Trends in continental temperature and humidity directly linked to ocean warming

In recent decades, the land surface has warmed substantially more than the ocean surface, and relative humidity has fallen over land. Amplified warming and declining relative humidity over land are also dominant features of future climate projections, with implications for climate-change impacts. An emerging body of research has shown how constraints from atmospheric dynamics and moisture budgets are important for projected future land–ocean contrasts, but these ideas have not been used to investigate temperature and humidity records over recent decades. Here we show how both the temperature and humidity changes observed over land between 1979 and 2016 are linked to warming over neighboring oceans. A simple analytical theory, based on atmospheric dynamics and moisture transport, predicts equal changes in moist static energy over land and ocean and equal fractional changes in specific humidity over land and ocean. The theory is shown to be consistent with the observed trends in land temperature and humidity given the warming over ocean. Amplified land warming is needed for the increase in moist static energy over drier land to match that over ocean, and land relative humidity decreases because land specific humidity is linked via moisture transport to the weaker warming over ocean. However, there is considerable variability about the best-fit trend in land relative humidity that requires further investigation and which may be related to factors such as changes in atmospheric circulations and land-surface properties.

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Understanding Decreases in Land Relative Humidity with Global Warming: Conceptual Model and GCM Simulations

Journal of Climate ◽

10.1175/jcli-d-16-0351.1 ◽

2016 ◽

Vol 29 (24) ◽

pp. 9045-9061 ◽

Cited By ~ 74

Author(s):

Michael P. Byrne ◽

Paul A. O’Gorman

Keyword(s):

Global Warming ◽

Relative Humidity ◽

Land Surface ◽

Moisture Transport ◽

General Circulation ◽

Stomatal Closure ◽

General Circulation Models ◽

Box Model ◽

Specific Humidity ◽

Near Surface

Abstract Climate models simulate a strong land–ocean contrast in the response of near-surface relative humidity to global warming; relative humidity tends to increase slightly over oceans but decrease substantially over land. Surface energy balance arguments have been used to understand the response over ocean but are difficult to apply over more complex land surfaces. Here, a conceptual box model is introduced, involving atmospheric moisture transport between the land and ocean and surface evapotranspiration, to investigate the decreases in land relative humidity as the climate warms. The box model is applied to simulations with idealized and full-complexity (CMIP5) general circulation models, and it is found to capture many of the features of the simulated changes in land humidity. The simplest version of the box model gives equal fractional increases in specific humidity over land and ocean. This relationship implies a decrease in land relative humidity given the greater warming over land than ocean and modest changes in ocean relative humidity, consistent with a mechanism proposed previously. When evapotranspiration is included, it is found to be of secondary importance compared to ocean moisture transport for the increase in land specific humidity, but it plays an important role for the decrease in land relative humidity. For the case of a moisture forcing over land, such as from stomatal closure, the response of land relative humidity is strongly amplified by the induced change in land surface–air temperature, and this amplification is quantified using a theory for the link between land and ocean temperatures.

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Impacts of Shallow Convection on MJO Simulation: A Moist Static Energy and Moisture Budget Analysis

Journal of Climate ◽

10.1175/jcli-d-12-00127.1 ◽

2013 ◽

Vol 26 (8) ◽

pp. 2417-2431 ◽

Cited By ~ 34

Author(s):

Qiongqiong Cai ◽

Guang J. Zhang ◽

Tianjun Zhou

Keyword(s):

