Local and remote atmospheric responses to soil moisture anomalies in Australia

2021 ◽  
pp. 1-48
Author(s):  
Olivia Martius ◽  
Kathrin Wehrli ◽  
Marco Rohrer
Keyword(s):  
Soil Moisture ◽  
Southern Oscillation ◽  
Southern Annular Mode ◽  
Storm Tracks ◽  
Near Surface ◽  
Flow Response ◽  
Moisture Advection ◽  
Anomalous Surface ◽  
Community Earth System Model ◽  
Upper Level

AbstractThree sets of model experiments are performed with the Community Earth System Model to study the role of soil moisture anomalies as a boundary forcing for the formation of upper-level Rossby wave patterns during Southern Hemisphere summer. In the experiments, soil moisture over Australia is set to ±1STD of an ERA-Interim reanalysis derived soil moisture reconstruction for the years 2009 to 2016 and 50 ensemble members are run. The local response is a positive heating anomaly in the dry simulations that results in a thermal low-like circulation anomaly with an anomalous surface low and upper-level anticyclone. Significant differences in convective rainfall over Australia are related to differences in convective instability and associated with changes in near surface moisture and moisture advection patterns. A circum-hemispheric flow response is identified both in the upper-level flow and in the surface storm tracks that overall resembles a positive Southern Annular Mode-like flow anomaly in the dry simulations. The structure of this atmospheric response strongly depends on the background flow. The results point to a modulation of the hemispheric flow response to the forcing over Australia by the El Niño Southern Oscillation. Significant changes of precipitation over the Maritime continent and South Africa are found and significant differences in the frequency of surface cyclones are present all along the storm tracks.

Local and remote Southern Hemisphere extratropical circulation responses to soil moisture anomalies in Australia

2021 ◽  
Author(s):  
Olivia Romppainen-Martius ◽  
Kathrin Wehrli ◽  
Marco Rohrer
Keyword(s):  
Soil Moisture ◽  
Southern Hemisphere ◽  
Rossby Wave ◽  
Wave Train ◽  
Southern Annular Mode ◽  
Linear Wave ◽  
Model Experiments ◽  
Flow Response ◽  
Upper Level ◽  
Set Up

<p>Hemisphere-wide remote Rossby wave responses of the upper-level flow to soil moisture anomalies have been reported for the Northern Hemisphere. Model experiments varying soil moisture over North America point to the involvement of both linear and non-linear wave dynamics. Here three sets of model experiments are performed with the Community Earth System Model to study the role of soil moisture anomalies as a boundary forcing for the formation of extra-tropical upper-level Rossby wave patterns during Southern Hemisphere summer.</p><p>In the model experiments, soil moisture over Australia is set to +1STD (wet) and to -1STD (dry) of the ERA-Interim reanalysis climatology for the years 2009 to 2016. With his set-up 50 ensemble members are run and the wet and dry simulations compared. The local response to the soil moisture forcing is a positive heating anomaly in the dry simulations that results in a thermal low-like circulation anomaly with an anomalous surface low and an anomalous upper-level anticyclone.</p><p>A circum-hemispheric flow response is identified both in the extra-tropical upper-level flow and in the surface storm tracks that overall resembles a positive Southern Annular Mode-like flow anomaly in the dry simulations. The structure of this atmospheric response strongly depends on the background flow. During two El Niño summers the response is strongly influenced by nonlinear Rossby wave forcing, while during two La Niña summers the flow response resembles a circum-hemispheric wave train reflecting linear wave propagation.</p>

Future changes in North Atlantic winter cyclones in CESM-LENS: cyclone intensity and horizontal wind speed

2021 ◽  
Author(s):  
Edgar Dolores Tesillos ◽  
Stephan Pfahl ◽  
Franziska Teubler
Keyword(s):  
Wind Speed ◽  
North Atlantic ◽  
Diabatic Heating ◽  
Horizontal Wind ◽  
Horizontal Wind Speed ◽  
Near Surface ◽  
Low Level ◽  
Current Century ◽  
Community Earth System Model ◽  
Upper Level

