The SPARC water vapor assessment II: intercomparison of satellite and ground-based microwave measurements
Gerald E. Nedoluha1,Michael Kiefer2,Stefan Lossow2,R. Michael Gomez1,Niklaus Kämpfer3,Martin Lainer3,Peter Forkman4,Ole Martin Christensen4,Jung Jin Oh5,Paul Hartogh6,John Anderson7,Klaus Bramstedt8,Bianca M. Dinelli9,Maya Garcia-Comas10,Mark Hervig11,Donal Murtagh4,Piera Raspollini12,William G. Read13,Karen Rosenlof14,Gabriele P. Stiller2,and Kaley A. Walker15Gerald E. Nedoluha et al.Gerald E. Nedoluha1,Michael Kiefer2,Stefan Lossow2,R. Michael Gomez1,Niklaus Kämpfer3,Martin Lainer3,Peter Forkman4,Ole Martin Christensen4,Jung Jin Oh5,Paul Hartogh6,John Anderson7,Klaus Bramstedt8,Bianca M. Dinelli9,Maya Garcia-Comas10,Mark Hervig11,Donal Murtagh4,Piera Raspollini12,William G. Read13,Karen Rosenlof14,Gabriele P. Stiller2,and Kaley A. Walker15
Received: 22 Jun 2017 – Discussion started: 20 Jul 2017 – Revised: 12 Oct 2017 – Accepted: 27 Oct 2017 – Published: 06 Dec 2017
Abstract. As part of the second SPARC (Stratosphere–troposphere Processes And their Role in Climate) water vapor assessment (WAVAS-II), we present measurements taken from or coincident with seven sites from which ground-based microwave instruments measure water vapor in the middle atmosphere. Six of the ground-based instruments are part of the Network for the Detection of Atmospheric Composition Change (NDACC) and provide datasets that can be used for drift and trend assessment. We compare measurements from these ground-based instruments with satellite datasets that have provided retrievals of water vapor in the lower mesosphere over extended periods since 1996.
We first compare biases between the satellite and ground-based instruments from the upper stratosphere to the upper mesosphere. We then show a number of time series comparisons at 0.46 hPa, a level that is sensitive to changes in H2O and CH4 entering the stratosphere but, because almost all CH4 has been oxidized, is relatively insensitive to dynamical variations. Interannual variations and drifts are investigated with respect to both the Aura Microwave Limb Sounder (MLS; from 2004 onwards) and each instrument's climatological mean. We find that the variation in the interannual difference in the mean H2O measured by any two instruments is typically ∼ 1%. Most of the datasets start in or after 2004 and show annual increases in H2O of 0–1 % yr−1. In particular, MLS shows a trend of between 0.5 % yr−1 and 0.7 % yr−1 at the comparison sites. However, the two longest measurement datasets used here, with measurements back to 1996, show much smaller trends of +0.1 % yr−1 (at Mauna Loa, Hawaii) and −0.1 % yr−1 (at Lauder, New Zealand).
As part of the second SPARC (Stratosphere–troposphere Processes And their Role in Climate) water vapor assessment (WAVAS-II), we present measurements taken from or coincident with seven sites from which ground-based microwave instruments measure water vapor in the middle atmosphere. In the lower mesosphere, we quantify instrumental differences in the observed trends and annual variations at six sites. We then present a range of observed trends in water vapor over the past 20 years.
As part of the second SPARC (Stratosphere–troposphere Processes And their Role in Climate) water...