Boundary Layer ◽

Deep Convection ◽

Lower Troposphere ◽

Longwave Radiation ◽

Reanalysis Data ◽

Specific Humidity ◽

Moist Static Energy ◽

Shallow Convection ◽

Budget Analysis ◽

Static Energy

Abstract The role of shallow convection in Madden–Julian oscillation (MJO) simulation is examined in terms of the moist static energy (MSE) and moisture budgets. Two experiments are carried out using the NCAR Community Atmosphere Model, version 3.0 (CAM3.0): a “CTL” run and an “NSC” run that is the same as the CTL except with shallow convection disabled below 700 hPa between 20°S and 20°N. Although the major features in the mean state of outgoing longwave radiation, 850-hPa winds, and vertical structure of specific humidity are reasonably reproduced in both simulations, moisture and clouds are more confined to the planetary boundary layer in the NSC run. While the CTL run gives a better simulation of the MJO life cycle when compared with the reanalysis data, the NSC shows a substantially weaker MJO signal. Both the reanalysis data and simulations show a recharge–discharge mechanism in the MSE evolution that is dominated by the moisture anomalies. However, in the NSC the development of MSE and moisture anomalies is weaker and confined to a shallow layer at the developing phases, which may prevent further development of deep convection. By conducting the budget analysis on both the MSE and moisture, it is found that the major biases in the NSC run are largely attributed to the vertical and horizontal advection. Without shallow convection, the lack of gradual deepening of upward motion during the developing stage of MJO prevents the lower troposphere above the boundary layer from being preconditioned for deep convection.

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Humidity profiles and their interactions with moisture transport and surface fluxes in the Antarctic

10.5194/egusphere-egu2020-20196 ◽

2020 ◽

Author(s):

Tuomas Naakka ◽

Tiina Nygård ◽

Timo Vihma

Keyword(s):

Relative Humidity ◽

Sea Ice ◽

Moisture Transport ◽

Vertical Structure ◽

Water Cycle ◽

Surface Fluxes ◽

Specific Humidity ◽

Near Surface ◽

The Antarctic ◽

Humidity Profiles

Atmospheric humidity profiles control occurrence of clouds, which in turn has a large impact on radiative fluxes in the Antarctic. In addition, humidity profiles strongly interact with surface moisture fluxes, which are an important component in the water cycle. Despite their important role in the climate system, specific and relative humidity profiles in the Antarctic have not so far been comprehensively studied. Here, we address the vertical structure of tropospheric specific and relative humidity in the area south of 50&#176;S and focus on interactions of this structure with horizontal and vertical moisture transport and surface fluxes of sensible and latent heat. The study is based on ERA5 reanalysis data from 15-years period, 2004 - 2018.&#160;We show that in the Antarctic, both moisture transport and surface fluxes shape the vertical structure of specific and relative humidity, but their relative contributions and effects vary considerably between regions. Therefore, we examined humidity profiles dividing the study area into five sub-regions: 1) open sea, 2) seasonal sea-ice area, 3) slopes of East Antarctica, 4) East Antarctica high plateau, and 5) West Antarctica. Expect west Antarctica, within each region the vertical structure of air moisture is relatively homogenous. Results indicate that each of these regions has own key processes (evaporation, condensation, vertical and horizontal moisture fluxes) controlling the vertical structure of relative and specific humidity.The open ocean is a source area for atmospheric moisture. Over the open sea, a thin unsaturated well-mixed layer is seen near the surface, which is caused by year-around upward moisture flux (evaporation) and upward sensible heat flux. Above this layer, there is a layer of high relative humidity and frequently occurring cloud cover. Over sea ice, seasonal variability is large. During most of the year, moisture surface fluxes over sea ice are small, near-surface relative humidity is high, and specific humidity inversions are frequent. In summer, however, evaporation over sea ice increases, near-surface relative humidity is lower, and humidity inversions are uncommon.The high plateau is the area where absolutely dry air masses are formed, as a consequence of near-surface condensation and downward moisture transport. There, the near-surface air is often saturated with respect to ice, and strong but thin surface-based specific humidity inversions are present during most of the year. On the slopes, adiabatic warming, due to katabatic winds, causes decrease of relative humidity when the air mass is advected downwards from the plateau. This leads to relatively high surface evaporation and makes surface-based specific humidity inversions rarer.This study comprehensively describes the vertical structure of relative and specific humidity in the Antarctic, and increases understanding on how this vertical structure interacts with moisture transport and surface fluxes. The results can further contribute to understanding of processes related to cloud formation and water cycle in the high southern latitudes.

