Workshop: Stratospheric predictability and impact on the troposphere
Session
Stratospheric Gravity-Wave Charatceristics in a Multi-Year Climatology over the Southern Hemisphere from 3-D Satellite Observations and Spectral Analyses.
Neil P. Hindley, Corwin J. Wright, Lars Hoffmann, Nicholas J. Mitchell
Atmospheric gravity waves play a key role in the coupling of different layers of the Earth’s atmosphere, acting as crucial drivers of the atmospheric circulation...
Simon H. Lee$^{1}$, Andrew J. Charlton-Perez$^{1}$, Jason C. Furtado$^{2}$, Steven J. Woolnough$^{3,1}$
$^{1}$ Department of Meteorology, University of Reading
$^{2}$ School of Meteorology, University of Oklahoma
$^{3}$ National Centre for Atmospheric Science, University of Reading
The sudden stratospheric warming (SSW) of 12 February 2018 was not forecast by any extended-range...
This study investigates the role of the eleven-year solar cycle on the Arctic climate during 1979–2016. It reveals that during those years, when the winter solar sunspot number (SSN) falls below 1.35 standard deviations (or mean value), the Arctic warming extends from the lower troposphere to high up in the upper stratosphere and vice versa when SSN is above. The warming in the atmospheric...
Convective sources are coupled to the Multi-Scale Gravity Wave Model (MS-GWaM) implemented in the upper atmosphere version of ICON to represent spatio-temporal variability and intermittency in parameterized gravity waves (GWs) in the model. The convective sources considered here have horizontal scales of a few kilometers, and GWs forced by these have horizontal wavelengths of 10–500 km....
Influence of stratospheric circulation changes related to sudden stratospheric warmings (SSW) on the tropical troposphere have been examined in many previous studies. However, due to small sample size of SSW and large internal variability in the tropical troposphere, influence of the SSW on the tropical troposphere is still uncertain. We examine impact of the stratospheric circulation changes...
Using the real-time predictions before the February 2018 and January 2019 stratospheric sudden warmings (SSWs) from 11 sub-seasonal to seasonal models, this study analyzes the prediction of the downward propagation and surface impact of these two SSWs. These two SSWs differed both in the type of SSW warming (2018: vortex split; 2019: displacement), and in their magnitude (the former being...
Abstract:
Transport of potential vorticity and Eliassen-Palm fluxes. Analysis and diagnostic of PV data from the stratosphere and upper troposphere. Applying the divergence of the Eliassen-Palm-Vector to mid- and long-term forecasts and together with seasonal variations of eddy fluxes of PV, heat and momentum in the stratosphere/ upper troposphere estimation and prognosis of sub-seasonal...
El Niño Southern Oscillation (ENSO) can exert a remote impact on North Atlantic and
European (NAE) winter climate. This teleconnection is influenced by the superposition and interaction of different pathways. In this study, we focus on the stratospheric and tropospheric pathways through the North Pacific. Due to potential non-linear and non-stationary behavior and due to the limited time...
The Madden-Julian Oscillation (MJO), an organized eastward propagating source of enhanced convection, acts as a Rossby wave source and as a global tropical driver of predictability. The pathway from the MJO to the stratosphere is known to be primarily driven by poleward and vertical Rossby wave propagation and persists for over a month. It has been shown that after MJO phase 7, warm anomalies...
The effect of unresolved gravity waves which play a crucial role for accurate numerical weather prediction (NWP) is parametrized separately as subgrid-scale orography (SSO) parametrization and non-orographic gravity waves (NGW) parametrization in global models. These parametrizations are known for large uncertainties due to lack of direct observations of momentum flux. However, it is still...
This study presents a numerical analysis of the ship wave gravity wave (GW) event observed over Auckland Island during the 2014 DEEPWAVE Campaign, as reported in Fritts et al., 2016, Pautet et al., 2016, and Eckermann et al., 2016. The event is simulated using the 3D, compressible EULAG model to evaluate 1. the stratospheric conditions that enable deep orographic GW propagation up to the...
Sudden stratospheric warmings (SSWs) are one of the most extreme phenomena in the atmosphere. They are associated with an abrupt increase in polar stratospheric temperature, preceded by the reversal or deceleration of zonal winds. Although they are stratospheric phenomena, the effects of SSWs extend from troposphere to ionosphere. These phenomena can trigger extreme winter events in surface...
