scholarly journals On the Robustness of the Water Vapor Feedback: GCM Vertical Resolution and Formulation

2002 ◽  
Vol 15 (9) ◽  
pp. 917-921 ◽  
Author(s):  
W. J. Ingram
Keyword(s):  
Water Vapor ◽  
Vertical Resolution ◽  
Water Vapor Feedback

scholarly journals Estimates of the Water Vapor Climate Feedback during El Niño–Southern Oscillation

2009 ◽  
Vol 22 (23) ◽  
pp. 6404-6412 ◽  
Author(s):  
A. E. Dessler ◽  
S. Wong
Keyword(s):  
Global Warming ◽  
Water Vapor ◽  
El Niño ◽  
Climate Models ◽  
El Nino ◽  
Southern Oscillation ◽  
Specific Humidity ◽  
El Niño Southern Oscillation ◽  
El Nino Southern Oscillation ◽  
Water Vapor Feedback

Abstract The strength of the water vapor feedback has been estimated by analyzing the changes in tropospheric specific humidity during El Niño–Southern Oscillation (ENSO) cycles. This analysis is done in climate models driven by observed sea surface temperatures [Atmospheric Model Intercomparison Project (AMIP) runs], preindustrial runs of fully coupled climate models, and in two reanalysis products, the 40-yr European Centre for Medium-Range Weather Forecasts Re-Analysis (ERA-40) and the NASA Modern Era Retrospective-Analysis for Research and Applications (MERRA). The water vapor feedback during ENSO-driven climate variations in the AMIP models ranges from 1.9 to 3.7 W m−2 K−1, in the control runs it ranges from 1.4 to 3.9 W m−2 K−1, and in the ERA-40 and MERRA it is 3.7 and 4.7 W m−2 K−1, respectively. Taken as a group, these values are higher than previous estimates of the water vapor feedback in response to century-long global warming. Also examined is the reason for the large spread in the ENSO-driven water vapor feedback among the models and between the models and the reanalyses. The models and the reanalyses show a consistent relationship between the variations in the tropical surface temperature over an ENSO cycle and the radiative response to the associated changes in specific humidity. However, the feedback is defined as the ratio of the radiative response to the change in the global average temperature. Differences in extratropical temperatures will, therefore, lead to different inferred feedbacks, and this is the root cause of spread in feedbacks observed here. This is also the likely reason that the feedback inferred from ENSO is larger than for long-term global warming.

scholarly journals Spaceborne differential absorption radar water vapor retrieval capabilities in tropical and subtropical boundary layer cloud regimes

2021 ◽  
Vol 14 (10) ◽  
pp. 6443-6468
Author(s):  
Richard J. Roy ◽  
Matthew Lebsock ◽  
Marcin J. Kurowski
Keyword(s):  
Boundary Layer ◽  
Water Vapor ◽  
Trade Wind ◽  
Retrieval Algorithm ◽  
Line Center ◽  
Vertical Resolution ◽  
Horizontal Integration ◽  
Differential Absorption ◽  
Near Surface ◽  
Cloud Regimes

