LT-TIME
Working Group on
Long-Term Trends in the Mesosphere, Thermosphere and Ionosphere
(A joint venture of IAGA & ICMA (IAMAS ) )

INTRODUCTION

Human activities in the last two centuries have been resulting in continuously growing level of man-made atmospheric pollution by trace gases, aerosols etc. An important group of polluting trace gases, so called greenhouse gases led by carbon dioxide, is expected to warm the troposphere and to cool higher layers of the atmosphere, including the mesosphere and thermosphere. Since the signal-to-noise ratio for the greenhouse gas effect is expected to be greater at higher atmospheric levels, the first unambiguous detection of the increasing greenhouse gas concentration effects on the atmosphere seems to be more probable at higher atmospheric levels than in the troposphere. To be able to determine unambiguously from those observations the natural changes and the greenhouse gas concentration increase induced changes in the atmosphere, we must know natural long-term changes of the atmosphere.

The greenhouse gas effect on the troposphere has carefully been studied within the World Climate Research Program (WCRP) of WMO. Several years ago, project SPARC (Stratospheric Processes and Their Role in Climate) was established to study related effects in the stratosphere and their impact on tropospheric climate. SPARC is now expanding into the lower mesosphere. However, investigations of greenhouse gas-induced and other long-term trends and changes at higher levels of the mesosphere, in the thermosphere and ionosphere have not been coordinated and have been lacking an official umbrella.

Informal meeting of scientists interested in the field, held during the IAGA Assembly in 1997, resulted in organizing the Workshop “Long-Term Changes and Trends in the Atmosphere”, held in Pune (India) in February 1999. The Workshop was followed by establishing this Working Group during the IUGG Assembly in Birmingham in July 1999.

RELATION TO IAGA, ICMA AND SCOSTEP

IAGA & IAMAS/ICMA and SCOSTEP/PSMOS were the “mother bodies” of the WG. However after the PSMOS program in 2002 the “mother bodies” are IAGA & IAMAS/ICMA.The WG is included in the structure of IAGA as its WG II.F. It is also included as an official Working Group within ICMA.