<p>Strong low-level winds are among the most impactful effects of extratropical cyclones on society.  The wind intensity and the spatial distribution of wind maxima may change in a warming climate, however, the dynamics involved are not clear. Here, structural and dynamical changes of North Atlantic cyclones in a warmer climate close to the end of the current century are investigated with storm-relative composites based on Community Earth System Model Large Ensemble (CESM-LE) simulations. Furthermore, a piecewise potential vorticity inversion is applied, to attribute such changes in low-level winds to changes in PV anomalies at different levels.</p><p>We identify an extended wind footprint southeast of the cyclone centre, where the wind speed tends to intensify in a warmer climate. Both an amplified low-level PV anomaly driven by enhanced diabatic heating and a dipole change in upper-level PV anomalies contribute to this wind intensification. On the contrary, wind changes associated with lower- and upper-level PV anomalies mostly compensate each other upstream of the cyclone center. Wind changes at upper levels are dominated by changes in upper-level PV anomalies and the background flow. All together, our results indicate that a complex interation of enhanced diabatic heating and altered upper-tropospheric wave dynamics shape future changes in near-surface winds in North Atlantic cyclones.</p>

scholarly journals Oppressive Heat Events in Illinois Related to Antecedent Wet Soils

2016 ◽  
Vol 17 (10) ◽  
pp. 2713-2726 ◽  
Author(s):  
Trent W. Ford ◽  
Justin T. Schoof
Keyword(s):  
Soil Moisture ◽  
Heat Content ◽  
Layer Growth ◽  
Maximum Temperature ◽  
Equivalent Temperature ◽  
Antecedent Soil Moisture ◽  
Near Surface ◽  
Extreme Heat Events ◽  
Upper Level ◽  
Heat Events

Abstract Extreme heat events have been connected with antecedent soil moisture in many global regions, such that dry soils increase sensible heat content of the near-surface atmosphere and impede precipitation through boundary layer growth. However, negative soil moisture–temperature feedbacks (dry soils = higher temperatures) are founded on investigations of maximum temperature that neglect the potentially important latent heating component provided by soil moisture. In this study, the association of spring soil moisture and subsequent summer oppressive heat events is quantified, defined by equivalent temperature. The advantage of equivalent temperature over maximum temperature is that it accounts for both the temperature and moisture components of atmospheric heat content. Quantile regression and composite analysis are used to determine the association between spring soil moisture and summer oppressive heat events using a 25-yr station observation record in Illinois. A consistent response of summer oppressive heat events to antecedent 5-cm soil moisture anomalies is found at all four stations. The frequency of oppressive summer equivalent temperature events is significantly increased following spring seasons with wetter-than-normal soils compared with spring seasons with dry soils. This provides evidence of a possible positive soil moisture–temperature feedback. Further, it is found that oppressive heat events correspond with the combination of wetter-than-normal spring soils and persistent summertime upper-level ridging to the northeast of the region, thereby leading to the conclusion that abundant-to-surplus spring soil moisture is necessary but not sufficient for the occurrence of oppressive heat in Illinois.

scholarly journals Catchment-scale drought: capturing the whole drought cycle using multiple indicators

2020 ◽  
Vol 24 (4) ◽  
pp. 1985-2002 ◽  
Author(s):  
Abraham J. Gibson ◽  
Danielle C. Verdon-Kidd ◽  
Greg R. Hancock ◽  
Garry Willgoose
Keyword(s):  
Soil Moisture ◽  
Large Scale ◽  
Climatic Factors ◽  
Southern Oscillation ◽  
Meteorological Drought ◽  
Southern Annular Mode ◽  
Agricultural Drought ◽  
Catchment Scale ◽  
Climate Resilience ◽  
Eastern Australia