Abstract. Differential absorption radar (DAR) near the 183 GHz water vapor absorption line is an emerging measurement technique for humidity profiling inside of clouds and precipitation with high vertical resolution, as well as for measuring integrated water vapor (IWV) in clear-air regions. For radar transmit frequencies on the water line flank away from the highly attenuating line center, the DAR system becomes most sensitive to water vapor in the planetary boundary layer (PBL), which is a region of the atmosphere that is poorly resolved in the vertical by existing spaceborne humidity and temperature profiling instruments. In this work, we present a high-fidelity, end-to-end simulation framework for notional spaceborne DAR instruments that feature realistically achievable radar performance metrics and apply this simulator to assess DAR's PBL humidity observation capabilities. Both the assumed instrument parameters and radar retrieval algorithm leverage recent technology and algorithm development for an existing airborne DAR instrument. To showcase the capabilities of DAR for humidity observations in a variety of relevant PBL settings, we implement the instrument simulator in the context of large eddy simulations (LESs) of five different cloud regimes throughout the trade-wind subtropical-to-tropical cloud transition. Three distinct DAR humidity observations are investigated: IWV between the top of the atmosphere and the first detected cloud bin or Earth's surface; in-cloud water vapor profiles with 200 meter vertical resolution; and IWV between the last detected cloud bin and the Earth's surface, which can provide a precise measurement of the sub-cloud humidity. We provide a thorough assessment of the systematic and random errors for all three measurement products for each LES case and analyze the humidity precision scaling with along-track measurement integration. While retrieval performance depends greatly on the specific cloud regime, we find generally that for a radar with cross-track scanning capability, in-cloud profiles with 200 m vertical resolution and 10 %–20 % uncertainty can be retrieved for horizontal integration distances of 100–200 km. Furthermore, column IWV can be retrieved with 10 % uncertainty for 10–20 km of horizontal integration. Finally, we provide some example science applications of the simulated DAR observations, including estimating near-surface relative humidity using the cloud-to-surface column IWV and inferring in-cloud temperature profiles from the DAR water vapor profiles by assuming a fully saturated environment.

Robustness of Dynamical Feedbacks from Radiative Forcing: 2% Solar versus 2 × CO2 Experiments in an Idealized GCM

2012 ◽  
Vol 69 (7) ◽  
pp. 2256-2271 ◽  
Author(s):  
Ming Cai ◽  
Ka-Kit Tung
Keyword(s):  
Water Vapor ◽  
Radiative Forcing ◽  
Lower Troposphere ◽  
Radiative Heating ◽  
Climate Feedback ◽  
Response Analysis ◽  
High Latitudes ◽  
Water Vapor Feedback ◽  
The Tropics ◽  
Heating Profile

Abstract Despite the differences in the spatial patterns of the external forcing associated with a doubling CO2 and with a 2% solar variability, the final responses in the troposphere and at the surface in a three-dimensional general circulation model appear remarkably similar. Various feedback processes are diagnosed and compared using the climate feedback–response analysis method (CFRAM) to understand the mechanisms responsible. At the surface, solar radiative forcing is stronger in the tropics than at the high latitudes, whereas greenhouse radiative forcing is stronger at high latitudes compared with the tropics. Also solar forcing is positive everywhere in the troposphere and greenhouse radiative forcing is positive mainly in the lower troposphere. The water vapor feedback strengthens the upward-decreasing radiative heating profile in the tropics and the poleward-decreasing radiative heating profile in the lower troposphere. The “evaporative” and convective feedbacks play an important role only in the tropics where they act to reduce the warming at the surface and lower troposphere in favor of upper-troposphere warming. Both water vapor feedback and enhancement of convection in the tropics further strengthen the initial poleward-decreasing profile of energy flux convergence perturbations throughout the troposphere. As a result, the large-scale dynamical poleward energy transport, which acts on the negative temperature gradient, is enhanced in both cases, contributing to a polar amplification of warming aloft and a warming reduction in the tropics. The dynamical amplification of polar atmospheric warming also contributes additional warming to the surface below via downward thermal radiation.

Anthropogenic greenhouse forcing and strong water vapor feedback increase temperature in Europe

2005 ◽  
Vol 32 (19) ◽  
pp. n/a-n/a ◽  
Author(s):  
Rolf Philipona ◽  
Bruno Dürr ◽  
Atsumu Ohmura ◽  
Christian Ruckstuhl
Keyword(s):  
Water Vapor ◽  
Water Vapor Feedback

scholarly journals Completeness of radiosonde humidity observations based on the IGRA

2018 ◽  
Author(s):  
António P. Ferreira ◽  
Raquel Nieto ◽  
Luis Gimeno
Keyword(s):  
Water Vapor ◽  
Climatic Variability ◽  
Precipitable Water ◽  
Radiosonde Data ◽  
Vertical Resolution ◽  
Radiosonde Station ◽  
Humidity Measurements ◽  
The Mean ◽  
One Year ◽  
Selection Of

