moisture fluxes
Recently Published Documents


TOTAL DOCUMENTS

152
(FIVE YEARS 31)

H-INDEX

29
(FIVE YEARS 4)

MAUSAM ◽  
2022 ◽  
Vol 46 (3) ◽  
pp. 257-262
Author(s):  
T. N. JHA ◽  
K. C. SINHA RAY

 ABSTRACT. MONTBLEX-90 data for an Intensive Observational Period (IOP) was extracted to investigate the thunderstorm and its impacts on surface layer at Varanasi on 27 July 1990. Sensible heat flux has been computed by profile, aerodynamic and eddy correlation methods. In addition to that. momentum and moisture fluxes have been computed for comparative diagnosis of situations before, at the time and after thunderstorm, Monin-Obukhov similarity theory has been used for quantification of the fluxes. Findings indicate that surface is more buoyant at the time of thunderstorm. Under this influence, maxima of moisture and momentum fluxes occur at the tin1e of thunderstorm. However, heat flux was found to be maximum before the thunderstorm, The results provide an understanding of surface layer turbulent transfer during stable and unstable conditions.    


2021 ◽  
pp. 1-33
Author(s):  
Mingfang Ting ◽  
Richard Seager ◽  
Cuihua Li ◽  
Haibo Liu ◽  
Naomi Henderson

AbstractDuring the summer, the Midwest United States, which covers the main US corn belt, has a net loss of surface water as evapotranspiration exceeds precipitation. The net moisture gain into the atmosphere is transported out of the region to northern high latitudes through transient eddy moisture fluxes. How this process may change in the future is not entirely clear despite the fact that the corn belt region is responsible for a large portion of the global supply of corn and soybeans. We find that increased CO2 and the associated warming increases evapotranspiration. while precipitation reduces in the region leading to further reduction in precipitation minus evaporation (P-E) in the future. At the same time, the poleward transient moisture flux increases leading to enhanced atmospheric moistures export from the corn belt region. However, storm track intensity is generally weakened in the summer due to reduced north-south temperature gradient associated with amplified warming in the midlatitudes. The intensified transient eddy moisture transport as storm track weakens can be reconciled by the stronger mean moisture gradient in the future. This is found to be caused by the climatological low-level jet transporting more moisture into the Great Plains region due to the thermodynamic mechanism under warmer conditions. Our results, for the first time, show that in the future, the US Midwest corn belt will experience more hydrological stress due to intensified transient eddy moisture export leading to drier soils in the region.


Author(s):  
Armin Sigmund ◽  
Jérôme Dujardin ◽  
Francesco Comola ◽  
Varun Sharma ◽  
Hendrik Huwald ◽  
...  

AbstractThe influence of drifting and blowing snow on surface mass and energy exchange is difficult to quantify due to limitations in both measurements and models, but is still potentially very important over large areas with seasonal or perennial snow cover. We present a unique set of measurements that make possible the calculation of turbulent moisture, heat, and momentum fluxes during conditions of drifting and blowing snow. From the data, Monin–Obukhov estimation of bulk fluxes is compared to eddy-covariance-derived fluxes. In addition, large-eddy simulations with sublimating particles are used to more completely understand the vertical profiles of the fluxes. For a storm period at the Syowa S17 station in East Antarctica, the bulk parametrization severely underestimates near-surface heat and moisture fluxes. The large-eddy simulations agree with the eddy-covariance fluxes when the measurements are minimally disturbed by the snow particles. We conclude that overall exchange over snow surfaces is much more intense than current models suggest, which has implications for the total mass balance of the Antarctic ice sheet and the cryosphere.


