Resolved Convection Improves the Representation of Equatorial Waves and Tropical Rainfall Variability in a Global Nonhydrostatic Model

Tropical rainfall variability is closely linked to meridional shifts of the Intertropical Convergence Zone (ITCZ) and zonal movements of the Walker circulation. The characteristics and mechanisms of tropical rainfall variations on centennial to decadal scales are, however, still unclear. Here, we reconstruct a replicated stalagmite-based 2,700-y-long, continuous record of rainfall for the deeply convective northern central Indo-Pacific (NCIP) region. Our record reveals decreasing rainfall in the NCIP over the past 2,700 y, similar to other records from the northern tropics. Notable centennial- to decadal-scale dry climate episodes occurred in both the NCIP and the southern central Indo-Pacific (SCIP) during the 20th century [Current Warm Period (CWP)] and the Medieval Warm Period (MWP), resembling enhanced El Niño-like conditions. Further, we developed a 2,000-y-long ITCZ shift index record that supports an overall southward ITCZ shift in the central Indo-Pacific and indicates southward mean ITCZ positions during the early MWP and the CWP. As a result, the drying trend since the 20th century in the northern tropics is similar to that observed during the past warm period, suggesting that a possible anthropogenic forcing of rainfall remains indistinguishable from natural variability.

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Disentangling the mechanisms of wave-convection coupling in the tropics

10.5194/egusphere-egu2020-17026 ◽

2020 ◽

Author(s):

Corinna Hoose ◽

Hyunju Jung ◽

Peter Knippertz ◽

Tijana Janjic ◽

Yvonne Ruckstuhl ◽

...

Keyword(s):

Data Assimilation ◽

General Circulation ◽

Rainfall Variability ◽

Weather Prediction ◽

Equatorial Waves ◽

Model Errors ◽

Grid Spacing ◽

Budget Analysis ◽

The Tropics ◽

Horizontal Grid

Tropical weather prediction remains one of the main challenges in atmospheric science due to a combination of insufficient observations, data assimilation algorithms optimized for midlatitudes and large model errors.&#160;Due to a strong dependency of many people in the tropics on rainfall variability, combined with a high vulnerability, improved precipitation forecasts have the potential to create substantial benefits in areas such as agriculture, water management, energy production and disease prevention.Recent studies found that the coupling of equatorial waves&#160;to convection is key to improving weather forecasts in the tropics on the synoptic to subseasonal timescale but many models struggle to realistically represent this coupling. Here we use aquaplanet simulations with the ICOsahedral Nonhydrostatic (ICON) model with a 13 km horizontal grid spacing to study the underlying mechanisms of convectively coupled equatorial waves in an idealized framework. We filter the divergence at 200 hPa using a standard wave filtering tool tapering to zero that allows us to identify dynamical characteristics of convectively coupled waves in our simulations. To diagnose thermodynamical aspects of wave-convection couplings, we compare the obtained waves to the total precipitable water and analyze the spatial variance of the budget analysis for column-integrated moist static energy. The same filtering tool and diagnostics are carried out on a realistic ICON simulation with a 2.5 km horizontal grid spacing from the DYnamics of the Atmospheric general circulation Modeled On Non-hydrostatic Domains (DYAMOND) project.In the future we plan to run and analyze idealized tropical channel simulations with 2.5 km horizontal resolution, i.e. using the same grid spacing as in the DYAMOND simulation. The comparison between the idealized and the realistic simulations identifies mechanisms&#160;of wave-convection coupling. In addition, we will apply this set of diagnostics to forecast experiments using different approaches of data assimilation.&#160;

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Tropical rainfall variability — The agroclimatic impact

Agriculture and Environment ◽

10.1016/0304-1131(82)90003-0 ◽

1982 ◽

Vol 7 (2) ◽

pp. 135-148 ◽

Cited By ~ 10

Author(s):

S. Nieuwolt

Keyword(s):

Rainfall Variability ◽

Tropical Rainfall

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Late Quaternary moisture export across Central America and to Greenland: evidence for tropical rainfall variability from Costa Rican stalagmites

Quaternary Science Reviews ◽

10.1016/j.quascirev.2009.09.018 ◽

2009 ◽

Vol 28 (27-28) ◽

pp. 3348-3360 ◽

Cited By ~ 21

Author(s):

Matthew S. Lachniet ◽

Leah Johnson ◽

Yemane Asmerom ◽

Stephen J. Burns ◽

Victor Polyak ◽

...

