H2O / Ice Feedbacks

Summary Water vapor plays an important role in global climate change through its influence in hydrological and energy cycles, and for its radiative effect as the dominant terrestrial greenhouse gas. The increase of water vapor with temperature leads to an important positive feedback for the estimate of global warming in response to the increase in CO2. This feedback is highly sensitive to upper tropospheric water vapor (UTWV). Meanwhile, water vapor and clouds are closely coupled, especially in the upper troposphere. Their interactions have significant impacts on the energy budget of the Earth-atmosphere system and large-scale circulation. The Microwave Limb Sounder on Aura satellite provides unprecedented simultaneous measurements of UTWV and cloud ice profiles. Analysis of these datasets has contributed and will continue contributing to our understanding of the dynamics controlling water vapor and cloud variations, and to help quantifying their feedbacks to climate change.
Recent Results Relationships of upper tropospheric water vapor, clouds, and SST: MLS observations, ECMWF analyses and GCM simulations Date: 18 November 2006 The relationships of upper tropospheric water vapor (UTWV), cloud ice and sea surface temperature (SST) are examined in the annual cycles of ECMWF analyses and simulations from 15 atmosphere-ocean coupled models which were contributed to the IPCC AR4. The results are compared with the observed relationships based on UTWV and cloud ice measurements from MLS on Aura. It is shown that the ECMWF analyses produce positive correlations between UTWV, cloud ice and SST, similar to the MLS data. The rate of the increase of cloud ice and UTWV with SST is about 30% larger than that for MLS. For the IPCC simulations, the relationships between UTWV, cloud ice and SST are qualitatively captured. However, the magnitudes of the simulated cloud ice show a considerable disagreement between models, by nearly a factor of 10. The amplitudes of the approximate linear relations between UTWV, cloud ice and SST vary by a factor up to 4. +Read More
Enhanced positive water vapor feedback associated with tropical deep convection: New evidence from Aura MLS Date: 11 May 2006 Recent simultaneous observations of upper tropospheric (UT) water vapor and cloud ice from the Microwave Limb Sounder (MLS) on the Aura satellite provide new evidence for tropical convective influence on UT water vapor and its associated greenhouse effect. The observations show that UT water vapor increases as cloud ice water content increases. They also show that, when sea surface temperature (SST) exceeds 300 K, UT cloud ice associated with tropical deep convection increases sharply with increasing SST. The moistening of the upper troposphere by deep convection leads to an enhanced positive water vapor feedback, about 3 times that implied solely by thermodynamics. Over tropical oceans when SST greater than 300 K, the 'convective UT water vapor feedback' inferred from the MLS observations contributes approximately 65% of the sensitivity of the clear-sky greenhouse parameter to SST. +Read More

MLS-related publications related to water vapor and ice feedbacks on climate

2007

1. Kahn, B.H., A. Eldering, A.J. Braverman, E.J. Fetzer, J.H. Jiang, E. Fishbein, D.L. Wu, "Towards the characterization of upper tropospheric clouds using AIRS and MLS observations", vol 112, pgs. D05202, 2007. Reprint

2006

1. Su, H., W.G. Read, J.H. Jiang, J.W. Waters, D.L. Wu, E.J. Fetzer, "Enhanced positive water vapor feedback associated with tropical deep convection: New evidence from Aura MLS", vol 33, pgs. L05709, 2006. Reprint
2. Su, H., D.E. Waliser, J.H. Jiang, J-L. Li, W.G. Read, J.W. Waters, A.M. Tompkins, "Relationships of upper tropospheric water vapor, clouds and SST: MLS observations, ECMWF analyses and GCM simulations", vol 33, pgs. L22802, 2006. Reprint

1998

1. Chandra, S., J.R. Ziemke, W. Min, W.G. Read, "Effects of 1997-1998 El Nino on tropospheric ozone and water vapor", vol 25, pgs. 3867-3870, 1998. Reprint
2. Clark, H.L., R.S. Harwood, P.W. Mote, W.G. Read, "Variability of water vapor in the tropical upper troposphere as measured by the Microwave Limb Sounder on UARS", vol 103, num D24, pgs. 31,695-31,707, 1998. Reprint
3. Hu, H., W.T. Liu, "The impact of upper tropospheric humidity from Microwave Limb Sounder on the midlatitude greenhouse effect", vol 25, pgs. 3151-3154, 1998. Reprint

1997

1. Newell, R.E., Y. Zhu, W.G. Read, J.W. Waters, "Relationship between tropical upper tropospheric moisture and eastern tropical Pacific sea surface temperature on seasonal and interannual time scales", vol 24, pgs. 25-28, 1997. Reprint