The Northeast China Persistent Drought in Spring-Summer of 2017: Joint Roles of Teleconnection and Land-atmosphere Coupling

2020 ◽  
Author(s):  
dingwen zeng ◽  
xing yuan
Keyword(s):  
Rossby Wave ◽  
Northeast China ◽  
Wave Train ◽  
Arctic Sea Ice ◽  
Height Anomaly ◽  
Drought Event ◽  
Coupling Index ◽  
Persistent Drought ◽  
Dry Coupling ◽  
Rossby Wave Train

<p>Northeast China (NEC) suffered its worst persistent drought event in recent decades from March to July of 2017 with devastating impacts on the environment and agriculture. Previous drought mechanism studies focused on the atmospheric remote response to Arctic sea ice and ENSO, while less attention was paid to synergistic effects of large-scale teleconnections and local land-atmosphere coupling. Here we show that a strong positive phase of Arctic Oscillation in March triggered the NEC drought, and a quasi-stationary Rossby wave train maintained the drought with an anticyclone located over the area south to Lake Baikal (ASLB) in April-July. By using a land-atmosphere coupling index based on the persistence of positive feedback between boundary layer and land surface, we find that the NEC and ASLB experienced a wet coupling in March while a persistently strengthened dry coupling in April-July. Over ASLB, the dry coupling and sinking motion increased surface sensible heat, decreased cloud cover, and weakened longwave absorption, resulting in a diabatic heating anomaly in the lower atmosphere and a diabatic cooling anomaly in the upper atmosphere. This anomalous vertical heating profile generated a negative anomaly of potential vorticity, indicating that the land-atmosphere coupling had a phase-lock effect on the Rossby wave train originating from upstream areas, and therefore maintained the NEC drought over downstream regions. Numerical simulations with and without surface sensible heating are being conducted to verify the influence of teleconnected land-atmosphere coupling, i.e., dry land conditions over ASLB in May can cause positive height anomaly over ASLB and NEC during June-July through heating the low level atmosphere. Our study suggests that upstream quasi-stationary wave pattern strengthened by land-atmosphere coupling should be considered in diagnosing persistent droughts especially over northern mid-latitudes.</p>

scholarly journals Effect of Teleconnected Land–Atmosphere Coupling on Northeast China Persistent Drought in Spring–Summer of 2017

2019 ◽  
Vol 32 (21) ◽  
pp. 7403-7420 ◽  
Author(s):  
Dingwen Zeng ◽  
Xing Yuan ◽  
Joshua K. Roundy
Keyword(s):  
Rossby Wave ◽  
Land Surface ◽  
Northeast China ◽  
Large Scale ◽  
Wave Train ◽  
Lower Atmosphere ◽  
The Arctic ◽  
Severe Drought ◽  
Coupling Index ◽  
Dry Coupling

Northeast China (NEC) suffered a severe drought that persisted from March to July of 2017 with profound impacts on agriculture and society, raising an urgent need to understand the mechanism for persistent droughts over midlatitudes. Previous drought mechanism studies focused on either large-scale teleconnections or local land–atmosphere coupling, while less attention was paid to their synergistic effects on drought persistence. Here we show that the 2017 NEC drought was triggered by a strong positive phase of the Arctic Oscillation in March, and maintained by the anticyclone over the area south to Lake Baikal (ASLB) through a quasi-stationary Rossby wave in April–July, accompanied by sinking motion and north wind anomaly. By using a land–atmosphere coupling index based on the persistence of positive feedbacks between the boundary layer and land surface, we find that the coupling states over NEC and ASLB shifted from a wet coupling in March to a persistently strengthened dry coupling in April–July. Over ASLB, the dry coupling and sinking motion increased surface sensible heat, decreased cloud cover, and weakened longwave absorption, resulting in a diabatic heating anomaly in the lower atmosphere and a diabatic cooling anomaly in the upper atmosphere. This anomalous vertical heating profile led to a negative anomaly of potential vorticity at low levels, indicating that the land–atmosphere coupling had a phase-lock effect on the Rossby wave train originating from upstream areas, and therefore maintained the NEC drought over downstream regions. Our study suggests that an upstream quasi-stationary wave pattern strengthened by land–atmosphere coupling should be considered in diagnosing persistent droughts, especially over northern midlatitudes.

scholarly journals Multi-model assessment of the late-winter stratospheric response to El Niño and La Niña

