 I'd like to welcome to the podium Yemu, whose presentation is titled Global Scale Forcing of South American Low-Level Jet and Associated Local Impacts of Precipitation Extremes. So, hi everyone, my name is Yemu, so today I'm going to present Global Scale Forcing of Xiaojie and associate local impacts on presentation extremes along with my co-authors, my Ph.D. advisors Dr. Charles Jones in the Kuala Lumpur and Tsinghua Ding, and my next summer mentors Luling Xue and Changhai Liu. So first I want to start with what is Xiaojie, or the full name, the South American Low-Level Jet. So, looking at the left figure here, here's the South America continent, and here's the Andes Mountain, which is one of the major mountains in the world. And we have the north-east trade winds that are coming from the east towards the Andes Mountain, and then the Andes can block and deflect the wind, and then with a strengthening of the northern flow in the low levels of the atmosphere along this eastern slope and the Andes, we call this low-level current the South American Low-Level Jet or Xiaojie. And in terms of the South America, in general, we well-known the Amazon Basin, as well as the biggest Amazon tropical forest in the world, transports or provides a lot of moisture into the atmosphere through evapotranspiration, and this moisture can be transported by the low-level jet downwind towards the La Plata Basin. So this transport is similar to like moisture transport like an atmosphere river, it helps you to illustrate that. And in the La Plata Basin is a favorable region for the development of mesoscale-connected systems. As the low-level jet, as Stephanie mentioned also, the low-level jet transport moisture towards its exit region, and then the exit region can have moisture convergence, and that helps form deep convection in the exit region, which can lead to convective system and therefore precipitation. So why do we care about Xiaojie? As I sort of explained here in the La Plata Basin in South America, it is one of the richest agriculture basin in the world. Xiaojie can affect the moisture balance of this basin through moisture transport. Recent study shows there is an increase in rainfall during austral summer when the low-level jet is the most frequent in that season in South America. And on the right is showing an extreme rainfall event caused by low-level jet inside the Carolina State in Brazil. So it can also impact agriculture production because Argentina, for example, is in the left of the basin, so significant floods and extreme events can impact food production and lots of other climate extreme events impacts here. So here is just a satellite imagery showing the chain of a mesoscale-connected system associated with a low-level jet event that caused the video, which is located at the exit region of the low-level jet. So in the title, I was talking about global scale forcing. So what global scale forcing am I looking at? On the top left figure here, I'm focusing on the ENSO, PDO, and MJO. So ENSO, or Alnino-Seismic Oscillation, refers to a global mechanism that drives climate. It has a warm phase called Alnino and the cold phase called Lanina. And then PDO, or the Pacific Dicado Oscillation that Nish also mentioned, is a dominant year-round pattern of monthly sea-level surface temperature anomalies in the northern Pacific. And the extreme phases of PDO also similar to ENSO has as a warm or cold phases. So in terms of timescale, ENSO is about inter-annual six to 18 months, and then PDO is a more inter-dicado scale from 20 to 30 years. So because they have warm and cold phases, so when they are in the same phases, when they're in both in warm phases, for example, PDO can enhance the ENSO impacts on climate globally, and when they're in different phases, PDO, however, can minimize ENSO impacts. So a little bit about the MJO, or the Medan-Julian Oscillation. So the MJO is basically a zone-oriented equatorial atmosphere disturbance that propagates eastward in the Pacific. It has a shorter life cycle of 40 to 60 days with eight different phases. Why do we care about that? Because the spatial temporal evolution of the South American low-level jet is remotely forced by the Rosby wave trains. So when the MJO started in the Indian Ocean, it can cause deep convection initiated by MJO passage, and then the MJO can trigger a Rosby wave train that you can see here that are geopotential anomalies that extends through the South Pacific to the tip of South America and then turns the equator over to reach subtropical South America, impacting the climate of South America. So that leads to my research objectives for this summer project. I want to answer what are the trends in the frequency and intensity of the SOJ, and then what are the remote forcings, including different time-scale remote forcings, mechanisms that drive these trends. And then lastly, what are the local impacts of SOJ on precipitation extremes? So first, starting with the data, I'm using Oceanic Nino Index to characterize ENSO and then NCEI PDO index for PDO. I'm also using a global analysis data that other interns mentioned before error five at already resolution to characterize SOJ. So first, how do we define and identify SOJ? We basically employed a new definition that we did recently. So I'm expanding this low-level jet index using the error five from 1957 to 2022, focusing on the austral summer when they're most frequent from November to March. So basically, we define a low-level jet in South America when the night time speed at 850 millibar and wind shear between 850 and 700 millibar exceeds the corresponding 70-phase percentiles of the monthly frequency distribution average. So once we have that identified, we want to quantify the spatial extent of the low-level jet. So in this case, we have five contiguous regions, then the spatial extent is identified by contiguous regions of these five regions with wind speeds that passes 10 meters per second at 850 millibar. So with that classification, we have defined three major types of low-level jet that occupies 99% of all cases for this 65-year period. The first one is the central type, or when the low-level jet is concentrated in the central Andes near Argentina and Bolivia. So this covers about 39% of low-level jet cases, then the second one is the northern type of low-level jet that covers Venezuela, Colombia, and northeastern Peru. So this one covers about 20% of all types. And then the last one is Andes type of low-level jet. That's when northern and central jet are occurring simultaneously. So that's the most frequent, about 40% of all cases. So what are the trends in the low-level jet frequency? On the left is the monthly frequency of low-level jet for each type. Here we are only looking at the dominant major three types, central, northern, and Andes low-level jet. So on the right is the trends of the frequency of the three major types. As you can see here, central and low-level jet is decreasing in terms of frequency over the time series. And then northern and