Emerging Technologies and Synergies for Airborne and Space-Based Measurements of Water Vapor Profiles

Abstract

A deeper understanding of how clouds will respond to a warming climate is one of the outstanding challenges in climate science. Uncertainties in the response of clouds, and particularly shallow clouds, have been identified as the dominant source of the discrepancy in model estimates of equilibrium climate sensitivity. As the community gains a deeper understanding of the many processes involved, there is a growing appreciation of the critical role played by fluctuations in water vapor and the coupling of water vapor and atmospheric circulations. Reduction of uncertainties in cloud-climate feedbacks and convection initiation as well as improved understanding of processes governing these effects will result from profiling of water vapor in the lower troposphere with improved accuracy and vertical resolution compared to existing airborne and space-based measurements. This paper highlights new technologies and improved measurement approaches for measuring lower tropospheric water vapor and their expected added value to current observations. Those include differential absorption lidar and radar, microwave occultation between lowEarth orbiters, and hyperspectral microwave remote sensing. Each methodology is briefly

Boundary Layer Clouds and Convection over Subtropical Oceans in our Current and in a Warmer Climate

“…Such variability in humidity may be set on larger scales, such as dry air intrusions from mid-latitudes or moist and dry layers set by nearby deep convection [63,74], but the importance of the moisture profile above the boundary layer for radiative effects within the boundary layer remains unclear and requires further study. Recent work assesses the ability of space-borne observing systems at mapping water vapor profiles and discusses new technologies that may provide better observations of lower tropospheric water vapor that can help unravel moistureradiation interactions [75][76][77].…”

Structure and Dynamical Influence of Water Vapor in the Lower Tropical Troposphere

“…The box and whisker plot shows the distribution of humidity values measured within a vertical height interval in terms of the values at the 10th and 90th percentile (whiskers), the interquartile (box) and the median (notch) of the distribution (2017). More information on emerging technologies for better (tropical) water vapor measurements has been compiled by Nehrir et al (2017).…”

Evaluation of differential absorption radars in the 183 GHz band for profiling water vapour in ice clouds

“…With realistic minimum detection thresholds, DARs can provide useful information in thick ice/mixed-phase clouds and they can complement other techniques (e.g. water vapor DIALs, Nehrir et al (2017)). Four tone DARs seem to be 5 the right balance between complexity (i.e.…”

“…Furthermore, there is interest in exploring the possibility of profiling the water vapor in cloudy areas Millán et al, 2016;Roy et al, 2018) by using differential absorption radar (DAR) measurements near the 183.3 GHz water vapor absorption line. Water vapor is one of the most critical atmospheric variables for numerical weather prediction models (Millán et al (2016)) and profiles of 15 humidity in cloudy areas are not adequately measured by current or planned systems as stated by WMO (Anderson, 2014;Nehrir et al, 2017). While Lebsock et al (2015) theoretically investigated the possibility of profiling water vapor within the cloudy boundary layer in presence of cumulus and stratocumulus clouds and of quantifying integrated column water vapor over ocean surfaces with a DAR system with channels on the left wing of the 183.3 GHz absorption line, Millán et al (2016) examined how the DAR technique can be applied to water vapor sounding in clouds at all levels by adopting multiple tones 20 within the whole absorption band (140 to 200 GHz).…”