Lifted temperature minimum during the atmospheric evening transition
E. Blay-Carreras1,E. R. Pardyjak2,D. Pino1,3,S. W. Hoch4,J. Cuxart5,D. Martínez6,and J. Reuder7E. Blay-Carreras et al. E. Blay-Carreras1,E. R. Pardyjak2,D. Pino1,3,S. W. Hoch4,J. Cuxart5,D. Martínez6,and J. Reuder7
1Department of Applied Physics, Universitat Politècnica de Catalunya, BarcelonaTech, Barcelona, Spain
2Department of Mechanical Engineering, University of Utah, Salt Lake City, UT, USA
3Institute for Space Studies of Catalonia (IEEC–UPC), Barcelona, Spain
4Department of Atmospheric Sciences, University of Utah, Salt Lake City, UT, USA
5Grup de Meteorologia, Departament de Física, Universitat de les Illes Balears, Palma de Mallorca, Spain
6Center for Applied Geoscience, University of Tübingen, Tübingen, Germany
7Geophysical Institute, University of Bergen, Bergen, Norway
1Department of Applied Physics, Universitat Politècnica de Catalunya, BarcelonaTech, Barcelona, Spain
2Department of Mechanical Engineering, University of Utah, Salt Lake City, UT, USA
3Institute for Space Studies of Catalonia (IEEC–UPC), Barcelona, Spain
4Department of Atmospheric Sciences, University of Utah, Salt Lake City, UT, USA
5Grup de Meteorologia, Departament de Física, Universitat de les Illes Balears, Palma de Mallorca, Spain
6Center for Applied Geoscience, University of Tübingen, Tübingen, Germany
7Geophysical Institute, University of Bergen, Bergen, Norway
Correspondence: E. Blay-Carreras (estel.blay@upc.edu)
Received: 18 Jul 2014 – Discussion started: 07 Nov 2014 – Revised: 26 Feb 2015 – Accepted: 27 Feb 2015 – Published: 29 Jun 2015
Abstract. Observations of lifted temperature minimum (LTM) profiles in the nocturnal boundary layer were first reported in 1932. It was defined by the existence of a temperature minimum some centimetres above the ground. During the following decades, several research studies analysed this phenomenon verifying its existence and postulating different hypotheses about its origin.
The aim of this work is to study the existence and characteristics of LTM during the evening transition by using observations obtained during the Boundary Layer Late Afternoon and Sunset Turbulence (BLLAST) campaign. Data obtained from two masts instrumented with thermocouples and wind sensors at different heights close to the ground and a mast with radiometers are used to study the role of mechanical turbulence and radiation in LTM development.
The study shows that LTM can be detected under calm conditions during the day–night transition, several hours earlier than reported in previous work. These conditions are fulfilled under weak synoptic forcing when the local flow shifts associated with a mountain–plain circulation in relatively complex orography. Under these special conditions, turbulence becomes a crucial parameter in determining the ideal conditions for observing LTM. Additionally, LTM observed profiles are also related to a change in the atmospheric radiative characteristics under calm conditions.
The study shows that lifted temperature minimum can be detected under calm conditions during the day-night transition, several hours earlier than reported in previous work. These conditions are fulfilled under weak synoptic forcing during local flow shifts associated with a mountain-plain complex orography. Under these special conditions, turbulence and radiation becomes a crucial parameter in determining the ideal conditions for observing LTM measurements.
The study shows that lifted temperature minimum can be detected under calm conditions during the...
