People in Weather – Q& A with Anthony Sagliani

A few weeks back we had started our People in Weather series by featuring Senior Meteorologist Jason Nicholls of AccuWeather.  The Q&A featuring Jason Nicholls is available in our Archives.  The idea behind the People in Weather series is to create a platform for the weather bloggers to ask Meteorologists questions on various weather intricacies.  Over time we hope to create an interactive platform for the bloggers to reach out to the meteorologists.

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Today we feature Anthony Sagliani Meteorologist & Scientist with Earth Networks. In the words of Anthony Sagliani a brief bio of him

I am a meteorologist and scientist at Earth Networks in Washington D.C. My job is basically to forecast and analyse extreme weather threats for both the short range and long range all around the world. My specialty is the creation of seasonal and subseasonal tropical cyclone, temperature, precipitation, drought and monsoon forecasts.

  1. I was in the impression that Westerly Wind Burst influence Elnino more than Lanina or the Westerly Wind Burst is the Elnino Mechanism? Please share your thoughts on this?

Yes, a Westerly Wind Burst (WWB) influences El Nino development rather than La Nina development. El Nino development is usually characterized by several major WWB events. A WWB is basically a weakening or reversal of typical easterly trade winds for several days or weeks. The easterly trade winds typically push water into a warm dome in the western Pacific, but a WWB ceases those easterly winds and the warm dome collapses, then begins to propagate eastward into the central and eastern Pacific.

  1. I am very much interested to know the mechanism (Ocean as well as Atmospheric level) behind possibility of formation of Cyclonic Circulation forming out of Borneo vortex and moving into Bay of Bengal. Can you share your thoughts about what timeline events should be for the formation including atmospheric and oceanic conditions

The Borneo Vortex is a feature of the winter Northeast Monsoon. The vortex is induced by a cold surge spilling into the South China Sea. Wind flow wraps around the island of Borneo and into the Java Sea, and gradually, a vortex evolves. It is highly unlikely that the subsequently formed Borneo Vortex would induce a tropical cyclone in the Bay of Bengal. However, this is a mechanism from which tropical cyclone development is possible very near the equator. The main case study on such a matter was the development of Typhoon Vamei in December of 2001. This Typhoon impacted the southern Malay Peninsula as well as Singapore, areas that are only a couple of degrees north of the equator. I should mention that the odds of such an event occurring are extremely low.

  1. South Atlantic are not known for regular cyclonic activity due to the very cooler SST, high Vertical wind shear, absence of tropical waves but still at least three possible such systems have been observed there since satellite monitoring began. The first was off Angola just west of Africa in 1991, another in January 2004 off Brazil, and most famously what has come to be named Cyclone Catarina, which reached apparent category 2 intensity before making landfall in southern Brazil on March 28, 2004.Can you share your thoughts what could be the mechanism(Ocean as well as Atmospheric level)  of the formation of this rare events apart from Low shear

Tropical cyclogenesis over the South Atlantic is indeed very rare.  Cases of South Atlantic cyclogenesis involve an extratropical mid or upper level low becoming cutoff and meandering around the subtropics for several days. The low will then become a subtropical cyclone if water temperatures are over 20C, and, if water temperatures are over 26C and the system continues to persist in a low shear environment, progress into a full tropical cyclone.

  1. There have few studies which I have come across showing easterly wind shear enhances cyclone genesis whereas westerly wind shear suppresses the cyclone genesis. But I feel that this may not be the same case and it varies with latitudes (In higher latitudes westerly shear is more favourable enhances cyclone genesis in other study).Please share your thought on this?

In general, no amount of wind shear is good for tropical cyclone development or sustainment. However, there are some catches. If the upper level winds are strong, but support good poleward, equatorward, or both kinds of outflow, then TC formation/development conditions can be good. In fact, a major staple for rapid intensification of a tropical cyclone is dual channel outflow (both poleward and equatorward flow) that rapidly evacuates mass from the centre of the cyclone. Cyclone Chapala, which impacted the Arabian Peninsula last fall, was a good example of this.

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  1. Is the two basins (Pacific and Indian Ocean) are coupled at the oceanic level as well at the atmospheric level? If so how can we observe that? Can you please provide any link?

The Indian and Pacific Oceans often do couple, especially in times of El Nino or La Nina. During El Nino, largescale sinking air is present over Indonesia and SE Asia. This often results in stronger trade winds over the Indian Ocean, and development of a positive Indian Ocean Dipole (IOD). In contrast, when La Nina conditions prevail, widespread rising motion is present over Indonesia and SE Asia, resulting in weaker trade winds in the Indian Ocean and this a negative IOD. A good way to track this behaviour is to monitor atmospheric velocity potential fields at 200 mb. Negative values of velocity potential indicate diverging winds at 200 mb, or upward motion, and vice versa. I like to use the JMA website for this: http://ds.data.jma.go.jp/tcc/tcc/products/clisys/anim/anim_tp.html

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  1. Have seen models showing in CPC about stream function. Just a brief description on its behaviour would be helpful

In meteorology, the main application of streamfunction is to indicate and measure the circulation of the atmosphere. This can mean monitoring Hadley cells or watching the evolution of MJO.

