Wednesday, May 17, 2017

Monsoon Watch --4 ...Quantum Analysis

Quantum Analysis is evaluated for the amount of summer monsoon rainfall over Indian monsoon region during June- July....

Forecasting Methods adopted for the Indian Monsoons:

Gowarikar(1989) developed parametric and multiple power regression (MPR) models with 15 predictors for LRF of AISMR, which were later modified in 1991 to include 16 predictor parameters. The parametric model is qualitative and indicates the likelihood of the monsoon rainfall to be excess or deficient.
Thapliyal (1990) evaluated the relative performance of multiple regression, and Navone and Ceccatto (1994) have used 'feed-forward' neural network technique for the prediction of Indian monsoon rainfall with two predictors (500 hPa ridge location and Darwin SLP tendency from January to April).
The results of a recent work by Krishna Kumar (1997) indicate that a single component accounts for about half of the total variance in the predictors

Most of the studies on LRF of Indian monsoon rainfall were based on empirical or statistical techniques till 2010. IITM, Pune has recently implemented the state-of-the-art coupled climate model, the Coupled Forecasting System (CFS) developed by the National Centers for Environmental Prediction (NCEP), USA. These statistical techniques range from simple correlation analysis to advanced procedures.

Vagaries' View Point:

Vagaries leans on, and believes in the "Gowarikar Method" with 16 parameters. The results of this old but proven method has been successful. For Vagaries' forecast and analysis made in the "Arrival and quantum Monsoon Watch" series, I combine a few of them along with Dynamical models for a personal analysis and estimate.
15 initial parameters from the months March, April and May are used to analysis and forecast the simulation of Indian monsoon rainfall during June to October. These initial conditions were carefully selected  to span the evolution of both the atmosphere and ocean.

We have to take into consideration most of the 15 parameters (Gowarikar Method) before making an assessment, and these have to be analysed one by one. The prominent among the 15 are , ENSO, March temperatures of North India and East Coast, Himalayan Snow cover till March and SOI to name a few.
Of-course, I am not going to take each and every one of the 15 here, but, derive at an estimate on these basis and on the new model developed. I hope readers of vagaries trust that I have tried my best to estimate as accurately as possible.

Calculating the amount of rainfall, region wise, is of utmost importance, as SWM contributes to almost 80% of the annual total rainfall over India.
In this article, Quantum Analysis is evaluated for the amount of summer monsoon rainfall over Indian monsoon region during June and July.

The 500 hpa parameter is of importance in April. The mean latitudinal location of the 500 hPa ridge along 75°E in April over India, first identified by Banerjee (1978), is considered to be one of the most important predictors. The mid-tropospheric anticyclone over southern India migrates from 11.5°N in January to its northern most position of 28.5°N during July.
From October, the ridge starts shifting back southward. A more Northward location indicates better performance of the monsoon and vice versa. It also showed that the negative correlation of the March ridge was more dominant with the monsoon rainfall of the peninsular India, while the positive correlation of the April ridge was more dominant with the monsoon rainfall of Northern India.

ENSO factor in arriving at the rainfall amount is also of importance. The interface is the sea surface: that is where the transfers of water (evaporation/precipitation)
and momentum occur. An accurate coupling of the fast atmosphere to the slow ocean is essential to simulate the ENSO, which in turn can simulate the interannual
variability of Indian monsoon. Unfortunately, getting an accurate, or near to accurate forecast of the ENSO for the next 2 months is difficult, with no guarantee of accuracy or performance surety.

We see neutral ENSO conditions persisting. But, there is a possibility of  Neutral event persisting till August. Now, this would result in normal Monsoon condition from June thru  August.( If no "Break Monsoon" occurs).
After August, a 50-50 chance of a weak El Nino.

We depend also on other parameters.
Normally, Pulses from the Eastern Pacific area, that is S.China sea, would mean depressions and systems originating from the Bay. 'In Situ" systems and systems from the Far east would contribute to the rainfall to the east Coast thru Central India and into Gujarat and even into Sindh (Pakistan). No El-Nino, would mean no stopping  these pulses, and in fact not encourage WDs into coming down south, (more South than normal).
This may persist till  June, and then rapidly the flow of systems should increase from Bay in July.

The performance of Vagaries' Monsoon Watch Quantum Analysis is evaluated for the amount of summer monsoon rainfall over Indian monsoon region during June to SWM withdrawal in 2 phases. (June/July and August/September).

Why in 2 phases ? Because, I believe it is impossible to give actual Quantum forecast now (In May) for sometime in September...that is 120 days ahead !). I am not competent to give a forecast 90 - 120 days in advance, 
so Monsoon forecast will be
1)...For June and July and
2)... August and September ..this is tentative and will be published in 2nd week July.

A) First 15 days of June sees 
i) Monsoon advancing from Kerala thru upto Central India, and into NE States and West Bengal.
ii) Heat ( Normal to above Normal) in Northern India, and Pakistan.
Monsoon advances into Central India and North India between 20th - 30th June.
iii) Monsoon moves into Pakistan around 1st - 12th of July.

B) Mid June to July end, we can see normal rainfall and progress of the SWM in all of  Sub-Continent regions. Neutral conditions in the Pacific Oceans will send a few "pulses" to create "in situ" systems in the Bay, and the first 2 months could see around 3/4 noteworthy systems traversing the Sub continent. WDs will be few, hence, we can expect a few systems from Bay to track towards Central and Northern India, resulting in good rains in the plains of N.India and Northern Pakistan regions..and fairly good above normal rains in Nepal.

Thus, June and July rains should be normal for these months.

This estimate is based absolutely on the situation as it shows and stands today.
Things, if and when they change (drastically) will be posted and Vagaries readers will be kept well informed, of any variation in the forecast.
These are my personal views, and should not be depended upon commercially or otherwise.  They may differ from other models.


Nilay Wankawala said...

Pleasant to read normal forecast both for rainfall and progress of SWM. Your work sir always been a masterpiece, this being too no exception.

sset said...

IMD puts red alert over SE India - extreme heat wave for next 3 days!

Vijayanand said...

Massive rain in bangalore and other near by area's. Kengeri in South west bangalore has recorded 120 mm rain. My place in extreme south got 44 mm last night.

Cumulus Arjun said...

So a good "first half of monsoon" likely for India. Good times ahead

sset said...

Banglore - time to plant trees and save lakes save every drop of water. Most of rains happen outside monsoon months (pre or post monsoon).

Machilipatnam AP records near 48c ! Is it highest temp for this summer 2017?

Vijayanand said...

sset: [Satish Shetty]
Planting trees is a very good activity. The same holds for Mumbai , Pune , Nagpur, Nasik as well. It needs to be a national passion.
Its such a Nobel activity. Grow UP.

Mohsin mulla said...

Rajesh sir,

According to bbc weather and other international module predict SSE Arabian sea formed depression on 23rd or 24th May,and it may become cyclone and headed to Yemen and Oman coast.
in this scenario all monsoon moisture taken by the cyclone and it will directly effect on onset date with Kerala. your view on that sir.....

rajesh said...

Moshin: Have given my views in latest post on 20th system seen in Arb sea on 23rd.