Large Anomalies in the Tropical Upper Troposphere Lower Stratosphere (UTLS) Trace Gases Observed during the Extreme 2015–16 El Niño Event by Using Satellite Measurements

Babu, Saginela Ravindra; Ratnam, M. Venkat; Basha, Ghouse; Liou, Yuei-An; Nelli, Narendra

doi:10.3390/rs11060687

Cited by 17 publications

(9 citation statements)

References 55 publications

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“…The most recent ENSO, which was developed in 2014 and strengthened in the summer, has caused global impacts [61]. In Ethiopia, the dry kiremt seasons are closely linked to the significantly warmer Pacific sea surface temperatures [39].…”

Section: Resultsmentioning

confidence: 99%

Spatio–temporal Assessment of Drought in Ethiopia and the Impact of Recent Intense Droughts

Liou

Mulualem

2019

Remote Sensing

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The recent droughts that have occurred in different parts of Ethiopia are generally linked to fluctuations in atmospheric and ocean circulations. Understanding these large-scale phenomena that play a crucial role in vegetation productivity in Ethiopia is important. In view of this, several techniques and datasets were analyzed to study the spatio-temporal variability of vegetation in response to a changing climate. In this study, 18 years (2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014)(2015)(2016)(2017)(2018) of Moderate Resolution Imaging Spectroscopy (MODIS) Terra/Aqua, normalized difference vegetation index (NDVI), land surface temperature (LST), Climate Hazards Group Infrared Precipitation with Stations (CHIRPS) daily precipitation, and the Famine Early Warning Systems Network (FEWS NET) Land Data Assimilation System (FLDAS) soil moisture datasets were processed. Pixel-based Mann-Kendall trend analysis and the Vegetation Condition Index (VCI) were used to assess the drought patterns during the cropping season. Results indicate that the central highlands and northwestern part of Ethiopia, which have land cover dominated by cropland, had experienced decreasing precipitation and NDVI trends. About 52.8% of the pixels showed a decreasing precipitation trend, of which the significant decreasing trends focused on the central and low land areas. Also, 41.67% of the pixels showed a decreasing NDVI trend, especially in major parts of the northwestern region of Ethiopia. Based on the trend test and VCI analysis, significant countrywide droughts occurred during the El Niño 2009 and 2015 years. Furthermore, the Pearson correlation coefficient analysis assures that the low NDVI was mainly attributed to the low precipitation and water availability in the soils. This study provides valuable information in identifying the locations with the potential concern of drought and planning for immediate action of relief measures. Furthermore, this paper presents the results of the first attempt to apply a recently developed index, the Normalized Difference Latent Heat Index (NDLI), to monitor drought conditions. The results show that the NDLI has a high correlation with NDVI (r = 0.96), precipitation (r = 0.81), soil moisture (r = 0.73), and LST (r = −0.67). NDLI successfully captures the historical droughts and shows a notable correlation with the climatic variables. The analysis shows that using the radiances of green, red, and short wave infrared (SWIR), a simplified crop monitoring model with satisfactory accuracy and easiness can be developed.

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Section: Resultsmentioning

confidence: 99%

Spatio–temporal Assessment of Drought in Ethiopia and the Impact of Recent Intense Droughts

Liou

Mulualem

2019

Remote Sensing

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“…They demonstrated the importance of the large-scale atmospheric dynamics and the stratospheric intrusions for high O 3 and low WV over Lhasa within the ASMA by using in situ balloon-borne measurements. The O 3 and WV changes strongly influence the background temperature structure within the UTLS region (Venkat Ratnam et al, 2016;Ravindra Babu et al, 2019b). Further, we investigated the tropopause temperature changes within the ASMA by using COSMIC RO data.…”

Section: Trace Gases Anomalies Observed Within the Asma In 2015mentioning

confidence: 99%

“…It is well known that the tropopause plays a crucial role in the exchange of WV, O 3 , and other chemical species between the troposphere and the stratosphere. Most of these exchanges (WV to the lower stratosphere and O 3 to the upper troposphere) known as stratosphere-troposphere exchange (STE) take place around the tropopause region (Fueglistaler et al, 2009;Venkat Ratnam et al, 2016;Ravindra Babu et al, 2019b). It is well reported that the tropopause within the ASMA is higher than the outside regions at the same latitude (Randel et al, 2010;Santee et al, 2017).…”