Abstract. Radiosonde measurements from the 1930s to present give unique information on the distribution and variability of water vapor in the troposphere. The sounding data compiled in the Integrated Global Radiosonde Archive (IGRA) Version 2 (released by the NOAA's National Centers for Environmental Information) are examined here until the end of 2016, aiming to describe the completeness of humidity observations from radiosondes in different times and locations. The IGRA stations reporting radiosonde data in at least 5 % of the annual soundings for at least one year are evaluated according to specified completeness parameters for every year in their period of record. The selection of source data essentially removes pilot-balloon sites, retaining a set of 1723 stations (designated IGRA-RS), including 1300 WMO upper-air stations, of which 178 belong to the current GUAN network. Completeness of humidity observations (either relative humidity or dewpoint-depression) for a radiosonde station and a full year is defined by: the number of humidity soundings; the fraction of days having humidity data; the mean vertical resolution of humidity data; the mean atmospheric pressure and altitude at the highest measuring level; and the maximum number of consecutive days without humidity data. The completeness of the observations qualified for calculating precipitable water vapor – i.e., having adequate vertical sampling between the surface and 500 hPa – is particularly studied. Individual soundings are described by the (vertically averaged) vertical resolution and the pressure level and altitude of the top of humidity measurements. For illustration, the study presents a global picture of the completeness of radiosonde humidity observations over the years, including their latitudinal coverage. This overview shows that the number of radiosonde stations having a long enough record length for studies on the climatic variability and trends of humidity-related quantities depends critically on the temporal continuity, regularity and vertical sampling of the humidity time-series. It is hoped that the derived metadata will help climate and environmental scientists to find the most appropriate radiosonde data for humidity studies by selecting upper-air stations, observing years or individual soundings according to various completeness criteria – even if differences in instrumentation and observing practices require extra attention. A dataset is presented for that purpose, consisting of two main sub-sets: 1) humidity metadata for each of the IGRA-RS stations and year within the period of record (yearly metadata); and 2) humidity metadata for individual observations from the same stations (ascent metadata). These are complemented by 3) a list of the stations represented in the dataset, along with the observing periods for humidity and the corresponding counts of observations. The dataset is to be updated on a two-year basis, starting in 2019, and is available at https://doi.org/10.5281/zenodo.1332686.

scholarly journals A Raman lidar at Maïdo Observatory (Reunion Island) to measure water vapor in the troposphere and lower stratosphere: calibration and validation

2017 ◽  
Author(s):  
Hélène Vérèmes ◽  
Guillaume Payen ◽  
Philippe Keckhut ◽  
Valentin Duflot ◽  
Jean-Luc Baray ◽  
...  
Keyword(s):  
Water Vapor ◽  
Lower Stratosphere ◽  
Calibration Coefficient ◽  
Integration Time ◽  
Relative Standard Error ◽  
Reunion Island ◽  
Vertical Resolution ◽  
Raman Lidar ◽  
Relative Standard ◽  
Réunion Island

Abstract. The Maïdo high-altitude observatory located in Reunion Island (21° S, 55.5° E) is equipped with Lidar1200, an innovative Raman lidar designed to measure the water vapor mixing ratio in the troposphere and the lower stratosphere. The calibration methodology is based on a GNSS (Global Navigation Satellite System) IWV (Integrated Water Vapor) dataset and lamp measurements. The mean relative standard error on the calibration coefficient is around 2.7 %. Two years of lidar water vapor measurements from November 2013 to October 2015 are now processed. By comparing CFH (Cryogenic Frost point Hygrometer) radiosonde profiles with the Raman lidar profiles, the ability of the lidar to provide accurate measurements is possible up to 22 km. The ability of measuring water vapor mixing ratios of a few ppmv in the lower stratosphere is demonstrated with a 48-hours integration time period, an absolute error lower than 0.8 ppmv and a relative error less than 20 %. This Raman lidar is dedicated to provide regular profiles of water vapor measurements with a high vertical resolution and low uncertainties to international networks; in the wider interest of research on stratosphere-troposphere exchange processes and on the long-term survey of water vapor in the upper troposphere and lower stratosphere in the Southern Hemisphere. A strategy of data sampling and filtering is proposed to meet these objectives with regard to the altitude range requested. 10-min time integration and 65–90 m vertical resolution ensure a vertical profile reaching 10 km, but more than 2800 minutes and a vertical resolution of 150–1300 m are necessary to reach the lower stratosphere with an uncertainty less than 20 %.

