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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) Composite of significant eddy streamfunction (×106 m2 s−1) anomalies at 850 hPa five days before TYPE1 events (DAY-5). (b,c and d) same as (a) but four days (DAY-4) before, two days (DAY-2) before and on the day (DAY0) respectively of the TYPE1 event. (e–h) same as (a–d) but for TYPE2 cold wave events. 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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f4: (a) Composite of significant eddy streamfunction (×106 m2 s−1) anomalies at 850 hPa five days before TYPE1 events (DAY-5). (b,c and d) same as (a) but four days (DAY-4) before, two days (DAY-2) before and on the day (DAY0) respectively of the TYPE1 event. (e–h) same as (a–d) but for TYPE2 cold wave events. 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: We composited the 850 hPa eddy streamfunction anomalies of all the TYPE1 cold wave events from 5 days (DAY-5) before the event to the day the event started (DAY0), to understand the initiation of the cold wave events over India and presented the results in Fig. 4. Day0 is considered the day when the events started. Five days before the TYPE1 cold wave events occurred over India (DAY-5) (Fig. 4a), anomalous high in the higher latitudes and the associated wave with anomalous trough over China and over India are oriented north to south. The trough has a maximum to the northwest of India (Fig. 4a). The anomalous trough is seen moving eastward from DAY-4 (Fig. 4b–d) and is seen covering whole of the Indian landmass. The maxima in the cyclonic anomaly is over India from DAY-2, two days before the events started (Fig. 4c). On DAY0, the anomalous wave is oriented such that an anomalous cyclone is seen anchored to Indo-China region. The anomalous cyclone to the south of equator in the Indian Ocean is seen from DAY-5 to DAY0 (Fig. 4a–d), however it intensifies from DAY-2 (Fig. 4c). As the TYPE1 events occurred during La Niña type of SST distribution in the equatorial Pacific, the spatial distribution of the equatorial convection in those years provides the required background for the anomalous Matsuno-Gill response (Fig. 3). The daily variations in the anomalous diabatic heating influence the intensity and location of the anomalous Matsuno-Gill response. Our study shows that the anomalous Matsuno-Gill response intensifies two days before the cold wave conditions over the Indian Landmass and anchors the wave to the Indian region. Most notably, the cyclonic anomaly over India and its corresponding pair in the equatorial South Indian Ocean persist through the life period of the cold wave event (Fig. 2d).


ENSO ’ s far reaching connection to Indian cold waves
(a) Composite of significant eddy streamfunction (×106 m2 s−1) anomalies at 850 hPa five days before TYPE1 events (DAY-5). (b,c and d) same as (a) but four days (DAY-4) before, two days (DAY-2) before and on the day (DAY0) respectively of the TYPE1 event. (e–h) same as (a–d) but for TYPE2 cold wave events. 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

f4: (a) Composite of significant eddy streamfunction (×106 m2 s−1) anomalies at 850 hPa five days before TYPE1 events (DAY-5). (b,c and d) same as (a) but four days (DAY-4) before, two days (DAY-2) before and on the day (DAY0) respectively of the TYPE1 event. (e–h) same as (a–d) but for TYPE2 cold wave events. 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: We composited the 850 hPa eddy streamfunction anomalies of all the TYPE1 cold wave events from 5 days (DAY-5) before the event to the day the event started (DAY0), to understand the initiation of the cold wave events over India and presented the results in Fig. 4. Day0 is considered the day when the events started. Five days before the TYPE1 cold wave events occurred over India (DAY-5) (Fig. 4a), anomalous high in the higher latitudes and the associated wave with anomalous trough over China and over India are oriented north to south. The trough has a maximum to the northwest of India (Fig. 4a). The anomalous trough is seen moving eastward from DAY-4 (Fig. 4b–d) and is seen covering whole of the Indian landmass. The maxima in the cyclonic anomaly is over India from DAY-2, two days before the events started (Fig. 4c). On DAY0, the anomalous wave is oriented such that an anomalous cyclone is seen anchored to Indo-China region. The anomalous cyclone to the south of equator in the Indian Ocean is seen from DAY-5 to DAY0 (Fig. 4a–d), however it intensifies from DAY-2 (Fig. 4c). As the TYPE1 events occurred during La Niña type of SST distribution in the equatorial Pacific, the spatial distribution of the equatorial convection in those years provides the required background for the anomalous Matsuno-Gill response (Fig. 3). The daily variations in the anomalous diabatic heating influence the intensity and location of the anomalous Matsuno-Gill response. Our study shows that the anomalous Matsuno-Gill response intensifies two days before the cold wave conditions over the Indian Landmass and anchors the wave to the Indian region. Most notably, the cyclonic anomaly over India and its corresponding pair in the equatorial South Indian Ocean persist through the life period of the cold wave event (Fig. 2d).

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