Projected Characteristic Changes of a Typical Tropical Cyclone under Climate Change in the South West Indian Ocean

During 2 January 2014, Cyclone Bejisa passed near La Réunion in the southwestern Indian Ocean, bringing wind speeds of 41 m s−1, an ocean swell of 7 m, and rainfall accumulations of 1025 mm over 48 h. As a typical cyclone to impact La Réunion, we investigate how the characteristics of this cyclone could change in response to future warming via high-resolution, atmosphere–ocean coupled simulations of Bejisa-like cyclones in historical and future environments. Future environments are constructed using the pseudo global warming method whereby perturbations are added to historical analyses from six Coupled Model Intercomparison Project 5 (CMIP5) climate models. These models follow the Intergovernmental Panel for Climate Change’s (IPCC) Representative Concentration Pathways (RCP) RCP8.5 emissions scenario and project ocean surface warming of 1.1–4.2 °C by 2100. Under these conditions, we find that future Bejisa-like cyclones are 6.5% more intense on average and reach their lifetime maximum intensity 2 degrees further poleward. Additionally, future cyclones produce heavier rainfall, with a 33.8% average increase in the median rainrate, and are 9.2% smaller, as measured by the radius of 17.5 m s−1 winds. Furthermore, when surface wind output is used to run an ocean wave model in post, we find a 4.6% increase in the significant wave height.

Download Full-text

Latitudinal and seasonal variability of gravity-wave energy in the South-West Indian Ocean

Annales Geophysicae ◽

10.5194/angeo-25-2479-2007 ◽

2007 ◽

Vol 25 (12) ◽

pp. 2479-2485 ◽

Cited By ~ 5

Author(s):

F. Chane-Ming ◽

D. Faduilhe ◽

J. Leveau

Keyword(s):

Energy Density ◽

Indian Ocean ◽

Total Energy ◽

Seasonal Variability ◽

La Réunion ◽

Raman Lidar ◽

Total Energy Density ◽

South West Indian Ocean ◽

South West ◽

West Indian Ocean

Abstract. Vertical temperature profiles obtained by radiosonde and Raman lidar measurements are used to investigate a climatology of total energy density of gravity waves (GW) in the Upper Troposphere (UT) and the Lower Stratosphere (LS) from 1992 to 2004 above Mahé (4° S, 55° E), Tromelin (15° S, 54° E) and La Réunion (21° S, 55° E) located in the tropical South-West Indian Ocean. The commonly used spectral index value (p≈5/3) of the intrinsic frequency spectrum is used for calculating estimated total energy density in the UT and LS. Estimated total energy density provides good estimation of total energy density in the LS but underestimates total energy density by one half in the UT above Mahé and Tromelin probably due to the activity of near-inertial frequency waves. Estimated total energy density reveals a strong seasonal variability as a function of latitude and convection as an evident active source of GW activity in the LS in austral summer. Above La Réunion, a semi-annual GW activity is observed in the LS with the signature of the subtropical barrier in the UT. Moreover, radiosondes and Raman lidar provide consistent GW surveys in the UT/LS at heights<23 km above La Réunion.

Download Full-text

The Benefits of Global High Resolution for Climate Simulation: Process Understanding and the Enabling of Stakeholder Decisions at the Regional Scale

Bulletin of the American Meteorological Society ◽

10.1175/bams-d-15-00320.1 ◽

2018 ◽

Vol 99 (11) ◽

pp. 2341-2359 ◽

Cited By ~ 44

Author(s):

M. J. Roberts ◽

P. L. Vidale ◽

C. Senior ◽

H. T. Hewitt ◽

C. Bates ◽

...