scholarly journals Characterization of blackbody inhomogeneity and its effect on the retrieval results of the GLORIA instrument

2018 ◽  
Author(s):  
Anne Kleinert ◽  
Isabell Krisch ◽  
Jörn Ungermann ◽  
Albert Adibekyan ◽  
Berndt Gutschwager ◽  
...  
Keyword(s):  
Water Vapor ◽  
Temperature Distribution ◽  
Vertical Resolution ◽  
Radiometric Calibration ◽  
Climate Trends ◽  
Trace Species ◽  
Calibration Uncertainty

Abstract. Limb sounding instruments play an important role for the monitoring of climate trends, as they provide a good vertical resolution. Traceability to the SI via onboard reference or transfer standards is needed to compare trend estimates from multiple instruments. This study investigates the required uncertainty of these radiation standards to properly resolve decadal trends of climate relevant trace species like ozone, water vapor and temperature distribution for the Gimballed Limb Observer for Radiance Imaging of the Atmosphere (GLORIA). Temperature nonuniformities of the onboard reference blackbodies, used for radiometric calibration, have an impact on the calibration uncertainty. The propagation of these nonuniformities through the retrieval is analyzed. A threshold for the maximum tolerable uncertainty of the blackbody temperature is derived, so that climate trends can be significantly identified with GLORIA.

Improvement of the Temperature and Moisture Retrievals in the Lower Troposphere Using AIRS and GPS Radio Occultation Measurements

2007 ◽  
Vol 24 (10) ◽  
pp. 1726-1739 ◽  
Author(s):  
Shu-Peng Ho ◽  
Ying-Hwa Kuo ◽  
Sergey Sokolovskiy
Keyword(s):  
Water Vapor ◽  
Radio Occultation ◽  
Water Cycle ◽  
Lower Troposphere ◽  
Resolving Power ◽  
Vertical Resolution ◽  
Gps Radio Occultation ◽  
Accurate Temperature ◽  
The Individual ◽  
Moisture Profiles

Abstract Accurate temperature and water vapor profiles in the middle and lower troposphere (LT) are crucial for understanding the water cycle, cloud systems, and energy balance. Global positioning system (GPS) radio occultation (RO) is the first technique that can provide a high-vertical-resolution all-weather refractivity profile, which is a function of pressure, temperature, and moisture. However, in the moist LT over the Tropics, the refractivity retrievals from GPS RO data are often significantly negatively biased because of tracking errors and propagation effects related to sharp vertical moisture gradients that may result in superrefraction (SR). The Atmospheric Infrared Sounder (AIRS) is a nadir-viewing sounder that can measure vertical temperature and moisture profiles with about 1–2-km vertical resolution. However, AIRS observations cannot usually obtain accurate temperature and water vapor profiles in the planetary boundary layer (PBL) because of the poor resolving power in the LT. This study uses simulations based on radiosonde profiles by combining the AIRS and the GPS RO measurements to obtain the best temperature and moisture retrievals in the LT. Different approaches are used for the drier LT and the moist LT. For the drier LT, where GPS RO data are not affected by SR errors, a multivariable regression algorithm for inverting the combined AIRS and GPS RO measurements is used. In the moist LT (e.g., SR on top of PBL), the combined AIRS and GPS RO regression inversion above the LT is used as the first guess for AIRS-only physical retrieval, which is extended into the LT. The results show that combining AIRS and GPS RO data effectively constrains the individual solutions, and therefore significantly improves inversion results. The algorithm is also applied for all available radiosonde profiles (19 profiles) over a 1-month period from the site characterized by strong SR on top of the PBL. Retrieved temperature and water vapor profiles yield unbiased low-resolution refractivity profiles in the PBL.

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