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ENSO ’ s far reaching connection to Indian cold waves

View Article: PubMed Central - PubMed

ABSTRACT

During boreal winters, cold waves over India are primarily due to transport of cold air from higher latitudes. However, the processes associated with these cold waves are not yet clearly understood. Here by diagnosing a suite of datasets, we explore the mechanisms leading to the development and maintenance of these cold waves. Two types of cold waves are identified based on observed minimum surface temperature and statistical analysis. The first type (TYPE1), also the dominant one, depicts colder than normal temperatures covering most parts of the country while the second type (TYPE2) is more regional, with significant cold temperatures only noticeable over northwest India. Quite interestingly the first (second) type is associated with La Niña (El Niño) like conditions, suggesting that both phases of ENSO provide a favorable background for the occurrence of cold waves over India. During TYPE1 cold wave events, a low-level cyclonic anomaly generated over the Indian region as an atmospheric response to the equatorial convective anomalies is seen advecting cold temperatures into India and maintaining the cold waves. In TYPE2 cold waves, a cyclonic anomaly generated over west India anomalously brings cold winds to northwest India causing cold waves only in those parts.

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(a) Significant OLR anomalies composited over Dec–Feb months during the La Niña years over the period 1982 to 2013. (b) same as (a) but is for significant eddy streamfunction (×106 m2 s−1) anomalies at 850 hPa and significant wind anomalies (vectors; either zonal or meridional component is significant). Significance is at 90% using two-tailed Student’s t-test. (Figure was created using a free software Grid Analysis and Display System (GrADS) version 2.1.a3 (http://cola.gmu.edu/grads/downloads.php)).
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f3: (a) Significant OLR anomalies composited over Dec–Feb months during the La Niña years over the period 1982 to 2013. (b) same as (a) but is for significant eddy streamfunction (×106 m2 s−1) anomalies at 850 hPa and significant wind anomalies (vectors; either zonal or meridional component is significant). Significance is at 90% using two-tailed Student’s t-test. (Figure was created using a free software Grid Analysis and Display System (GrADS) version 2.1.a3 (http://cola.gmu.edu/grads/downloads.php)).

Mentions: The low level cyclonic anomaly observed over India during the TYPE1 cold wave events (Fig. 2d) may be partly attributed to the seasonal mean equatorial cyclonic anomaly observed during La Niña events. Figure 3 shows composite OLR anomalies, 850 hPa eddy streamfunction (shaded) and 850 hPa wind (vector) anomalies constructed by averaging December-February monthly anomalies during La Niña years over the period 1982 to 2013. In response to a spatially coherent negative OLR anomaly noted over the Maritime Continent and the west Pacific regions (Fig. 3a), a pair of cyclones straddling the equator is seen (Fig. 3b) over the Indian Ocean. The poleward flank of the Northern Hemisphere part of the cyclonic anomalies (Fig. 3b) is favorable to advect cold temperatures from higher latitudes into the Indian region during La Niña years.


ENSO ’ s far reaching connection to Indian cold waves
(a) Significant OLR anomalies composited over Dec–Feb months during the La Niña years over the period 1982 to 2013. (b) same as (a) but is for significant eddy streamfunction (×106 m2 s−1) anomalies at 850 hPa and significant wind anomalies (vectors; either zonal or meridional component is significant). Significance is at 90% using two-tailed Student’s t-test. (Figure was created using a free software Grid Analysis and Display System (GrADS) version 2.1.a3 (http://cola.gmu.edu/grads/downloads.php)).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5120324&req=5

f3: (a) Significant OLR anomalies composited over Dec–Feb months during the La Niña years over the period 1982 to 2013. (b) same as (a) but is for significant eddy streamfunction (×106 m2 s−1) anomalies at 850 hPa and significant wind anomalies (vectors; either zonal or meridional component is significant). Significance is at 90% using two-tailed Student’s t-test. (Figure was created using a free software Grid Analysis and Display System (GrADS) version 2.1.a3 (http://cola.gmu.edu/grads/downloads.php)).
Mentions: The low level cyclonic anomaly observed over India during the TYPE1 cold wave events (Fig. 2d) may be partly attributed to the seasonal mean equatorial cyclonic anomaly observed during La Niña events. Figure 3 shows composite OLR anomalies, 850 hPa eddy streamfunction (shaded) and 850 hPa wind (vector) anomalies constructed by averaging December-February monthly anomalies during La Niña years over the period 1982 to 2013. In response to a spatially coherent negative OLR anomaly noted over the Maritime Continent and the west Pacific regions (Fig. 3a), a pair of cyclones straddling the equator is seen (Fig. 3b) over the Indian Ocean. The poleward flank of the Northern Hemisphere part of the cyclonic anomalies (Fig. 3b) is favorable to advect cold temperatures from higher latitudes into the Indian region during La Niña years.

View Article: PubMed Central - PubMed

ABSTRACT

During boreal winters, cold waves over India are primarily due to transport of cold air from higher latitudes. However, the processes associated with these cold waves are not yet clearly understood. Here by diagnosing a suite of datasets, we explore the mechanisms leading to the development and maintenance of these cold waves. Two types of cold waves are identified based on observed minimum surface temperature and statistical analysis. The first type (TYPE1), also the dominant one, depicts colder than normal temperatures covering most parts of the country while the second type (TYPE2) is more regional, with significant cold temperatures only noticeable over northwest India. Quite interestingly the first (second) type is associated with La Niña (El Niño) like conditions, suggesting that both phases of ENSO provide a favorable background for the occurrence of cold waves over India. During TYPE1 cold wave events, a low-level cyclonic anomaly generated over the Indian region as an atmospheric response to the equatorial convective anomalies is seen advecting cold temperatures into India and maintaining the cold waves. In TYPE2 cold waves, a cyclonic anomaly generated over west India anomalously brings cold winds to northwest India causing cold waves only in those parts.

No MeSH data available.


Related in: MedlinePlus