Abstract. Global agricultural drought policy has shifted towards promoting drought preparedness and climate resilience in favor of disaster-relief-based strategies. For this approach to be successful, drought predictability and methods for assessing the many aspects of drought need to be improved. Therefore, this study aims to bring together meteorological and hydrological measures of drought as well as vegetation and soil moisture data to assess how droughts begin, propagate and subsequently terminate for a catchment in eastern Australia. For the study area, 13 meteorological drought periods persisting more than 6 months were identified over the last 100 years. During these periods, vegetation health, soil moisture and streamflow declined; however, all of the indicators recovered quickly post-drought, with no evidence of extended impacts on the rainfall–runoff response, as has been observed elsewhere. Furthermore, drought initiation and propagation were found to be tightly coupled to the combined state of large-scale ocean–atmosphere climate drivers (e.g., the El Niño–Southern Oscillation, the Indian Ocean Dipole and the Southern Annular Mode), whereas termination was caused by persistent synoptic systems (e.g., low-pressure troughs). The combination of climatic factors, topography, soils and vegetation are believed to be what makes the study catchments more resilient to drought than others in eastern Australia. This study diversifies traditional approaches to studying droughts by quantifying the catchment response to drought using a range of measures that could also be applied in other catchments globally. This is a key step towards improved drought management.

scholarly journals The Hurricane Harvey (2017) Texas Rainstorm: Synoptic Analysis and Sensitivity to Soil Moisture

2020 ◽  
Vol 148 (6) ◽  
pp. 2479-2502
Author(s):  
Thomas J. Galarneau ◽  
Xubin Zeng
Keyword(s):  
Soil Moisture ◽  
Gulf Coast ◽  
Sensitivity Experiment ◽  
Southern Plains ◽  
Near Surface ◽  
Synoptic Analysis ◽  
The North ◽  
Steering Flow ◽  
Upper Level ◽  
Upper Level Jet

Abstract A synoptic analysis and soil moisture (SM) sensitivity experiment is conducted on the record-breaking rainstorm in Texas associated with Hurricane Harvey on 26–30 August 2017. The rainstorm occurred as the moist tropical air mass associated with Harvey was lifted along a frontogenetical near-surface coastal baroclinic zone beneath the equatorward entrance region of an upper-level jet streak. The weak steering winds in Harvey’s environment, allowing Harvey to remain nearly stationary, were associated with a deformation steering flow pattern characterized by a trough to the north and flanking ridges to the west and east. This pattern has occurred with other notable tropical cyclone rainstorms along the Gulf Coast, except in Harvey’s case it contributed to the collocation of deep tropical moisture and a persistent midlatitude lifting mechanism. Motivated by marked increases in SM during the rainstorm, a suite of six numerical simulations is used to test the sensitivity of the Harvey rainstorm (track, intensity, and rainfall) to varying SM. These simulations include dry, realistic, and wet SM conditions and an additional three runs with the initial SM held constant throughout the simulations. The results showed that track and prelandfall intensity were most sensitive to SM. Decreased SM resulted in the 1) development of an anticyclone in the southern plains that steered Harvey farther southwest in Texas, and 2) interruption in the intensification of Harvey in the Gulf of Mexico as dry air in the Yucatan Peninsula was entrained into Harvey’s circulation, contributing to a weaker system at landfall. Implications of these findings on the evolution of tropical systems are also discussed.

scholarly journals How Oceanic Oscillation Drives Soil Moisture Variations over Mainland Australia: An Analysis of 32 Years of Satellite Observations*

2013 ◽  
Vol 26 (24) ◽  
pp. 10159-10173 ◽  
Author(s):  
Bernhard Bauer-Marschallinger ◽  
Wouter A. Dorigo ◽  
Wolfgang Wagner ◽  
Albert I. J. M. van Dijk
Keyword(s):  
Soil Moisture ◽  
Southern Oscillation ◽  
Southern Annular Mode ◽  
Total Variance ◽  
The West ◽  
Climate Modes ◽  
North East ◽  
The North ◽  
Strongly Connected ◽  
Droughts And Floods

Abstract Australia is frequently subject to droughts and floods. Its hydrology is strongly connected to oceanic and atmospheric oscillations (climate modes) such as the El Niño–Southern Oscillation (ENSO), Indian Ocean dipole (IOD), and southern annular mode (SAM). A global 32-yr dataset of remotely sensed surface soil moisture (SSM) was used to examine hydrological variations in mainland Australia for the period 1978–2010. Complex empirical orthogonal function (CEOF) analysis was applied to extract independent signals and to investigate their relationships to climate modes. The annual cycle signal represented 46.3% of the total variance and a low but highly significant connection with SAM was found. Two multiannual signals with a lesser share in total variance (6.3% and 4.2%) were identified. The first one had an unstable period of 2–5 yr and reflected an east–west pattern that can be associated with ENSO and SAM but not with IOD. The second one, a 1- to 5-yr oscillation, formed a dipole pattern between the west and north and can be linked to ENSO and IOD. As expected, relationships with ENSO were found throughout the year and are especially strong during southern spring and summer in the east and north. Somewhat unexpectedly, SAM impacts strongest in the north and east during summer and is proposed as the key driver of the annual SSM signal. The IOD explains SSM variations in the north, east, and southeast during spring and also in the west during winter.

