal sampling biases in the HIRS record for the tropospheric temperature channels, but for the upper-tropospheric water vapor channel, differences in the contributions of the 24- and 12-hourly diurnal harmonics lead to differences in the implied bias. Comparison of diurnal cycles derived from HIRS-like and full model sampling suggests that the HIRS measurements are sufficient to fully constrain the diurnal behavior. Overall, the results suggest that recent climate models well represent the major processes driving the diurnal behavior of clear-sky brightness temperature in the HIRS channels. This encourages further studies of observed and simulated climate trends over the HIRS era.

scholarly journals Characteristics of VIRS Signals within Pixels of TRMM PR for Warm Rain in the Tropics and Subtropics

2017 ◽  
Vol 56 (3) ◽  
pp. 789-801 ◽  
Author(s):  
Yilun Chen ◽  
Yunfei Fu
Keyword(s):  
High Resolution ◽  
Weighted Average ◽  
Tropical Rainfall Measuring Mission ◽  
Low Resolution ◽  
Clear Sky ◽  
Data Merging ◽  
Brightness Temperatures ◽  
Average Brightness ◽  
Warm Rain ◽  
The Tropics

AbstractMany data-merging studies of the Tropical Rainfall Measuring Mission (TRMM) satellite involve the integration of high-resolution Visible and Infrared Scanner (VIRS) signals (~2 km) with low-resolution Precipitation Radar (PR) footprint (~5 km) to obtain comprehensive information from observations. Based on the merged dataset, “warm rain” is generally identified as having averaging 10.8-μm brightness temperatures (TB10.8) exceeding 273 K and the existence of surface rainfall. However, this integration may lead to the misidentification of warm rain because the beam-filling problem (nonuniform TB10.8 in PR pixels) is not fully considered through the method using high-resolution TB10.8 to match low-resolution rainfall. To assess the bias that is associated with identifying warm rain, a new dataset that includes all VIRS signals within the PR resolution is established, and the characteristics of this warm rain in the summers of 1998–2012 are analyzed. The results show that clear-sky pixels and “cold” pixels probably exist in some apparent warm-rain cases (60.5% and 11.2% of the time, respectively). According to this finding, warm-rain pixels are divided into pixels with and without clear sky. Statistical analysis shows that the existence of clear-sky pixels has a huge influence on the characteristics of the warm-rain pixels. The implications of this study are that many of the warm-rain cases are in fact not warm rain. When studying warm rain, the situation whereby the edges of pixels are clear sky should be fully considered. Also, when computing the weighted average brightness temperature and other characteristics of warm-rain pixels, parts that are clear-sky or cold pixels should be expelled to mitigate beam-filling problems.

scholarly journals A Novel Approach for Selective Reconstruction of Cloud-Contaminated Satellite Images

2011 ◽  
Vol 28 (8) ◽  
pp. 1028-1035 ◽  
Author(s):  
Bipasha Paul Shukla ◽  
P. K. Pal ◽  
P. C. Joshi
Keyword(s):  
High Resolution ◽  
Brightness Temperature ◽  
Satellite Imagery ◽  
Satellite Images ◽  
Weather Prediction ◽  
Climate Research ◽  
Clear Sky ◽  
Novel Approach ◽  
Sky Brightness ◽  
Very High

Abstract The paper presents a robust technique for cloud clearing of satellite imagery. The proposed algorithm combines mathematical morphological techniques with a conventional cloud clearing scheme to restore clear sky values. The derived equivalent clear sky brightness temperature plays a very important role in numerical weather prediction, climate research, and monitoring. The developed methodology uses distinct approaches for reconstruction of partially clouded domains and overcast regions. It is found that the algorithm is especially suitable for pre- or postmonsoon months, where there is a high percentage of partially cloudy and small overcast cloudy regions. The algorithm is tested for the Kalpana Very High Resolution Radiometer (VHRR) thermal infrared (TIR) band data acquired over the oceanic region adjoining India throughout the month of May 2009. It is found that the algorithm is able to clear 25% of cloudy pixels with an RMSE of 1.2 K for brightness temperature.

scholarly journals Exploring the robustness of Keplerian signals to the removal of active and telluric features

2020 ◽  
Vol 500 (1) ◽  
pp. 548-557
Author(s):  
M Lisogorskyi ◽  
H R A Jones ◽  
F Feng ◽  
R P Butler ◽  
S Vogt
Keyword(s):  
Monte Carlo ◽  
High Resolution ◽  
Monte Carlo Simulations ◽  
Large Amplitude ◽  
Absorption Cell ◽  
Stellar Rotation ◽  
Long Period ◽  
Active Line ◽  
Low Amplitude ◽  
Rotation Signal