The trend analysis needs homogenous datasets without any artificial breakpoints. The aim of this study is a detection of breakpoints in the temperature time series from the MERRA -2 and ERA 5 reanalyses with the help of the Pettit homogeneity test for all pressure layers above 500 hPa in December, January and February. We are looking for grid points where these breakpoints occur and also for...
Observational impacts of satellite data assimilation on extended-range forecasts of sudden stratospheric warmings (SSWs) are investigated by conducting ensemble reforecast experiments starting from the Japanese novel reanalysis products: the Japanese 55-year reanalysis (JRA-55) and its equivalent assimilating conventional observations only (JRA-55C). A comparative examination on the...
It is concluded, from piecewise potential vorticity (PV) inversion in isentropic coordinates (Hinssen et al., 2011), that changes in the stratospheric potential vorticity distribution, associated with a Sudden Stratospheric Warming (SSW), may result in substantially less westerly or more easterly winds in the mid-troposphere at middle to high latitudes. During a major SSW, such as the major...
Version 15 of the NCEP Global Forecast System (GFS) was implemented into operation on June 12, 2019. The spectral dynamic core, which had been in use by NCEP global forecast models in the past few decades was replaced by the GFDL Finite¬ Volume Cubed-Sphere Dynamical Core (FV3). Major changes in model physics include the replacement of Zhao-Carr microphysics with the GFDL microphysics,...
Using multiple data sources, favorable conditions for the 2019 New Year SSW event and its predictive skill from 11 sub-seasonal to seasonal (S2S) forecast models are explored in this study. This mixeddisplacement-type (displacement to split) SSW event occurred under moderate El Niño conditions in the Pacific, easterly quasi-biennial oscillation (QBO) winds, collaborated with solar cycle...
Gravity waves play an important role in upper tropospheric and stratospheric dynamics but are largely unresolved in GCMs. Instead, the effects of gravity waves of small scales and high frequencies in models are parameterized. Small scale, high-frequency gravity waves in the lower stratosphere can be observed in superpressure balloon (SPB) flights, but SPB studies have traditionally been able...
The ability to seasonally forecast the Quasi-Biennial Oscillation (QBO) was examined using NASA S2S (Sub-seasonal to Seasonal), 9-month, retrospective forecasts. Analysis of these QBO forecasts demonstrated that the S2S model has skill in predicting the QBO amplitude and phase over a simple QBO phase propagation model at forecast lead times of 1 to 3 months. Results from an initial assessment...
Subseasonal forecasts of Northern Hemisphere (NH) extratropical winter weather patterns remain a large challenge for the forecasting community. Previous studies have looked to the individual influence of two key modes of climate variability – the Madden-Julian Oscillation (MJO) and the strength / orientation of stratospheric polar vortex (SPV) – on changing the NH polar jet stream and...
Midwinter sudden stratospheric warmings (SSWs), characterised by the reversal of the temperature gradient poleward of 60°N and the 10 hPa climatological zonal mean wind from westerly to easterly at 60°N, are known to have pronounced impacts on tropospheric circulation which lead to regional changes in temperature, precipitation and other meteorological variables. Such abrupt events are...
The stratosphere can have a substantial impact on surface weather in winter, in particular during stratospheric extreme events, so-called sudden stratospheric warming (SSW) events. The tropospheric response tends to dominate in the Atlantic basin and is characterized by a significant equatorward shift of the tropospheric jet stream over the North Atlantic, leading to a change in weather...
The aim of the presented work is to improve the parameterization of sub-grid scale gravity wave (GW) effects on the resolved flow in atmospheric models in a large altitude range from the upper troposphere ($\sim5km$) to the lower thermosphere ($\sim110km$). State of the art GW parameterization schemes are using the steady-state approximation for the wave field and therefore assume an...
The large-scale circulation of the stratosphere is affected by increasing greenhouse gas concentrations in various ways. The meridional transport circulation of the stratosphere is projected to speed-up in a future climate, and the strength of the winter polar vortex is projected to decrease in the northern hemisphere, but increase in strength in the southern hemisphere. In the current study,...
Sudden Stratospheric Warming (SSW) events during the Northern Hemisphere winter and shoulder seasons are investigated using a 300-year run of the Whole Atmosphere Community Climate Model (WACCM). This model features relatively fine vertical resolution in key regions of the stratosphere, and the multi-century run provides far more SSW events than are seen in the observations, allowing for more...