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Evapo-Transpiration calculated from the new regional climate projections data set DRIAS-2020 over France

10.5194/ems2021-109 ◽

2021 ◽

Author(s):

Sébastien Bernus ◽

Lola Corre ◽

Agathe Drouin ◽

Genaro Saavedra Soriano ◽

Pascal Simon ◽

...

Keyword(s):

Relative Humidity ◽

Agricultural Sector ◽

Regional Climate ◽

Specific Humidity ◽

Climate Projections ◽

Visible Radiation ◽

Adaptation Measures ◽

Data Set ◽

Thermal Amplitude ◽

Regional Climate Projections

&#160;Evapo-Transpiration calculated from the new regional climate projections data set DRIAS-2020 over FranceChanges in climatic variables such as temperature, precipitation, relative humidity or solar radiation strongly affect the agricultural sector. Relevant indicators are strongly needed to quantify the expected impacts and implement adaptation measures. Information on the future trend of Evapo-Transpiration (ET) is one of the key issues in order to take up the water management challenge.In 2020, a new set of climate indicators based on regional climate projections corrected over France was produced and published on the French national climate service DRIAS (www.drias-climat.fr) and the associated report was published in January 2021. The latter portal provides climate information in a variety of graphical or numerical forms. The climate projections are based on the EURO-CORDEX ensemble and have been corrected using the ADAMONT method according to the SAFRAN reference data set.ET is calculated from this new data set with the aim of making it freely available on the DRIAS portal. Various calculation methods are used and compared. First, ET is calculated upstream and downstream of the ADAMONT method. Second, different calculation procedures are tested for the FAO recommended formula. One uses the average specific humidity instead of minimum and maximum of daily relative humidity which are not available in all selected models. ET is also calculated using the Hargreaves proxy for the visible radiation based on the square root of the maximum daily thermal amplitude multiplied by a coefficient. Three different values were tested for this coefficient&#160;: 0.16, 0.175 and 0.19.These various ET are then analyzed with a view to quantify the influence of the calculation method on the resulting estimated trends.Authors&#160;: BERNUS S.1, CORRE L.2, DROUIN A.2, SAAVEDRA SORIANO G.3, SIMON P.2, PRATS&#160;S.4, &#160;1 M&#233;t&#233;o-France, Direction de la Climatologie et des Services Climatiques, Toulouse, France, [email protected]2M&#233;t&#233;o-France, Direction de la Climatologie et des Services Climatiques, Toulouse, France, [email protected]3&#201;cole des Mines, Antibes, France, [email protected]4M&#233;t&#233;o-France, Direction des Services M&#233;t&#233;orologiques, Toulouse, France, [email protected]&#160;References&#160;:FAO (1998). Crop evapotranspiration: Guidelines for computing crop water requirements. FAO Irrigation and drainage paper 56, Rome, Italy

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Comparison of land surface humidity between observations and CMIP5 models

Earth System Dynamics ◽

10.5194/esd-8-719-2017 ◽

2017 ◽

Vol 8 (3) ◽

pp. 719-747 ◽

Cited By ~ 9

Author(s):

Robert J. H. Dunn ◽

Kate M. Willett ◽

Andrew Ciavarella ◽

Peter A. Stott

Keyword(s):

