The Climatological Effect of Saharan Dust on Global Tropical Cyclones in a Fully Coupled GCM

The global analyses and medium range forecasts from the European Centre for Medium range Weather Forecasts rely on a state-of-the-art Numerical Weather Prediction (NWP) system. To best represent the air-sea exchanges, it is tightly coupled to an ocean wave model.&#160; As part of ECMWF approach to Earth System Model, it is also coupled to a global ocean model for all its forecasting systems from the medium range up to the seasonal time scale.Because the feedback from and to the ocean can be significant, it is only in the fully coupled system that parameterisation for air-sea processes should be revisited. For instance, it is now accepted that the drag coefficient should generally attained maximum values for storm winds but should level or even decrease for very strong winds, namely in tropical cyclones or intense mid-latitude wind storms.A modification of the wind input source was tested, whereby the Charnock coefficient estimated by the wave model and therefore the drag coefficient sharply reduce for large winds (> 30 m/s). As a consequence, ECMWF tendency to under predict strong tropical cyclones was sharply alleviated, in better agreement with observational evidence. This change is now planned for operational implementation with the next model cycle (CY47R1, June 2020).Experimental evidences also point to a sea state/wind dependency of the heat and moisture fluxes.&#160; Following an extension of the wind wave generation theory, a sea state dependent parameterisation for the roughness length scales for heat and humidity has been tested. Again, a proper assessment of the different parameterisations warrants the fully coupled system. Experimentations so far indicate the benefit of such change. Ongoing work aims at future operational implementation.

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The role of ocean dynamics in tropical Pacific SST response to warm climate in a fully coupled GCM

Geophysical Research Letters ◽

10.1029/2007gl033097 ◽

2008 ◽

Vol 35 (8) ◽

Cited By ~ 8

Author(s):

Changfang Fang ◽

Lixin Wu

Keyword(s):

Tropical Pacific ◽

Ocean Dynamics ◽

Warm Climate ◽

Coupled Gcm ◽

Fully Coupled

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Impacts of Saharan Dust on Atlantic Regional Climate and Implications for Tropical Cyclones

Journal of Climate ◽

10.1175/jcli-d-16-0776.1 ◽

2018 ◽

Vol 31 (18) ◽

pp. 7621-7644 ◽

Cited By ~ 12

Author(s):

Bowen Pan ◽

Yuan Wang ◽

Jiaxi Hu ◽

Yun Lin ◽

Jen-Shan Hsieh ◽

...

Keyword(s):

Tropical Cyclones ◽

Wind Shear ◽

Large Scale ◽

Hydrological Cycle ◽

Regional Climate ◽

Vertical Wind Shear ◽

Saharan Dust ◽

Specific Humidity ◽

Shortwave Radiation ◽

Cloud Formation

The radiative and microphysical properties of Saharan dust are believed to impact the Atlantic regional climate and tropical cyclones (TCs), but the detailed mechanism remains uncertain. In this study, atmosphere-only simulations are performed from 2002 to 2006 using the Community Atmospheric Model, version 5.1, with and without dust emission from the Sahara Desert. The Saharan dust exhibits noticeable impacts on the regional longwave and shortwave radiation, cloud formation, and the convective systems over West Africa and the tropical Atlantic. The African easterly jet and West African monsoon are modulated by dust, leading to northward shifts of the intertropical convergence zone and the TC genesis region. The dust events induce positive midlevel moisture and entropy deficit anomalies, enhancing the TC genesis. On the other hand, the increased vertical wind shear and decreased low-level vorticity and potential intensity by dust inhibit TC formation in the genesis region. The ventilation index shows a decrease in the intensification region and an increase in the genesis region by dust, corresponding to favorable and unfavorable TC activities, respectively. The comparison of nondust scenarios in 2005 and 2006 shows more favorable TC conditions in 2005 characterized by higher specific humidity and potential intensity, but lower ventilation index, wind shear, and entropy deficit. Those are attributable to the observed warmer sea surface temperature (SST) in 2005, in which dust effects can be embedded. Our results imply significant dust perturbations on the radiative budget, hydrological cycle, and large-scale environments relevant to TC activity over the Atlantic.

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When Does the Saharan Air Layer Impede the Intensification of Tropical Cyclones?

Journal of Climate ◽

10.1175/jcli-d-19-0854.1 ◽

2020 ◽

Vol 33 (24) ◽

pp. 10609-10626

Author(s):

W. T. K. Huang ◽

C. Schnadt Poberaj ◽

B. Enz ◽

C. Horat ◽

U. Lohmann

Keyword(s):

Tropical Cyclones ◽

North Atlantic Ocean ◽

Negative Impact ◽

Saharan Dust ◽

Air Masses ◽

Saharan Air Layer ◽

The North ◽

Weak Negative Correlation ◽

Central Atlantic ◽

Hurricane Tracking

AbstractWe investigate the circumstances under which the Saharan air layer (SAL) has a negative impact on the intensification of tropical cyclones (TCs) over the North Atlantic Ocean. Using hurricane tracking, aerosol optical depth (AOD) data, and meteorological analyses, we analyze the interaction of the SAL with 52 named TCs that formed over the east and central Atlantic south of the Cape Verde islands between 2004 and 2017. Following the categorization of negative SAL influences on TC intensification by Dunion and Velden, only 21% of the investigated storms can be classified (28% of all storms that encountered the SAL), and 21% of the storms continue to intensify despite the presence of the SAL. We show that among TCs that encounter the SAL, there is evidence supporting a weak negative correlation between the magnitude of TC intensification and the ambient AOD. However, above-average Saharan dust abundance in the vicinity of TCs is not a good independent indicator for storm nonintensification. To better understand the specific processes involved, a composite study is carried out, contrasting storms that intensify in the presence of the SAL against those that do not. We find that sheared air masses on the north side and drier air from the northeast of the storm early on during its lifetime, in addition to higher AOD, are associated with TC nonintensification in proximity to the SAL.