2021 ◽  
Vol 25 (6) ◽  
pp. 3519-3538
Author(s):  
Markus Merk ◽  
Nadine Goeppert ◽  
Nico Goldscheider

Abstract. Availability of long-term and high-resolution measurements of soil moisture is crucial when it comes to understanding all sorts of changes to past soil moisture variations and the prediction of future dynamics. This is particularly true in a world struggling against climate change and its impacts on ecology and the economy. Feedback mechanisms between soil moisture dynamics and meteorological influences are key factors when it comes to understanding the occurrence of drought events. We used long-term high-resolution measurements of soil moisture on a large inclined lysimeter at a test site near Karlsruhe, Germany. The measurements indicate (i) a seasonal evaporation depth of over 2 m. Statistical analysis and linear regressions indicate (ii) a significant decrease in soil moisture levels over the past 2 decades. This decrease is most pronounced at the start and the end of the vegetation period. Furthermore, Bayesian change-point detection revealed (iii) that this decrease is not uniformly distributed over the complete observation period. The largest changes occur at tipping points during years of extreme drought, with significant changes to the subsequent soil moisture levels. This change affects not only the overall trend in soil moisture, but also the seasonal dynamics. A comparison to modeled data showed (iv) that the occurrence of deep desiccation is not merely dependent on the properties of the soil but is spatially heterogeneous. The study highlights the importance of soil moisture measurements for the understanding of moisture fluxes in the vadose zone.


2021 ◽  
Author(s):  
Ambroise Dufour ◽  
Sergey Gulev ◽  
Olga Zolina

<p>The prevailing westerly winds provide Europe with an average flow of moisture from the North Atlantic. We document the climatological transport of water vapour across Europe's western border, from the south of the Iberic Peninsula to Northern Scandinavia. Four state-of-the-art reanalyses (NCEP CFSR, JRA 55, MERRA 2 and ERA 5) are confronted to satellite observations (QUIKSCAT and ASCAT) and to radiosoundings (IGRA) from six coastal sites.  Over the datasets' common time range (2000-2011), the agreement is generally good in terms of yearly and monthly fluxes. The satellite products have generally lower values than the rest of the ensemble. Some disparities appear on the vertical. A longer time range (1980-2020) excludes satellite data but allows to detect local increases in moisture transport in the later years.</p><p>Beyond the climatological picture, day to day moisture fluxes present significant fluctuations, both in the dry and wet directions. The variability is consistent between reanalyses and radiosondes but slightly weaker in the satellite data. The fluxes on pressure levels are strongly correlated to their vertically integrated counterpart. We take advantage of the vertical coherence to stratify humidity and wind profiles according to quantiles of integrated moisture transport. The respective role of humidity and wind changes becomes apparent. Wind speed and direction determines the moisture transport more than the humidity field on a short term basis. On the scale of decades, there was no discernable change of circulation. It was moistening that drove the increase in water vapour transport. The effect was disproportionate for higher quantiles as a consequence of the non-linear Clausius-Clapeyron equation.</p>


2021 ◽  
Vol 149 (5) ◽  
pp. 1517-1534
Author(s):  
Benjamin Jaimes de la Cruz ◽  
Lynn K. Shay ◽  
Joshua B. Wadler ◽  
Johna E. Rudzin

AbstractSea-to-air heat fluxes are the energy source for tropical cyclone (TC) development and maintenance. In the bulk aerodynamic formulas, these fluxes are a function of surface wind speed U10 and air–sea temperature and moisture disequilibrium (ΔT and Δq, respectively). Although many studies have explained TC intensification through the mutual dependence between increasing U10 and increasing sea-to-air heat fluxes, recent studies have found that TC intensification can occur through deep convective vortex structures that obtain their local buoyancy from sea-to-air moisture fluxes, even under conditions of relatively low wind. Herein, a new perspective on the bulk aerodynamic formulas is introduced to evaluate the relative contribution of wind-driven (U10) and thermodynamically driven (ΔT and Δq) ocean heat uptake. Previously unnoticed salient properties of these formulas, reported here, are as follows: 1) these functions are hyperbolic and 2) increasing Δq is an efficient mechanism for enhancing the fluxes. This new perspective was used to investigate surface heat fluxes in six TCs during phases of steady-state intensity (SS), slow intensification (SI), and rapid intensification (RI). A capping of wind-driven heat uptake was found during periods of SS, SI, and RI. Compensation by larger values of Δq > 5 g kg−1 at moderate values of U10 led to intense inner-core moisture fluxes of greater than 600 W m−2 during RI. Peak values in Δq preferentially occurred over oceanic regimes with higher sea surface temperature (SST) and upper-ocean heat content. Thus, increasing SST and Δq is a very effective way to increase surface heat fluxes—this can easily be achieved as a TC moves over deeper warm oceanic regimes.


