Technical Note: 30 years of HIRS data of upper tropospheric humidity

Gierens, Klaus; Eleftheratos, Kostas; Shi, Lei

doi:10.5194/acp-14-7533-2014

Cited by 18 publications

(34 citation statements)

References 19 publications

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“…The latest IPCC report (IPCC, 2013) states that the knowledge about potential trends and feedback mechanisms of upper tropospheric water vapour is low because of its large natural variability in the troposphere and relatively short records of observations. Although balloon-borne data collected over Boulder, CO (Hurst et al, 2011), and data from satellite-borne instruments like the AURA Microwave Limb Sounder (MLS; Read et al, 2007) or the High-Resolution Infrared Radiation Sounder (HIRS; Gierens et al, 2014) permit investigating long-term trends, over specific regions, there is still an urgent need for in situ observation of UTH on a global scale.…”

Section: Introductionmentioning

confidence: 99%

Technical Note: Reanalysis of upper troposphere humidity data from the MOZAIC programme for the period 1994 to 2009

et al. 2014

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Abstract. In situ observational data on the relative humidity (RH) in the upper troposphere and lowermost stratosphere (UT/LS), or tropopause region, collected aboard civil passenger aircraft in the MOZAIC (Measurements of OZone, water vapour, carbon monoxide and nitrogen oxides by in-service AIrbus airCraft) programme were reanalysed for the period 2000 to 2009. Previous analyses of probability distribution functions (PDFs) of upper troposphere humidity (UTH) data from MOZAIC observations from year 2000 and later indicated a bias of UTH data towards higher RH values compared to data of the period 1994 to 1999. As a result, the PDF of UTH data show a substantial fraction of observations above 100 % relative humidity with respect to liquid water. Such supersaturations, however, do not occur in the atmosphere because there is always a sufficient number of condensation nuclei available, that trigger condensation as soon as liquid saturation is slightly exceeded. An in-depth reanalysis of the data set identified a coding error in the calibration procedure from year 2000 on. The error did not affect earlier data from 1994 to 1999. The full data set for 2000-2009 was reanalysed applying the corrected calibration procedure. Applied correction schemes and a revised error analysis are presented along with the reanalysed PDF of relative humidity with respect to liquid water (RH liquid ) and ice (RH ice ).

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Section: Introductionmentioning

confidence: 99%

Technical Note: Reanalysis of upper troposphere humidity data from the MOZAIC programme for the period 1994 to 2009

et al. 2014

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“…The intercalibrated time series was used for several studies (e.g. Gierens et al, 2014;Chung et al, 2016). Yet problems remained in the lower tail of the distribution of brightness temperatures, that is, at the lowest values of brightness temperatures, as has been detected by Gierens and Eleftheratos (2017, in the following cited as GE17).…”

Section: Introductionmentioning

confidence: 99%

Intercalibration between HIRS/2 and HIRS/3 channel 12 based on physical considerations

2018

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Abstract. High-resolution Infrared Radiation Sounder (HIRS) brightness temperatures at channel 12 (T 12 ) can be used to assess the water vapour content of the upper troposphere. The transition from HIRS/2 to HIRS/3 in 1999 involved a shift in the central wavelength of channel 12 from 6.7 to 6.5 µm, causing a discontinuity in the time series of T 12 . To understand the impact of this change in the measured brightness temperatures, we have performed radiative transfer calculations for channel 12 of HIRS/2 and HIRS/3 instruments, using a large set of radiosonde profiles of temperature and relative humidity from three different sites. Other possible changes within the instrument, apart from the changed spectral response function, have been assumed to be of minor importance, and in fact, it was necessary to assume as a working hypothesis that the spectral and radiometric calibration of the two instruments did not change during the relatively short period of their common operation. For each radiosonde profile we performed two radiative transfer calculations, one using the HIRS/2 channel response function of NOAA 14 and one using the HIRS/3 channel response function of NOAA 15, resulting in negative differences of T 12 (denoted as T 12 := T 12/15 − T 12/14 ) ranging between −12 and −2 K. Inspection of individual profiles for large, medium and small values of T 12 pointed to the role of the mid-tropospheric humidity. This guided us to investigate the relation between T 12 and the channel 11 brightness temperatures which are typically used to detect signals from the mid-troposphere. This allowed us to construct a correction for the HIRS/3 T 12 , which leads to a pseudo-channel 12 brightness temperature as if a HIRS/2 instrument had measured it. By applying this correction we find an excellent agreement between the original HIRS/2 T 12 and the HIRS/3 data inferred from the correction method with R = 0.986. Upper-tropospheric humidity (UTH) derived from the pseudo HIRS/2 T 12 data compared well with that calculated from intersatellite-calibrated data, providing independent justification for using the two intercalibrated time series (HIRS/2 and HIRS/3) as a continuous HIRS time series for long-term UTH analyses.

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“…Determining decadal changes (2000-2009 vs. 1980-1989) of UTHi for the northern midlatitudes, 30-60 • N, from intercalibrated HIRS data (Gierens et al, 2014) resulted in statistically highly significant increases of more than 2 % in a large fraction of this latitude belt. As we see from the present analyses, such an increase would be unexpected under the assumption that the relative humidity would have stayed nearly constant during these 30 years, both for the size of the effect (exceeding 1 %) and its main direction (positive).…”

Section: Discussionmentioning

confidence: 99%

“…However, a recent comparison of decadal means of upper tropospheric humidity (UTH, a radiance-based quantity defined later in Eq. 2), for the decades 1980-1989 and 2000-2009, respectively, and performed for the 30 to 60 • N latitude belt, showed a moderate (few percent) but statistically significant increase of UTHi (UTH with respect to ice) over large regions in this zone (Gierens et al, 2014). The data for this study had been obtained from 30 years of intercalibrated satellite data from the High-resolution Infrared Radiation Sounder (HIRS) instruments on the NOAA polar orbiting satellite series (Shi and Bates, 2011).…”

Section: Introductionmentioning

confidence: 99%

Upper tropospheric humidity changes under constant relative humidity

Gierens

Eleftheratos

2016

Atmos. Chem. Phys.

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Abstract. Theoretical derivations are given on the change of upper tropospheric humidity (UTH) in a warming climate. The considered view is that the atmosphere, which is getting moister with increasing temperatures, will retain a constant relative humidity. In the present study, we show that the upper tropospheric humidity, a weighted mean over a relative humidity profile, will change in spite of constant relative humidity. The simple reason for this is that the weighting function that defines UTH changes in a moister atmosphere. Through analytical calculations using observations and through radiative transfer calculations, we demonstrate that two quantities that define the weighting function of UTH can change: the water vapour scale height and the peak emission altitude. Applying these changes to real profiles of relative humidity shows that absolute UTH changes typically do not exceed 1 %. If larger changes would be observed they would be an indication of climatological changes of relative humidity. As such, an increase in UTH between 1980 and 2009 in the northern midlatitudes, as shown by earlier studies using the High-resolution Infrared Radiation Sounder (HIRS) data, may be an indication of an increase in relative humidity as well.

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Technical Note: 30 years of HIRS data of upper tropospheric humidity

Cited by 18 publications

References 19 publications

Technical Note: Reanalysis of upper troposphere humidity data from the MOZAIC programme for the period 1994 to 2009

Technical Note: Reanalysis of upper troposphere humidity data from the MOZAIC programme for the period 1994 to 2009

Intercalibration between HIRS/2 and HIRS/3 channel 12 based on physical considerations

Upper tropospheric humidity changes under constant relative humidity

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