Universität zu Köln

De Angelis, Francesco, Cimini, Domenico ORCID: 0000-0002-5962-223X, Loehnert, Ulrich, Caumont, Olivier ORCID: 0000-0002-6470-2023, Haefele, Alexander, Pospichal, Bernhard ORCID: 0000-0001-9517-8300, Martinet, Pauline, Navas-Guzman, Francisco, Klein-Baltink, Henk, Dupont, Jean-Charles and Hocking, James (2017). Long-term observations minus background monitoring of ground-based brightness temperatures from a microwave radiometer network. Atmos. Meas. Tech., 10 (10). S. 3947 - 3962. GOTTINGEN: COPERNICUS GESELLSCHAFT MBH. ISSN 1867-8548

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Abstract

Ground-based microwave radiometers (MWRs) offer the capability to provide continuous, high-temporal-resolution observations of the atmospheric thermodynamic state in the planetary boundary layer (PBL) with low maintenance. This makes MWR an ideal instrument to supplement radiosonde and satellite observations when initializing numerical weather prediction (NWP) models through data assimilation. State-of-the-art data assimilation systems (e.g. variational schemes) require an accurate representation of the differences between model (background) and observations, which are then weighted by their respective errors to provide the best analysis of the true atmospheric state. In this perspective, one source of information is contained in the statistics of the differences between observations and their background counterparts (O-B). Monitoring of O-B statistics is crucial to detect and remove systematic errors coming from the measurements, the observation operator, and/or the NWP model. This work illustrates a 1-year O-B analysis for MWR observations in clear-sky conditions for an European-wide network of six MWRs. Observations include MWR brightness temperatures (TB) measured by the two most common types of MWR instruments. Background pro-files are extracted from the French convective-scale model AROME-France before being converted into TB. The observation operator used to map atmospheric profiles into TB is the fast radiative transfer model RTTOV-gb. It is shown that O-B monitoring can effectively detect instrument malfunctions. O-B statistics (bias, standard deviation, and root mean square) for water vapour channels (22.24-30.0 GHz) are quite consistent for all the instrumental sites, decreasing from the 22.24 GHz line centre (similar to 2-2.5 K) towards the high-frequency wing (similar to 0.8-1.3 K). Statistics for zenith and lower-elevation observations show a similar trend, though values increase with increasing air mass. O-B statistics for temperature channels show different behaviour for relatively transparent (51-53 GHz) and opaque channels (54-58 GHz). Opaque channels show lower uncertainties (< 0.8-0.9 K) and little variation with elevation angle. Transparent channels show larger biases (similar to 2-3 K) with relatively low standard deviations (similar to 1-1.5 K). The observations minus analysis TB statistics are similar to the O-B statistics, suggesting a possible improvement to be expected by assimilating MWR TB into NWP models. Lastly, the O-B TB differences have been evaluated to verify the normal-distribution hypothesis under- lying variational and ensemble Kalman filter-based DA systems. Absolute values of excess kurtosis and skewness are generally within 1 and 0.5, respectively, for all instrumental sites, demonstrating O-B normal distribution for most of the channels and elevations angles.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code De Angelis, Francesco UNSPECIFIED UNSPECIFIED UNSPECIFIED Cimini, Domenico UNSPECIFIED orcid.org/0000-0002-5962-223X UNSPECIFIED Loehnert, Ulrich UNSPECIFIED UNSPECIFIED UNSPECIFIED Caumont, Olivier UNSPECIFIED orcid.org/0000-0002-6470-2023 UNSPECIFIED Haefele, Alexander UNSPECIFIED UNSPECIFIED UNSPECIFIED Pospichal, Bernhard UNSPECIFIED orcid.org/0000-0001-9517-8300 UNSPECIFIED Martinet, Pauline UNSPECIFIED UNSPECIFIED UNSPECIFIED Navas-Guzman, Francisco UNSPECIFIED UNSPECIFIED UNSPECIFIED Klein-Baltink, Henk UNSPECIFIED UNSPECIFIED UNSPECIFIED Dupont, Jean-Charles UNSPECIFIED UNSPECIFIED UNSPECIFIED Hocking, James UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-213967
DOI:	10.5194/amt-10-3947-2017
Journal or Publication Title:	Atmos. Meas. Tech.
Volume:	10
Number:	10
Page Range:	S. 3947 - 3962
Date:	2017
Publisher:	COPERNICUS GESELLSCHAFT MBH
Place of Publication:	GOTTINGEN
ISSN:	1867-8548
Language:	English
Faculty:	Faculty of Mathematics and Natural Sciences
Divisions:	Faculty of Mathematics and Natural Sciences > Department of Geosciences > Institute for Geophysics and Meteorology
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language RADIATIVE-TRANSFER MODEL; WATER-VAPOR; CLOUD LIQUID; ASSIMILATION; HUMIDITY; PART; ABSORPTION Multiple languages Meteorology & Atmospheric Sciences Multiple languages
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/21396