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Faculty Opinions recommendation of “Sunshade World”: A fully coupled GCM evaluation of the climatic impacts of geoengineering.

Faculty Opinions – Post-Publication Peer Review of the Biomedical Literature ◽

10.3410/f.1115681.571749 ◽

2008 ◽

Author(s):

Barry Brook

Keyword(s):

Coupled Gcm ◽

Climatic Impacts ◽

Fully Coupled

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A fully coupled GCM simulation of the climate of the mid-Holocene

Geophysical Research Letters ◽

10.1029/97gl03721 ◽

1998 ◽

Vol 25 (3) ◽

pp. 361-364 ◽

Cited By ~ 108

Author(s):

Chris D. Hewitt ◽

John F. B. Mitchell

Keyword(s):

Coupled Gcm ◽

Fully Coupled

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Influence of Saharan dust on Atlantic tropical cyclones

10.5194/acp-2020-761 ◽

2020 ◽

Author(s):

Zhenxi Zhang ◽

Wen Zhou

Keyword(s):

Tropical Cyclones ◽

North Atlantic ◽

Radiative Forcing ◽

Saharan Dust ◽

Tropical Atlantic ◽

Atmospheric Moisture ◽

The North ◽

The North Atlantic ◽

Atlantic Itcz ◽

Atlantic Tropical Cyclone

Abstract. The influence of Saharan dust outbreaks on summertime Atlantic tropical cyclone (TC) activity is explored using continuous atmospheric reanalysis products and TC track data from 1980 to 2019. Analyses reveal that the Saharan dust plume over the tropical Atlantic can affect TC activity by affecting the atmospheric hydrology and radiation absorbed by the earth's surface, which can be classified into three mechanisms. (1) A strong Saharan dust plume indirectly induces the reduction of atmospheric moisture, which further suppresses TC track, number of TC days, and intensity, with the influence covering the whole tropical Atlantic. (2) A strong Saharan dust plume enhances atmospheric moisture just along the North Atlantic ITCZ through the dust microphysical effect, which further promotes TC activity along 10º N latitude in June. (3) The climatological influence of dust on TC activity is caused by the strong radiative forcing of Saharan dust over the eastern tropical Atlantic in June, which produces an evident reduction in SST and lessens the duration and intensity of regional TC activity in June, according to the 40-yr average from 1980 to 2019.

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Improving Regional Model Skills During Typhoon Events: A Case Study for Super Typhoon Lingling Over the Northwest Pacific Ocean

Frontiers in Marine Science ◽

10.3389/fmars.2021.613913 ◽

2021 ◽

Vol 8 ◽

Author(s):

Delei Li ◽

Joanna Staneva ◽

Jean-Raymond Bidlot ◽

Sebastian Grayek ◽

Yuchao Zhu ◽

...

Keyword(s):

Wind Speed ◽

Pacific Ocean ◽

Tropical Cyclones ◽

Large Scale ◽

Northwest Pacific ◽

Surface Drag ◽

Momentum Exchange ◽

Northwest Pacific Ocean ◽

The Northwest Pacific Ocean ◽

Fully Coupled

The ability of forecasting systems to simulate tropical cyclones is still insufficient, and currently, there is an increased interest in improving model performance for intense tropical cyclones. In this study, the impact of reducing surface drag at high wind speeds on modeling wind and wave conditions during the super Typhoon Lingling event over the northwest Pacific Ocean in 2019 is investigated. The model response with respect to the parameterization for momentum exchange at the ocean surface is demonstrated using a fully coupled regional atmosphere model (the Consortium for Small-Scale Modeling-Climate Limited-area Modeling, CCLM) and a wind wave model (WAM). The active two-way coupling between the atmosphere and ocean waves model is enabled through the introduction of sea state-dependent surface drag into the CCLM and updated winds into the WAM. The momentum exchange with the sea surface is modeled via the dependency of the roughness length (Z0) on the surface stress itself and, when applicable, on the wind speed. Several high-resolution runs are performed using one-way or two-way fully coupled regional atmosphere-wave (CCLM-WAM) models. The model simulations are assessed against the best track data as well as against buoy and satellite observations. The results show that the spectral nudging technique can improve the model’s ability to capture the large-scale circulation, track and intensity of Typhoon Lingling at regional scales. Under the precondition of large-scale constraining, the two-way coupling simulation with the proposed new roughness parameterization performs much better than the simulations used in older studies in capturing the maximum wind speed of Typhoon Lingling due to the reduced drag at extreme wind conditions for the new Z0.

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