I need to plot the Y value 0.1 and 0.2 percentile into the existing scatter plot.Part of the code for the scatter plot as below: 

```
install.packages("ncdf4")
library(ncdf4)
install.packages("ggplot2")
library("ggplot2")
setwd("***ailind")
hp=nc_open("aeob20140910.nc")
hs=nc_open("Ha910L3C_CONUS.nc")
var1_prob<-ncvar_get(hp,"HailProb",verbose=FALSE)
var1_prob[var1_prob==0]<-NA
var2_indx<-ncvar_get(hs,"HailIndx",verbose=FALSE)
var2_indx[var2_indx==0]<-NA
plot(var1_prob,var2_indx,xlim=c(1, 100),ylim=c(1,1000),gridded=TRUE)
var2_indx_0.1<-quantile(var2_indx,0.1)
var2_indx_0.2<-quantile(var2_indx,0.2)

```

the scatter plot look like this :
[![enter image description here](https://i.stack.imgur.com/T1cXG.jpg)](https://i.stack.imgur.com/T1cXG.jpg)

how to add the y value percentile into the existing scatter plot?