Relative Humidity ◽

Land Surface ◽

Radiative Forcing ◽

Specific Humidity ◽

Cmip5 Models ◽

High Latitudes ◽

Entire Study ◽

Temporal Behaviour ◽

Global Average ◽

The Tropics

Abstract. We compare the latest observational land surface humidity dataset, HadISDH, with the latest generation of climate models extracted from the CMIP5 archive and the ERA-Interim reanalysis over the period 1973 to present. The globally averaged behaviour of HadISDH and ERA-Interim are very similar in both humidity measures and air temperature, on decadal and interannual timescales. The global average relative humidity shows a gradual increase from 1973 to 2000, followed by a steep decline in recent years. The observed specific humidity shows a steady increase in the global average during the early period but in the later period it remains approximately constant. None of the CMIP5 models or experiments capture the observed behaviour of the relative or specific humidity over the entire study period. When using an atmosphere-only model, driven by observed sea surface temperatures and radiative forcing changes, the behaviour of regional average temperature and specific humidity are better captured, but there is little improvement in the relative humidity. Comparing the observed climatologies with those from historical model runs shows that the models are generally cooler everywhere, are drier and less saturated in the tropics and extra-tropics, and have comparable moisture levels but are more saturated in the high latitudes. The spatial pattern of linear trends is relatively similar between the models and HadISDH for temperature and specific humidity, but there are large differences for relative humidity, with less moistening shown in the models over the tropics and very little at high latitudes. The observed drying in mid-latitudes is present at a much lower magnitude in the CMIP5 models. Relationships between temperature and humidity anomalies (T–q and T–rh) show good agreement for specific humidity between models and observations, and between the models themselves, but much poorer for relative humidity. The T–q correlation from the models is more steeply positive than the observations in all regions, and this over-correlation may be due to missing processes in the models. The observed temporal behaviour appears to be a robust climate feature rather than observational error. It has been previously documented and is theoretically consistent with faster warming rates over land compared to oceans. Thus, the poor replication in the models, especially in the atmosphere-only model, leads to questions over future projections of impacts related to changes in surface relative humidity. It also precludes any formal detection and attribution assessment.

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Interaction of Vegetation and Atmospheric Dynamical Mechanisms in the Mid-Holocene African Monsoon*

Journal of Climate ◽

10.1175/jcli3833.1 ◽

2006 ◽

Vol 19 (16) ◽

pp. 4105-4120 ◽

Cited By ~ 13

Author(s):

Katrina Hales ◽

J. David Neelin ◽

Ning Zeng

Keyword(s):

Land Surface ◽

Climate Modeling ◽

Atmospheric Model ◽

Moist Static Energy ◽

North African ◽

Orbital Parameters ◽

Model Studies ◽

Vegetation Feedbacks ◽

Highly Sensitive ◽

Static Energy

Abstract Paleoevidence indicates that generally wetter conditions existed in the Sahara during the mid-Holocene. Climate modeling studies addressing this issue generally agree that mid-Holocene values of the earth’s orbital parameters favored an enhanced North African summer monsoon but also suggest that land surface and vegetation feedbacks must have been important factors. Attempts to reproduce the “green” mid-Holocene Sahara in model studies with interactive vegetation may be interpreted to indicate that the problem is highly sensitive to the atmospheric dynamics of each model employed. In other work, dynamical mechanisms have been hypothesized to affect monsoon poleward extent, particularly ventilation, by import of low-moist static energy air to the continent. Here, interactive vegetation and the ventilation mechanism are studied in an intermediate complexity atmospheric model coupled to simple land and vegetation components. Interactive vegetation is found to be effective at enhancing the precipitation and vegetation amount in regions where the monsoon has advanced because of changes in orbital parameters or ventilation yet not very effective in moving the monsoon boundary if ventilation is strong. The poleward extent of the mid-Holocene monsoon and the steppe boundary are primarily controlled by the strength of ventilation in the atmospheric model. Within this boundary, the largest changes in monsoon precipitation and vegetation occur when interactive vegetation and reduced ventilation act simultaneously, as these greatly reinforce each other.