2021 ◽  
Author(s):  
Eli Dennis ◽  
Ernesto Berbery

<p>Soil hydrophysical properties are necessary components in weather and climate simulation; yet, the parameter inaccuracies may introduce considerable uncertainty in the representation of surface water and energy fluxes. The surface fluxes not only affect the terrestrial water and energy budgets, but through land-atmosphere interactions, they can influence the boundary layer, atmospheric stability, moisture transports, and regional precipitation characteristics. This study uses seasonal coupled simulations to examine the uncertainties in the North American atmospheric water cycle that result from the use of different soil datasets. Two soil datasets are considered: State Soil Geographic dataset (STATSGO) from the United States Department of Agriculture and Global Soil Dataset for Earth System Modeling (GSDE) from Beijing Normal University.  Each dataset's dominant soil category allocations differ significantly at the model's resolution (15 km). It is found that large coherent regional discrepancies exist in the assignments of soil category, such that, for instance, in the Midwestern United States (hereafter, Midwest), there is a systematic reduction in soil grain size. Because the soil grain size is regionally biased, it allows for analysis of the impact of soil hydrophysical properties projected onto regional scales.</p><p>The two simulations are conducted from June 1–August 31, 2016–2018 using the Weather Research and Forecasting Model (WRF) coupled with the Community Land Model (CLM) version 4. It is found that in the Midwest, where the soil grain size decreases from STATSGO to GSDE, the GSDE simulation experiences reduced mean latent heat flux (–15 W m<sup>-2</sup>), and increased sensible heat flux (+15 W m<sup>-2</sup>).  The differences in fluxes lead to differences in low-level specific humidity and 2-m temperature. The boundary layer thermodynamic structure responds to these changes resulting in differences in mean CAPE and CIN. In the GSDE simulation, there is more energy available for convection (CAPE: +200 J kg<sup>-1</sup>) in the Midwest, but it is more difficult to access that energy (CIN: +75 J kg<sup>-1</sup>). Furthermore, a reduction in low-level moisture generates a similar reduction in column-integrated moisture (i.e., precipitable water), resulting in conditions that are less conducive for precipitation.</p><p>Interestingly, the soil-texture-related surface fluxes are not confined to thermodynamic influence, but their influence extends to dynamic fields as well. Differences in the vertically-integrated wind field suggest a weakening of the continental low-pressure system (i.e., denoted by a reduction in cyclonic rotation) co-located with the decrease in latent heat flux in the Midwest. The associated vertically-integrated moisture fluxes mirror the dissimilarities in the wind fields. Consequently, the moisture fluxes yield differences in vertically-integrated moisture flux convergence in the same region, as well. This combination of thermodynamic and dynamic variable differences culminates in a reduction of average precipitation in the Midwest, which can be related to changes in the placement of soil hydrophysical properties via soil texture. Through land-atmosphere interactions, it is shown that soil parameters can affect each component of the atmospheric water budget.</p>


2021 ◽  
Author(s):  
Emmanuel Likoya ◽  
Cathryn Birch ◽  
Sarah Chapman ◽  
Andrew Dougill