2021 ◽  
Author(s):  
Bianca Mezzina ◽  
Froila M. Palmeiro ◽  
Javier García-Serrano ◽  
Ileana Bladé ◽  
Lauriane Batté ◽  
...  
Keyword(s):  
Rossby Wave ◽  
Geopotential Height ◽  
Lower Stratosphere ◽  
Wave Train ◽  
Height Anomaly ◽  
Late Winter ◽  
Model Assessment ◽  
Polar Cap ◽  
Rossby Wave Train ◽  
The Impact

<p>The impact of El Niño-Southern Oscillation (ENSO) on the late-winter extra-tropical stratosphere (January-March) is assessed in a multi-model framework. Three state-of-the-art atmospheric models are run with prescribed SST anomalies representative of a strong ENSO event, with symmetric patterns for El Niño and La Niña. The well-known temperature perturbation in the lower stratosphere during El Niño is captured by two models, in which the anomalous warming at polar latitudes is accompanied by a positive geopotential height anomaly that extends over the polar cap. In the third model, which shows a lack of temperature anomalies over the pole, the anomalous anticyclone is confined over Canada and does not expand to the polar cap. This anomalous center of action emerges from the large-scale tropospheric Rossby wave train forced by ENSO, and conservation of potential vorticity around the polar vortex is invoked to link it to the temperature response. No disagreement across models is found in the lower stratosphere for La Niña, whose teleconnection is opposite in sign but weaker. In the middle-upper stratosphere (above 50 hPa) the geopotential height anomalies project on a wavenumber-1 (WN1) pattern for both El Niño and, more weakly, La Niña, and show a westward tilt with height up to the stratopause. It is suggested that this WN1 pattern arises from the high-latitude lower-stratospheric anomalies, and that the ENSO teleconnection to the polar stratosphere can be interpreted in terms of upward propagation of the stationary Rossby wave train and quasi-geostrophic balance, instead of wave breaking. <br>The multi-model assessment, with 50 members for each experiment, contributes to the ERA4CS-funded MEDSCOPE project and includes: EC-EARTH/IFS (L91, 0.01hPa), CNRM/ARPEGE (L91, 0.01hPa), CMCC/CAM (L46, 0.3hPa).</p>

scholarly journals Mechanisms of Intraseasonal Amplification of the Cold Siberian High

2005 ◽  
Vol 62 (12) ◽  
pp. 4423-4440 ◽  
Author(s):  
Koutarou Takaya ◽  
Hisashi Nakamura
Keyword(s):  
Rossby Wave ◽  
Rossby Waves ◽  
Wave Train ◽  
The Tibetan Plateau ◽  
Cold Air ◽  
Thermal Anomalies ◽  
Siberian High ◽  
Vertical Coupling ◽  
Rossby Wave Train ◽  
Upper Level

Abstract Mechanisms of intraseasonal amplification of the Siberian high are investigated on the basis of composite anomaly evolution for its strongest events at each of the grid points over Siberia. At each location, the amplification of the surface high is associated with formation of a blocking ridge in the upper troposphere. Over central and western Siberia, what may be called “wave-train (Atlantic-origin)” type is common, where a blocking ridge forms as a component of a quasi-stationary Rossby wave train propagating across the Eurasian continent. A cold air outbreak follows once anomalous surface cold air reaches the northeastern slope of the Tibetan Plateau. It is found through the potential vorticity (PV) inversion technique that interaction between the upper-level stationary Rossby wave train and preexisting surface cold anomalies is essential for the strong amplification of the surface high. Upper-level PV anomalies associated with the wave train reinforce the cold anticyclonic anomalies at the surface by inducing anomalous cold advection that counteracts the tendency of the thermal anomalies themselves to migrate eastward as surface thermal Rossby waves. The surface cold anomalies thus intensified, in turn, act to induce anomalous vorticity advection aloft that reinforces the blocking ridge and cyclonic anomalies downstream of it that constitute the propagating wave train. The baroclinic development of the anomalies through this vertical coupling is manifested as a significant upward flux of wave activity emanating from the surface cold anomalies, which may be interpreted as dissipative destabilization of the incoming external Rossby waves.

scholarly journals Diversity of the Global Teleconnections Associated with the Madden–Julian Oscillation

2021 ◽  
Vol 34 (1) ◽  
pp. 397-414
Author(s):  
Guosen Chen
Keyword(s):  
Rossby Wave ◽  
Potential Vorticity ◽  
Wave Train ◽  
Boreal Winter ◽  
Madden Julian Oscillation ◽  
The Pacific ◽  
Weather And Climate ◽  
Baroclinic Model ◽  
Rossby Wave Train ◽  
Upper Level