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Analysis of the Meridional Energy Transport by Atmospheric Overturning Circulations

Journal of the Atmospheric Sciences ◽

10.1175/2010jas3493.1 ◽

2011 ◽

Vol 68 (8) ◽

pp. 1806-1820 ◽

Cited By ~ 20

Author(s):

Kristofer Döös ◽

Johan Nilsson

Keyword(s):

Mass Transport ◽

Energy Transport ◽

Cell Structure ◽

Meridional Overturning Circulation ◽

Specific Humidity ◽

Moist Static Energy ◽

Mean Flow ◽

Vertical Coordinate ◽

Meridional Overturning ◽

Static Energy

Abstract The atmospheric meridional overturning circulation is computed using the interim European Centre for Medium-Range Weather Forecasts Re-Analysis (ERA-Interim) data. Meridional mass transport streamfunctions are calculated not only using pressure as a vertical coordinate but also using temperature, specific humidity, and geopotential height as generalized vertical coordinates. Moreover, mass transport streamfunctions are calculated using the latent, the dry static, or the moist static energy as generalized vertical coordinates. The total meridional energy transport can be obtained by integrating these streamfunctions “vertically” over their entire energy range. The time-averaged mass transport streamfunctions are also decomposed into mean-flow and eddy-induced components. The meridional mass transport streamfunctions with temperature and specific humidity as independent variables yield a two-cell structure with a tropical Hadley-like cell and a pronounced extratropical Ferrel-like cell, which carries warm and moist air poleward. These Ferrel-like cells are much stronger than the Eulerian zonal-mean Ferrel cell, a feature that can be understood by considering the residual circulation related to specific humidity or temperature. Regardless of the generalized vertical coordinate, the present meridional mass transport streamfunctions yield essentially a two-layer structure with one poleward and one equatorward branch. The strongest meridional overturning in the midlatitudes is obtained when the specific humidity or the moist static energy is used as the vertical coordinate, indicating that the specific humidity is the variable that best distinguishes between poleward- and equatorward-moving air in the lower troposphere.

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Comparison of land–surface humidity between observations and CMIP5 models

10.5194/esd-2017-9 ◽

2017 ◽

Cited By ~ 1

Author(s):

Robert J. H. Dunn ◽

Kate M. Willett ◽

Andrew Ciavarella ◽

Peter A. Stott

Keyword(s):

Relative Humidity ◽

Land Surface ◽

Radiative Forcing ◽

Specific Humidity ◽

Cmip5 Models ◽

High Latitudes ◽

Entire Study ◽

Temporal Behaviour ◽

Global Average ◽

The Tropics

Abstract. We compare the latest observational land-surface humidity dataset, HadISDH, with the latest generation of climate models extracted from the CMIP5 archive and the ERA-Interim reanalysis over the period 1973 to present. The globally averaged behaviour of HadISDH and ERA-Interim are very similar in both humidity measures and air temperature, at decadal and interannual timescales. The global average relative humidity shows a gradual increase from 1973 to 2000, followed by a steep decline in recent years. The observed specific humidity shows a steady increase in the global average during the early period but in the later period it remains approximately constant. None of the CMIP5 models or experiments capture the observed behaviour of the relative or specific humidity over the entire study period. When using an atmosphere-only model, driven by observed sea-surface temperatures and radiative forcing changes, the behaviour of regional average temperature and specific humidity are better captured, but there is little improvement in the relative humidity. Comparing the observed and historical model climatologies show that the models are generally cooler everywhere, are drier and less saturated in the tropics and extra tropics, and have comparable moisture levels but are more saturated in the high latitudes. The spatial pattern of linear trends are relatively similar between the models and HadISDH for temperature and specific humidity, but there are large differences for relative humidity, with less moistening shown in the models over the Tropics, and very little at high latitudes. The observed drying in mid-latitudes is present at a much lower magnitudes. Relationships between temperature and humidity anomalies (T–q and T–rh) show good agreement for specific humidity between models and observations, and between the models themselves, but much poorer for relative humidity. The T–q correlation from the models is more steeply positive in all regions than the observations, and this over-correlation may be due to missing processes in the models. The observed temporal behaviour appears to be a robust climate feature rather than observational error. It has been previously documented and is theoretically consistent with faster warming rates over land compared to oceans. Thus, the poor replication in the models, especially in the atmosphere only model, leads to questions over future projections of impacts related to changes in surface relative humidity. It also precludes any formal detection and attribution assessment.