Section: Tropopause Temperature Anomalies In 2015mentioning

confidence: 99%

Structure, dynamics, and trace gas variability within the Asian summer monsoon anticyclone in the extreme El Niño of 2015–2016

et al. 2021

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Abstract. A weak El Niño during 2014–2015 boreal winter developed as a strong boreal summer event in 2015 which continued and even enhanced during the following winter. In this work, the detailed changes in the structure, dynamics, and trace gases within the Asian summer monsoon anticyclone (ASMA) during the extreme El Niño of 2015–2016 is delineated by using Aura Microwave Limb Sounder (MLS) measurements, COSMIC radio occultation (RO) temperature, and National Centers for Environmental Prediction (NCEP) reanalysis products. Our analysis concentrates only on the summer months of July and August 2015 when the Niño 3.4 index started to exceed values of 1.5. The results show that the ASMA structure was quite different in summer 2015 as compared to the long-term (2005–2014) mean. In July, the spatial extension of the ASMA is greater than the long-term mean in all the regions except over northeastern Asia, where it exhibits a strong southward shift in its position. The ASMA splits into two, and the western Pacific mode is evident in August. Interestingly, the subtropical westerly jet (STJ) shifted southward from its normal position over northeastern Asia, and as a result midlatitude air moved southward in 2015. Intense Rossby wave breaking events along with STJ are also found in July 2015. Due to these dynamical changes in the ASMA, pronounced changes in the ASMA tracers are noticed in 2015 compared to the long-term mean. A 30 % (20 %) decrease in carbon monoxide (water vapor) at 100 hPa is observed in July over most of the ASMA region, whereas in August the drop is strongly concentrated at the edges of the ASMA. A prominent increase in O3 (> 40 %) at 100 hPa is clearly evident within the ASMA in July, whereas in August the increase is strongly located (even at 121 hPa) over the western edges of the ASMA. Further, the temperature around the tropopause shows significant positive anomalies (∼ 5 K) within the ASMA in 2015. The present results clearly reveal the El-Niño-induced dynamical changes caused significant changes in the trace gases within the ASMA in summer 2015.

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“…The uplifting of boundary layer pollutants to the tropopause level occurs primarily on the eastern side of the anticyclone, centered near the southern flank of the Tibetan Plateau, north-eastern India, Nepal, and north of the Bay of Bengal. However, a more detailed and a higher quality of dataset is needed to further understand the effects of the Tibetan Plateau on the transport of different tracers and pollutants to the UTLS region (Ravindrababu et al, 2019…”

Section: Variability Of the Anticyclonementioning

confidence: 99%

Asian Summer Monsoon Anticyclone: Trends and Variability

Basha¹,

Ratnam²,

Kishore³

2019

Preprint

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Abstract. The Asian Summer Monsoon (ASM) dynamics act as a pathway for the transport of trace gases and pollutants both vertically (through convection) and horizontally (through low-level jet and tropical easterly jet). These pollutants will be trapped in the anticyclone present during the same period in the upper troposphere and lower stratosphere (UTLS). Since the anticyclone extends from the Middle East to East Asia, trapped pollutants are expected to make a large radiative forcing to the background atmosphere. Thus, it is essential to understand the anticyclone features in detail and its relation to long-term oscillations. This work explores the spatial variability and the trends of the Asian Summer Monsoon Anticyclone (ASMA) using observational and reanalysis data sets. Emphasis is made to investigate the temporal, spatial, and long-term trends of ASMA. Our analysis indicates that the spatial extent and magnitude of ASMA is greater during July and August compared to June and September. The decadal variability of the anticyclone is very large at the edges of anticyclone than at the core region. Significant deviations in the northeast and southwest parts of ASMA are also observed in the decadal variability with reference to 1951−1960 period. The strength of the ASMA shows a drastic increase from the easterlies to the westerlies in terms of temporal variation. Further, our results show that the extent of anticyclone is greater during the active phase of the monsoon, strong monsoon years, and during La Niña events. Significant warming with strong westerlies is observed exactly over the Tibetan Plateau during the active phase of the monsoon, strong monsoon years, and during La Niña events. Over the Tibetan Plateau, there is strong elevated heating from the surface to the tropopause, which is observed with strong westerlies during active and strong monsoon years. Our results support the transport process over Tibetan Plateau and the Indian region during active, strong monsoon years and during strong La Niña years. It is suggested to consider different phases of monsoon while interpreting the pollutants/trace gases in the anticyclone.

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Large Anomalies in the Tropical Upper Troposphere Lower Stratosphere (UTLS) Trace Gases Observed during the Extreme 2015–16 El Niño Event by Using Satellite Measurements

Cited by 17 publications

References 55 publications

Spatio–temporal Assessment of Drought in Ethiopia and the Impact of Recent Intense Droughts

Spatio–temporal Assessment of Drought in Ethiopia and the Impact of Recent Intense Droughts

Structure, dynamics, and trace gas variability within the Asian summer monsoon anticyclone in the extreme El Niño of 2015–2016

Asian Summer Monsoon Anticyclone: Trends and Variability

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