Keyword(s):

Central America ◽

Late Quaternary ◽

Rainfall Variability ◽

Costa Rican ◽

Tropical Rainfall

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Exploring Temporal Rainfall Variability and Trends Over a Tropical Region Using Tropical Rainfall Measurement Mission (TRMM) and Observatory Data

Hydrospatial Analysis ◽

10.21523/gcj3.2021050202 ◽

2021 ◽

Vol 5 (2) ◽

pp. 56-71

Author(s):

Anu David Raj ◽

K. R. Sooryamol ◽

Aju David Raj

Keyword(s):

Time Scales ◽

Water Resource Management ◽

Rainfall Variability ◽

Winter Season ◽

India Meteorological Department ◽

Southwest Monsoon ◽

Rainfall Data ◽

Tropical Rainfall Measurement Mission ◽

Tropical Rainfall ◽

Observatory Data

Kerala is the gateway of the Indian southwest monsoon. The Tropical Rainfall Measurement Mission (TRMM) rainfall data is an efficient approach to rainfall measurement. This study explores the temporal variability in rainfall and trends over Kerala from 1998-2019 using TRMM data and observatory data procured from India Meteorological Department (IMD). Direct comparison with observatory data at various time scales proved the reliability of the TRMM data (monthly, seasonal and annual). The temporal rainfall converted by averaging the data on an annual, monthly and seasonal time scale, and the results have confirmed that the rainfall estimated based on satellite data is dependable. The station wise comparison of rainfall in monsoon season provides satisfactory results. However, estimation of rainfall in mountainous areas is challenging task using the TRMM. In the basins of humid tropical regions, TRMM data can be a valuable source of rainfall data for water resource management and monitoring with some vigilance. In Kerala, the study found an insignificant increase in the southwest monsoon and winter season rainfall during last two decades. The rainfall over Kerala showed uncertainty in the distribution of monthly, seasonal and yearly time scales. This study provides a preview of recent weather patterns that would enable us to make better decisions and improve public policy against climate change.

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Validation of Satellite Estimates (Tropical Rainfall Measuring Mission, TRMM) for Rainfall Variability over the Pacific Slope and Coast of Ecuador

Water ◽

10.3390/w10020213 ◽

2018 ◽

Vol 10 (2) ◽

pp. 213 ◽

Cited By ~ 13

Author(s):

Bolívar Erazo ◽

Luc Bourrel ◽

Frédéric Frappart ◽

Oscar Chimborazo ◽

David Labat ◽

...

Keyword(s):

Rainfall Variability ◽

Tropical Rainfall Measuring Mission ◽

Tropical Rainfall ◽

The Pacific ◽

Pacific Slope

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Comparison of forecasting accuracy for Madden Julian Oscillation (MJO) and Convectively Coupled Equatorial Waves (CCEW) using Tropical Rainfall Measuring Mission (TRMM) and ERA-Interim precipitation forecast data for Indonesia

10.20937/atm.53009 ◽

2021 ◽

Author(s):

Ida Pramuwardani ◽

Hartono ◽

Sunarto ◽

Arhasena Sopaheluwakan

Keyword(s):