Keyword(s):

Climate Change ◽

Climate Variability ◽

Time Scales ◽

Climate Models ◽

Water Cycle ◽

Regional Scale ◽

Coupled Model ◽

Convective Precipitation ◽

Climate Simulation ◽

Intergovernmental Panel

AbstractThe time scales of the Paris Climate Agreement indicate urgent action is required on climate policies over the next few decades, in order to avoid the worst risks posed by climate change. On these relatively short time scales the combined effect of climate variability and change are both key drivers of extreme events, with decadal time scales also important for infrastructure planning. Hence, in order to assess climate risk on such time scales, we require climate models to be able to represent key aspects of both internally driven climate variability and the response to changing forcings. In this paper we argue that we now have the modeling capability to address these requirements—specifically with global models having horizontal resolutions considerably enhanced from those typically used in previous Intergovernmental Panel on Climate Change (IPCC) and Coupled Model Intercomparison Project (CMIP) exercises. The improved representation of weather and climate processes in such models underpins our enhanced confidence in predictions and projections, as well as providing improved forcing to regional models, which are better able to represent local-scale extremes (such as convective precipitation). We choose the global water cycle as an illustrative example because it is governed by a chain of processes for which there is growing evidence of the benefits of higher resolution. At the same time it comprises key processes involved in many of the expected future climate extremes (e.g., flooding, drought, tropical and midlatitude storms).

Download Full-text

A Multimodel Assessment of Future Projections of North Atlantic and European Extratropical Cyclones in the CMIP5 Climate Models*

Journal of Climate ◽

10.1175/jcli-d-12-00573.1 ◽

2013 ◽

Vol 26 (16) ◽

pp. 5846-5862 ◽

Cited By ~ 194

Author(s):

Giuseppe Zappa ◽

Len C. Shaffrey ◽

Kevin I. Hodges ◽

Phil G. Sansom ◽

David B. Stephenson

Keyword(s):

Central Europe ◽

North Atlantic ◽

Climate Models ◽

Storm Track ◽

Coupled Model ◽

Extratropical Cyclones ◽

Strong Wind ◽

Wind Speeds ◽

High Emission ◽

Strong Winds

Abstract The response of North Atlantic and European extratropical cyclones to climate change is investigated in the climate models participating in phase 5 of the Coupled Model Intercomparison Project (CMIP5). In contrast to previous multimodel studies, a feature-tracking algorithm is here applied to separately quantify the responses in the number, the wind intensity, and the precipitation intensity of extratropical cyclones. Moreover, a statistical framework is employed to formally assess the uncertainties in the multimodel projections. Under the midrange representative concentration pathway (RCP4.5) emission scenario, the December–February (DJF) response is characterized by a tripolar pattern over Europe, with an increase in the number of cyclones in central Europe and a decreased number in the Norwegian and Mediterranean Seas. The June–August (JJA) response is characterized by a reduction in the number of North Atlantic cyclones along the southern flank of the storm track. The total number of cyclones decreases in both DJF (−4%) and JJA (−2%). Classifying cyclones according to their intensity indicates a slight basinwide reduction in the number of cyclones associated with strong winds, but an increase in those associated with strong precipitation. However, in DJF, a slight increase in the number and intensity of cyclones associated with strong wind speeds is found over the United Kingdom and central Europe. The results are confirmed under the high-emission RCP8.5 scenario, where the signals tend to be larger. The sources of uncertainty in these projections are discussed.

Download Full-text

Assessing the performance of Intergovernmental Panel on Climate Change AR5 climate models in simulating and projecting wind speeds over China

Journal of Geophysical Research Atmospheres ◽

10.1029/2012jd017533 ◽

2012 ◽

Vol 117 (D24) ◽

pp. n/a-n/a ◽

Cited By ~ 32

Author(s):

Lian Chen ◽

S. C. Pryor ◽

Dongliang Li

Keyword(s):

Climate Change ◽

Climate Models ◽

Intergovernmental Panel ◽

Wind Speeds

Download Full-text

Extreme IOD induced tropical Indian Ocean warming in 2020

Geoscience Letters ◽

10.1186/s40562-021-00207-6 ◽

2021 ◽

Vol 8 (1) ◽

Author(s):

Ying Zhang ◽

Yan Du

Keyword(s):