  1. What’s the actual factor that influences for a TC in sub-tropical region especially in Atlantic Basin?

There are several ways that a subtropical storm can evolve, but formation generally occurs when a cold core mid-level extratropical low finds its way into the subtropics and then, for one reason or another, stalls and meanders slowly in the region for a number of days. As the system lurks about surface water temperatures generally above 20C, large lapse rates due to the cold core low aloft allow thunderstorms to develop, and a new low pressure at the surface typically develops beneath these thunderstorms. Depending on what happens after this point determines whether the system becomes tropical or subtropical. If sea surface temperatures are between 24-26C, the system will usually become subtropical in nature. If sea surface temperatures are above 26C, the system can become a true warm core tropical cyclone.

  1. With Nino 3.4 still staying in Feb, MJO moving to Pacific in late Feb, enhanced convection prevailing, what’s your probability of another set of tropics in C Pacific and also in Australia by mid-feb?

With the MJO moving into Pacific, large-scale subsidence looks to prevail over the Indian Ocean and much of the Australian basin through the end of February. Some low risk for a tropical cyclone is present in the south Pacific.

  1. Among all Tropical Waves like MJO / Rossby etc which one is the master wave in your opinion and why so?

Each equatorial wave is important for its own reasons. But if I were to choose the “most” important, it would be MJO. MJO allows us to predict tropical cyclone risk out up to several weeks. It is a big factor responsible for ENSO modes. And it can manipulate longwave patterns around the globe.

  1. In the North Indian Ocean Basin some of the strongest cyclones happen during the Pre Monsoon season (April / May) or Post Monsoon Season (Oct. / Nov.) what are the reasons for this?

This phenomenon is closely related to the movement of the monsoon trough as it progresses through the northern Indian Ocean pre-monsoon and retreats post-monsoon. During the summer Southwest Monsoon, winds are blowing from the southwest over the entire basin, and there is little surface vorticity able to be generated for tropical cyclone development. During the winter Northeast Monsoon prevails, with northeast winds over the entire basin. It is in the months of April/May and Oct/Nov when the transition between wind directions takes place that the tropical cyclone threat is highest.

  1. We have come across studies which correlate rainfall pattern to indexes like SOI. In some cases these studies talk of lagged relationship.  How could lagged relationship work in atmosphere particularly when studies talk of time lag in terms of months in few cases.

When a study mentions a lagged relationship it is usually referring to the ocean vs atmosphere response or vice versa. For instance, warm water anomalies in the eastern Pacific are likely before a large scale atmospheric response during El Nino. Similarly, the atmospheric response to El Nino is more than likely to begin diminishing before the ocean response.

  1. While the SST Anomaly values are being constantly corrected based on newer climatological data what we cannot ignore is the absolute increase in the sea temperatures for e.g the El Nino threshold in absolute terms today is higher than say a couple of decades back.  But on account of the increase in absolute SST values I think we are seeing more extreme weather events like more intense typhoons or heavy rainfall events etc.  Is there merit in this argument?

Yes, I think there is some merit in this argument. The warmer the average water temperature is, the more ocean heat content is available. The fiercest tropical cyclones feed off of a very warm and deep supply of warm water. A warming world with warming oceans will have more of this, and thus more in the way of stronger tropical cyclones. Further, warmer ocean waters lead to more water vapour in the atmosphere, which leads to a greater risk for a heavy rainfall event at any given location.

  1. A lot of meteorologists talk about teleconnections, can you please explain us how teleconnections work?

A teleconnection is a pattern that we as meteorologists recognize as a recurring weather and climatological event in a certain location in the world that has subsequent predictable outcomes in another location in the world. For instance, if El Nino is present, then we can expect an increased likelihood of a diminished summer monsoon in parts of India. Or, if there is a ridge across the western United States, we can surmise that an increased potential for a trough is found over the eastern United States.

We take this opportunity to thank Anthony Sagliani to take time out from his schedule and answer the questions from our bloggers.  If anyone would like to reach out to Anthony Sagliani to discuss about possible doubts / questions he is available on Twitter.  His Twitter handle is @anthonywx.

The next People in Weather series will feature ace Typhoon Chaser James Reynolds of Earth Uncut TV who has cased some memorable Typhoons like Haiyan & Soudelor. As usual you can mail your questions to chennairain2014@gmail.com. Do share you feedback & suggestions on this edition of People in Weather.