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The Met Office Operational Soil Moisture Analysis System

Remote Sensing ◽

10.3390/rs12223691 ◽

2020 ◽

Vol 12 (22) ◽

pp. 3691

Author(s):

Breogán Gómez ◽

Cristina L. Charlton-Pérez ◽

Huw Lewis ◽

Brett Candy

Keyword(s):

Soil Moisture ◽

Data Assimilation ◽

Air Temperature ◽

Land Surface ◽

River Flow ◽

Surface Air Temperature ◽

Specific Humidity ◽

Surface Data ◽

Temperature And Humidity ◽

Soil Wetness

In this study, the current Met Office operational land surface data assimilation system used to produce soil moisture analyses is presented. The main aim of including Land Surface Data Assimilation (LSDA) in both the global and regional systems is to improve forecasts of surface air temperature and humidity. Results from trials assimilating pseudo-observations of 1.5 m air temperature and specific humidity and satellite-derived soil wetness (ASCAT) observations are analysed. The pre-processing of all the observations is described, including the definition and construction of the pseudo-observations. The benefits of using both observations together to produce improved forecasts of surface air temperature and humidity are outlined both in the winter and summer seasons. The benefits of using active LSDA are quantified by the root mean squared error, which is computed using both surface observations and European Centre for Medium-Range Weather Forecasts (ECMWF) analyses as truth. For the global model trials, results are presented separately for the Northern (NH) and Southern (SH) hemispheres. When compared against ground-truth, LSDA in winter NH appears neutral, but in the SH it is the assimilation of ASCAT that contributes to approximately a 2% improvement in temperatures at lead times beyond 48 h. In NH summer, the ASCAT soil wetness observations degrade the forecasts against observations by about 1%, but including the screen level pseudo-observations provides a compensating benefit. In contrast, in the SH, the positive effect comes from including the ASCAT soil wetness observations, and when both observations types are assimilated there is a compensating effect. Finally, we demonstrate substantial improvements to hydrological prediction when using land surface data assimilation in the regional model. Using the Nash-Sutcliffe Efficiency (NSE) metric as an aggregated measure of river flow simulation skill relative to observations, we find that NSE was improved at 106 of 143 UK river gauge locations considered after LSDA was introduced. The number of gauge comparisons where NSE exceeded 0.5 is also increased from 17 to 28 with LSDA.

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Mechanisms of Climate Change in the Semiarid African Sahel: The Local View

Journal of Climate ◽

10.1175/2009jcli3123.1 ◽

2010 ◽

Vol 23 (3) ◽

pp. 743-756 ◽

Cited By ~ 64

Author(s):

Alessandra Giannini

Keyword(s):

Climate Change ◽

Land Surface ◽

Southern Oscillation ◽

Net Energy ◽

Moist Static Energy ◽

Near Surface ◽

Vertical Stability ◽

First Case ◽

Static Energy ◽

The Impact

Abstract Application of the moist static energy framework to analyses of vertical stability and net energy in the Sahel sheds light on the divergence of projections of climate change. Two distinct mechanisms are sketched. In one, anthropogenic warming changes continental climate indirectly: warming of the oceans increases moist static energy at upper levels, affecting vertical stability globally, from the top down, and driving drying over the Sahel, in a way analogous to the impact of El Niño–Southern Oscillation on the global tropical atmosphere. In the other, the increase in anthropogenic greenhouse gases drives a direct continental change: the increase in net terrestrial radiation at the surface increases evaporation, favoring vertical instability and near-surface convergence from the bottom up. In both cases the surface warms, but in the first precipitation and evaporation decrease, while in the second they increase. In the first case, land surface warming is brought about by the remotely forced decrease in precipitation and consequent decrease in evaporation and increase in net solar radiation at the surface. In the second, it is brought about by the increase in net terrestrial radiation at the surface, amplified by the water vapor feedback associated with an increase in near-surface humidity.

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