Indian Ocean ◽

Surface Wind ◽

Tropical Indian Ocean ◽

First Record ◽

Early Summer ◽

Wind Anomaly ◽

Surface Warming ◽

Positive Indian Ocean Dipole ◽

Indian Ocean Warming ◽

The 1960S

AbstractThe tropical Indian Ocean (TIO) basin-wide warming occurred in 2020, following an extreme positive Indian Ocean Dipole (IOD) event instead of an El Niño event, which is the first record since the 1960s. The extreme 2019 IOD induced the oceanic downwelling Rossby waves and thermocline warming in the southwest TIO, leading to sea surface warming via thermocline-SST feedback during late 2019 to early 2020. The southwest TIO warming triggered equatorially antisymmetric SST, precipitation, and surface wind patterns from spring to early summer. Subsequently, the cross-equatorial “C-shaped” wind anomaly, with northeasterly–northwesterly wind anomaly north–south of the equator, led to basin-wide warming through wind-evaporation-SST feedback in summer. This study reveals the important role of air–sea coupling processes associated with the independent and extreme IOD in the TIO basin-warming mode, which allows us to rethink the dynamic connections between the Indo-Pacific climate modes.

Download Full-text

Assessing the Quality of Southern Ocean Circulation in CMIP5 AOGCM and Earth System Model Simulations

Journal of Climate ◽

10.1175/jcli-d-19-0263.1 ◽

2019 ◽

Vol 32 (18) ◽

pp. 5915-5940 ◽

Cited By ~ 5

Author(s):

R. L. Beadling ◽

J. L. Russell ◽

R. J. Stouffer ◽

P. J. Goodman ◽

M. Mazloff

Keyword(s):

Southern Ocean ◽

Wind Stress ◽

Ocean Circulation ◽

Climate Models ◽

Dominant Role ◽

Surface Wind ◽

Coupled Model ◽

Observational Uncertainty ◽

Mean State

Abstract The Southern Ocean (SO) is vital to Earth’s climate system due to its dominant role in exchanging carbon and heat between the ocean and atmosphere and transforming water masses. Evaluating the ability of fully coupled climate models to accurately simulate SO circulation and properties is crucial for building confidence in model projections and advancing model fidelity. By analyzing multiple biases collectively across large model ensembles, physical mechanisms governing the diverse mean-state SO circulation found across models can be identified. This analysis 1) assesses the ability of a large ensemble of models contributed to phase 5 of the Coupled Model Intercomparison Project (CMIP5) to simulate observationally based metrics associated with an accurate representation of the Antarctic Circumpolar Current (ACC), and 2) presents a framework by which the quality of the simulation can be categorized and mechanisms governing the resulting circulation can be deduced. Different combinations of biases in critical metrics including the magnitude and position of the zonally averaged westerly wind stress maximum, wind-driven surface divergence, surface buoyancy fluxes, and properties and transport of North Atlantic Deep Water entering the SO produce distinct mean-state ACC transports. Relative to CMIP3, the quality of the CMIP5 SO simulations has improved. Eight of the thirty-one models simulate an ACC within observational uncertainty (2σ) for approximately the right reasons; that is, the models achieve accuracy in the surface wind stress forcing and the representation of the difference in the meridional density across the current. Improved observations allow for a better assessment of the SO circulation and its properties.

Download Full-text

Accelerated warming in the northern midlatitude summer since the 1990s

10.5194/egusphere-egu21-6506 ◽

2021 ◽

Author(s):

Haiyan Teng ◽

Ruby Leung ◽

Grant Branstator ◽

Jian Lu ◽

Qinghua Ding

Keyword(s):

Climate Models ◽

Wave Train ◽

Coupled Model ◽

Wave Model ◽

Warming Trend ◽

Forced Response ◽

Regional Warming ◽

Arctic Regions ◽

Rossby Wave Train ◽

A Chain

The northern midlatitude summer has experienced rapid warming since the 1990s, especially in Europe, Central Siberia-Mongolia, the West Coast of North America as well as several continental Arctic regions. These &#8220;hot spots&#8221; are connected by a chain of high-pressure ridges from an anomalous wavenumber-5 Rossby wave train in the upper troposphere. &#160;Here by cross-examining reanalysis datasets and a suite of Coupled Model Intercomparison Project Phase 6 (CMIP6) baseline experiments, we demonstrate that the anthropogenically forced response may be intertwined with internal multidecadal variability, making it difficult to partition the 1979-2020 trend with state-of-the-art climate models. Instead, we take a &#8220;storyline&#8221; approach with a planetary wave model and sensitivity experiments with an Earth system model to explore key underlying driving factors. Our results highlight the importance of multiscale interaction with synoptic eddy via atmosphere-ocean and atmosphere-land coupling in shaping the multidecadal regional warming trend which has enormous socioeconomic implications.&#160;

