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  • Space-borne observation of methane from atmospheric infrared sounder: data analysis and distribution over Iraq
    Methane (CH4) Volume Mixing Ratio (VMR) at pressure level 925hPa data extracted from Atmospheric Infrared Sounder (AIRS) with spatial resolution of 1°× 1° covering whole of Iraq and surrounding regions (28.5°–38.5°N, 37.5°–49.5°E) have been examined for the period from January 2003 to December 2013. The results show a considerable increasing of CH4 with maximum values at north and north eastern regions during autumn and the early winter, whereas the minimum values appeared at the pristine desert environment at the west and the south-west region during spring months. For more accuracy validation the trend analysis was applied on the retrieved AIRS data at three different stations are Mosul, Baghdad and Basrah. The mean and standard deviation in Mosul, Baghdad and Basrah was (1.8657 ± 0.0198, 1.8536 ± 0.0196, 1.8448 ± 0.0212) ppmv respectively for monthly long term trend analysis. Monthly trend analyses have positive trends (0.0040, 0.0039 and 0.0042) ppmv.y-1 for Mosul, Baghdad and Basrah Consecutively. These results indicate that Satellite observations efficiently present the temporal and spatial variations of the CH4 for the considered study Area. more
  • Inter-comparison of integrated water vapor from satellite instruments using reference GPS data at the Iberian Peninsula
    This paper focuses on the inter-comparison of integrated water vapor (IWV) products derived from the following satellite instruments: Global Ozone Monitoring Instrument (GOME-2), Moderate-Resolution Imaging Spectroradiometer (MODIS) on the Terra and Aqua satellites, Ozone Monitoring Instrument (OMI), Spining Enhanced Visible and InfraRed Imager (SEVIRI), Atmospheric Infrared Sounder (AIRS), and Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY). IWV data from GPS in nine ground- based stations located in the Iberian Peninsula are used as reference. The study period extends from 2007 to 2012. The results show that, in general, OMI has good accuracy (pseudomedian of the relative differences between OMI and GPS IWV of (−0.7±1.1)%). However, OMI, SCIAMACHY and AIRS show higher inter- quartile range (IQR) (which indicates lower precision) than the rest of satellite instruments. Both MODIS satellite instruments and SEVIRI products tend to slightly underestimate reference IWV data while GOME-2 exhibits a notable overestimation (16.7 ± 0.8%). All satellite instruments showed a tendency to reduce IWV extreme va- lues: low IWV is overestimated while high IWV is underestimated. As for the influence of solar zenith angle (SZA), it can be observed that GOME-2 strongly overestimates the reference for high SZA values (by around 60% for SZA 60−80°). OMI shows, however, a high IQR for high SZA values. Both MODIS instruments show an increase in the pseudomedian of relative differences and IQR with SZA at daytime, with more stable values at night. Seasonal dependence is mainly due to the SZA and IWV typical values in each season. In general, in summer the tendency is to underestimate with low IQR (which happens when IWV is high and SZA is low), and in winter the trend is to overestimate with high IQR (which happens when IWV is low and SZA is high). SCIAMACHY shows a high pseudomedian in summer and autumn, and lower in winter and spring. It must be noted that GOME-2 shows a higher overestimation and OMI shows a higher IQR than other satellite instruments in winter and autumn. The influence of clouds was also studied, showing an increase of IQR as cloudiness increases in all satellites. Pseudomedian also worsens as cloudiness increases, generally. more
  • Unusual enhancement in tropospheric and surface ozone due to orography induced gravity waves
    In this study, we investigate the causative processes responsible for the observed enhancement in the tropospheric and surface ozone during December 09–11, 2008 orography induced gravity wave event over Himalayan region. The analysis is done using surface ozone measurements and satellite datasets from Atmospheric Infrared Sounder/Advanced Microwave Sounding Unit-A (AIRS/AMSU-A), COSMIC, TES and Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO). Observations depict a two fold increase in surface and tropospheric ozone during the event as compared to normal days in both AIRS and TES ozone measurements. COSMIC temperature perturbations show generation of shorter vertical wavelengths efficient for the sub-tropical tropopause folding due to orography induced gravity waves. Moreover, the intense tropopause folding as evidenced by upward-downward vertical velocities couplet could trigger the intrusion of stratospheric ozone rich air into upper tropospheric ozone poor air as also confirmed by high values of potential vorticity during the observational period. Hence, present study reemphasizes the importance of wave induced atmospheric dynamics on atmospheric constituents' especially tropospheric ozone over Himalayan region. more
  • Diurnal Cycle Variability of Surface Temperature Inferred from AIRS data
    The Diurnal Cycle of the Earth surface temperature is investigated using the daily range of the satellite skin temperature data (DTR) provided by measurements of Atmospheric InfraRed Sounder (AIRS) in 2002-2015. The AIRS is on the Aqua satellite, which is in a polar orbit with two crossing times per day at every location on the Earth. Its measurements from the ascending (day) and descending (night) orbits can serve as a proxy for the diurnal cycle. The spatial pattern of the DTR of the skin temperature and its time variability for 14 years of the AIRS operation allows to evaluate the diurnal cycle change on the decadal time scale. Using the Empirical Mode Decomposition of the data time series it is found that the DTR of the surface (skin) temperature over the global Earth has a temporal small positive trend in the decade of the AIRS measurements indicating that the day temperatures grew slightly more rapidly than the night temperatures. A possible cause of the observed DTR increase is a decrease of the low cloud fraction at nighttime found for the same time period from the AIRS retrievals. more