Tropical Rainfall Measuring Mission ◽

Forecast Model ◽

Precipitation Forecast ◽

Poor Correlation ◽

Equatorial Waves ◽

Madden Julian Oscillation ◽

Tropical Rainfall ◽

Convectively Coupled Equatorial Waves ◽

Zonal Wavenumber ◽

Forecast Data

Tropical Rainfall Measuring Mission (TRMM) and ERA-Interim forecast data analyzed using second-order autoregressive AR(2) and space-time-spectra analysis methods (respectively) revealed contrasting results for predicting Madden Julian Oscillation (MJO) and Convectively Coupled Equatorial Waves (CCEW) phenomena over Indonesia. This research used the same 13-year series of daily TRMM 3B42 V7 derived datasets and ERA-Interim reanalysis model datasets from the European Center for Medium-Range Weather Forecasts (ECMWF) for precipitation forecasts. Three years (2016 to 2018) of the filtered 3B42 and ERA-Interim forecast data was then used to evaluate forecast accuracy by looking at correlation coefficients for forecast leads from day +1 through day +7. The results revealed that rainfall estimation data from 3B42 provides better results for the shorter forecast leads, particularly for MJO, equatorial Rossby (ER), mixed Rossby-gravity (MRG), and inertia-gravity phenomena in zonal wavenumber 1 (IG1), but gives poor correlation for Kelvin waves for all forecast leads. A consistent correlation for all waves was achieved from the filtered ERA-Interim precipitation forecast model, and although this was quite weak for the first forecast leads it did not reach a negative correlation in the later forecast leads except for IG1. Furthermore, Root Mean Square Error (RMSE) was also calculated to complement forecasting skills for both data sources, with the result that residual RMSE for the filtered ERA-Interim precipitation forecast was quite small during all forecast leads and for all wave types. These findings prove that the ERA-Interim precipitation forecast model remains an adequate precipitation model in the tropics for MJO and CCEW forecasting, specifically for Indonesia.

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Tropical Rainfall Variability Accompanying Global Normal Mode Oscillations

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-20-0288.1 ◽

2021 ◽

Author(s):

Takatoshi Sakazaki

Keyword(s):

Normal Mode ◽

Amazon Basin ◽

Rainfall Variability ◽

Normal Modes ◽

Low Frequency ◽

Phase Relationship ◽

Moisture Flux ◽

Tropical Rainfall ◽

Zonal Wavenumber ◽

Rainfall Variations

AbstractUsing global precipitation datasets (GSMaP, TRMM) and the latest reanalysis data (ERA5) we performed a comprehensive analysis of the tropical rainfall variability that accompanies global-scale, low-frequency normal modes: Rossby, Rossby-gravity and Kelvin modes. Cross spectral analysis and lag-regression analysis both showed that coherent rainfall variations accompany not only the wavenumber 1 gravest Rossby mode (“5 day” wave) but other low-frequency modes. The normal mode rainfall variations are enhanced in regions such as the Amazon basin, but also include circumglobally travelling structures with substantial amplitude over the open ocean. These results are remarkably consistent among the three datasets including even ERA5 rainfall data. The circumglobal rainfall signals may be considered primarily as a response to the normal mode dynamical variations. We found that the phase relationship between rainfall and dynamical field variability is strongly dependent on the type of mode and even on the zonal wavenumber. We suggest that this is explained by the difference in relative importance of two underlying processes: (1) moisture-flux convergence and (2) rainfall enhancement associated with adiabatic cooling. Our determined rainfall signals are the response to quasi-monochromatic, periodic waves that have a simple vertical structure and represent one special case of tropospheric wave-rainfall coupling. Implications for the mechanism of 12-hr rainfall oscillations believed to be forced by the atmospheric tide are also considered.

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Tropical rainfall linked to stronger future ENSO-NAO teleconnection in CMIP5 models

10.5194/egusphere-egu21-8425 ◽

2021 ◽

Author(s):

David Fereday ◽

Rob Chadwick ◽

Jeff Knight ◽

Adam Scaife

Keyword(s):

Southern Oscillation ◽

Rainfall Variability ◽

Storm Track ◽

Polar Vortex ◽

Cmip5 Models ◽

Stratospheric Polar Vortex ◽

Tropical Rainfall ◽

The Pacific ◽

Downward Influence ◽

The Caribbean

The El Ni&#241;o-Southern Oscillation (ENSO) has previously been shown to influence the winter North Atlantic Oscillation (NAO).&#160; In this presentation we investigate the ENSO-NAO teleconnection in historical and RCP8.5 scenario CMIP5 simulations, and show a future strengthening of the teleconnection under RCP8.5. &#160;The teleconnection strength is associated with increased tropical east Pacific rainfall variability. &#160;Stratospheric and tropospheric teleconnection pathways are examined, with both pathways having stronger links in future. &#160;The stratospheric pathway involves the Aleutian Low and the stratospheric polar vortex, with a downward influence on the NAO. &#160;This pathway is clearest in the high-top models that better resolve the stratosphere. &#160;The tropospheric pathway is driven by the Pacific subtropical jet strengthening and extending further into the Atlantic in future, generating increased baroclinicity in the Caribbean and influencing the Atlantic storm track.&#160; Our results suggest increasing influence of tropical rainfall on extratropical circulation in future.

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