A new approach to homogenize daily radiosonde humidity data

Autor(en)

Aiguo Dai, Junhong Wang, Peter W. Thorne, D.E. Parker, Leopold Haimberger, X L Wang

Abstrakt

Radiosonde humidity records represent the only in situ observations of tropospheric water vapor content with multidecadal length and quasi-global coverage. However, their use has been hampered by ubiquitous and large discontinuities resulting from changes to instrumentation and observing practices. Here a new approach is developed to homogenize historical records of tropospheric (up to 100 hPa) dewpoint depression (DPD), the archived radiosonde humidity parameter. Two statistical tests are used to detect changepoints, which aremost apparent in histograms and occurrence frequencies of the daily DPD: a variant of the Kolmogorov-Smirnov (K-S) test for changes in distributions and the penalized maximal F test (PMFred) for mean shifts in the occurrence frequency for different bins of DPD. These tests capture most of the apparent discontinuities in the daily DPD data, with an average of 8.6 changepoints (~1 changepoint per 5 yr) in each of the analyzed radiosonde records, which begin as early as the 1950s and ended in March 2009. Before applying breakpoint adjustments, artificial sampling effects are first adjusted by estimating missingDPDreports for cold (T <-30°C) and dry (DPD artificially set to 30°C) conditions using empirical relationships at each station between the anomalies of air temperature and vapor pressure derived from recent observations when DPD reports are available under these conditions. Next, the samplin-adjusted DPD is detrended separately for each of the 4-10 quantile categories and then adjusted using a quantile-matching algorithm so that the earlier segments have histograms comparable to that of the latest segment. Neither the changepoint detection nor the adjustment uses a reference series given the stability of the DPD series. Using this new approach, a homogenized global, twice-dailyDPDdataset (available online at www.cgd.ucar.edu/cas/catalog/) is created for climate and other applications based on the Integrated Global Radiosonde Archive (IGRA) and two other data sources. The adjusted-daily DPD has much smaller and spatially more coherent trends during 1973-2008 than the raw data. It implies only small changes in relative humidity in the lower and middle troposphere. When combined with homogenized radiosonde temperature, other atmospheric humidity variables can be calculated, and these exhibit spatially more coherent trends than without the DPD homogenization. The DPD adjustment yields a different pattern of change in humidity parameters compared to the apparent trends from the raw data. The adjusted estimates show an increase in troposphericwater vapor globally

Organisation(en)

Institut für Meteorologie und Geophysik

Externe Organisation(en)

Rutherford Appleton Laboratory, Met Office, University of Wollongong

Journal

Journal of Climate

Band

24

Seiten

965-991

Anzahl der Seiten

27

ISSN

0894-8755

DOI

https://doi.org/10.1175/2010JCLI3816.1

Publikationsdatum

2011

Peer-reviewed

Ja

ÖFOS 2012

105206 Meteorologie

Sustainable Development Goals

SDG 13 – Maßnahmen zum Klimaschutz

Link zum Portal

https://ucrisportal.univie.ac.at/de/publications/a-new-approach-to-homogenize-daily-radiosonde-humidity-data(bdda3dff-2d60-4cb3-b757-ec865c95b44e).html