AbstractA recent study has revealed that the Madden–Julian oscillation (MJO) during boreal winter exhibits diverse propagation patterns that consist of four archetypes: standing MJO, jumping MJO, slow eastward propagating MJO, and fast eastward propagating MJO. This study has explored the diversity of teleconnection associated with these four MJO groups. The results reveal that each MJO group corresponds to distinct global teleconnections, manifested as diverse upper-tropospheric Rossby wave train patterns. Overall, the teleconnections in the fast and slow MJO are similar to those in the canonical MJO constructed by the real-time multivariate MJO (RMM) indices, while the teleconnections in the jumping and standing MJO generally lose similarities to those in the canonical MJO. The causes of this diversity are investigated using a linearized potential vorticity equation. The various MJO tropical heating patterns in different MJO groups are the main cause of the diverse MJO teleconnections, as they induce assorted upper-level divergent flows that act as Rossby-wave sources through advecting the background potential vorticity. The variation of the Asian jet could affect the teleconnections over the Pacific jet exit region, but it plays an insignificant role in causing the diversity of global teleconnections. The numerical investigation with a linear baroclinic model shows that the teleconnections can be interpreted as linear responses to the MJO’s diabatic heating to various degrees for different MJO groups, with the fast and slow MJO having higher linear skill than the jumping and standing MJO. The results have broad implications in the MJO’s tropical–extratropical interactions and the associated impacts on global weather and climate.

scholarly journals Stratospheric Influences on the MJO-Induced Rossby Wave Train: Effects on Intraseasonal Climate

2020 ◽  
Vol 33 (1) ◽  
pp. 365-389 ◽  
Author(s):  
Lon L. Hood ◽  
Malori A. Redman ◽  
Wes L. Johnson ◽  
Thomas J. Galarneau
Keyword(s):  
Solar Cycle ◽  
Rossby Wave ◽  
Southern Oscillation ◽  
Wave Train ◽  
Winter Season ◽  
Surface Air Temperature ◽  
Quasi Biennial Oscillation ◽  
Sea Level Pressure ◽  
The North ◽  
Rossby Wave Train

AbstractThe tropical Madden–Julian oscillation (MJO) excites a northward propagating Rossby wave train that largely determines the extratropical surface weather consequences of the MJO. Previous work has demonstrated a significant influence of the tropospheric El Niño–Southern Oscillation (ENSO) on the characteristics of this wave train. Here, composite analyses of ERA-Interim sea level pressure (SLP) and surface air temperature (SAT) data during the extended northern winter season are performed to investigate the additional role of stratospheric forcings [the quasi-biennial oscillation (QBO) and the 11-yr solar cycle] in modifying the wave train and its consequences. MJO phase composites of 20–100-day filtered data for the two QBO phases show that, similar to the cool phase of ENSO, the easterly phase of the QBO (QBOE) produces a stronger wave train and associated modulation of SLP and SAT anomalies. In particular, during MJO phases 5–7, positive SLP and negative SAT anomalies in the North Atlantic/Eurasian sector are enhanced during QBOE relative to the westerly phase of the QBO (QBOW). The opposite occurs during the earliest MJO phases. SAT anomalies over eastern North America are also more strongly modulated during QBOE. Although less certain because of the short data record, there is some evidence that the minimum phase of the solar cycle (SMIN) produces a similar increased modulation of SLP and SAT anomalies. The strongest modulations of SLP and SAT anomalies are produced when two or more of the forcings are superposed (e.g., QBOE/cool ENSO, SMIN/QBOE, etc.).

scholarly journals Rossby Wave Propagation from the Arctic into the Midlatitudes: Does It Arise from In Situ Latent Heating or a Trans-Arctic Wave Train?

2020 ◽  
Vol 33 (9) ◽  
pp. 3619-3633 ◽  
Author(s):  
Tingting Gong ◽  
Steven B. Feldstein ◽  
Sukyoung Lee
Keyword(s):  
Wave Propagation ◽  
Rossby Wave ◽  
Wave Train ◽  
The Arctic ◽  
Latent Heating ◽  
Latent Heat Release ◽  
Rossby Wave Propagation ◽  
Rossby Wave Train ◽  
In Situ Generation