<p>The societal relevance of droughts in Africa underscores the need for improved understanding of the atmospheric processes that drive them. This study examined drought characteristics across Malawi, and the associated atmospheric circulation patterns, in observations, reanalysis and global climate models. Droughts were identified using the Standardised Precipitation and Evapotranspiration Index (SPEI) for the period 1965 to 2018. Atmospheric circulation patterns during droughts were examined and the main moisture fluxes into Malawi were identified. Despite differences in the frequency, and events being asynchronous at times, droughts exhibited characteristics that were statistically similar between northern and southern Malawi. Droughts in both regions were associated with anomalous circulation that typically worked to diminish moisture advection and thus convection. Differences in the structure of the anomalies were indicative of differences in mechanisms associated with droughts in the north and south of Malawi. Three main moisture flux pathways were identified, and categorized as northeasterly, southeasterly, and northwesterly, each with a unique correlation structure with precipitation and global SSTs. Positive and negative biases of varying magnitudes were noted for drought and rainfall characteristics across the range of CMIP5 models. Such biases can be attributed to biases in moisture fluxes whose variability was found to be a key driver of summer precipitation variability across Malawi. Despite biases in moisture fluxes and their influence on precipitation biases, the majority of models exhibited moisture flux-precipitation correlations consistent with observations and reanalysis. Results from the study highlight the extent to which climate models are reliable in simulating droughts and therefore of value in developing narratives of climate variability essential for long-term development planning.</p>


2021 ◽  
Author(s):  
Maximilien Bolot ◽  
Stephan Fueglistaler

<p>The role played by tropical storms in the tropical tropopause layer (TTL), the transitional layer regulating the flux into the stratosphere of trace gases affecting radiation and the ozone layer, has been a long-standing open question. Progress has been slow because of computational limitations and challenging conditions for measurements and most numerical studies have used simulations over limited domains whose results must be upscaled to the tropical surface to infer global impacts. We compute the first global observational estimate of the convective ice flux at near tropical tropopause levels by using spaceborne lidar measurements from CALIOP. The calculation uses a method to convert from lidar extinction to sedimenting ice flux and uses error propagation to provide margins of uncertainty. We show that, at any given level in the TTL, the sedimenting ice flux exceeds the inflow of vapor computed from ERA5 reanalysis, revealing additional ice transport and allowing to deduce the advective ice flux as a function of altitude. The contribution to this flux of large-scale motions (resolved by ERA5) is computed and the residual is hypothesized to represent the flux of ice on the convective scale. Results show without ambiguity that the upward ice flux in deep convection dominates moisture transport up to close to the level of the cold point tropopause.</p>


2021 ◽  
Author(s):  
Iris Thurnherr ◽  
Heini Wernli ◽  
Franziska Aemisegger

<p>Stable water isotopes in marine boundary layer water vapour are strongly influenced by the strength of air-sea moisture fluxes and are thus tracers of air-sea interaction. Air-sea moisture fluxes in the extratropics are modulated by large-scale air advection, for instance the advection of warm and moist air masses in the warm sector of extratropical cyclones. A distinct isotopic composition of water vapour in the latter environment has been observed in near-surface water vapour over the Southern Ocean during the 2016/17 Antarctic Circumnavigation coordinated by the Swiss Polar Institute. Most prominently, the second-order isotope variable d-excess shows negative values in the cyclones’ warm sector. Here, we present three single-process air parcel models, which simulate the evolution of d-excess and specific humidity in an air parcel induced by dew deposition, decreasing ocean evaporation or upstream cloud formation, respectively. The air-parcel models are combined with simulations with the isotope-enabled numerical weather prediction model COSMO<sub>iso</sub> (i) to validate the air parcel models, (ii) to study the extent of non-linear interactions between the different processes, and (iii) to quantify the relevance of the three processes for stable water isotopes in the warm sector of the investigated extratropical cyclone. This analysis reveals that dew deposition and decreasing ocean evaporation lead to the strongest d-excess decrease in near-surface water vapour in the warm sector. Furthermore, COSMO<sub>iso</sub> air parcel trajectories show that the persistent low d-excess observed in the warm sector of extratropical cyclones is not a result of material conservation of low d-excess. Instead the latter feature is sustained by the continuous production of low d-excess values in new air parcels entering the warm sector. We show that with the mechanistic approach of using single-process air parcel models we are able to simulate the evolution of d-excess during the air parcel’s transport. This improves our understanding of the effect of air-sea interaction and boundary layer cloud formation on the stable water isotope variability of marine boundary layer water vapour.</p>


Sign in / Sign up

Export Citation Format

Share Document