Local and remote Rossby wave responses to an anomalously dry or wet Australian continent

2020 ◽  
Author(s):  
Olivia Martius ◽  
Kathrin Wehrli ◽  
Sonia Seneviratne
Keyword(s):  
Soil Moisture ◽  
Rossby Wave ◽  
Wave Train ◽  
Heat Fluxes ◽  
Linear Wave ◽  
Main Mode ◽  
Near Surface ◽  
Wave Dynamics ◽  
Australian Continent ◽  
Upper Level

<p>An ensemble of CESM atmosphere only experiments with varying soil moisture anomalies over Australia (+1 , 0 ,-1 STD) is analysed with respect to the atmospheric response. Locally an intensification of the surface heat low and an upper-level anticyclone is found for the negative anomaly. The local response to the low soil moisture content is driven by increase sensible heat fluxes and associated positive near-surface temperature anomalies.</p><p>A remote response of the upper-level flow consists of a downstream Rossby wave train extending along the jet waveguide and an upstream response projecting upon the main mode of variability the southern annular. The downstream response is driven by linear wave dynamics while the upstream response is modulated by non-linear wave dynamics and associated eddy fluxes. The sensitivity of the response to the background flow, i.e., different phases of ENSO is explored.</p>

scholarly journals Summertime circumglobal Rossby waves in climate models: Small biases in upper-level circulation create substantial biases in surface imprint

2021 ◽  
Author(s):  
Fei Luo ◽  
Frank Selten ◽  
Kathrin Wehrli ◽  
Kai Kornhuber ◽  
Philippe Le Sager ◽  
...  
Keyword(s):  
Soil Moisture ◽  
Sea Level ◽  
General Circulation ◽  
Climate Models ◽  
Rossby Waves ◽  
Boreal Summer ◽  
Sea Level Pressure ◽  
Near Surface ◽  
Level Pressure ◽  
Upper Level

Abstract. In boreal summer, circumglobal Rossby waves can promote stagnating weather systems that favor extreme events like heatwaves or droughts. Recent work highlighted the risks associated with amplified Rossby wavenumber 5 and 7 in triggering simultaneous warm anomalies in specific agricultural breadbaskets in the Northern Hemisphere. These type of wave patterns thus pose potential risks for food production, as well as human health, and other impacts. The representation of such summertime wave events and their surface imprints in general circulation models (GCMs) has not been  systematically analyzed. Here we validate three state-of-the-art global climate models (EC-Earth, CESM, and MIROC), quantify their biases and provide insights into the underlying physical reasons for the biases. To do so, the ExtremeX  experiments output data were used, which are (1) historic simulations (1979–2015/2016) of a freely running atmosphere with prescribed ocean, and experiments that additionally nudge toward the observed (2) upper-level horizontal winds in the atmosphere, (3) soil moisture conditions, or (4) both. The nudged experiments are used to trace the sources of the model biases to either the large-scale atmospheric circulation or surface feedback processes. We show that while the wave position and magnitude is represented well compared to ERA5 reanalysis data. During high amplitudes (> 1.5 s.d.) wave-5 and wave- 7 events, the imprint on surface variables temperature, precipitation and sea level pressure is substantially underestimated: typically, by a factor of 1.5 in correlation and normalized standard deviations (n.s.d.) for near-surface temperature and mean sea level pressure. As for the precipitation, it’s still a factor of 1.5 for n.s.d. but 2 for correlation. The correlations and n.s.d. for surface variables do not improve if only the soil moisture is prescribed, but considerably increased when the upper-level atmosphere circulation is nudged. The underestimation factors are corrected almost entirely. When applying both soil moisture prescription and the nudging of upper-level atmosphere, both the correlation and n.s.d. values are quite similar to  only atmosphere component is nudged experiments. Hence, the near-surface biases can be substantially improved when nudging the upper-level circulation providing evidence that relatively small biases in the models’ representation of the upper-level waves can strongly affect associated temperature and rainfall anomalies.