AbstractThe relationship between latent heating over the Greenland, Barents, and Kara Seas (GBKS hereafter) and Rossby wave propagation between the Arctic and midlatitudes is investigated using global reanalysis data. Latent heating is the focus because it is the most likely source of Rossby wave activity over the Arctic Ocean. Given that the Rossby wave time scale is on the order of several days, the analysis is carried out using a daily latent heating index that resembles the interdecadal latent heating trend during the winter season. The results from regression calculations find a trans-Arctic Rossby wave train that propagates from the subtropics, through the midlatitudes, into the Arctic, and then back into midlatitudes over a period of about 10 days. Upon entering the GBKS, this wave train transports moisture into the region, resulting in anomalous latent heat release. At high latitudes, the overlapping of a negative latent heating anomaly with an anomalous high is consistent with anomalous latent heat release fueling the Rossby wave train before it propagates back into the midlatitudes. This implies that the Rossby wave propagation from the Arctic into the midlatitudes arises from trans-Arctic wave propagation rather than from in situ generation. The method used indicates the variance of the trans-Arctic wave train, but not in situ generation, and implies that the variance of the former is greater than that of latter. Furthermore, GBKS sea ice concentration regression against the latent heating index shows the largest negative value six days afterward, indicating that sea ice loss contributes little to the latent heating.

scholarly journals Tropical Cyclogenesis Associated with Rossby Wave Energy Dispersion of a Preexisting Typhoon. Part I: Satellite Data Analyses*

2006 ◽  
Vol 63 (5) ◽  
pp. 1377-1389 ◽  
Author(s):  
Tim Li ◽  
Bing Fu
Keyword(s):  
Rossby Wave ◽  
Satellite Data ◽  
Wave Energy ◽  
Large Scale ◽  
Wave Train ◽  
Vertical Shear ◽  
Energy Dispersion ◽  
Data Analyses ◽  
Wave Trains ◽  
Rossby Wave Train

Abstract The structure and evolution characteristics of Rossby wave trains induced by tropical cyclone (TC) energy dispersion are revealed based on the Quick Scatterometer (QuikSCAT) and Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) data. Among 34 cyclogenesis cases analyzed in the western North Pacific during 2000–01 typhoon seasons, six cases are associated with the Rossby wave energy dispersion of a preexisting TC. The wave trains are oriented in a northwest–southeast direction, with alternating cyclonic and anticyclonic vorticity circulation. A typical wavelength of the wave train is about 2500 km. The TC genesis is observed in the cyclonic circulation region of the wave train, possibly through a scale contraction process. The satellite data analyses reveal that not all TCs have a Rossby wave train in their wakes. The occurrence of the Rossby wave train depends to a certain extent on the TC intensity and the background flow. Whether or not a Rossby wave train can finally lead to cyclogenesis depends on large-scale dynamic and thermodynamic conditions related to both the change of the seasonal mean state and the phase of the tropical intraseasonal oscillation. Stronger low-level convergence and cyclonic vorticity, weaker vertical shear, and greater midtropospheric moisture are among the favorable large-scale conditions. The rebuilding process of a conditional unstable stratification is important in regulating the frequency of TC genesis.

scholarly journals Multi-model assessment of the late-winter stratospheric response to El Niño and La Niña

2021 ◽  
Author(s):  
Bianca Mezzina ◽  
Froila M. Palmeiro ◽  
Javier García-Serrano ◽  
Ileana Bladé ◽  
Lauriane Batté ◽  
...  
Keyword(s):  
Rossby Wave ◽  
El Niño ◽  
Lower Stratosphere ◽  
El Nino ◽  
Wave Train ◽  
La Niña ◽  
Late Winter ◽  
Polar Cap ◽  
La Nina ◽  
Rossby Wave Train

AbstractThe impact of El Niño-Southern Oscillation (ENSO) on the late-winter extra-tropical stratosphere (January–March) is assessed in a multi-model framework. Three state-of-the-art atmospheric models are run with prescribed SST anomalies representative of a strong ENSO event, with symmetric patterns for El Niño and La Niña. The well-known temperature perturbation in the lower stratosphere during El Niño is captured by two models, in which the anomalous warming at polar latitudes is accompanied by a positive geopotential height anomaly that extends over the polar cap. In the third model, which shows a lack of temperature anomalies over the pole, the anomalous anticyclone is confined over Canada and does not expand to the polar cap. This anomalous center of action emerges from the large-scale tropospheric Rossby wave train forced by ENSO, and shrinking/stretching around the polar vortex is invoked to link it to the temperature response. No disagreement across models is found in the lower stratosphere for La Niña, whose teleconnection is opposite in sign but weaker. In the middle-upper stratosphere (above 50 hPa) the geopotential height anomalies project on a wavenumber-1 (WN1) pattern for both El Niño and, more weakly, La Niña, and show a westward tilt with height up to the stratopause. It is suggested that this WN1 pattern arises from the high-latitude lower-stratospheric anomalies, and that the ENSO teleconnection to the polar stratosphere can be interpreted in terms of upward propagation of the stationary Rossby wave train and quasi-geostrophic balance, instead of wave breaking.