Andes are increasing in trend in terms of time series. And they all pass the significant test. Then we look at the subject winds intensity trends. In this case, only the northern low-level jet type wind speed is increasing, and that trend is significant. So our first conclusion, like for frequency trends, central low-level jet has significant negative trends, and the northern and Andes low-level jet show positive trends, combined with the low-level jet wind intensity, where only northern low-level jet is increasing. So we have the conclusion that the frequency intensity of this low-level jet has been increasing the last 65 years. Then we look at the PDO and so annual frequencies, classified with positive and negative phases. We found that central jet is more frequent, where northern are more frequent during the warm phases, and northern and Andes low-level jet are more frequent during the cold phases. And this is driven by the recent decades where there are more lanina and cold PDO years occurring. So here we're looking at central-level jet circulation anomalies. On the top is 850 millibar wind anomalies, and the shaded color is just the wind climatology. And then on the bottom is 200 millibar wind anomalies during central-level jet. And then on the right is the Rosby wave trends of geopartential high 200 millibar anomalies to characterize the Rosby wave trend. So we conclude that our Nino plus warm PDO phases on top of the wave trend forcing and where we also see the enhanced subtropical jet favor the central-level jet. That's why it's more frequent during the positive phase. So because northern low-level jet and Andes type are more frequent during the cold phases, we look at them together. We see basically a different signs or phases of the Rosby wave trend as they're approaching South America. We also see an enhanced northeastern winds here in the northern Atlantic to flowing to northern South America to favor the northern Andes. On top of that, there's also this lanina and cold PDO provides the remote forcing that drive the Andes and northern-level jet during the cold phases. So although the wave trends phases don't change significantly for different and so PDO phases, but their special patterns are modified during those phases. And we found that the low-level jet, they persist longer days in their favored and so PDO phases. So central persist longer in the warm phases, northern and Andes-level jet persist longer in the cold phases. Because low-level jet transport moisture, so if they persist longer, they can lead to longer rainfall events and more intense rainfall events, what we call precipitation extremes. So we look at precipitation extremes anomalies at 99 percentile. We found that during the positive phase, when central jet is more dominant, there's more rainfall extremes event in the laptop basin. When northern Andes jet are more dominant during the cold phases, or they can transport moisture into the western Amazon basin and Paraguay, where we will see more precipitation extremes. So the key takes ways is that include the first the frequency and intensity of northern South American low-level jet has increased in the past 65 years. These South J trends are possibly remotely forced by and so and PDO phases. Warm phases favor the central low-level jet, while cold phases favor the northern and Andes-level jet. And although this Rosby wave-trans phases do not change significantly by and so PDO phases, but their spatial patterns were modified for different phases, which causes the low-level jet persist longer in their favored phases, leading to more precipitation extremes in their exit region. So my future work will look at how low-level jet and MCS interacts in South America using different trackers and how the variability of their diurnal cycles. I'm also planning to compare the analysis results with the NCAR research application lab, South American group, high-resolution warp simulations, as well looking at how the low-level jet might change in future projections in different climate models and scenarios to help us forecast precipitation extremes in the future. So for acknowledgement, this feature is founded by NCAR-NSC program and the National Science Foundation grant for Dr. Charles Jones. And NCAR, I also want to thank NSC co-hosts and everyone and my mentors who support me for this research. Thank you. All right. We have some questions from the audience. Yeah. I'm getting there. Thank you for that really interesting presentation. You started out by talking a little bit about the MGO and showing us how the wave trend was triggered by the MGO. Is there a relationship between ENSO and the PDO and the occurrence of MGOs? Like, could you link that back? Yeah. So I'm not showing you here, but our recent work showed that because MGO has different eight phases. So when there's MGO plus different phase of ENSO PDO, there is different enhancement of the level jet in different regions, which leads to different enhancement of rainfall in different spatial temporal regions. So we do believe there is a relationship with that, but it's just not presented here. Yeah. Great work. So I have a question and a comment. I think it's great that you want to look at the SAG simulations where you worked on that. TAMPS is part of one of those trackers and it would be really great to kind of make that connection with the inter-annual viability. My question is not so much about the inter-annual viability. I think this is great. It's more on the topography as I look at South America. And you know, I see the Andes. They're much, not so much in altitude, but more on the side of the width of the Andes, like over 20 South. It's much more thicker than over zero degrees, right, or 10. And I'm, I'm asking you, say it was thicker closer to the tropics. Would you expect those three categories as you describe them? Would you expect changes to that? Just your thoughts there about how in modulating the width of the topography across the latitudes, would that change the definitions of your three regions of the jet? Yeah. So, so currently in this research, basically we're trying to explain the trends of the lava jet in terms of the climatology using large-scale forcings. There are also other local mechanisms that drive the lava jet that, that we're not looking at. So yeah, I do believe in the, for the central jet where you mentioned Andes is more wide. There is a, like a previous theory, a paper about a cross-Andes mechanism where the wave train or the wind or the trough crossing this part of the Andes that creates a favorable condition for the central jet where it seems more like a local mechanism because with the upper divergence and low-level convergence that triggers the lava jet, for the, for the northern Andes is still less explored. So that's why we're trying to explore more for this different types of level jet in terms of their forcing. Yes, I do agree that the topography would definitely play a role, even especially in the warp simulation. Any other questions? Thank you, Efren.