Download Full-text

On the decadal scale correlation between African dust and Sahel rainfall: The role of Saharan heat low–forced winds

Science Advances ◽

10.1126/sciadv.1500646 ◽

2015 ◽

Vol 1 (9) ◽

pp. e1500646 ◽

Cited By ~ 21

Author(s):

Weijie Wang ◽

Amato T. Evan ◽

Cyrille Flamant ◽

Christophe Lavaysse

Keyword(s):

Interannual Variability ◽

Climate Models ◽

Surface Wind ◽

Large Body ◽

Dust Emission ◽

Wind Speeds ◽

African Dust ◽

Decadal Scale ◽

Sahelian Rainfall ◽

Heat Low

A large body of work has shown that year-to-year variations in North African dust emission are inversely proportional to previous-year monsoon rainfall in the Sahel, implying that African dust emission is highly sensitive to vegetation changes in this narrow transitional zone. However, such a theory is not supported by field observations or modeling studies, as both suggest that interannual variability in dust is due to changes in wind speeds over the major emitting regions, which lie to the north of the Sahelian vegetated zone. We reconcile this contradiction showing that interannual variability in Sahelian rainfall and surface wind speeds over the Sahara are the result of changes in lower tropospheric air temperatures over the Saharan heat low (SHL). As the SHL warms, an anomalous tropospheric circulation develops that reduces wind speeds over the Sahara and displaces the monsoonal rainfall northward, thus simultaneously increasing Sahelian rainfall and reducing dust emission from the major dust “hotspots” in the Sahara. Our results shed light on why climate models are, to date, unable to reproduce observed historical variability in dust emission and transport from this region.

Download Full-text

Assessing Sting-Jets in Convection-Permitting Climate Simulations

10.5194/egusphere-egu2020-9158 ◽

2020 ◽

Author(s):

Colin Manning ◽

Elizabeth Kendon ◽

Hayley Fowler ◽

Nigel Roberts ◽

Ségolène Berthou

Keyword(s):

Climate Models ◽

Climate Model ◽

Surface Wind ◽

Severity Index ◽

Added Value ◽

Reanalysis Dataset ◽

Objective Indicator ◽

Wind Speeds ◽

Climate Simulations ◽

Strong Winds

This study assesses the added-value offered by a regional convection-permitting climate model (CPM) in its representation of sting-jets (SJs); a mesoscale slanted core of strong winds within a Shapiro-Keyser type of cyclone that can lead to extremely damaging surface wind speeds close to southern side of a cyclone&#8217;s centre. Low-resolution climate models cannot resolve SJs, and so estimates of risk posed by extreme winds due to SJs are difficult to determine and will likely be underestimated in coarse-resolution climate simulations.We analyse three 10-year simulations from the UK Met Office, run at a 2.2km resolution over a European domain. The simulations include a hindcast driven by the ERA-Interim reanalysis dataset (ERAI) for the period 2001-2010, as well as a present day (2001-2010) and future simulation (2100-2109) that follows the RCP8.5 scenario. Both climate simulations are driven by a 25km GCM. To diagnose potential SJ storms in each simulation, we firstly identify cyclone tracks with a cyclone tracking algorithm and apply an objective indicator that identifies the warm seclusion of a Shapiro-Keyser cyclone and the slanted core of strong winds of the sting-jet.Within this presentation, we will present the objective indicator as well as results of the added value seen in the CPM. In order to identify any added value of the CPM, we analyse differences between the CPM and its respective driving data, in terms of storm severity metrics and their future projections. &#160;An example metric used is the Storm Severity Index that quantifies the overall severity of a storm. In all simulations, the conditional PDF of SSI for sting-jet storms is shifted towards higher values compared to PDF of the SSI from all storms within the studied domain. However, we see little difference in the SSI derived from the CPM and its respective driving model/reanalysis when CPM wind speeds are upscaled to the respective driving reanalysis/GCM grid. In further analysis, we will look to explore the added value at a local scale on the native CPM grid.

Download Full-text