On the Development and Demise of the Fall 2019 Southeast U. S. Flash Drought: Links to an Extreme Positive IOD

2020 ◽  
pp. 1-60
Author(s):  
Siegfried D. Schubert ◽  
Yehui Chang ◽  
Anthony M. DeAngelis ◽  
Hailan Wang ◽  
Randal D. Koster
Keyword(s):  
Indian Ocean ◽  
Rossby Wave ◽  
Wave Train ◽  
Temperature And Precipitation ◽  
Ocean Region ◽  
Dry Conditions ◽  
Underlying Causes ◽  
The Indian Ocean ◽  
Precipitation Anomalies ◽  
Rossby Wave Train

AbstractMuch of the southeast United States experienced record dry conditions during September of 2019, with the area in abnormally dry to exceptional drought conditions growing from 25% at the beginning of the month to 80% by the end of the month. The drought ended just as abruptly due to above normal rain that fell during the second half of October. In this study we employed MERRA-2 and the GEOS-5 AGCM to diagnose the underlying causes of the drought’s onset, maintenance, and demise. The basic approach involves performing a series of AGCM simulations in which the model is constrained to remain close to MERRA-2 over pre-specified areas that are external to the drought region. The start of the drought appears to have been forced by anomalous heating in the central/western tropical Pacific that resulted in low level anti-cyclonic flow and a tendency for descending motion over much of the southeast. An anomalous ridge associated with a Rossby wave train (emanating from the Indian Ocean region) is found to be the main source of the most intense temperature and precipitation anomalies that develop over the southeast during the last week of September. A second Rossby wave train (emanating from the same region) is responsible for the substantial rain that fell during the second half of October to end the drought. The links to the Indian Ocean Dipole (with record positive values) as well as a waning El Nino allow some speculation as to the likelihood of similar events occurring in the future.

scholarly journals Internal Variability in Projections of Twenty-First-Century Arctic Sea Ice Loss: Role of the Large-Scale Atmospheric Circulation

2014 ◽  
Vol 27 (2) ◽  
pp. 527-550 ◽  
Author(s):  
Justin J. Wettstein ◽  
Clara Deser
Keyword(s):  
Sea Ice ◽  
Atmospheric Circulation ◽  
Large Scale ◽  
Wave Train ◽  
Internal Variability ◽  
Arctic Sea Ice ◽  
The Arctic ◽  
Arctic Sea ◽  
Rossby Wave Train ◽  
Arctic Sea Ice Loss

Abstract Internal variability in twenty-first-century summer Arctic sea ice loss and its relationship to the large-scale atmospheric circulation is investigated in a 39-member Community Climate System Model, version 3 (CCSM3) ensemble for the period 2000–61. Each member is subject to an identical greenhouse gas emissions scenario and differs only in the atmospheric model component's initial condition. September Arctic sea ice extent trends during 2020–59 range from −2.0 × 106 to −5.7 × 106 km2 across the 39 ensemble members, indicating a substantial role for internal variability in future Arctic sea ice loss projections. A similar nearly threefold range (from −7.0 × 103 to −19 × 103 km3) is found for summer sea ice volume trends. Higher rates of summer Arctic sea ice loss in CCSM3 are associated with enhanced transpolar drift and Fram Strait ice export driven by surface wind and sea level pressure patterns. Over the Arctic, the covarying atmospheric circulation patterns resemble the so-called Arctic dipole, with maximum amplitude between April and July. Outside the Arctic, an atmospheric Rossby wave train over the Pacific sector is associated with internal ice loss variability. Interannual covariability patterns between sea ice and atmospheric circulation are similar to those based on trends, suggesting that similar processes govern internal variability over a broad range of time scales. Interannual patterns of CCSM3 ice–atmosphere covariability compare well with those in nature and in the newer CCSM4 version of the model, lending confidence to the results. Atmospheric teleconnection patterns in CCSM3 suggest that the tropical Pacific modulates Arctic sea ice variability via the aforementioned Rossby wave train. Large ensembles with other coupled models are needed to corroborate these CCSM3-based findings.

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