ABSTRACT We examine the influence of activity- and telluric-induced radial velocity (RV) signals on high-resolution spectra taken with an iodine absorption cell. We exclude 2-$\mathring{\rm A}$ spectral chunks containing active and telluric lines based on the well-characterized K1V star α Centauri B and illustrate the method on Epsilon Eridani – an active K2V star with a long-period, low-amplitude planetary signal. After removal of the activity- and telluric-sensitive parts of the spectrum from the RV calculation, the significance of the planetary signal is increased and the stellar rotation signal disappears. In order to assess the robustness of the procedure, we perform Monte Carlo simulations based on removing random chunks of the spectrum. Simulations confirm that the removal of lines impacted by activity and tellurics provides a method for checking the robustness of a given Keplerian signal. We also test the approach on HD 40979, which is an active F8V star with a large-amplitude planetary signal. Our Monte Carlo simulations reveal that the significance of the Keplerian signal in the F star is much more sensitive to wavelength. Unlike the K star, the removal of active lines from the F star greatly reduces the RV precision. In this case, our removal of a K star active line from an F star does not a provide a simple useful diagnostic because it has far less RV information and heavily relies on the strong active lines.

scholarly journals Worldwide variations in artificial skyglow

2015 ◽  
Vol 5 (1) ◽  
Author(s):  
Christopher C. M. Kyba ◽  
Kai Pong Tong ◽  
Jonathan Bennie ◽  
Ignacio Birriel ◽  
Jennifer J. Birriel ◽  
...  
Keyword(s):  
Monitoring Program ◽  
Artificial Light ◽  
Clear Sky ◽  
International Monitoring ◽  
Sky Brightness ◽  
Ground Truthing ◽  
Study Sites ◽  
Night Sky Brightness ◽  
Key Questions

Abstract Despite constituting a widespread and significant environmental change, understanding of artificial nighttime skyglow is extremely limited. Until now, published monitoring studies have been local or regional in scope and typically of short duration. In this first major international compilation of monitoring data we answer several key questions about skyglow properties. Skyglow is observed to vary over four orders of magnitude, a range hundreds of times larger than was the case before artificial light. Nearly all of the study sites were polluted by artificial light. A non-linear relationship is observed between the sky brightness on clear and overcast nights, with a change in behavior near the rural to urban landuse transition. Overcast skies ranged from a third darker to almost 18 times brighter than clear. Clear sky radiances estimated by the World Atlas of Artificial Night Sky Brightness were found to be overestimated by ~25%; our dataset will play an important role in the calibration and ground truthing of future skyglow models. Most of the brightly lit sites darkened as the night progressed, typically by ~5% per hour. The great variation in skyglow radiance observed from site-to-site and with changing meteorological conditions underlines the need for a long-term international monitoring program.

scholarly journals 92 Years of the Ising Model: A High Resolution Monte Carlo Study

2018 ◽  
Vol 1012 ◽  
pp. 012002 ◽  
Author(s):  
Jiahao Xu ◽  
Alan M. Ferrenberg ◽  
David P. Landau
Keyword(s):  
Monte Carlo ◽  
Ising Model ◽  
High Resolution ◽  
Monte Carlo Study

scholarly journals The global 3-D distribution of tropospheric aerosols as characterized by CALIOP

2013 ◽  
Vol 13 (6) ◽  
pp. 3345-3361 ◽  
Author(s):  
D. M. Winker ◽  
J. L. Tackett ◽  
B. J. Getzewich ◽  
Z. Liu ◽  
M. A. Vaughan ◽  
...  
Keyword(s):  
Lower Troposphere ◽  
Aerosol Extinction ◽  
Transport Pathways ◽  
3 Dimensional ◽  
Clear Sky ◽  
Tropospheric Aerosol ◽  
Vertical Distributions ◽  
Dimensional Distribution ◽  
Level 3 ◽  
Sky Conditions

Abstract. The CALIOP lidar, carried on the CALIPSO satellite, has been acquiring global atmospheric profiles since June 2006. This dataset now offers the opportunity to characterize the global 3-D distribution of aerosol as well as seasonal and interannual variations, and confront aerosol models with observations in a way that has not been possible before. With that goal in mind, a monthly global gridded dataset of daytime and nighttime aerosol extinction profiles has been constructed, available as a Level 3 aerosol product. Averaged aerosol profiles for cloud-free and all-sky conditions are reported separately. This 6-yr dataset characterizes the global 3-dimensional distribution of tropospheric aerosol. Vertical distributions are seen to vary with season, as both source strengths and transport mechanisms vary. In most regions, clear-sky and all-sky mean aerosol profiles are found to be quite similar, implying a lack of correlation between high semi-transparent cloud and aerosol in the lower troposphere. An initial evaluation of the accuracy of the aerosol extinction profiles is presented. Detection limitations and the representivity of aerosol profiles in the upper troposphere are of particular concern. While results are preliminary, we present evidence that the monthly-mean CALIOP aerosol profiles provide quantitative characterization of elevated aerosol layers in major transport pathways. Aerosol extinction in the free troposphere in clean conditions, where the true aerosol extinction is typically 0.001 km−1 or less, is generally underestimated, however. The work described here forms an initial global 3-D aerosol climatology which we plan to extend and improve over time.

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