scholarly journals Catchment-scale drought: capturing the whole drought cycle using multiple indicators

2019 ◽  
Author(s):  
Abraham J. Gibson ◽  
Danielle C. Verdon-Kidd ◽  
Greg R. Hancock ◽  
Garry Willgoose
Keyword(s):  
Soil Moisture ◽  
Large Scale ◽  
Climatic Factors ◽  
Southern Oscillation ◽  
Meteorological Drought ◽  
Southern Annular Mode ◽  
Agricultural Drought ◽  
Catchment Scale ◽  
Climate Resilience ◽  
Eastern Australia

Abstract. Global agricultural drought policy has shifted towards promoting drought preparedness and climate resilience in favor of disaster relief-based strategies. For this approach to be successful, drought predictability and methods for assessing the many aspects of drought need to be improved. Therefore, this study aims to bring together meteorological and hydrological measures of drought, along with vegetation and soil moisture data to assess how droughts begin, propagate and subsequently terminate for a catchment in eastern Australia. For the study area, thirteen meteorological drought periods persisting more than six months were identified over the last 100 years. During these, vegetation health, soil moisture and streamflow declined, however, all indicators recovered quickly post drought, with no evidence of extended impacts on the rainfall-runoff response, as has been observed elsewhere. Further, drought initiation and propagation were found to be tightly coupled to the combined state of large-scale ocean-atmosphere climate drivers (e.g. El Niño Southern Oscillation, Indian Ocean Dipole and Southern Annular Mode), while termination is caused by persistent synoptic systems (e.g. low-pressure troughs). The combination of climatic factors, topography, soils and vegetation are believed to be what makes the study catchments more resilient to drought than others in eastern Australia. The study diversifies traditional approaches to studying droughts by quantifying catchment response to drought using a range of measures that could also be applied in other catchments globally. This is a key step towards improved drought management.

An Automated Climatology of Cool Season Cutoff Lows over South-Eastern Australia, and Relationships with the Remote Climate Drivers

2021 ◽  
Keyword(s):  
Southern Oscillation ◽  
Low Frequency ◽  
Southern Annular Mode ◽  
Cool Season ◽  
South Eastern ◽  
Eastern Australia ◽  
The Indian Ocean ◽  
Cutoff Low ◽  
Upper Level ◽  
South Eastern Australia

Abstract Cutoff low pressure systems have been found to be the synoptic system responsible for the majority of rainfall in South-Eastern Australia during the cool season (April to October inclusive). Meanwhile, rainfall in South-Eastern Australia at the seasonal and interannual scale is known to be related to remote climate drivers, such as the El Niño Southern Oscillation, the Indian Ocean Dipole, and the Southern Annular Mode. In this study, a new automated tracking scheme to identify synoptic scale cutoff lows is developed, then applied to 500 hPa geopotential height data from the NCEP1 and ERA-Interim reanalyses, to create two databases of cool season cutoff lows for South Eastern Australia for the years 1979 to 2018 inclusive. Climatological characteristics of cutoff lows identified in both reanalyses are presented and compared, highlighting differences between the NCEP1 and ERA-Interim reanalyses over the Australian region. Finally, cool-season and monthly characteristics of cutoff low frequency, duration and location are plotted against cool-season and monthly values of climate driver indices (Oceanic Nino Index, Dipole Mean Index, and Antarctic Oscillation), to identify any evidence of linear correlation. Correlations between these aspects of cutoff low occurrence and the remote drivers were found to be statistically significant at the 95% level for only a single isolated month at a time, in contrast to results predicted by previous works. It is concluded that future studies of cutoff low variability over SEA should employ identification criteria that capture systems of only upper-level origin, and differentiate between cold-cored and cold-trough systems.

Sign in / Sign up

Export Citation Format

Share Document